Renderer: the ExternalPipeline hook, with the shadow request and its culling in gfx/external.rs

Step a of #14035 (layer plan M6). An external shader pipeline implements
ExternalPipeline; the renderer calls begin_frame and shadow_request on world
frames, resize and reset_history, and draws vanilla's way where it doesn't
answer. Nothing sets one yet: each point is one Option test.

ShadowView moves from pack_post (re-exported there) and ShadowCull,
shadow_box, shadow_runs and shadow_casters from gfx.rs, unchanged: the
engine's side of the shadow frame point.

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

crates/horizon-client-render/src/gfx.rs

@@ -74,6 +74,7 @@ pub use entity_batch::{
     WATER_MASK_OVERLAY, WORLD_TEXT_OVERLAY, WORLD_TEXT_POLYGON_OFFSET_OVERLAY, is_native_terrain,
     mark_oit,
 };
+use external::{ShadowCull, shadow_box, shadow_casters, shadow_runs};
 pub use view::{View, ViewSet};
 
 /// Window.getAppropriateLineWidth, in framebuffer pixels.
@@ -189,6 +190,7 @@ mod cull;
 mod dx12_compiler;
 mod end_sky;
 pub mod entity_skin;
+pub mod external;
 mod flat;
 mod frame_gen;
 mod gpu_culling;
@@ -1418,8 +1420,10 @@ pub struct Renderer {
     /// Per-frame scratch, kept to avoid allocating every frame.
     visible: Vec<resident::Visible>,
     visible_lods: Vec<lod::Visible>,
-    /// The sections a shader pack's shadow camera sees (`pack_post::ShadowView`).
+    /// The sections a shader pack's shadow camera sees (`external::ShadowView`).
     shadow_visible: Vec<resident::Visible>,
+    /// The external shader pipeline world frames call (`external`); `None` draws vanilla's way.
+    external: Option<Box<dyn external::ExternalPipeline>>,
     translucent_draws: Vec<(u64, usize, [u32; 5], (u32, Option<u32>))>,
     origins: Vec<[f32; 4]>,
     /// `DrawIndexedIndirectArgs` words: index count, instance count, first
@@ -5290,6 +5294,7 @@ impl Renderer {
             solid_runs: page_runs::PageRuns::default(),
             phase2_runs: page_runs::PageRuns::default(),
             shadow_runs: page_runs::PageRuns::default(),
+            external: None,
             block_entities: Default::default(),
             block_entity_section_revisions: Default::default(),
             block_entity_membership_revisions: Default::default(),
@@ -5673,6 +5678,9 @@ impl Renderer {
             self.offscreen = Some(Self::offscreen_target(&self.device, &self.config));
         }
         self.depth = Self::depth(&self.device, &self.config);
+        if let Some(pipeline) = &mut self.external {
+            pipeline.resize([width, height]);
+        }
     }
     /// Whether sections are drawn as one index list per frame (`flat`).
     pub fn flat_draws(&self) -> bool {
@@ -7289,12 +7297,19 @@ impl Renderer {
         }
         Ok(report)
     }
+    /// Sets the external shader pipeline world frames call (`external`), or none.
+    pub fn set_external_pipeline(&mut self, pipeline: Option<Box<dyn external::ExternalPipeline>>) {
+        self.external = pipeline;
+    }
     /// Makes the running shader pack, of either kind, forget what it kept from earlier frames:
     /// the next frame draws as a freshly loaded pack's first. Nothing to do without a pack.
     pub fn reset_shader_pack_history(&mut self) {
         // A frame still on the submit thread uses the targets and readbacks replaced
         // here.
         self.land_frame();
+        if let Some(pipeline) = &mut self.external {
+            pipeline.reset_history();
+        }
         if let Some((_, Some(post))) = &mut self.pack_post {
             post.reset_history(&self.device);
         }
@@ -8629,6 +8644,13 @@ impl Renderer {
         // A shader pack's shadow pass draws the sections in its camera's box, all of them (the
         // occlusion graph follows the eye, not the light), within shadowDistanceRenderMul; for
         // an Iris-format pack, only those whose shadow can fall into the camera's view.
+        let state = external::FrameState {
+            frame,
+            output: &output,
+        };
+        if let Some(pipeline) = self.external.as_mut().filter(|_| !frame.title) {
+            pipeline.begin_frame(&state);
+        }
         let shadow_view = self
             .pack_post
             .as_ref()
@@ -8640,6 +8662,12 @@ impl Renderer {
                 let native = self.native.as_ref().filter(|_| !frame.title)?;
                 native.shadow.as_ref()?;
                 native.frame.shadow_view(frame)
+            })
+            .or_else(|| {
+                self.external
+                    .as_ref()
+                    .filter(|_| !frame.title)?
+                    .shadow_request(&state)
             });
