Satisfy clippy in the hand module

Co-Authored-By: Claude Opus 5.5 <[email protected]>

README.md

@@ -20,7 +20,7 @@
 
 # Horizon
 
-A Rust rewrite of Minecraft: Java Edition 26.3 with one-to-one vanilla parity, checked against the game itself with differential tests.
+A Rust rewrite of Minecraft: Java Edition 26.3 built for one-to-one vanilla parity, checked against the game itself with differential tests.
 
 Every subsystem matches vanilla in all 281 parity harnesses, on Linux and macOS: 100% of what the harnesses compare (see [Project status](#project-status)). The native client is playable on Linux, macOS (Apple Silicon) and Windows.
 

crates/horizon-client/examples/camera_probe.rs

@@ -5,7 +5,7 @@ use horizon_client::{
     Result,
     camera::{
         AvatarBob, BobState, Camera, CameraEntity, CameraFluid, CameraType, FovPlayer, HurtBob,
-        LivingCamera, UseItem, bob_matrix, field_of_view_modifier,
+        LivingCamera, UseItem, bob_matrix, field_of_view_modifier, perspective,
     },
 };
 use horizon_core::{
@@ -258,6 +258,15 @@ fn camera(c: &Value, out: &mut impl Write) -> Result<()> {
                     fb(fov),
                     fb(hud)
                 )?;
+                let (w, h, far) = (fl(&op[4]), fl(&op[5]), fl(&op[6]));
+                let matrix =
+                    |m: [f32; 16]| m.iter().map(|&x| format!(" {}", fb(x))).collect::<String>();
+                writeln!(
+                    out,
+                    "projection{}{}",
+                    matrix(perspective(fov, w, h, far, 0.05, true)),
+                    matrix(perspective(hud, w, h, far, 0.05, true))
+                )?;
             }
             other => panic!("{other}"),
         }

crates/horizon-client/examples/first_person_probe.rs

@@ -0,0 +1,461 @@
+//! Probe for test_first_person_parity.py: drives horizon_client::first_person
+//! and attack_strength over the harness's scripted clicks, targets and use
+//! results, printing what VanillaFirstPersonOracle prints.
+use horizon_client::{
+    Result,
+    attack_strength::{AttackStrength, HeldStack},
+    first_person::{
+        Clicks, Hand, HandHeights, HandWorld, Hit, SwingAnimation, SwingState, UseResult,
+        swing_duration,
+    },
+};
+use serde_json::Value;
+use std::{
+    collections::HashMap,
+    fs::File,
+    io::{BufRead, BufReader, BufWriter, Write},
+};
+
+fn fb(v: f32) -> String {
+    format!("{:08x}", v.to_bits())
+}
+fn fl(v: &Value) -> f32 {
+    f32::from_bits(u32::from_str_radix(v.as_str().unwrap(), 16).unwrap())
+}
+fn dl(v: &Value) -> f64 {
+    f64::from_bits(u64::from_str_radix(v.as_str().unwrap(), 16).unwrap())
+}
+
+/// An `ItemStack` object: the hands hold indices into `Probe::stacks`, so
+/// shrinking keeps its identity as vanilla's in-place `shrink` does.
+#[derive(Clone)]
+struct Stack {
+    item: String,
+    count: i32,
+}
+impl Stack {
+    fn empty(&self) -> bool {
+        self.item == "minecraft:air" || self.count <= 0
+    }
+    /// `getItem` and `getCount` of an empty stack are air and 0.
+    fn effective(&self) -> (&str, i32) {
+        if self.empty() {
+            ("minecraft:air", 0)
+        } else {
+            (&self.item, self.count)
+        }
+    }
+}
+
+struct Probe<'a> {
+    case: &'a Value,
+    step: &'a Value,
+    creative: bool,
+    stacks: Vec<Stack>,
+    /// The stacks in the main and off hand.
+    hands: [usize; 2],
+    blocks: HashMap<[i32; 3], String>,
+    swing: SwingState,
+    events: Vec<String>,
+    heights: HandHeights,
+}
+fn hand_name(hand: Hand) -> &'static str {
+    match hand {
+        Hand::Main => "main",
+        Hand::Off => "off",
+    }
+}
+impl Probe<'_> {
+    fn stack(&self, hand: Hand) -> &Stack {
+        &self.stacks[self.hands[hand as usize]]
+    }
+    fn new_stack(&mut self, v: &Value) -> usize {
+        // ItemStack.EMPTY is index 0.
+        if v.is_null() {
+            return 0;
+        }
+        self.stacks.push(Stack {
+            item: v[0].as_str().unwrap().into(),
+            count: v[1].as_i64().unwrap() as i32,
+        });
+        self.stacks.len() - 1
+    }
+    fn table<'b>(&'b self, name: &str) -> &'b Value {
+        &self.case["rust"][name]
+    }
+    fn attack_speed(&self) -> f64 {
+        let item = self.stack(Hand::Main).effective().0;
+        self.table("attack_speed").get(item).map_or(4.0, dl)
+    }
+    fn scripted(&mut self, kind: &str, hand: Hand) -> UseResult {
+        let name = self.step["uses"][kind].as_str().unwrap().to_string();
+        self.events
+            .push(format!("use {kind} {} {name}", hand_name(hand)));
+        let result = match name.as_str() {
+            "success" => UseResult::Success { swing: true },
+            "server" | "consume" => UseResult::Success { swing: false },
+            "fail" => UseResult::Fail,
+            _ => UseResult::Pass,
+        };
+        if matches!(result, UseResult::Success { .. }) && self.step["shrink"].as_bool().unwrap() {
+            let i = self.hands[hand as usize];
+            if i != 0 {
+                self.stacks[i].count -= 1;
+            }
+        }
+        result
+    }
+}
+impl HandWorld for Probe<'_> {
+    fn hit(&mut self) -> Hit {
+        let h = &self.step["hit"];
+        match h[0].as_str().unwrap() {
+            "block" => Hit::Block {
+                pos: [0, 1, 2].map(|i| h[i + 1].as_i64().unwrap() as i32),
+                face: h[4].as_u64().unwrap() as u8,
+            },
+            "entity" => Hit::Entity,
+            _ => Hit::Miss,
+        }
+    }
+    fn is_air(&mut self, pos: [i32; 3]) -> bool {
+        self.blocks.get(&pos).is_none_or(|b| b == "minecraft:air")
+    }
+    fn creative(&self) -> bool {
+        self.creative
+    }
+    fn spectator(&self) -> bool {
+        false
+    }
+    fn instabuild(&self) -> bool {
+        self.creative
+    }
+    fn hands_busy(&self) -> bool {
+        self.step["busy"].as_bool().unwrap()
+    }
+    fn using_item(&self) -> bool {
+        self.step["using"].as_bool().unwrap()
+    }
+    fn item_enabled(&mut self, _: Hand) -> bool {
+        true
+    }
+    fn held_empty(&mut self, hand: Hand) -> bool {
+        self.stack(hand).empty()
+    }
+    fn held_count(&mut self, hand: Hand) -> i32 {
+        self.stack(hand).effective().1
+    }
+    fn infinite_materials(&self) -> bool {
+        self.creative
+    }
+    fn cannot_attack(&mut self) -> bool {
+        false
+    }
+    fn piercing_weapon(&mut self) -> bool {
+        false
+    }
+    fn attack_animation(&mut self) -> SwingAnimation {
+        SwingAnimation::DEFAULT
+    }
+    fn interact_animation(&mut self, _: Hand) -> SwingAnimation {
+        SwingAnimation::DEFAULT
+    }
+    fn piercing_attack(&mut self, _: SwingAnimation) {
+        unreachable!()
+    }
+    fn attack_entity(&mut self) -> bool {
+        self.events.push("attack".into());
+        true
+    }
+    fn block_action_restricted(&mut self, _: [i32; 3]) -> bool {
+        false
+    }
+    fn within_border(&mut self, _: [i32; 3]) -> bool {
+        true
+    }
+    fn attack_block(&mut self, _: [i32; 3]) {}
+    /// `BlockBehaviour.getDestroyProgress` with `Player.getDestroySpeed` for
+    /// a player on the ground, out of water, with no mining efficiency.
+    fn destroy_progress(&mut self, pos: [i32; 3]) -> f32 {
+        let block = self.blocks.get(&pos).cloned().unwrap_or_default();
+        let b = &self.table("blocks")[block.as_str()];
+        let hardness = fl(&b[0]);
+        if hardness == -1.0 {
+            return 0.0;
+        }
+        let item = self.stack(Hand::Main).effective().0.to_string();
+        let tool = &self.table("tools")[format!("{item} {block}").as_str()];
+        let (mut speed, correct) = if tool.is_null() {
+            (1.0f32, false)
+        } else {
+            (fl(&tool[0]), tool[1].as_bool().unwrap())
+        };
+        if let Some(amp) = self.case["haste"].as_i64() {
+            speed *= 1.0 + (amp as i32 + 1) as f32 * 0.2;
+        }
+        if let Some(amp) = self.case["fatigue"].as_i64() {
+            speed *= horizon_core::jmath::pow(0.3, f64::from(amp as i32 + 1)) as f32;
+        }
+        let harvest = !b[1].as_bool().unwrap() || correct;
+        speed / hardness / if harvest { 30.0 } else { 100.0 }
+    }
+    fn destroy_block(&mut self, pos: [i32; 3]) -> bool {
+        let item = self.stack(Hand::Main).effective().0;
+        // Item.canDestroyBlock: swords' tools cannot destroy in creative.
+        let sword = item.ends_with("_sword");
+        let ok = !(sword && self.creative) && !self.is_air(pos);
+        if ok {
+            self.blocks.insert(pos, "minecraft:air".into());
+        }
+        self.events
+            .push(format!("destroy {} {} {} {ok}", pos[0], pos[1], pos[2]));
+        ok
+    }
+    /// The stack object itself: `destroyingItem` is a reference.
+    fn main_hand_key(&mut self) -> String {
+        self.hands[0].to_string()
+    }
+    fn same_destroying_item(&mut self, key: &str) -> bool {
+        // ItemStack.EMPTY (index 0) before any break.
+        let then = &self.stacks[key.parse::<usize>().unwrap_or(0)];
+        then.effective().0 == self.stack(Hand::Main).effective().0
+    }
+    fn destroy_stage(&mut self, pos: [i32; 3], stage: Option<i32>) {
+        self.events.push(format!(
+            "stage {} {} {} {}",
+            pos[0],
+            pos[1],
+            pos[2],
+            stage.unwrap_or(-1)
+        ));
+    }
+    fn swing(&mut self, hand: Hand, animation: SwingAnimation) {
+        let duration = swing_duration(
+            animation,
+            self.case["haste"].as_i64().map(|a| a as i32),
+            self.case["fatigue"].as_i64().map(|a| a as i32),
+        );
+        let started = self.swing.start_if_able(hand, animation, duration);
+        self.events.push(format!(
+            "swing {} {} {started}",
+            hand_name(hand),
+            animation.duration
+        ));
+    }
+    fn reset_attack_strength(&mut self) {
+        unreachable!("ResetWorld resets the tickers")
+    }
+    fn entity_within_border(&mut self) -> bool {
+        true
+    }
+    fn use_on_entity(&mut self, hand: Hand) -> Option<UseResult> {
+        self.step["hit"][1]
+            .as_bool()
+            .unwrap()
+            .then(|| self.scripted("entity", hand))
+    }
+    fn use_on_block(&mut self, hand: Hand) -> UseResult {
+        self.scripted("block", hand)
+    }
+    fn use_item(&mut self, hand: Hand) -> UseResult {
+        self.scripted("item", hand)
+    }
+    fn item_used(&mut self, hand: Hand) {
+        self.events.push(format!("used {}", hand_name(hand)));
+        self.heights.item_used(hand);
+    }
+    fn release_using(&mut self) {
+        self.events.push("release".into());
+    }
+}
+fn held(stack: &Stack) -> Option<HeldStack> {
+    (!stack.empty()).then(|| HeldStack {
+        item: stack.item.clone(),
+        rest: stack.count.to_string(),
+    })
+}
+
+fn run(case: &Value, out: &mut impl Write) -> Result<()> {
+    let empty = Value::Null;
+    let mut probe = Probe {
+        case,
+        step: &empty,
+        creative: case["creative"].as_bool().unwrap(),
+        stacks: vec![Stack {
+            item: "minecraft:air".into(),
+            count: 0,
+        }],
+        hands: [0, 0],
+        blocks: case["blocks"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .map(|b| {
+                (
+                    [0, 1, 2].map(|i| b[i].as_i64().unwrap() as i32),
+                    b[3].as_str().unwrap().to_string(),
+                )
+            })
+            .collect(),
+        swing: SwingState::default(),
+        events: Vec::new(),
+        heights: HandHeights::default(),
+    };
+    probe.hands[0] = probe.new_stack(&case["main"]);
+    probe.hands[1] = probe.new_stack(&case["off"]);
+    writeln!(out, "attack_speed {:x}", probe.attack_speed().to_bits())?;
+    let mut clicks = Clicks::default();
+    let mut strength = AttackStrength::default();
+    // FirstPersonHandsAndItems' visible items start as ItemStack.EMPTY.
+    let mut visible = [0usize, 0usize];
+    for (s, step) in case["steps"].as_array().unwrap().iter().enumerate() {
+        probe.step = step;
+        probe.events.clear();
+        if !step["set"].is_null() {
+            let i = probe.new_stack(&step["set"]["stack"]);
+            let hand = if step["set"]["hand"] == "main" { 0 } else { 1 };
+            probe.hands[hand] = i;
+        }
+        clicks.tick(
+            &mut ResetWorld {
+                probe: &mut probe,
+                strength: &mut strength,
+            },
+            step["ac"].as_u64().unwrap() as u32,
+            step["uc"].as_u64().unwrap() as u32,
+            step["ad"].as_bool().unwrap(),
+            step["ud"].as_bool().unwrap(),
+        );
+        probe.swing.tick();
+        let main = probe.stack(Hand::Main).clone();
+        strength.tick(held(&main));
+        // FirstPersonHandsAndItems.tick: shouldInstantlyReplaceVisibleItem
+        // (ItemStack.matchesIgnoringComponents; every item plays the swap
+        // animation), then the heights.
+        let mut changed = [false; 2];
+        for h in 0..2 {
+            let (a, b) = (visible[h], probe.hands[h]);
+            let same = a == b || probe.stacks[a].effective() == probe.stacks[b].effective();
+            if same {
+                visible[h] = b;
+            }
+            changed[h] = visible[h] != b;
+        }
+        let speed = probe.attack_speed();
+        let replace = probe.heights.tick(
+            probe.step["busy"].as_bool().unwrap(),
+            strength.swap_scale(1.0, speed),
+            changed,
+        );
+        for h in 0..2 {
+            if replace[h] {
+                visible[h] = probe.hands[h];
+            }
+        }
+        for e in &probe.events {
+            writeln!(out, "{e}")?;
+        }
+        let sw = &probe.swing;
+        let current = sw.current.map_or("- 0".to_string(), |c| {
+            format!("{} {}", hand_name(c.hand), c.duration_ticks)
+        });
+        let h = &probe.heights;
+        let d = &clicks.destroying;
+        writeln!(
+            out,
+            "tick {s} {current} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {}",
+            sw.ticks,
+            fb(sw.animation),
+            fb(sw.old_animation),
+            fb(sw.animation(0.5)),
+            strength.ticker,
+            strength.swap_ticker,
+            fb(strength.swap_scale(1.0, speed)),
+            fb(h.main),
+            fb(h.old_main),
+            fb(h.off),
+            fb(h.old_off),
+            clicks.miss_time,
+            clicks.right_click_delay,
+            d.delay,
+            d.active,
+            fb(d.progress)
+        )?;
+    }
+    Ok(())
+}
+
+/// The probe with the attack-strength tickers it resets.
+struct ResetWorld<'p, 'c> {
+    probe: &'p mut Probe<'c>,
+    strength: &'p mut AttackStrength,
+}
+macro_rules! forward {
+    ($($name:ident($($arg:ident: $t:ty),*) -> $r:ty;)*) => {
+        $(fn $name(&mut self, $($arg: $t),*) -> $r { self.probe.$name($($arg),*) })*
+    };
+}
+impl HandWorld for ResetWorld<'_, '_> {
+    forward! {
+        hit() -> Hit;
+        is_air(pos: [i32; 3]) -> bool;
+        item_enabled(hand: Hand) -> bool;
+        held_empty(hand: Hand) -> bool;
+        held_count(hand: Hand) -> i32;
+        cannot_attack() -> bool;
+        piercing_weapon() -> bool;
+        attack_animation() -> SwingAnimation;
+        interact_animation(hand: Hand) -> SwingAnimation;
+        piercing_attack(a: SwingAnimation) -> ();
+        attack_entity() -> bool;
+        block_action_restricted(pos: [i32; 3]) -> bool;
+        within_border(pos: [i32; 3]) -> bool;
+        attack_block(pos: [i32; 3]) -> ();
+        destroy_progress(pos: [i32; 3]) -> f32;
+        destroy_block(pos: [i32; 3]) -> bool;
+        main_hand_key() -> String;
+        same_destroying_item(key: &str) -> bool;
+        destroy_stage(pos: [i32; 3], stage: Option<i32>) -> ();
+        swing(hand: Hand, a: SwingAnimation) -> ();
+        entity_within_border() -> bool;
+        use_on_entity(hand: Hand) -> Option<UseResult>;
+        use_on_block(hand: Hand) -> UseResult;
+        use_item(hand: Hand) -> UseResult;
+        item_used(hand: Hand) -> ();
+        release_using() -> ();
+    }
+    fn creative(&self) -> bool {
+        self.probe.creative()
+    }
+    fn spectator(&self) -> bool {
+        false
+    }
+    fn instabuild(&self) -> bool {
+        self.probe.instabuild()
+    }
+    fn hands_busy(&self) -> bool {
+        self.probe.hands_busy()
+    }
+    fn using_item(&self) -> bool {
+        self.probe.using_item()
+    }
+    fn infinite_materials(&self) -> bool {
+        self.probe.infinite_materials()
+    }
+    fn reset_attack_strength(&mut self) {
+        self.strength.reset();
+    }
+}
+
+fn main() -> Result<()> {
+    let args: Vec<String> = std::env::args().collect();
+    let input = BufReader::new(File::open(&args[1])?);
+    let mut out = BufWriter::new(File::create(&args[2])?);
+    for (n, line) in input.lines().enumerate() {
+        let c: Value = serde_json::from_str(&line?)?;
+        writeln!(out, "== {n}")?;
+        run(&c, &mut out)?;
+    }
+    out.flush()?;
+    Ok(())
+}

crates/horizon-client/src/camera.rs

@@ -583,6 +583,44 @@ impl Camera {
         modify_fov_based_on_death_or_fluid(partial, 70.0, effect_scale, dead, fluid)
     }
 }
+/// `Projection.getMatrix` for a perspective set up by `setupPerspective`:
+/// JOML's `Matrix4f.setPerspective(fov * DEG_TO_RAD, width / height, near,
+/// far, zZeroToOne)`, column-major. Vanilla passes its planes reversed
+/// (`near` is `zFar`); the hand pass here keeps them in order.
+pub fn perspective(
+    fov_degrees: f32,
+    width: f32,
+    height: f32,
+    near: f32,
+    far: f32,
+    zero_to_one: bool,
+) -> [f32; 16] {
+    let h = horizon_core::jmath::tan(f64::from(fov_degrees * DEG_TO_RAD * 0.5)) as f32;
+    let aspect = width / height;
+    let mut m = [0.0f32; 16];
+    m[0] = 1.0 / (h * aspect);
+    m[5] = 1.0 / h;
+    let e = 1.0e-6f32;
+    if far > 0.0 && far.is_infinite() {
+        m[10] = e - 1.0;
+        m[14] = (e - if zero_to_one { 1.0 } else { 2.0 }) * near;
+    } else if near > 0.0 && near.is_infinite() {
+        m[10] = (if zero_to_one { 0.0 } else { 1.0 }) - e;
+        m[14] = ((if zero_to_one { 1.0 } else { 2.0 }) - e) * far;
+    } else {
+        m[10] = (if zero_to_one { far } else { far + near }) / (near - far);
+        m[14] = (if zero_to_one { far } else { far + far }) * near / (near - far);
+    }
+    m[11] = -1.0;
+    m
+}
+/// `GameRenderer.render3dHud`: the first-person hand and held items are
+/// drawn with their own projection at `hudFov` (70 degrees, changed only by
+/// death and fluids), never the FOV option or the sprint, speed and bow
+/// modifier.
+pub fn hand_projection(hud_fov: f32, width: f32, height: f32, far: f32) -> [f32; 16] {
+    perspective(hud_fov, width, height, 0.05, far, true)
+}
 /// `Camera.modifyFovBasedOnDeathOrFluid`. `dead` is the camera entity's
 /// `deathTime` while it is a living entity that is dead or dying.
 pub fn modify_fov_based_on_death_or_fluid(

crates/horizon-client/src/effects.rs

@@ -365,12 +365,7 @@ impl PlayerEffects {
             f *= 1.0 + (a + 1) as f32 * 0.2;
         }
         if let Some(a) = self.amplifier("mining_fatigue") {
-            f *= match a {
-                0 => 0.3,
-                1 => 0.09,
-                2 => 0.0027,
-                _ => 8.1e-4,
-            };
+            f *= horizon_core::jmath::pow(0.3, f64::from(a + 1)) as f32;
         }
         f
     }