         // `LevelRenderer.extractSectionDrawGroups`' fade-in time, for the instances.
         let fade_ms = fade_millis(frame.chunk_fade);
@@ -12771,61 +12799,6 @@ impl Cull for Frusta {
         self.0.contains(min, max) || self.1.is_some_and(|f| f.contains(min, max))
     }
 }
-/// A shader pack's shadow camera's box, and with `casters` only what can shade the camera's view
-/// (`shadow_casters`): a box must meet all of them.
-#[derive(Clone, Copy, Debug)]
-pub struct ShadowCull {
-    pub light: Frustum,
-    pub casters: Option<[Frustum; 2]>,
-    /// `shadowDistance × shadowDistanceRenderMul`: only what lies within this many blocks of the
-    /// camera along each axis, a cube around it. Our probe's Iris 1.11.7 maps keep the sections
-    /// whose box, grown by `SHADOW_CASTER_MARGIN` as for the casters, meets that cube (#8464):
-    /// out to its corners, and a section 1 block past its side but not one 1.5 blocks past.
-    pub reach: Option<f32>,
-}
-impl ShadowCull {
-    /// Whether the camera-relative box `min..max`, grown by the margin, meets (`whole`: lies
-    /// within) `reach`'s cube.
-    fn within_reach(&self, min: Vec3, max: Vec3, whole: bool) -> bool {
-        let (min, max) = (min - SHADOW_CASTER_MARGIN, max + SHADOW_CASTER_MARGIN);
-        self.reach.is_none_or(|d| {
-            if whole {
-                min.cmpge(Vec3::splat(-d)).all() && max.cmple(Vec3::splat(d)).all()
-            } else {
-                max.cmpge(Vec3::splat(-d)).all() && min.cmple(Vec3::splat(d)).all()
-            }
-        })
-    }
-}
-/// How far past a section's 16 blocks the shadow pass looks for what can shade the view: our
-/// probes' Iris 1.11.7 maps keep the sections whose box, grown by this much on every side, meets
-/// `shadow_casters`' shape. Over 76 scenes at fields of view 30 to 110, Iris keeps every section
-/// that needs up to 1.1224 blocks and drops every one that needs 1.1252 or more (#8464): one
-/// growth, whatever the field of view, of 9/8 (a fit, not Iris's code). Without it the edges of
-/// the wedge lose a column of terrain.
-const SHADOW_CASTER_MARGIN: f32 = 1.125;
-impl Cull for ShadowCull {
-    fn intersects(&self, min: Vec3, max: Vec3) -> bool {
-        let (grown_min, grown_max) = (min - SHADOW_CASTER_MARGIN, max + SHADOW_CASTER_MARGIN);
-        self.within_reach(min, max, false)
-            && self.light.intersects(min, max)
-            && self
-                .casters
-                .is_none_or(|c| c.iter().all(|f| f.intersects(grown_min, grown_max)))
-    }
-    fn contains(&self, min: Vec3, max: Vec3) -> bool {
-        let (grown_min, grown_max) = (min - SHADOW_CASTER_MARGIN, max + SHADOW_CASTER_MARGIN);
-        self.within_reach(min, max, true)
-            && self.light.contains(min, max)
-            && self
-                .casters
-                .is_none_or(|c| c.iter().all(|f| f.contains(grown_min, grown_max)))
-    }
-    /// Our probe's Iris 1.11.7 maps fit testing the casters' whole sections (a guess that matched).
-    fn tight(&self) -> bool {
-        self.casters.is_none()
-    }
-}
 /// The block entities of `sections` whose box, a block wider on every side, comes within the
 /// 64 blocks block entities are drawn to (`Renderer::visible_block_entities_in_frustum`).
 fn block_entities_within_reach<'a>(
@@ -12848,17 +12821,6 @@ fn block_entities_within_reach<'a>(
         })
         .flatten()
 }
-/// The shadow camera's box that the shadow pass draws terrain in: the sides of `view.cull`, and
-/// its near and far planes only with `depth_planes`.
-fn shadow_box(view: &pack_post::ShadowView) -> Frustum {
-    let mut planes = frustum(view.cull);
-    if !view.depth_planes {
-        // `frustum`'s faces at depth 0 and 1 take in everything.
-        planes[4] = Vec4::W;
-        planes[5] = Vec4::W;
-    }
-    Frustum { planes }
-}
 /// Camera-relative clip planes (`Frustum`).
 #[derive(Clone, Copy, Debug)]
 pub struct Frustum {
@@ -12982,21 +12944,6 @@ fn projection_center(view_proj: Mat4) -> Option<Vec3> {
     let b = DVec3::new(rows[0].w, rows[1].w, rows[2].w);
     Some((a.inverse() * -b).as_vec3())
 }
-/// The runs of a section's solid quads the shadow pass draws: every face within the unculled
-/// distance, or everywhere for `every_face`; else the quads that can face the light.
-fn shadow_runs(
-    sides: &Sides,
-    view: &pack_post::ShadowView,
-    origin: [f32; 3],
-    draw: impl FnMut(u32, u32),
-) {
-    let unculled = view.unculled.is_some_and(|d| {
-        let o = Vec3::from(origin) + 8.0;
-        o.x.abs().max(o.z.abs()) <= d + 8.0
-    });
-    let toward = (!unculled && !view.every_face).then_some(view.light * 1.0e5);
-    facing_runs(sides, toward, origin, draw);
-}
 