crates/horizon-client/src/first_person.rs

@@ -0,0 +1,601 @@
+//! The local player's hand: the arm swing (`LivingEntity.SwingState`,
+//! `getModifiedSwingDuration`), the first-person equip heights
+//! (`FirstPersonHandsAndItems.tick` and `itemUsed`), and the click handling
+//! that starts swings: `Minecraft.startAttack`, `continueAttack`,
+//! `startUseItem` and `handleKeybinds`' attack and use part, with
+//! `MultiPlayerGameMode`'s block breaking (`startDestroyBlock`,
+//! `continueDestroyBlock`, `stopDestroyBlock`).
+//!
+//! What those read and do in the world is behind [`HandWorld`].
+
+/// `InteractionHand`.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Hand {
+    Main,
+    Off,
+}
+impl Hand {
+    pub const BOTH: [Hand; 2] = [Hand::Main, Hand::Off];
+}
+
+/// `SwingAnimation`: its type (`SwingAnimationType` ordinal) and duration.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct SwingAnimation {
+    pub kind: u8,
+    pub duration: i32,
+}
+impl SwingAnimation {
+    /// `SwingAnimation.DEFAULT`: WHACK for 6 ticks.
+    pub const DEFAULT: SwingAnimation = SwingAnimation {
+        kind: 1,
+        duration: 6,
+    };
+}
+
+/// `LivingEntity.SwingDescription`.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct SwingDescription {
+    pub hand: Hand,
+    pub animation: SwingAnimation,
+    pub duration_ticks: i32,
+}
+
+/// `LivingEntity.SwingState`.
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+pub struct SwingState {
+    pub current: Option<SwingDescription>,
+    pub ticks: i32,
+    pub old_animation: f32,
+    pub animation: f32,
+}
+impl SwingState {
+    /// `startIfAble`: a swing restarts unless the current one is in its
+    /// first half (past its first tick).
+    pub fn start_if_able(&mut self, hand: Hand, animation: SwingAnimation, duration: i32) -> bool {
+        if let Some(c) = self.current
+            && self.ticks <= c.duration_ticks / 2
+            && self.ticks > 0
+        {
+            return false;
+        }
+        let swing = SwingDescription {
+            hand,
+            animation,
+            duration_ticks: duration,
+        };
+        if self.current != Some(swing) {
+            self.old_animation = 0.0;
+            self.animation = 0.0;
+        }
+        self.current = Some(swing);
+        self.ticks = 0;
+        true
+    }
+    /// `tick` (from `LivingEntity.baseTick`).
+    pub fn tick(&mut self) {
+        self.old_animation = self.animation;
+        if let Some(c) = self.current {
+            if c.duration_ticks > 0 {
+                self.animation = (self.ticks as f32 / c.duration_ticks as f32).min(1.0);
+            }
+            let ticks = self.ticks;
+            self.ticks += 1;
+            if ticks > c.duration_ticks {
+                self.current = None;
+                self.animation = 0.0;
+            }
+        } else {
+            self.animation = 0.0;
+        }
+    }
+    /// `getAnimation(partialTicks)`: a restarted swing keeps moving forward.
+    pub fn animation(&self, partial: f32) -> f32 {
+        if self.animation >= self.old_animation {
+            crate::camera::lerp(partial, self.old_animation, self.animation)
+        } else {
+            crate::camera::lerp(partial, self.old_animation, self.animation + 1.0)
+        }
+    }
+    pub fn swinging(&self) -> bool {
+        self.current.is_some()
+    }
+    /// The hand of the current swing (`state.attackHand`), main by default.
+    pub fn attack_hand(&self) -> Hand {
+        self.current.map_or(Hand::Main, |c| c.hand)
+    }
+}
+
+/// `LivingEntity.getModifiedSwingDuration`: `dig_speed` is
+/// `MobEffectUtil.getDigSpeedAmplification` while haste or conduit power is
+/// active, `fatigue` the mining fatigue amplifier.
+pub fn swing_duration(
+    animation: SwingAnimation,
+    dig_speed: Option<i32>,
+    fatigue: Option<i32>,
+) -> i32 {
+    let duration = animation.duration;
+    if let Some(amplification) = dig_speed {
+        duration - (1 + amplification)
+    } else if let Some(amplifier) = fatigue {
+        duration + (1 + amplifier) * 2
+    } else {
+        duration
+    }
+}
+
+/// `FirstPersonHandsAndItems`' equip heights.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct HandHeights {
+    pub main: f32,
+    pub old_main: f32,
+    pub off: f32,
+    pub old_off: f32,
+}
+impl Default for HandHeights {
+    fn default() -> Self {
+        HandHeights {
+            main: 0.0,
+            old_main: 0.0,
+            off: 0.0,
+            old_off: 0.0,
+        }
+    }
+}
+/// What `FirstPersonHandsAndItems.tick` decides about a hand's visible item.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct HandChange {
+    /// The visible item is not the hand's item after the instant replacement
+    /// (`mainHandItem != nextMainHand`): the hand lowers.
+    pub changed: bool,
+    /// The visible item becomes the hand's item this tick.
+    pub replace: bool,
+}
+impl HandHeights {
+    /// `FirstPersonHandsAndItems.tick`'s heights. `changed` says per hand
+    /// whether the visible item differs from the held one once
+    /// `shouldInstantlyReplaceVisibleItem` has run; `swap_scale` is
+    /// `getItemSwapScale(1.0F)`. Returns whether each hand's visible item
+    /// is replaced at the end.
+    pub fn tick(&mut self, hands_busy: bool, swap_scale: f32, changed: [bool; 2]) -> [bool; 2] {
+        self.old_main = self.main;
+        self.old_off = self.off;
+        if hands_busy {
+            self.main = (self.main - 0.4).clamp(0.0, 1.0);
+            self.off = (self.off - 0.4).clamp(0.0, 1.0);
+        } else {
+            let attack = swap_scale;
+            let main_target = if changed[0] {
+                0.0
+            } else {
+                attack * attack * attack
+            };
+            let off_target = if changed[1] { 0.0 } else { 1.0 };
+            self.main += (main_target - self.main).clamp(-0.4, 0.4);
+            self.off += (off_target - self.off).clamp(-0.4, 0.4);
+        }
+        [self.main < 0.1, self.off < 0.1]
+    }
+    /// `itemUsed`: the hand drops to the bottom and rises again.
+    pub fn item_used(&mut self, hand: Hand) {
+        match hand {
+            Hand::Main => self.main = 0.0,
+            Hand::Off => self.off = 0.0,
+        }
+    }
+    /// `Mth.lerp(partialTicks, oMainHandHeight, mainHandHeight)` and the
+    /// off hand's.
+    pub fn interpolated(&self, partial: f32) -> [f32; 2] {
+        [
+            crate::camera::lerp(partial, self.old_main, self.main),
+            crate::camera::lerp(partial, self.old_off, self.off),
+        ]
+    }
+}
+
+/// `HitResult` at the crosshair (`Minecraft.hitResult`).
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum Hit {
+    Miss,
+    Block { pos: [i32; 3], face: u8 },
+    Entity,
+}
+
+/// `InteractionResult` as `startUseItem` reads it.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum UseResult {
+    /// `Success` with its `SwingSource`: whether the client swings.
+    Success {
+        swing: bool,
+    },
+    Pass,
+    Fail,
+}
+
+/// What the click handling reads and does in the world.
+pub trait HandWorld {
+    fn hit(&mut self) -> Hit;
+    fn is_air(&mut self, pos: [i32; 3]) -> bool;
+    /// `MultiPlayerGameMode.localPlayerMode`.
+    fn creative(&self) -> bool;
+    fn spectator(&self) -> bool;
+    /// `Abilities.instabuild`.
+    fn instabuild(&self) -> bool;
+    fn hands_busy(&self) -> bool;
+    fn using_item(&self) -> bool;
+    /// `ItemStack.isItemEnabled` for the item in a hand.
+    fn item_enabled(&mut self, hand: Hand) -> bool;
+    fn held_empty(&mut self, hand: Hand) -> bool;
+    fn held_count(&mut self, hand: Hand) -> i32;
+    /// `Player.hasInfiniteMaterials`.
+    fn infinite_materials(&self) -> bool;
+    /// `Player.cannotAttackWithItem(heldItem, 0)`.
+    fn cannot_attack(&mut self) -> bool;
+    /// The main-hand item is a `PIERCING_WEAPON`.
+    fn piercing_weapon(&mut self) -> bool;
+    fn attack_animation(&mut self) -> SwingAnimation;
+    fn interact_animation(&mut self, hand: Hand) -> SwingAnimation;
+    /// `MultiPlayerGameMode.piercingAttack`.
+    fn piercing_attack(&mut self, animation: SwingAnimation);
+    /// `Player.attack` on the targeted entity when the item's attack range
+    /// allows it; false when out of range.
+    fn attack_entity(&mut self) -> bool;
+    /// `Player.blockActionRestricted` for the game mode.
+    fn block_action_restricted(&mut self, pos: [i32; 3]) -> bool;
+    /// `WorldBorder.isWithinBounds`.
+    fn within_border(&mut self, pos: [i32; 3]) -> bool;
+    /// `BlockState.attack` on the first hit of a break.
+    fn attack_block(&mut self, pos: [i32; 3]);
+    /// `BlockState.getDestroyProgress` for the player.
+    fn destroy_progress(&mut self, pos: [i32; 3]) -> f32;
+    /// `MultiPlayerGameMode.destroyBlock`.
+    fn destroy_block(&mut self, pos: [i32; 3]) -> bool;
+    /// A key for the main-hand stack, kept as `destroyingItem`.
+    fn main_hand_key(&mut self) -> String;
+    /// `ItemStack.isSameItemSameComponents(selected, destroyingItem)` for
+    /// the stack `main_hand_key` gave when the break started. Vanilla keeps
+    /// a reference to that stack, so it compares what it holds now.
+    fn same_destroying_item(&mut self, key: &str) -> bool {
+        self.main_hand_key() == key
+    }
+    /// Breaking progress shown (`destroyBlockProgress`), or cleared with `None`.
+    fn destroy_stage(&mut self, pos: [i32; 3], stage: Option<i32>);
+    /// `player.swing(hand, animation, false)`.
+    fn swing(&mut self, hand: Hand, animation: SwingAnimation);
+    /// `Player.resetAttackStrengthTicker`.
+    fn reset_attack_strength(&mut self);
+    /// The targeted entity's block position is inside the world border.
+    fn entity_within_border(&mut self) -> bool;
+    /// The use attempts of `startUseItem`: on the targeted entity (`None`
+    /// when it is out of interaction range), the targeted block, and the
+    /// item alone.
+    fn use_on_entity(&mut self, hand: Hand) -> Option<UseResult>;
+    fn use_on_block(&mut self, hand: Hand) -> UseResult;
+    fn use_item(&mut self, hand: Hand) -> UseResult;
+    /// `LocalPlayer.itemUsed`.
+    fn item_used(&mut self, hand: Hand);
+    /// `MultiPlayerGameMode.releaseUsingItem`.
+    fn release_using(&mut self);
+}
+
+/// `MultiPlayerGameMode`'s block breaking.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Destroying {
+    pub delay: i32,
+    pub active: bool,
+    pub pos: [i32; 3],
+    pub face: u8,
+    pub item: String,
+    pub progress: f32,
+    pub ticks: f32,
+}
+impl Default for Destroying {
+    /// `destroyBlockPos` starts at (-1, -1, -1) and `destroyingItem` empty
+    /// (an empty key).
+    fn default() -> Self {
+        Destroying {
+            delay: 0,
+            active: false,
+            pos: [-1; 3],
+            face: 0,
+            item: String::new(),
+            progress: 0.0,
+            ticks: 0.0,
+        }
+    }
+}
+impl Destroying {
+    /// `getDestroyStage`.
+    pub fn stage(&self) -> i32 {
+        if self.progress > 0.0 {
+            (self.progress * 10.0) as i32
+        } else {
+            -1
+        }
+    }
+    fn same_target(&self, w: &mut impl HandWorld, pos: [i32; 3]) -> bool {
+        pos == self.pos && w.same_destroying_item(&self.item)
+    }
+    /// `startDestroyBlock`.
+    pub fn start(&mut self, w: &mut impl HandWorld, pos: [i32; 3], face: u8) -> bool {
+        if w.block_action_restricted(pos) || !w.within_border(pos) {
+            return false;
+        }
+        if w.instabuild() {
+            w.destroy_block(pos);
+            self.delay = 5;
+        } else if !self.active || !self.same_target(w, pos) {
+            let not_air = !w.is_air(pos);
+            if not_air && self.progress == 0.0 {
+                w.attack_block(pos);
+            }
+            if not_air && w.destroy_progress(pos) >= 1.0 {
+                w.destroy_block(pos);
+            } else {
+                self.active = true;
+                self.pos = pos;
+                self.face = face;
+                self.item = w.main_hand_key();
+                self.progress = 0.0;
+                self.ticks = 0.0;
+                w.destroy_stage(pos, Some(self.stage()));
+            }
+        }
+        true
+    }
+    /// `stopDestroyBlock`.
+    pub fn stop(&mut self, w: &mut impl HandWorld) {
+        if self.active {
+            self.active = false;
+            self.progress = 0.0;
+            w.destroy_stage(self.pos, None);
+            w.reset_attack_strength();
+        }
+    }
+    /// `continueDestroyBlock`: true while the hand keeps swinging.
+    pub fn continue_destroy(&mut self, w: &mut impl HandWorld, pos: [i32; 3], face: u8) -> bool {
+        if self.delay > 0 {
+            self.delay -= 1;
+            return true;
+        }
+        if w.instabuild() && w.within_border(pos) {
+            self.delay = 5;
+            w.destroy_block(pos);
+            return true;
+        }
+        if !self.same_target(w, pos) {
+            return self.start(w, pos, face);
+        }
+        if w.is_air(pos) {
+            self.active = false;
+            return false;
+        }
+        self.progress += w.destroy_progress(pos);
+        self.ticks += 1.0;
+        if self.progress >= 1.0 {
+            self.active = false;
+            w.destroy_block(pos);
+            self.progress = 0.0;
+            self.ticks = 0.0;
+            self.delay = 5;
+        } else if self.face != face {
+            self.face = face;
+        }
+        w.destroy_stage(self.pos, Some(self.stage()));
+        true
+    }
+}
+
+/// `Minecraft`'s attack and use handling.
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct Clicks {
+    pub miss_time: i32,
+    pub right_click_delay: i32,
+    pub destroying: Destroying,
+}
+impl Clicks {
+    /// `Minecraft.startAttack`: whether the click ended the attack (broke
+    /// the block outright).
+    pub fn start_attack(&mut self, w: &mut impl HandWorld) -> bool {
+        if self.miss_time > 0 || w.hands_busy() {
+            return false;
+        }
+        if w.spectator() {
+            return true;
+        }
+        if !w.item_enabled(Hand::Main) || w.cannot_attack() {
+            return false;
+        }
+        let animation = w.attack_animation();
+        if w.piercing_weapon() {
+            w.piercing_attack(animation);
+            return true;
+        }
+        let mut end = false;
+        let mut miss = false;
+        match w.hit() {
+            // MultiPlayerGameMode.attack.
+            Hit::Entity => {
+                if w.attack_entity() {
+                    w.reset_attack_strength();
+                    if w.instabuild() {
+                        self.destroying.delay = 5;
+                    }
+                }
+            }
+            Hit::Block { pos, face } if !w.is_air(pos) => {
+                self.destroying.start(w, pos, face);
+                end = w.is_air(pos);
+            }
+            Hit::Block { .. } | Hit::Miss => miss = true,
+        }
+        if miss {
+            if !w.creative() {
+                self.miss_time = 10;
+            }
+            w.reset_attack_strength();
+        }
+        w.swing(Hand::Main, animation);
+        end
+    }
+    /// `Minecraft.continueAttack`.
+    pub fn continue_attack(&mut self, w: &mut impl HandWorld, down: bool) {
+        if !down {
+            self.miss_time = 0;
+        }
+        if self.miss_time > 0 || w.using_item() || w.piercing_weapon() {
+            return;
+        }
+        let animation = w.attack_animation();
+        match w.hit() {
+            Hit::Block { pos, face } if down => {
+                if !w.is_air(pos) && self.destroying.continue_destroy(w, pos, face) {
+                    w.swing(Hand::Main, animation);
+                }
+            }
+            _ => self.destroying.stop(w),
+        }
+    }
+    /// `Minecraft.startUseItem`.
+    pub fn start_use_item(&mut self, w: &mut impl HandWorld) {
+        if self.destroying.active {
+            return;
+        }
+        self.right_click_delay = 4;
+        if w.hands_busy() {
+            return;
+        }
+        for hand in Hand::BOTH {
+            if !w.item_enabled(hand) {
+                return;
+            }
+            let animation = w.interact_animation(hand);
+            match w.hit() {
+                Hit::Entity => {
+                    if !w.entity_within_border() {
+                        return;
+                    }
+                    if let Some(UseResult::Success { swing }) = w.use_on_entity(hand) {
+                        if swing {
+                            w.swing(hand, animation);
+                        }
+                        return;
+                    }
+                }
+                Hit::Block { .. } => {
+                    let count = w.held_count(hand);
+                    match w.use_on_block(hand) {
+                        UseResult::Success { swing } => {
+                            if swing {
+                                w.swing(hand, animation);
+                                if !w.held_empty(hand)
+                                    && (w.held_count(hand) != count || w.infinite_materials())
+                                {
+                                    w.item_used(hand);
+                                }
+                            }
+                            return;
+                        }
+                        UseResult::Fail => return,
+                        UseResult::Pass => {}
+                    }
+                }
+                Hit::Miss => {}
+            }
+            if !w.held_empty(hand)
+                && let UseResult::Success { swing } = w.use_item(hand)
+            {
+                if swing {
+                    w.swing(hand, animation);
+                }
+                w.item_used(hand);
+                return;
+            }
+        }
+    }
+    /// The attack and use part of `Minecraft.tick`: `rightClickDelay`, the
+    /// clicks `handleKeybinds` consumes, held use and attack, then
+    /// `missTime`. `attack_down` is `keyAttack.isDown()` with no screen and
+    /// the mouse grabbed.
+    pub fn tick(
+        &mut self,
+        w: &mut impl HandWorld,
+        attack_clicks: u32,
+        use_clicks: u32,
+        attack_down: bool,
+        use_down: bool,
+    ) {
+        if self.right_click_delay > 0 {
+            self.right_click_delay -= 1;
+        }
+        let mut instant = false;
+        if w.using_item() {
+            if !use_down {
+                w.release_using();
+            }
+        } else {
+            for _ in 0..attack_clicks {
+                instant |= self.start_attack(w);
+            }
+            for _ in 0..use_clicks {
+                self.start_use_item(w);
+            }
+        }
+        if use_down && self.right_click_delay == 0 && !w.using_item() {
+            self.start_use_item(w);
+        }
+        self.continue_attack(w, !instant && attack_down);
+        if self.miss_time > 0 {
+            self.miss_time -= 1;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn a_swing_lasts_its_duration_and_restarts_after_half() {
+        let mut s = SwingState::default();
+        assert!(s.start_if_able(Hand::Main, SwingAnimation::DEFAULT, 6));
+        let mut seen = Vec::new();
+        for _ in 0..9 {
+            s.tick();
+            seen.push(s.animation);
+        }
+        assert_eq!(
+            seen,
+            [
+                0.0,
+                1.0 / 6.0,
+                2.0 / 6.0,
+                0.5,
+                4.0 / 6.0,
+                5.0 / 6.0,
+                1.0,
+                0.0,
+                0.0
+            ]
+        );
+        assert!(!s.swinging());
+        s.start_if_able(Hand::Main, SwingAnimation::DEFAULT, 6);
+        s.tick();
+        s.tick();
+        assert!(!s.start_if_able(Hand::Main, SwingAnimation::DEFAULT, 6));
+        s.tick();
+        s.tick();
+        assert!(s.start_if_able(Hand::Main, SwingAnimation::DEFAULT, 6));
+        s.tick();
+        // Restarting the same swing wraps forward rather than snapping back.
+        assert_eq!(
+            s.animation(0.5),
+            (s.old_animation + s.animation + 1.0) / 2.0
+        );
+    }
+    #[test]
+    fn haste_shortens_and_fatigue_lengthens_swings() {
+        let d = SwingAnimation::DEFAULT;
+        assert_eq!(swing_duration(d, None, None), 6);
+        assert_eq!(swing_duration(d, Some(1), Some(0)), 4);
+        assert_eq!(swing_duration(d, None, Some(2)), 12);
+    }
+}

crates/horizon-client/src/game.rs

@@ -39,6 +39,7 @@ mod game_mode;
 mod ghasts;
 mod golems;
 mod growth;
+mod hand;
 mod item_draw;
 mod jukebox;
 mod lan;
@@ -685,12 +686,18 @@ struct Game<'a> {
     orbs: Vec<ExperienceOrb>,
     xp_delay: u32,
     last_level_up: u64,
-    /// Arm swing: ticks into the 6-tick swing (None when idle), previous/current progress.
-    swing: Option<u32>,
-    swing_anim: (f32, f32),
-    /// Main-hand equip height (previous, current) and the item it shows.
-    hand_height: (f32, f32),
-    hand_item: Option<ItemStack>,
+    /// The arm swing (`LivingEntity.SwingState`) and how many swings started.
+    swing: horizon_client::first_person::SwingState,
+    swings_started: u32,
+    /// The first-person equip heights and the items the hands show (with
+    /// the slot each came from).
+    heights: horizon_client::first_person::HandHeights,
+    visible_hands: [(usize, Option<ItemStack>); 2],
+    /// `Minecraft`'s attack handling, attack clicks since the last tick and
+    /// the attack strength tickers the hand reads.
+    clicks: horizon_client::first_person::Clicks,
+    attack_clicks: u32,
+    hand_strength: horizon_client::attack_strength::AttackStrength,
     settings: Settings,
     /// Where the options screen returns: true = title, false = pause menu.
     options_from_title: bool,
@@ -2789,7 +2796,7 @@ impl Game<'_> {
         // ticks; ServerLevel.tick then runs the scheduled and random block
         // ticks before any entity, so what they drop or spawn (dispensed
         // items, popped crops) moves on the tick it appears, as in vanilla.
-        self.tick_mining()?;
+        self.tick_local_hand()?;
         self.postprocess_chunks()?;
         if running {
             self.tick_blocks()?;
@@ -2841,7 +2848,7 @@ impl Game<'_> {
             self.tick_particles();
         }
         if self.right && self.use_delay == 0 && self.screen == Screen::Playing {
-            self.use_item()?;
+            self.use_with_hand()?;
             self.use_delay = 4;
         }
         Ok(())
@@ -6374,38 +6381,6 @@ impl Game<'_> {
         }
         self.damage_held(1);
     }
-    /// LivingEntity.swing: restart the 6-tick arm swing.
-    fn swing_arm(&mut self) {
-        if self.swing.is_none_or(|t| t >= 3) {
-            self.swing = Some(0);
-        }
-    }
-    /// LivingEntity.updateSwingTime and ItemInHandRenderer.tick (equip height).
-    fn tick_hand(&mut self) {
-        self.swing_anim.0 = self.swing_anim.1;
-        if let Some(t) = self.swing {
-            let t = t + 1;
-            if t >= 6 {
-                self.swing = None;
-                self.swing_anim.1 = 0.0;
-            } else {
-                self.swing = Some(t);
-                self.swing_anim.1 = t as f32 / 6.0;
-            }
-        }
-        self.hand_height.0 = self.hand_height.1;
-        let held = self.inventory[self.selected].clone();
-        let same = match (&held, &self.hand_item) {
-            (Some(a), Some(b)) => a.item == b.item,
-            (None, None) => true,
-            _ => false,
-        };
-        let target = if same { 1.0 } else { 0.0 };
-        self.hand_height.1 += (target - self.hand_height.1).clamp(-0.4, 0.4);
-        if self.hand_height.1 < 0.1 {
-            self.hand_item = held;
-        }
-    }
     /// FirstPersonHandsAndItemsRenderer: the right arm or held item in view
     /// space, converted to camera-relative world space.
     fn hand_geometry(&mut self, alpha: f64) -> Vec<Vertex> {
@@ -6423,14 +6398,15 @@ impl Game<'_> {
             return out;
         }
         let a = alpha as f32;
-        let attack = self.swing_anim.0 + (self.swing_anim.1 - self.swing_anim.0) * a;
-        let attack = if self.swing.is_none() && self.swing_anim.1 == 0.0 {
-            0.0
+        // FirstPersonHandsAndItemsRenderer: the swing of the hand that
+        // swings, and its inverse arm height (the swap scale is 1 for every
+        // item but spears).
+        let attack = if self.swing.attack_hand() == horizon_client::first_person::Hand::Main {
+            self.swing.animation(a)
         } else {
-            attack
+            0.0
         };
-        let height = self.hand_height.0 + (self.hand_height.1 - self.hand_height.0) * a;
-        let inverse_height = 1.0 - height;
+        let inverse_height = 1.0 - self.heights.interpolated(a)[0];
         let (yaw, pitch) = (self.yaw.to_radians(), self.pitch.to_radians());
         let forward = glam::Vec3::new(
             -yaw.sin() * pitch.cos(),
@@ -6451,7 +6427,8 @@ impl Game<'_> {
         if self.held_map_geometry(to_world, attack, inverse_height, packed, &mut out) {
             return out;
         }
-        match self.hand_item.clone() {
+        let [main_item, _] = self.visible_hand_items();
+        match main_item {
             None => {
                 let Some(arm) = self.res.player_arm.clone() else {
                     return out;
@@ -7319,6 +7296,7 @@ impl Game<'_> {
             additive: &additive,
             celestial: &celestial,
             hand: &hand,
+            hand_fov_degrees: self.hud_fov_degrees(alpha as f32, camera.to_array()),
             screen: &screen,
             border,
             game_time: self.world.game_time as f32,
@@ -7491,22 +7469,20 @@ impl Game<'_> {
         }
         match button {
             MouseButton::Left => {
-                if pressed && self.attack() {
-                    return Ok(());
+                // KeyMapping.click: Minecraft.tick starts the attack.
+                if pressed {
+                    self.attack_clicks += 1;
                 }
                 self.toggles
                     .button(2, pressed, false, self.settings.toggle_attack);
                 self.left = self.toggles.is_down(2);
-                if pressed {
-                    self.destroy_delay = 0;
-                }
             }
             MouseButton::Right => {
                 self.toggles
                     .button(3, pressed, false, self.settings.toggle_use);
                 self.right = self.toggles.is_down(3);
                 if pressed {
-                    self.use_item()?;
+                    self.use_with_hand()?;
                     self.use_delay = 4;
                 }
             }
@@ -8357,10 +8333,13 @@ pub fn run() -> Result<()> {
         orbs: Vec::new(),
         xp_delay: 0,
         last_level_up: 0,
-        swing: None,
-        swing_anim: (0.0, 0.0),
-        hand_height: (1.0, 1.0),
-        hand_item: None,
+        swing: Default::default(),
+        swings_started: 0,
+        heights: Default::default(),
+        visible_hands: [(0, None), (0, None)],
+        clicks: Default::default(),
+        attack_clicks: 0,
+        hand_strength: Default::default(),
         settings,
         options_from_title: false,
         dragging: false,

crates/horizon-client/src/game/armor_stands.rs

@@ -183,7 +183,7 @@ impl Game<'_> {
         true
     }
     /// The armor stand under the crosshair, its distance and the hit point.
-    fn armor_stand_hit(&self) -> Option<(usize, f64, [f64; 3])> {
+    pub(super) fn armor_stand_hit(&self) -> Option<(usize, f64, [f64; 3])> {
         let eye = self.eye_position()?;
         let dir = view_vector(self.yaw, self.pitch);
         let reach: f64 = if self.creative { 5.0 } else { 3.0 };

crates/horizon-client/src/game/boats.rs

@@ -597,7 +597,7 @@ impl Game<'_> {
         self.swing_arm();
         true
     }
-    fn boat_hit(&self) -> Option<(usize, f64)> {
+    pub(super) fn boat_hit(&self) -> Option<(usize, f64)> {
         let eye = self.eye_position()?;
         let dir = view_vector(self.yaw, self.pitch);
         let reach: f64 = if self.creative { 5.0 } else { 3.0 };

crates/horizon-client/src/game/dragon.rs

@@ -722,10 +722,9 @@ impl Game<'_> {
             .play("minecraft:entity.ender_dragon.hurt", Some(at), 5.0, pitch);
     }
     /// Player melee on the dragon's parts or a crystal under the crosshair.
-    pub(super) fn attack_dragon(&mut self) -> bool {
-        let Some(eye) = self.eye_position() else {
-            return false;
-        };
+    /// The dragon part under the crosshair within reach: its id and distance.
+    pub(super) fn dragon_hit(&self) -> Option<(u32, f64)> {
+        let eye = self.eye_position()?;
         let dir = super::view_vector(self.yaw, self.pitch);
         let reach: f64 = if self.creative { 5.0 } else { 3.0 };
         let mut best: Option<(u32, f64)> = None;
@@ -750,7 +749,12 @@ impl Game<'_> {
                 best = Some((id, t0));
             }
         }
-        let Some((id, d)) = best else { return false };
+        best
+    }
+    pub(super) fn attack_dragon(&mut self) -> bool {
+        let Some((id, d)) = self.dragon_hit() else {
+            return false;
+        };
         if !self.before_block(d) || self.mob_hit().is_some_and(|m| m.1 < d) {
             return false;
         }

crates/horizon-client/src/game/fov.rs

@@ -86,6 +86,15 @@ impl Game<'_> {
             false,
         )
     }
+    /// `Camera.calculateHudFov`: the first-person hand's field of view.
+    pub(super) fn hud_fov_degrees(&self, partial: f32, camera: [f64; 3]) -> f32 {
+        self.view.calculate_hud_fov(
+            partial,
+            self.fov_effect_scale(),
+            self.death_time(),
+            self.camera_fluid(camera),
+        )
+    }
     /// The pose `GameRenderer.renderLevel` multiplies into the projection:
     /// `bobHurt`, then `bobView` with the View Bobbing option.
     pub(super) fn bob_matrix(&self, partial: f32) -> glam::Mat4 {

crates/horizon-client/src/game/hand.rs

@@ -0,0 +1,372 @@
+//! The local player's hand: clicks and held attack through
+//! `horizon_client::first_person` (`Minecraft.startAttack` /
+//! `continueAttack`, `MultiPlayerGameMode` block breaking), the arm swing
+//! (`LivingEntity.SwingState`) and the first-person equip heights
+//! (`FirstPersonHandsAndItems`) with the item swap ticker they read.
+use super::{Game, Mining, Screen};
+use horizon_client::{
+    Result,
+    attack_strength::HeldStack,
+    first_person::{Hand, HandWorld, Hit, SwingAnimation, UseResult, swing_duration},
+    items::ItemStack,
+};
+
+/// The off hand's place in `visible_hands` (the main hand uses its hotbar slot).
+const OFFHAND: usize = usize::MAX;
+
+impl Game<'_> {
+    /// `LivingEntity.swing` with `getModifiedSwingDuration`.
+    pub(super) fn swing_hand(&mut self, hand: Hand, animation: SwingAnimation) {
+        let effects = &self.potions.effects;
+        let dig_speed = effects
+            .amplifier("haste")
+            .max(effects.amplifier("conduit_power"));
+        let fatigue = effects.amplifier("mining_fatigue");
+        let duration = swing_duration(animation, dig_speed, fatigue);
+        if self.swing.start_if_able(hand, animation, duration) {
+            self.swings_started += 1;
+        }
+    }
+    /// `swing(InteractionHand.MAIN_HAND)` with the default animation.
+    pub(super) fn swing_arm(&mut self) {
+        self.swing_hand(Hand::Main, SwingAnimation::DEFAULT);
+    }
+    /// `Player.resetAttackStrengthTicker`.
+    pub(super) fn reset_attack_strength(&mut self) {
+        self.attack_ticks = 0;
+        self.hand_strength.reset();
+    }
+    /// The attack and use part of `Minecraft.tick` for the local player:
+    /// attack clicks since the last tick and the held attack button.
+    pub(super) fn tick_local_hand(&mut self) -> Result<()> {
+        let attack_clicks = std::mem::take(&mut self.attack_clicks);
+        if self.screen == Screen::Playing && self.title.is_none() {
+            let mut clicks = std::mem::take(&mut self.clicks);
+            // keyAttack.isDown(); playing implies the grabbed mouse here
+            // (scripts under --control hold buttons without grabbing it).
+            let down = self.left;
+            let ticks = self.clicks.destroying.ticks;
+            let mut world = GameHands {
+                game: self,
+                error: None,
+            };
+            clicks.tick(&mut world, attack_clicks, 0, down, false);
+            let error = world.error.take();
+            self.clicks = clicks;
+            if let Some(e) = error {
+                return Err(e);
+            }
+            // A tick of breaking: the hit sound every fourth tick and the
+            // cracking particles.
+            let d = &self.clicks.destroying;
+            if d.active && d.ticks > ticks {
+                let (pos, first) = (d.pos, (d.ticks as u32 - 1).is_multiple_of(4));
+                let state = self.world.block(pos[0], pos[1], pos[2]);
+                if first {
+                    let sounds = self.res.facts.get(state).sounds.clone();
+                    self.audio.play(
+                        &sounds.hit,
+                        Some(pos.map(|v| f64::from(v) + 0.5)),
+                        (sounds.volume + 1.0) / 8.0,
+                        sounds.pitch * 0.5,
+                    );
+                }
+                if let Some(hit) = self.pick() {
+                    self.crack_particle(pos, hit.face, state);
+                }
+            }
+        } else {
+            // Minecraft.tick: a screen keeps the attack from starting.
+            self.clicks.miss_time = 10000;
+        }
+        let d = &self.clicks.destroying;
+        self.mining = d.active.then_some(Mining {
+            pos: d.pos,
+            progress: d.progress,
+            ticks: d.ticks as u32,
+        });
+        Ok(())
+    }
+    /// `BlockBehaviour.getDestroyProgress` with `Player.getDestroySpeed`.
+    pub(super) fn destroy_progress(&self, pos: [i32; 3]) -> f32 {
+        let state = self.world.block(pos[0], pos[1], pos[2]);
+        let facts = self.res.facts.get(state);
+        if facts.hardness == -1.0 {
+            return 0.0;
+        }
+        let held = self.held();
+        let mut speed = self.res.items.mining_speed(held, &facts.name);
+        speed = self.modify_destroy_speed(speed);
+        if let Some(eye) = self.eye_position()
+            && self
+                .res
+                .facts
+                .get(self.world.block(
+                    eye[0].floor() as i32,
+                    eye[1].floor() as i32,
+                    eye[2].floor() as i32,
+                ))
+                .fluid
+                == horizon_client::blocks::Fluid::Water
+        {
+            speed *= self.submerged_mining_speed();
+        }
+        if self.player.as_ref().is_some_and(|p| !p.ground.on_ground) {
+            speed /= 5.0;
+        }
+        let harvest = !facts.requires_tool || self.res.items.correct_for_drops(held, &facts.name);
+        speed / facts.hardness / if harvest { 30.0 } else { 100.0 }
+    }
+    /// Whether an attack would hit an entity rather than the block behind
+    /// it: the crosshair's `EntityHitResult`.
+    fn entity_targeted(&self) -> bool {
+        let before = |d: Option<f64>| d.is_some_and(|d| self.before_block(d));
+        before(self.painting_hit().map(|h| h.1))
+            || before(self.frame_hit().map(|h| h.1))
+            || before(self.armor_stand_hit().map(|h| h.1))
+            || before(self.boat_hit().map(|h| h.1))
+            || before(self.cart_hit().map(|h| h.1))
+            || before(self.dragon_hit().map(|h| h.1))
+            || before(self.mob_hit().map(|h| h.1))
+    }
+    /// `LocalPlayer.isHandsBusy`: paddling a boat.
+    fn hands_busy(&self) -> bool {
+        self.riding
+            .is_some_and(|id| self.boats.iter().any(|b| b.id == id))
+            && [
+                winit::keyboard::KeyCode::KeyW,
+                winit::keyboard::KeyCode::KeyS,
+                winit::keyboard::KeyCode::KeyA,
+                winit::keyboard::KeyCode::KeyD,
+            ]
+            .iter()
+            .any(|k| self.keys.contains(k))
+    }
+    /// `MultiPlayerGameMode.startUseItem`'s bookkeeping around the game's
+    /// use: nothing starts while a block is being broken or the hands are
+    /// busy, and `LocalPlayer.itemUsed` drops the hand after a use that
+    /// swung and spent (or, with infinite materials, kept) the item, or that
+    /// started using it.
+    pub(super) fn use_with_hand(&mut self) -> Result<()> {
+        if self.clicks.destroying.active || self.hands_busy() {
+            return Ok(());
+        }
+        let before = self.held().cloned();
+        let swings = self.swings_started;
+        let using = self.using.is_some();
+        self.use_item()?;
+        let swung = self.swings_started != swings;
+        let after = self.held().cloned();
+        let spent = match (&before, &after) {
+            (Some(a), Some(b)) => a.count != b.count || a.item != b.item || self.creative,
+            _ => false,
+        };
+        if (swung && spent) || (!using && self.using.is_some() && after.is_some()) {
+            self.heights.item_used(Hand::Main);
+        }
+        Ok(())
+    }
+    /// `LocalPlayer.tick`: the swing (`LivingEntity.baseTick`), the attack
+    /// strength and item swap tickers (`Player.tick`), then
+    /// `FirstPersonHandsAndItems.tick`.
+    pub(super) fn tick_hand(&mut self) {
+        self.swing.tick();
+        let main = self.inventory[self.selected].clone();
+        self.hand_strength.tick(main.as_ref().map(|s| HeldStack {
+            item: s.item.to_string(),
+            rest: format!("{} {} {:?}", s.count, s.damage, s.extra),
+        }));
+        let next = [(self.selected, main), (OFFHAND, self.offhand.clone())];
+        // shouldInstantlyReplaceVisibleItem: the same stack, or an equal one
+        // (matchesIgnoringComponents; every item plays the swap animation).
+        // A stack that stays in its slot with the same item is the same
+        // stack, whatever its count (vanilla shrinks and grows it in place).
+        let mut changed = [false; 2];
+        for h in 0..2 {
+            let same = match (&self.visible_hands[h], &next[h]) {
+                ((_, None), (_, None)) => true,
+                ((slot, Some(a)), (next_slot, Some(b))) => {
+                    a.item == b.item
+                        && (slot == next_slot || (a.count == b.count && a.extra == b.extra))
+                }
+                _ => false,
+            };
+            if same {
+                self.visible_hands[h] = next[h].clone();
+            }
+            changed[h] = !same;
+        }
+        let speed = self.main_hand_attack_speed();
+        let replace = self.heights.tick(
+            self.hands_busy(),
+            self.hand_strength.swap_scale(1.0, speed),
+            changed,
+        );
+        for h in 0..2 {
+            if replace[h] {
+                self.visible_hands[h] = next[h].clone();
+            }
+        }
+    }
+    /// `Attributes.ATTACK_SPEED` with the main-hand item's modifier.
+    fn main_hand_attack_speed(&self) -> f64 {
+        horizon_client::attack_strength::BASE_ATTACK_SPEED
+            + self
+                .held()
+                .and_then(|h| self.res.items.get(&h.item))
+                .map_or(0.0, |i| f64::from(i.attack_speed))
+    }
+    /// The visible main- and off-hand items.
+    pub(super) fn visible_hand_items(&self) -> [Option<ItemStack>; 2] {
+        [
+            self.visible_hands[0].1.clone(),
+            self.visible_hands[1].1.clone(),
+        ]
+    }
+}
+
+/// The game as `first_person`'s world: the crosshair, breaking and attacking.
+struct GameHands<'g, 'a> {
+    game: &'g mut Game<'a>,
+    error: Option<Box<dyn std::error::Error>>,
+}
+impl GameHands<'_, '_> {
+    fn keep(&mut self, r: Result<()>) {
+        if let Err(e) = r
+            && self.error.is_none()
+        {
+            self.error = Some(e);
+        }
+    }
+}
+impl HandWorld for GameHands<'_, '_> {
+    fn hit(&mut self) -> Hit {
+        if self.game.entity_targeted() {
+            return Hit::Entity;
+        }
+        match self.game.pick() {
+            Some(h) => Hit::Block {
+                pos: h.pos,
+                face: match h.face {
+                    [0, -1, 0] => 0,
+                    [0, 1, 0] => 1,
+                    [0, 0, -1] => 2,
+                    [0, 0, 1] => 3,
+                    [-1, 0, 0] => 4,
+                    _ => 5,
+                },
+            },
+            None => Hit::Miss,
+        }
+    }
+    fn is_air(&mut self, pos: [i32; 3]) -> bool {
+        let state = self.game.world.block(pos[0], pos[1], pos[2]);
+        self.game.res.facts.get(state).name.ends_with("air")
+    }
+    fn creative(&self) -> bool {
+        self.game.creative
+    }
+    fn spectator(&self) -> bool {
+        self.game.spectator()
+    }
+    fn instabuild(&self) -> bool {
+        self.game.creative
+    }
+    fn hands_busy(&self) -> bool {
+        self.game.hands_busy()
+    }
+    fn using_item(&self) -> bool {
+        self.game.using.is_some()
+    }
+    fn item_enabled(&mut self, _: Hand) -> bool {
+        true
+    }
+    fn held_empty(&mut self, hand: Hand) -> bool {
+        match hand {
+            Hand::Main => self.game.held().is_none(),
+            Hand::Off => self.game.offhand.is_none(),
+        }
+    }
+    fn held_count(&mut self, hand: Hand) -> i32 {
+        let stack = match hand {
+            Hand::Main => self.game.held(),
+            Hand::Off => self.game.offhand.as_ref(),
+        };
+        stack.map_or(0, |s| s.count as i32)
+    }
+    fn infinite_materials(&self) -> bool {
+        self.game.creative
+    }
+    fn cannot_attack(&mut self) -> bool {
+        false
+    }
+    fn piercing_weapon(&mut self) -> bool {
+        false
+    }
+    fn attack_animation(&mut self) -> SwingAnimation {
+        SwingAnimation::DEFAULT
+    }
+    fn interact_animation(&mut self, _: Hand) -> SwingAnimation {
+        SwingAnimation::DEFAULT
+    }
+    fn piercing_attack(&mut self, _: SwingAnimation) {}
+    fn attack_entity(&mut self) -> bool {
+        self.game.attack()
+    }
+    fn block_action_restricted(&mut self, _: [i32; 3]) -> bool {
+        !self.game.may_build()
+    }
+    fn within_border(&mut self, _: [i32; 3]) -> bool {
+        true
+    }
+    fn attack_block(&mut self, _: [i32; 3]) {}
+    fn destroy_progress(&mut self, pos: [i32; 3]) -> f32 {
+        self.game.destroy_progress(pos)
+    }
+    fn destroy_block(&mut self, pos: [i32; 3]) -> bool {
+        if self.is_air(pos) {
+            return false;
+        }
+        // Item.canDestroyBlock: swords, tridents and maces cannot break
+        // blocks in creative.
+        let held = self.game.held().map(|s| s.item.to_string());
+        if self.game.creative
+            && held.is_some_and(|i| {
+                i.ends_with("_sword") || i == "minecraft:trident" || i == "minecraft:mace"
+            })
+        {
+            return false;
+        }
+        let r = self.game.break_block(pos);
+        self.keep(r);
+        true
+    }
+    fn main_hand_key(&mut self) -> String {
+        self.game
+            .held()
+            .map_or(String::new(), |s| format!("{} {:?}", s.item, s.extra))
+    }
+    fn destroy_stage(&mut self, _: [i32; 3], _: Option<i32>) {}
+    fn swing(&mut self, hand: Hand, animation: SwingAnimation) {
+        self.game.swing_hand(hand, animation);
+    }
+    fn reset_attack_strength(&mut self) {
+        self.game.reset_attack_strength();
+    }
+    fn entity_within_border(&mut self) -> bool {
+        true
+    }
+    fn use_on_entity(&mut self, _: Hand) -> Option<UseResult> {
+        None
+    }
+    fn use_on_block(&mut self, _: Hand) -> UseResult {
+        UseResult::Pass
+    }
+    fn use_item(&mut self, _: Hand) -> UseResult {
+        UseResult::Pass
+    }
+    fn item_used(&mut self, hand: Hand) {
+        self.game.heights.item_used(hand);
+    }
+    fn release_using(&mut self) {}
+}

crates/horizon-client/src/game/lan_actions.rs

@@ -29,8 +29,7 @@ pub(super) struct GuestPlay {
     using: Option<(usize, u32)>,
     use_delay: u32,
     attack_ticks: u32,
-    swing: Option<u32>,
-    swing_anim: (f32, f32),
+    swing: horizon_client::first_person::SwingState,
     /// The block being dug and the face the client aimed at.
     digging: Option<([i32; 3], [i32; 3])>,
     last_progress: i32,
@@ -131,8 +130,7 @@ impl Game<'_> {
         let using = std::mem::replace(&mut self.using, play.using.take());
         let use_delay = std::mem::replace(&mut self.use_delay, play.use_delay);
         let attack_ticks = std::mem::replace(&mut self.attack_ticks, play.attack_ticks);
-        let swing = std::mem::replace(&mut self.swing, play.swing.take());
-        let swing_anim = std::mem::replace(&mut self.swing_anim, play.swing_anim);
+        let swing = std::mem::replace(&mut self.swing, play.swing);
         let (left, right) = (self.left, self.right);
         self.left = play.digging.is_some();
         self.right = play.using.is_some() || self.using.is_some();
@@ -153,7 +151,6 @@ impl Game<'_> {
         play.use_delay = std::mem::replace(&mut self.use_delay, use_delay);
         play.attack_ticks = std::mem::replace(&mut self.attack_ticks, attack_ticks);
         play.swing = std::mem::replace(&mut self.swing, swing);
-        play.swing_anim = std::mem::replace(&mut self.swing_anim, swing_anim);
         self.container = container;
         self.screen = screen;
         if sneak {
@@ -689,7 +686,7 @@ impl Game<'_> {
             .mining
             .as_ref()
             .map_or(-1, |m| (m.progress.clamp(0.0, 1.0) * 10.0) as i32 - 1);
-        let swinging = play.swing.is_some();
+        let swinging = play.swing.swinging();
         if progress != play.last_progress && progress >= 0 {
             play.last_progress = progress;
             host.hub.broadcast_near(
@@ -779,7 +776,7 @@ impl Game<'_> {
             };
             let (id, at) = (g.entity_id, g.position);
             let play = host.play.get_mut(&conn).expect("play");
-            let swinging = play.swing == Some(0);
+            let swinging = play.swing.swinging() && play.swing.ticks == 0;
             if swinging && !play.swung {
                 host.hub.swing(id, 0, at, Some(conn));
             }

crates/horizon-client/src/game/minecarts.rs

@@ -890,7 +890,7 @@ impl Game<'_> {
         self.swing_arm();
         true
     }
-    fn cart_hit(&self) -> Option<(usize, f64)> {
+    pub(super) fn cart_hit(&self) -> Option<(usize, f64)> {
         let eye = self.eye_position()?;
         let dir = view_vector(self.yaw, self.pitch);
         let reach: f64 = if self.creative { 5.0 } else { 3.0 };

crates/horizon-client/src/game/perspective.rs

@@ -297,8 +297,8 @@ impl Game<'_> {
         }
         let crouching = p.pose == Pose::Crouching;
         let (position, flying) = (p.position, p.flying || p.fall_flying);
-        let attack = self.swing_anim;
-        let swinging = self.swing.is_some();
+        let attack = (self.swing.old_animation, self.swing.animation);
+        let swinging = self.swing.swinging();
         let (yaw, pitch) = (self.yaw, self.pitch);
         let main = self.inventory[self.selected]
             .as_ref()

crates/horizon-client/src/gfx.rs

@@ -78,6 +78,9 @@ pub struct Frame<'a> {
     pub celestial: &'a [Vertex],
     /// First-person hand and held item, drawn after clearing depth.
     pub hand: &'a [Vertex],
+    /// `CameraRenderState.hudFov`: the hand's own field of view
+    /// (`GameRenderer.render3dHud`).
+    pub hand_fov_degrees: f32,
     /// Full-screen camera effects drawn over the world and hand, under the HUD.
     pub screen: &'a [crate::screen_effects::ScreenQuad],
     /// The world border wall, when near enough to be drawn.
@@ -139,6 +142,9 @@ pub struct Renderer {
     screen_buffer: wgpu::Buffer,
     screen_capacity: u64,
     entity_group: wgpu::BindGroup,
+    /// The entity resources with the hand's projection (`hand_globals`).
+    hand_group: wgpu::BindGroup,
+    hand_globals: wgpu::Buffer,
     entity_buffer: wgpu::Buffer,
     entity_capacity: u64,
     group: wgpu::BindGroup,
@@ -470,6 +476,12 @@ impl Renderer {
             usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
             mapped_at_creation: false,
         });
+        let hand_globals = device.create_buffer(&wgpu::BufferDescriptor {
+            label: Some("First-person hand globals"),
+            size: std::mem::size_of::<Globals>() as u64,
+            usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
+            mapped_at_creation: false,
+        });
         let (mips, mip_levels) = mip_chain(sprite_pixels, sprite_size, layers);
         let sprite_texture = device.create_texture_with_data(
             &queue,
@@ -665,6 +677,32 @@ impl Renderer {
                 },
             ],
         });
+        let hand_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
+            label: Some("First-person hand resources"),
+            layout: &entity_bindings,
+            entries: &[
+                wgpu::BindGroupEntry {
+                    binding: 0,
+                    resource: hand_globals.as_entire_binding(),
+                },
+                wgpu::BindGroupEntry {
+                    binding: 1,
+                    resource: wgpu::BindingResource::TextureView(&atlas_view),
+                },
+                wgpu::BindGroupEntry {
+                    binding: 2,
+                    resource: wgpu::BindingResource::Sampler(&atlas_sampler),
+                },
+                wgpu::BindGroupEntry {
+                    binding: 3,
+                    resource: wgpu::BindingResource::TextureView(&lightmap_view),
+                },
+                wgpu::BindGroupEntry {
+                    binding: 4,
+                    resource: wgpu::BindingResource::Sampler(&lightmap_sampler),
+                },
+            ],
+        });
         let entity_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
             label: Some("Entity layout"),
             bind_group_layouts: &[Some(&entity_bindings)],
@@ -1065,6 +1103,8 @@ impl Renderer {
             screen_buffer,
             screen_capacity,
             entity_group,
+            hand_group,
+            hand_globals,
             entity_buffer,
             entity_capacity,
             group,
@@ -1492,6 +1532,20 @@ impl Renderer {
         };
         self.queue
             .write_buffer(&self.globals, 0, bytemuck::bytes_of(&globals));
+        // GameRenderer.render3dHud: the hand's projection at hudFov, with the
+        // bob in its pose rather than the projection (same product).
+        let hand_projection = Mat4::from_cols_array(&crate::camera::hand_projection(
+            frame.hand_fov_degrees,
+            self.config.width as f32,
+            self.config.height.max(1) as f32,
+            (frame.distance * 4.0).max(1024.0),
+        ));
+        let hand_globals = Globals {
+            view_proj: (hand_projection * frame.bob * view).to_cols_array_2d(),
+            ..globals
+        };
+        self.queue
+            .write_buffer(&self.hand_globals, 0, bytemuck::bytes_of(&hand_globals));
         // Frustum culling and camera-relative origins.
         let planes = frustum(view_proj);
         let camera = frame.camera;
@@ -1803,7 +1857,7 @@ impl Renderer {
                 ..Default::default()
             });
             pass.set_pipeline(&self.entity_pipeline);
-            pass.set_bind_group(0, &self.entity_group, &[]);
+            pass.set_bind_group(0, &self.hand_group, &[]);
             pass.set_index_buffer(self.indices.slice(..), wgpu::IndexFormat::Uint32);
             pass.set_vertex_buffer(0, self.entity_buffer.slice(..));
             pass.draw_indexed(

crates/horizon-client/src/lib.rs

@@ -41,6 +41,7 @@ pub mod entities;
 pub mod entity_nbt;
 pub mod environment;
 pub mod fastutil_order;
+pub mod first_person;
 pub mod flatgen;
 pub mod fog;
 pub mod font;

mods/horizon/src/test/java/dev/horizonlab/parity/VanillaCameraOracle.java

@@ -299,6 +299,11 @@ public final class VanillaCameraOracle {
                         + " " + fb(up.x()) + " " + fb(up.y()) + " " + fb(up.z())
                         + " " + fb(left.x()) + " " + fb(left.y()) + " " + fb(left.z())
                         + " " + camera.isDetached() + " " + fb(fv) + " " + fb(hv));
+                    // Camera.setupPerspective and GameRenderer.render3dHud's hudProjection:
+                    // Projection.getMatrix's setPerspective (planes reversed, zero-to-one depth).
+                    float w = f(op.get(4)), h = f(op.get(5)), far = f(op.get(6));
+                    out.println("projection" + matrix(new Matrix4f().setPerspective(fv * (float) (Math.PI / 180.0), w / h, far, 0.05F, true))
+                        + matrix(new Matrix4f().setPerspective(hv * (float) (Math.PI / 180.0), w / h, far, 0.05F, true)));
                 }
                 default -> throw new IllegalArgumentException(op.toString());
             }
@@ -388,6 +393,16 @@ public final class VanillaCameraOracle {
         out.println(sb);
     }
 
+    static String matrix(Matrix4f m) {
+        var sb = new StringBuilder();
+        for (int col = 0; col < 4; col++) {
+            for (int row = 0; row < 4; row++) {
+                sb.append(' ').append(fb(m.get(col, row)));
+            }
+        }
+        return sb.toString();
+    }
+
     static void avatar(JsonObject c, PrintWriter out) throws Exception {
         StubPlayer p = make(StubPlayer.class);
         var state = new ClientAvatarState();

mods/horizon/src/test/java/dev/horizonlab/parity/VanillaFirstPersonOracle.java

@@ -0,0 +1,385 @@
+package dev.horizonlab.parity;
+
+import com.google.gson.*;
+import java.io.*;
+import java.lang.reflect.*;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.*;
+import java.util.*;
+import net.minecraft.client.Minecraft;
+import net.minecraft.client.multiplayer.ClientLevel;
+import net.minecraft.client.multiplayer.ClientPacketListener;
+import net.minecraft.client.multiplayer.MultiPlayerGameMode;
+import net.minecraft.client.multiplayer.prediction.BlockStatePredictionHandler;
+import net.minecraft.client.player.FirstPersonHandsAndItems;
+import net.minecraft.client.player.LocalPlayer;
+import net.minecraft.client.renderer.item.ItemModelResolver;
+import net.minecraft.client.tutorial.Tutorial;
+import net.minecraft.core.*;
+import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.network.protocol.Packet;
+import net.minecraft.resources.Identifier;
+import net.minecraft.tags.TagKey;
+import net.minecraft.world.InteractionHand;
+import net.minecraft.world.InteractionResult;
+import net.minecraft.world.effect.*;
+import net.minecraft.world.entity.*;
+import net.minecraft.world.entity.ai.attributes.*;
+import net.minecraft.world.entity.player.*;
+import net.minecraft.world.flag.FeatureFlagSet;
+import net.minecraft.world.flag.FeatureFlags;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.item.component.SwingAnimation;
+import net.minecraft.world.level.GameType;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.border.WorldBorder;
+import net.minecraft.world.level.gameevent.GameEvent;
+import net.minecraft.world.level.material.*;
+import net.minecraft.world.phys.*;
+
+/**
+ * Drives the real Minecraft.startAttack, continueAttack and startUseItem,
+ * MultiPlayerGameMode's startDestroyBlock, continueDestroyBlock,
+ * stopDestroyBlock, destroyBlock and attack, LivingEntity.swing with its
+ * SwingState and getModifiedSwingDuration, Player's attack strength and item
+ * swap tickers and getItemSwapScale, and FirstPersonHandsAndItems.tick and
+ * itemUsed, tick by tick over scripted clicks and crosshair targets. The
+ * player is a LocalPlayer shell with a real Inventory and attributes; the
+ * level, connection and item model resolver are shells answering what these
+ * read, and the results of using items on blocks, entities and the air are
+ * scripted. The attack and use part of Minecraft.handleKeybinds and the
+ * ticker lines of Player.tick are mirrored here in vanilla's order.
+ */
+public final class VanillaFirstPersonOracle {
+    static Object unsafe;
+    static Method allocate;
+
+    @SuppressWarnings("unchecked")
+    static <T> T make(Class<T> type) throws Exception {
+        return (T) allocate.invoke(unsafe, type);
+    }
+
+    static Field field(Class<?> type, String name) throws Exception {
+        for (Class<?> c = type; c != null; c = c.getSuperclass()) {
+            try {
+                Field f = c.getDeclaredField(name);
+                f.setAccessible(true);
+                return f;
+            } catch (NoSuchFieldException e) {
+                // try the superclass
+            }
+        }
+        throw new NoSuchFieldException(type + "." + name);
+    }
+
+    static Method method(Class<?> type, String name, Class<?>... args) throws Exception {
+        Method m = type.getDeclaredMethod(name, args);
+        m.setAccessible(true);
+        return m;
+    }
+
+    static String fb(float v) {
+        return String.format("%08x", Float.floatToRawIntBits(v));
+    }
+
+    static List<String> events = new ArrayList<>();
+    static Map<BlockPos, BlockState> blocks = new HashMap<>();
+    static JsonObject step;
+
+    static String hand(InteractionHand h) {
+        return h == InteractionHand.MAIN_HAND ? "main" : "off";
+    }
+
+    static InteractionResult result(String name) {
+        return switch (name) {
+            case "success" -> InteractionResult.SUCCESS;
+            case "server" -> InteractionResult.SUCCESS_SERVER;
+            case "consume" -> InteractionResult.CONSUME;
+            case "fail" -> InteractionResult.FAIL;
+            default -> InteractionResult.PASS;
+        };
+    }
+
+    static final class Level0 extends ClientLevel {
+        Level0() {
+            super(null, null, null, null, 0, 0, null, false, 0L, 0);
+        }
+
+        @Override public BlockState getBlockState(BlockPos pos) { return blocks.getOrDefault(pos, Blocks.AIR.defaultBlockState()); }
+        @Override public FluidState getFluidState(BlockPos pos) { return Fluids.EMPTY.defaultFluidState(); }
+        @Override public boolean setBlock(BlockPos pos, BlockState state, int flags, int limit) {
+            blocks.put(pos.immutable(), state);
+            return true;
+        }
+        @Override public void levelEvent(Entity source, int type, BlockPos pos, int data) { }
+        @Override public void gameEvent(Holder<GameEvent> event, Vec3 pos, GameEvent.Context context) { }
+        @Override public void destroyBlockProgress(int id, BlockPos pos, int progress) {
+            events.add("stage " + pos.getX() + " " + pos.getY() + " " + pos.getZ() + " " + progress);
+        }
+        @Override public void addBreakingBlockEffects(BlockPos pos, Direction direction, boolean sound) { }
+        @Override public FeatureFlagSet enabledFeatures() { return FeatureFlags.REGISTRY.allFlags(); }
+    }
+
+    static final class Connection0 extends ClientPacketListener {
+        Connection0() {
+            super(null, null, null);
+        }
+
+        @Override public void send(Packet<?> packet) { }
+    }
+
+    static final class Resolver extends ItemModelResolver {
+        Resolver() {
+            super(null);
+        }
+
+        // No vanilla item model turns hand_animation_on_swap off, and only
+        // spears (not scripted here) scale the swap animation.
+        @Override public boolean shouldPlaySwapAnimation(ItemStack stack) { return true; }
+        @Override public float swapAnimationScale(ItemStack stack) { return 1.0F; }
+    }
+
+    static final class Player0 extends LocalPlayer {
+        AttributeMap attributes;
+        boolean inRange;
+
+        Player0() {
+            super(null, null, null, null, null, Input.EMPTY, false, null, null);
+        }
+
+        @Override public AttributeMap getAttributes() { return attributes; }
+        @Override public boolean isEyeInFluid(TagKey<Fluid> type) { return false; }
+        @Override public boolean onGround() { return true; }
+        @Override public boolean isWithinEntityInteractionRange(Entity entity, double buffer) { return inRange; }
+        @Override public void attack(Entity entity) { events.add("attack"); }
+        @Override public boolean swing(InteractionHand hand, SwingAnimation animation, boolean send) {
+            boolean started = super.swing(hand, animation, send);
+            events.add("swing " + hand(hand) + " " + animation.duration() + " " + started);
+            return started;
+        }
+        @Override public void itemUsed(InteractionHand hand) {
+            events.add("used " + hand(hand));
+            super.itemUsed(hand);
+        }
+    }
+
+    static final class GameMode0 extends MultiPlayerGameMode {
+        GameMode0(Minecraft minecraft, ClientPacketListener connection) {
+            super(minecraft, connection);
+        }
+
+        @Override public boolean destroyBlock(BlockPos pos) {
+            boolean changed = super.destroyBlock(pos);
+            events.add("destroy " + pos.getX() + " " + pos.getY() + " " + pos.getZ() + " " + changed);
+            return changed;
+        }
+        @Override public void releaseUsingItem(Player player) { events.add("release"); }
+
+        InteractionResult scripted(String kind, Player player, InteractionHand hand) {
+            String name = step.getAsJsonObject("uses").get(kind).getAsString();
+            events.add("use " + kind + " " + hand(hand) + " " + name);
+            InteractionResult r = result(name);
+            if (r instanceof InteractionResult.Success && step.get("shrink").getAsBoolean()) {
+                player.getItemInHand(hand).shrink(1);
+            }
+            return r;
+        }
+
+        @Override public InteractionResult useItemOn(LocalPlayer player, InteractionHand hand, BlockHitResult hit) { return scripted("block", player, hand); }
+        @Override public InteractionResult useItem(Player player, InteractionHand hand) { return scripted("item", player, hand); }
+        @Override public InteractionResult interact(Player player, Entity entity, EntityHitResult hit, InteractionHand hand) {
+            return scripted("entity", player, hand);
+        }
+    }
+
+    static ItemStack stack(JsonElement e) {
+        if (e.isJsonNull()) {
+            return ItemStack.EMPTY;
+        }
+        var a = e.getAsJsonArray();
+        return new ItemStack(BuiltInRegistries.ITEM.getValue(Identifier.parse(a.get(0).getAsString())), a.get(1).getAsInt());
+    }
+
+    /** LivingEntity.collectEquipmentChanges for the main hand: the item's attribute modifiers. */
+    static AttributeMap attributes(ItemStack main) {
+        var map = new AttributeMap(Player.createAttributes().build());
+        main.forEachModifier(EquipmentSlot.MAINHAND, (attribute, modifier) -> {
+            var instance = map.getInstance(attribute);
+            if (instance != null) {
+                instance.addTransientModifier(modifier);
+            }
+        });
+        return map;
+    }
+
+    public static void main(String[] args) throws Exception {
+        // The vanilla data pack: item components (tools, attribute modifiers) and block tags.
+        ParityData.init();
+        var u = Class.forName("sun.misc.Unsafe");
+        unsafe = field(u, "theUnsafe").get(null);
+        allocate = u.getMethod("allocateInstance", Class.class);
+        Method startAttack = method(Minecraft.class, "startAttack");
+        Method continueAttack = method(Minecraft.class, "continueAttack", boolean.class);
+        Method startUseItem = method(Minecraft.class, "startUseItem");
+        Field missTime = field(Minecraft.class, "missTime");
+        Field rightClickDelay = field(Minecraft.class, "rightClickDelay");
+        Field swingState = field(LivingEntity.class, "swingState");
+        Field attackTicker = field(LivingEntity.class, "attackStrengthTicker");
+        Field swapTicker = field(LivingEntity.class, "itemSwapTicker");
+        Field lastItem = field(Player.class, "lastItemInMainHand");
+        Field hands = field(LocalPlayer.class, "firstPersonHandsAndItems");
+        Field handsBusy = field(LocalPlayer.class, "handsBusy");
+        Field using = field(LocalPlayer.class, "startedUsingItem");
+        Field destroyDelay = field(MultiPlayerGameMode.class, "destroyDelay");
+        Field destroying = field(MultiPlayerGameMode.class, "isDestroying");
+        Field progress = field(MultiPlayerGameMode.class, "destroyProgress");
+        Field mainHeight = field(FirstPersonHandsAndItems.class, "mainHandHeight");
+        Field oMainHeight = field(FirstPersonHandsAndItems.class, "oMainHandHeight");
+        Field offHeight = field(FirstPersonHandsAndItems.class, "offHandHeight");
+        Field oOffHeight = field(FirstPersonHandsAndItems.class, "oOffHandHeight");
+        Field ticks = field(LivingEntity.SwingState.class, "ticks");
+        Field animation = field(LivingEntity.SwingState.class, "animation");
+        Field oldAnimation = field(LivingEntity.SwingState.class, "oldAnimation");
+        try (var out = new PrintWriter(Files.newBufferedWriter(Path.of(args[1]), StandardCharsets.UTF_8));
+             var lines = Files.lines(Path.of(args[0]))) {
+            int n = 0;
+            for (var line : (Iterable<String>) lines::iterator) {
+                var c = JsonParser.parseString(line).getAsJsonObject();
+                out.println("== " + n++);
+                blocks.clear();
+                for (var e : c.getAsJsonArray("blocks")) {
+                    var b = e.getAsJsonArray();
+                    blocks.put(new BlockPos(b.get(0).getAsInt(), b.get(1).getAsInt(), b.get(2).getAsInt()),
+                        BuiltInRegistries.BLOCK.getValue(Identifier.parse(b.get(3).getAsString())).defaultBlockState());
+                }
+                Minecraft mc = make(Minecraft.class);
+                Level0 level = make(Level0.class);
+                field(ClientLevel.class, "worldBorder").set(level, new WorldBorder());
+                field(ClientLevel.class, "blockStatePredictionHandler").set(level, new BlockStatePredictionHandler());
+                Connection0 connection = make(Connection0.class);
+                Player0 player = make(Player0.class);
+                field(LocalPlayer.class, "minecraft").set(player, mc);
+                field(LocalPlayer.class, "connection").set(player, connection);
+                field(Entity.class, "level").set(player, level);
+                field(Entity.class, "id").setInt(player, 1);
+                var equipment = new PlayerEquipment(player);
+                field(LivingEntity.class, "equipment").set(player, equipment);
+                field(Player.class, "inventory").set(player, new Inventory(player, equipment));
+                var abilities = new Abilities();
+                boolean creative = c.get("creative").getAsBoolean();
+                abilities.instabuild = creative;
+                field(Player.class, "abilities").set(player, abilities);
+                swingState.set(player, new LivingEntity.SwingState());
+                lastItem.set(player, ItemStack.EMPTY);
+                hands.set(player, new FirstPersonHandsAndItems());
+                var effects = new HashMap<Holder<MobEffect>, MobEffectInstance>();
+                if (!c.get("haste").isJsonNull()) {
+                    effects.put(MobEffects.HASTE, new MobEffectInstance(MobEffects.HASTE, 100000, c.get("haste").getAsInt()));
+                }
+                if (!c.get("fatigue").isJsonNull()) {
+                    effects.put(MobEffects.MINING_FATIGUE, new MobEffectInstance(MobEffects.MINING_FATIGUE, 100000, c.get("fatigue").getAsInt()));
+                }
+                field(LivingEntity.class, "activeEffects").set(player, effects);
+                player.getInventory().setItem(0, stack(c.get("main")));
+                equipment.set(EquipmentSlot.OFFHAND, stack(c.get("off")));
+                player.attributes = attributes(player.getMainHandItem());
+                field(Minecraft.class, "player").set(mc, player);
+                field(Minecraft.class, "level").set(mc, level);
+                field(Minecraft.class, "tutorial").set(mc, make(Tutorial.class));
+                field(Minecraft.class, "itemModelResolver").set(mc, make(Resolver.class));
+                var gameMode = new GameMode0(mc, connection);
+                field(MultiPlayerGameMode.class, "localPlayerMode").set(gameMode, creative ? GameType.CREATIVE : GameType.SURVIVAL);
+                field(Minecraft.class, "gameMode").set(mc, gameMode);
+                out.println("attack_speed " + Long.toHexString(Double.doubleToRawLongBits(player.getAttributeValue(Attributes.ATTACK_SPEED))));
+                var entity = make(net.minecraft.world.entity.item.ItemEntity.class);
+                field(Entity.class, "blockPosition").set(entity, BlockPos.ZERO);
+                field(Entity.class, "id").setInt(entity, 2);
+                int s = 0;
+                for (var e : c.getAsJsonArray("steps")) {
+                    step = e.getAsJsonObject();
+                    events.clear();
+                    if (!step.get("set").isJsonNull()) {
+                        var set = step.getAsJsonObject("set");
+                        if (set.get("hand").getAsString().equals("main")) {
+                            player.getInventory().setItem(0, stack(set.get("stack")));
+                        } else {
+                            equipment.set(EquipmentSlot.OFFHAND, stack(set.get("stack")));
+                        }
+                    }
+                    var hit = step.getAsJsonArray("hit");
+                    HitResult hitResult = switch (hit.get(0).getAsString()) {
+                        case "block" -> new BlockHitResult(Vec3.ZERO, Direction.from3DDataValue(hit.get(4).getAsInt()),
+                            new BlockPos(hit.get(1).getAsInt(), hit.get(2).getAsInt(), hit.get(3).getAsInt()), false);
+                        case "entity" -> {
+                            player.inRange = hit.get(1).getAsBoolean();
+                            yield new EntityHitResult(entity, Vec3.ZERO);
+                        }
+                        default -> BlockHitResult.miss(Vec3.ZERO, Direction.UP, BlockPos.ZERO);
+                    };
+                    field(Minecraft.class, "hitResult").set(mc, hitResult);
+                    handsBusy.setBoolean(player, step.get("busy").getAsBoolean());
+                    using.setBoolean(player, step.get("using").getAsBoolean());
+                    boolean attackDown = step.get("ad").getAsBoolean();
+                    boolean useDown = step.get("ud").getAsBoolean();
+                    // Minecraft.tick: rightClickDelay, then handleKeybinds' attack and use part.
+                    if (rightClickDelay.getInt(mc) > 0) {
+                        rightClickDelay.setInt(mc, rightClickDelay.getInt(mc) - 1);
+                    }
+                    boolean instant = false;
+                    if (player.isUsingItem()) {
+                        if (!useDown) {
+                            gameMode.releaseUsingItem(player);
+                        }
+                    } else {
+                        for (int i = 0; i < step.get("ac").getAsInt(); i++) {
+                            instant |= (boolean) startAttack.invoke(mc);
+                        }
+                        for (int i = 0; i < step.get("uc").getAsInt(); i++) {
+                            startUseItem.invoke(mc);
+                        }
+                    }
+                    if (useDown && rightClickDelay.getInt(mc) == 0 && !player.isUsingItem()) {
+                        startUseItem.invoke(mc);
+                    }
+                    continueAttack.invoke(mc, !instant && attackDown);
+                    if (missTime.getInt(mc) > 0) {
+                        missTime.setInt(mc, missTime.getInt(mc) - 1);
+                    }
+                    // LocalPlayer.tick: LivingEntity.baseTick's swing, the equipment's
+                    // attribute modifiers, Player.tick's tickers, then
+                    // FirstPersonHandsAndItems.tick.
+                    var swing = (LivingEntity.SwingState) swingState.get(player);
+                    swing.tick();
+                    // LivingEntity.tick's detectEquipmentUpdates: the main hand's modifiers.
+                    player.attributes = attributes(player.getMainHandItem());
+                    attackTicker.setInt(player, attackTicker.getInt(player) + 1);
+                    swapTicker.setInt(player, swapTicker.getInt(player) + 1);
+                    ItemStack main = player.getMainHandItem();
+                    if (!ItemStack.matches((ItemStack) lastItem.get(player), main)) {
+                        if (!ItemStack.isSameItem((ItemStack) lastItem.get(player), main)) {
+                            player.resetAttackStrengthTicker();
+                        }
+                        lastItem.set(player, main.copy());
+                    }
+                    var fp = (FirstPersonHandsAndItems) hands.get(player);
+                    fp.tick(player);
+                    for (var ev : events) {
+                        out.println(ev);
+                    }
+                    var current = player.getCurrentSwing();
+                    out.println("tick " + s++ + " " + (current == null ? "- 0" : hand(current.hand()) + " " + current.durationTicks())
+                        + " " + ticks.getInt(swing) + " " + fb(animation.getFloat(swing)) + " " + fb(oldAnimation.getFloat(swing))
+                        + " " + fb(player.getSwingAnimation(0.5F))
+                        + " " + attackTicker.getInt(player) + " " + swapTicker.getInt(player) + " " + fb(player.getItemSwapScale(1.0F))
+                        + " " + fb(mainHeight.getFloat(fp)) + " " + fb(oMainHeight.getFloat(fp))
+                        + " " + fb(offHeight.getFloat(fp)) + " " + fb(oOffHeight.getFloat(fp))
+                        + " " + missTime.getInt(mc) + " " + rightClickDelay.getInt(mc) + " " + destroyDelay.getInt(gameMode)
+                        + " " + destroying.getBoolean(gameMode) + " " + fb(progress.getFloat(gameMode)));
+                }
+            }
+        }
+        System.exit(0);
+    }
+}

tools/test_camera_parity.py

@@ -4,8 +4,10 @@ field-of-view easing), alignWithEntity (view rotation quaternion and basis,
 interpolated eye, third person back and front, camera distance and scale
 attributes with mounts, getMaxZoom clipping against visual shapes, sleeping),
 calculateFov/calculateHudFov (option, modifier, death and fluid effects,
-panoramic mode), AbstractClientPlayer.getFieldOfViewModifier (flight, speed
-attribute against walking speed, bow draw, spyglass), the walk and bob
+panoramic mode) with the world projection and the first-person hand's
+(GameRenderer.render3dHud at hudFov, whatever the FOV option),
+AbstractClientPlayer.getFieldOfViewModifier (flight, speed attribute against
+walking speed, bow draw, spyglass), the walk and bob
 history (ClientAvatarState, updateBob) and GameRenderer.bobHurt/bobView,
 driven tick by tick and frame by frame with identical scripted states."""
 import json
@@ -91,6 +93,12 @@ def entity_state(rng, center):
     return s
 
 
+def window(rng):
+    """Window size and Camera.depthFar for the world and hand projections."""
+    w, h = rng.choice([(1600, 1000), (854, 480), (1920, 1080), (800, 1200), (1, 1), (rng.randint(1, 4000), rng.randint(1, 3000))])
+    return [fbits(w), fbits(h), fbits(rng.choice([768.0, 128.0, 2048.0, 4096.0, rng.uniform(32, 4096)]))]
+
+
 def camera_cases(rng):
     for n in range(2500):
         center = rng.choice([(0, 64, 0), (-10, -60, 7), (1000, 120, -3000), (0, 0, 0)])
@@ -105,12 +113,27 @@ def camera_cases(rng):
                 ops.append(['tick'])
             elif kind == 'frame':
                 pt = rng.choice([0.0, 1.0, 0.5, 0.25, 0.999, rng.random()])
-                ops.append(['frame', fbits(pt), rng.choice([0, 0, 0, 1, 2, 3]), rng.random() < 0.05])
+                ops.append(['frame', fbits(pt), rng.choice([0, 0, 0, 1, 2, 3]), rng.random() < 0.05] + window(rng))
             else:
                 ops.append(['type', rng.randrange(3)])
         yield dict(t='camera', fov=rng.choice([70, 30, 110, 90, rng.randint(30, 110)]),
                    effect=dbits(rng.choice([1.0, 0.0, 0.5, rng.random()])), type=rng.choice([0, 1, 1, 2]),
                    cells=world(rng, center), ops=ops)
+    # The hand's projection at FOV 30, 70 and 110 while walking, sprinting, under
+    # speed, drawing a bow, dying and in fluids: GameRenderer.render3dHud uses
+    # hudFov, never the option or the modifier.
+    for fov in (30, 70, 110):
+        for speed in (f32(0.1), f32(0.1) * 1.3, 0.2, 0.05):
+            for use in (None, ['bow', 10]):
+                for dead in (None, 5):
+                    for fluid in (0, 1, 2):
+                        s = dict(kind='player', pos=[dbits(0.5), dbits(64.0), dbits(0.5)], prev=[dbits(0.5), dbits(64.0), dbits(0.5)],
+                                 xr=fbits(0.0), yr=fbits(0.0), xro=fbits(0.0), yro=fbits(0.0), eye=fbits(1.62), flying=False,
+                                 ws=fbits(0.1), speed=dbits(speed), use=use, scale_attr=dbits(1.0), dist=dbits(4.0),
+                                 sleeping=None, dead=dead, mount=None)
+                        ops = [['entity', s]] + [['tick']] * 8 + [['frame', fbits(pt), fluid, False, fbits(1600.0), fbits(1000.0), fbits(768.0)]
+                                                                 for pt in (0.0, 0.5, 1.0)]
+                        yield dict(t='camera', fov=fov, effect=dbits(1.0), type=0, cells={}, ops=ops)
     # A walled-in third-person camera stepping through every distance bound.
     for dist in [0.0, 0.5, 1.0, 2.0, 4.0, 8.0, 32.0]:
         for wall in range(0, 6):
@@ -124,7 +147,7 @@ def camera_cases(rng):
                          xr=fbits(15.0), yr=fbits(yaw), xro=fbits(15.0), yro=fbits(yaw), eye=fbits(1.62), flying=False,
                          ws=fbits(0.1), speed=dbits(f32(0.1)), use=None, scale_attr=dbits(1.0), dist=dbits(dist),
                          sleeping=None, dead=None, mount=None)
-                ops = [['entity', s]] + [['tick']] * 6 + [['frame', fbits(pt), 0, False] for pt in (0.0, 0.5, 1.0)]
+                ops = [['entity', s]] + [['tick']] * 6 + [['frame', fbits(pt), 0, False] + window(rng) for pt in (0.0, 0.5, 1.0)]
                 yield dict(t='camera', fov=70, effect=dbits(1.0), type=1 + (wall % 2), cells=cells, ops=ops)
 
 
@@ -184,7 +207,9 @@ def main():
              'interpolated eye with eye-height easing, first person, third person back and mirrored front, scale and '
              'camera_distance attributes including a living mount, getMaxZoom over the actual Level.clip with '
              'ClipContext.Block.VISUAL against controlled visual shapes, sleeping bed orientation), calculateFov and '
-             'calculateHudFov (option, eased modifier, death, water/lava with the effect scale, panoramic), '
+             'calculateHudFov (option, eased modifier, death, water/lava with the effect scale, panoramic), the world projection '
+             '(Camera.setupPerspective) and the hand projection GameRenderer.render3dHud sets up at hudFov, as JOML setPerspective '
+             'matrices, at FOV options 30, 70 and 110 among others, '
              'AbstractClientPlayer.getFieldOfViewModifier with real Abilities, attribute maps and item stacks, '
              'ClientAvatarState walk/bob history with AbstractClientPlayer.updateBob, and GameRenderer.bobHurt/bobView '
              'as the full JOML pose matrix with its property flags. The camera entity is a shell with controlled '

tools/test_first_person_parity.py

@@ -0,0 +1,175 @@
+#!/usr/bin/env python3
+"""Compare the local player's hand with the pinned client, tick by tick over
+scripted clicks: Minecraft.startAttack, continueAttack and startUseItem with
+handleKeybinds' attack and use part (missTime, rightClickDelay, held
+buttons), MultiPlayerGameMode's block breaking (survival progress, creative
+instant breaking and its destroy delay, swords that cannot break in
+creative, stopping), LivingEntity.swing with SwingState and haste or mining
+fatigue durations, Player's attack strength and item swap tickers, and
+FirstPersonHandsAndItems' equip heights (swap animation, itemUsed after
+placing or using an item, busy hands)."""
+import json
+import random
+import struct
+
+try:
+    from . import lab, oracle_harness as harness
+except ImportError:
+    import lab, oracle_harness as harness
+
+
+def fbits(v):
+    return struct.pack('>f', v).hex()
+
+
+def dbits(v):
+    return struct.pack('>d', v).hex()
+
+
+def f32(v):
+    return struct.unpack('>f', struct.pack('>f', v))[0]
+
+
+# What the probe needs about the scripted blocks and items, checked against
+# the client through the progress and attack speed both print:
+# Block.destroyTime and requiresCorrectToolForDrops,
+BLOCKS = {'minecraft:dirt': (0.5, False), 'minecraft:stone': (1.5, True), 'minecraft:glass': (0.3, False),
+          'minecraft:bedrock': (-1.0, False), 'minecraft:short_grass': (0.0, False), 'minecraft:oak_planks': (2.0, False)}
+# the Tool component's speed and correct-for-drops per item and block (1.0
+# and incorrect otherwise),
+TOOLS = {'minecraft:diamond_pickaxe minecraft:stone': (8.0, True), 'minecraft:diamond_shovel minecraft:dirt': (8.0, True),
+         'minecraft:diamond_pickaxe minecraft:glass': (1.0, False)}
+# and ATTACK_SPEED with the main-hand item's modifier (4.0 without one).
+SPEEDS = {'minecraft:diamond_sword': 4.0 + f32(-2.4), 'minecraft:diamond_pickaxe': 4.0 + f32(-2.8),
+          'minecraft:diamond_shovel': 4.0 + f32(-3.0)}
+ITEMS = [None, ['minecraft:diamond_sword', 1], ['minecraft:diamond_pickaxe', 1], ['minecraft:diamond_shovel', 1],
+         ['minecraft:dirt', 64], ['minecraft:dirt', 2], ['minecraft:bread', 3], ['minecraft:bow', 1], ['minecraft:shield', 1]]
+TARGETS = [(0, 64, 0), (1, 64, 0), (0, 65, 2)]
+
+
+def step(hit=('miss',), ac=0, uc=0, ad=False, ud=False, busy=False, using=False, uses=None, shrink=False, set=None):
+    return dict(hit=list(hit), ac=ac, uc=uc, ad=ad, ud=ud, busy=busy, using=using,
+                uses=uses or dict(entity='pass', block='pass', item='pass'), shrink=shrink, set=set)
+
+
+def case(steps, creative=False, main=None, off=None, blocks=None, haste=None, fatigue=None):
+    return dict(creative=creative, main=main, off=off, haste=haste, fatigue=fatigue,
+                blocks=[[*p, b] for p, b in (blocks or {}).items()], steps=steps,
+                rust=dict(blocks={k: [fbits(v[0]), v[1]] for k, v in BLOCKS.items()},
+                          tools={k: [fbits(v[0]), v[1]] for k, v in TOOLS.items()},
+                          attack_speed={k: dbits(v) for k, v in SPEEDS.items()}))
+
+
+def block_hit(pos, face=1):
+    return ('block', *pos, face)
+
+
+def scenarios():
+    stone = {TARGETS[0]: 'minecraft:stone', TARGETS[1]: 'minecraft:dirt', TARGETS[2]: 'minecraft:glass'}
+    for creative in (False, True):
+        for main in ITEMS:
+            # Hold attack on blocks until they break, then on the air behind.
+            for target, block in [(TARGETS[1], 'minecraft:dirt'), (TARGETS[0], 'minecraft:stone'), (TARGETS[0], 'minecraft:bedrock'),
+                                  (TARGETS[2], 'minecraft:short_grass'), (TARGETS[2], 'minecraft:glass')]:
+                steps = [step(block_hit(target), ac=1, ad=True)] + [step(block_hit(target), ad=True)] * 40 + [step()] * 8
+                yield case(steps, creative, main, blocks={target: block})
+            # Sweep across three blocks while holding, as when mining a tunnel.
+            steps = [step(block_hit(TARGETS[0]), ac=1, ad=True)]
+            for i in range(60):
+                steps.append(step(block_hit(TARGETS[(i // 7) % 3]), ad=True))
+            yield case(steps + [step()] * 6, creative, main, blocks=stone)
+            # Clicking the air, quickly and slowly; and clicking an entity.
+            for gap in (0, 1, 2, 3, 5, 9, 10, 11, 15):
+                steps = []
+                for _ in range(5):
+                    steps += [step(ac=1)] + [step()] * gap
+                yield case(steps + [step()] * 8, creative, main)
+                steps = []
+                for _ in range(5):
+                    steps += [step(('entity', True), ac=1)] + [step(('entity', True))] * gap
+                yield case(steps + [step(('entity', True), ac=1, ad=True)] + [step(('entity', True), ad=True)] * 8, creative, main)
+            # Placing and using: held right button on a block and in the air.
+            for result in ('success', 'server', 'consume', 'pass', 'fail'):
+                for shrink in (False, True):
+                    uses = dict(entity=result, block=result, item=result)
+                    steps = [step(block_hit(TARGETS[0]), uc=1, ud=True, uses=uses, shrink=shrink)]
+                    steps += [step(block_hit(TARGETS[0]), ud=True, uses=uses, shrink=shrink)] * 14 + [step(uses=uses)] * 8
+                    yield case(steps, creative, main, off=['minecraft:shield', 1], blocks=stone)
+                    steps = [step(uc=1, ud=True, uses=uses, shrink=shrink)] + [step(ud=True, uses=uses, shrink=shrink)] * 10
+                    yield case(steps + [step(uses=uses)] * 8, creative, main, blocks=stone)
+                    steps = [step(('entity', inr), uc=1, ud=True, uses=uses, shrink=shrink) for inr in (True, False, True)]
+                    yield case(steps + [step(('entity', True), uses=uses)] * 8, creative, main)
+            # Eating or drawing a bow: using the item, then releasing.
+            uses = dict(entity='pass', block='pass', item='consume')
+            steps = [step(uc=1, ud=True, uses=uses)] + [step(ud=True, using=True, ac=k % 2, ad=True, uses=uses) for k in range(12)]
+            steps += [step(using=True, uses=uses), step(uses=uses)] + [step()] * 8
+            yield case(steps, creative, main, off=['minecraft:bread', 3])
+    # Changing the held item: other items, the same item with another count,
+    # emptying the hand, while the attack recharges or the hands are busy.
+    for a in ITEMS:
+        for b in ITEMS:
+            for busy in (False, True):
+                steps = [step()] * 25 + [step(set=dict(hand='main', stack=b), busy=busy)] + [step(busy=busy)] * 25
+                steps += [step(set=dict(hand='off', stack=a))] + [step()] * 12 + [step(ac=1)] + [step()] * 30
+                yield case(steps, False, a)
+    # Haste and mining fatigue change the swing's length.
+    for haste in (None, 0, 1, 2, 4):
+        for fatigue in (None, 0, 1, 2):
+            steps = [step(block_hit(TARGETS[1]), ac=1, ad=True)] + [step(block_hit(TARGETS[1]), ad=True)] * 60 + [step(ac=1)] + [step()] * 20
+            yield case(steps, False, ['minecraft:diamond_shovel', 1], blocks={TARGETS[1]: 'minecraft:dirt'}, haste=haste, fatigue=fatigue)
+            yield case(steps, True, None, blocks={TARGETS[1]: 'minecraft:dirt'}, haste=haste, fatigue=fatigue)
+
+
+def random_cases(rng):
+    results = ['success', 'server', 'consume', 'pass', 'fail']
+    for _ in range(3000):
+        blocks = {p: rng.choice(list(BLOCKS) + ['minecraft:air']) for p in TARGETS}
+        steps = []
+        for _ in range(rng.randrange(5, 80)):
+            hit = rng.choice([('miss',), ('entity', rng.random() < 0.7)] + [block_hit(p, rng.randrange(6)) for p in TARGETS] * 2)
+            setting = None
+            if rng.random() < 0.04:
+                setting = dict(hand=rng.choice(['main', 'off']), stack=rng.choice(ITEMS))
+            steps.append(step(hit, ac=rng.choice([0] * 6 + [1, 1, 2]), uc=rng.choice([0] * 8 + [1, 2]), ad=rng.random() < 0.5,
+                              ud=rng.random() < 0.3, busy=rng.random() < 0.05, using=rng.random() < 0.08,
+                              uses=dict(entity=rng.choice(results), block=rng.choice(results), item=rng.choice(results)),
+                              shrink=rng.random() < 0.3, set=setting))
+        yield case(steps, rng.random() < 0.4, rng.choice(ITEMS), rng.choice(ITEMS), blocks,
+                   rng.choice([None] * 6 + [0, 1, 3]), rng.choice([None] * 6 + [0, 2]))
+
+
+def make_cases(build):
+    rng = random.Random(0x48414e44)
+    path = build / 'cases.jsonl'
+    cases = build / 'cases'
+    cases.mkdir(exist_ok=True)
+    count = 0
+    with path.open('w') as out:
+        for generator in (scenarios(), random_cases(rng)):
+            for c in generator:
+                text = json.dumps(c, separators=(',', ':'))
+                out.write(text + '\n')
+                if count < 20000:
+                    (cases / str(count)).write_text(text)
+                count += 1
+    return path, count
+
+
+def main():
+    scope = ('Real Minecraft.startAttack, continueAttack and startUseItem (with the attack and use part of handleKeybinds and '
+             'missTime mirrored in order), MultiPlayerGameMode.startDestroyBlock, continueDestroyBlock, stopDestroyBlock, '
+             'destroyBlock and attack, LivingEntity.swing with SwingState and getModifiedSwingDuration under haste and mining '
+             'fatigue, Player.getItemSwapScale and resetAttackStrengthTicker with the ticker lines of Player.tick, and '
+             'FirstPersonHandsAndItems.tick and itemUsed, on a LocalPlayer shell with a real Inventory, effects and attribute '
+             'modifiers, over scripted clicks, held buttons, crosshair targets, item changes and use results. Level effects '
+             '(particles, game events), packets and the outcome of using items on blocks, entities and the air are scripted '
+             'or absorbed; every vanilla item plays the swap animation unscaled except spears, which are not scripted.')
+    harness.differential(
+        'rust-first-person-parity', 'VanillaFirstPersonOracle', 'first_person_probe', make_cases, scope,
+        sources=[lab.ROOT / 'crates/horizon-client/src/first_person.rs', lab.ROOT / 'crates/horizon-client/src/attack_strength.rs',
+                 lab.ROOT / 'crates/horizon-client/src/camera.rs',
+                 lab.ROOT / 'mods/horizon/src/test/java/dev/horizonlab/parity/ParityData.java'])
+
+
+if __name__ == '__main__':
+    main()

tools/test_native_scene_motion.py

@@ -334,6 +334,31 @@ def sprint_corpus():
     for gap in range(12):
         seq=[0,1,0]+[0]*gap+[1]*12+[0]*3+[65]*20+[1]*12+[0]
         yield dict(position=vec((12,4,0)),ops=[op('controlled_tick',k) for k in seq])
+    # Sprint-jumping: Player.jumpFromGround's forward impulse while sprinting,
+    # with sprint held (65) or started by double-tapping forward, and jump
+    # pressed with it, tapped, held through landings (bunny hops) or held
+    # before sprinting; at several headings, with too little food to sprint,
+    # under a two-block ceiling and up onto a slab.
+    runs={
+        'held':[65]*12+[81]+[65]*14+[81]*2+[65]*14+[0]*10,
+        'together':[0,81]+[81]*30+[0]*10,
+        'hop':[65]*8+[81]*40+[0]*10,
+        'jump_first':[16]*3+[17]*3+[81]*30+[0]*10,
+        'double_tap':[1,0,1]+[1]*12+[17]+[1]*14+[17]*25+[0]*10,
+        'release_sprint':[65]*10+[81]*6+[17]*20+[1]*10+[0]*5,
+    }
+    for name,seq in runs.items():
+        for yaw in [0,45,90,180,300]:
+            for food in [20,6]:
+                for scene in ['open','ceiling','slab']:
+                    ops=[op('food',food=food,saturation=single(5),exhaustion=single(0),timer=0),op('yaw',single(yaw))]
+                    blocks=[]
+                    if scene=='ceiling':blocks=[([8,6,8+i],'stone',{}) for i in range(14)]
+                    elif scene=='slab':blocks=[([8,4,12],'stone_slab',{'type':'bottom'}),([8,4,13],'stone',{})]
+                    ops += [op('block',name='minecraft:'+b,position=pos,properties=props) for pos,b,props in blocks]
+                    ops += [op('controlled_tick',k) for k in seq]
+                    ops += [op('block',name='minecraft:air',position=pos) for pos,_,_ in blocks]
+                    yield dict(position=vec((8.5,4,8.5)),ops=ops)
 
 def main():
     parser=argparse.ArgumentParser(description=__doc__);parser.add_argument('--sprint-input',action='store_true');args=parser.parse_args()