 /// Calls `draw(first, quads)` for each run of a mesh's solid quads that can
 /// face `eye` (`projection_center`), the mesh at the camera-relative
@@ -13023,68 +12970,6 @@ fn facing_runs_from(
         None => sides.every(part, draw),
     }
 }
-/// The camera's view `view_proj` (wgpu depth, reversed or not) stretched without end toward
-/// `light` (a direction): the boxes whose shadow, cast away from the light, can fall into the
-/// view. Its planes are the view's faces turned toward the light, and through each edge between
-/// such a face and one turned away, the plane along the light; unused ones take in everything.
-fn shadow_casters(view_proj: Mat4, light: Vec3) -> [Frustum; 2] {
-    let faces = frustum(view_proj);
-    let toward = faces.map(|p| p.truncate().dot(light) >= 0.0);
-    let inverse = view_proj.inverse();
-    // Corner (x, y, z) of clip space's box; `frustum`'s faces at x -1 and 1 are 0 and 1, at
-    // y -1 and 1 are 2 and 3, at depth 0 and 1 are 4 and 5.
-    let corner = |c: [usize; 3]| {
-        inverse.project_point3(Vec3::new(
-            c[0] as f32 * 2.0 - 1.0,
-            c[1] as f32 * 2.0 - 1.0,
-            c[2] as f32,
-        ))
-    };
-    let corners: Vec<[usize; 3]> = (0..8).map(|i| [i & 1, (i >> 1) & 1, i >> 2]).collect();
-    let centre = corners.iter().map(|&c| corner(c)).sum::<Vec3>() / 8.0;
-    let mut planes = [Vec4::W; 12];
-    let mut n = 0;
-    for (k, &face) in faces.iter().enumerate() {
-        if toward[k] {
-            planes[n] = face;
-            n += 1;
-        }
-    }
-    for a in &corners {
-        for axis in 0..3 {
-            if a[axis] == 1 {
-                continue;
-            }
-            let mut b = *a;
-            b[axis] = 1;
-            // The edge from a to b lies on the faces of the two other axes.
-            let [f, g] = [(axis + 1) % 3, (axis + 2) % 3].map(|o| o * 2 + a[o]);
-            if toward[f] == toward[g] {
-                continue;
-            }
-            let (p, q) = (corner(*a), corner(b));
-            let normal = (q - p).cross(light);
-            if normal.length_squared() < 1e-12 {
-                continue;
-            }
-            let normal = normal.normalize();
-            let side = if normal.dot(centre - p) < 0.0 {
-                -1.0
-            } else {
-                1.0
-            };
-            // At most six such edges with at most four faces toward the light: 12 planes.
-            if let Some(plane) = planes.get_mut(n) {
-                *plane = (normal * side).extend(-normal.dot(p) * side);
-                n += 1;
-            }
-        }
-    }
-    let [a, b] = [0, 6].map(|i| Frustum {
-        planes: planes[i..i + 6].try_into().expect("six planes"),
-    });
-    [a, b]
-}
 fn taa_frustum(view_proj: Mat4, rendered_size: [u32; 2]) -> Frustum {
     // TAA shifts clip x/y by at most half a rendered pixel times clip w.
     // Widen x/y before extracting the planes: this includes every such shifted
@@ -15383,7 +15268,7 @@ mod shadow_face_tests {
     }
 
     /// The layers (faces) of the quads the shadow pass draws of `solid`.
-    fn drawn(view: &pack_post::ShadowView, origin: [f32; 3]) -> Vec<u16> {
+    fn drawn(view: &external::ShadowView, origin: [f32; 3]) -> Vec<u16> {
         let mut solid = block([7.0, 7.0, 7.0]);
         let sides = crate::mesher::sort_tinted(&mut solid, &mut Vec::new());
         let mut layers = Vec::new();
@@ -15396,8 +15281,8 @@ mod shadow_face_tests {
         layers
     }
 
-    fn view(every_face: bool) -> pack_post::ShadowView {
-        pack_post::ShadowView {
+    fn view(every_face: bool) -> external::ShadowView {
+        external::ShadowView {
             cull: Mat4::IDENTITY,
             light: Vec3::Y,
             distance: None,
@@ -15611,7 +15496,7 @@ mod shadow_caster_tests {
                 ..horizon_shaders::Shadow::default()
             };
             let camera = DVec3::new(13.5, y + 1.62, -13.5);
-            let view = pack_post::ShadowView {
+            let view = external::ShadowView {
                 cull: pack_uniforms::shadow_culling_at(Vec3::Y, camera, &shadow),
                 light: Vec3::Y,
                 distance: None,

crates/horizon-client-render/src/gfx/external.rs

@@ -0,0 +1,214 @@
+//! The hook an external shader pipeline fills (#14035, layer plan M6). A shader pack's runtime
+//! (a platform crate, later) implements [`ExternalPipeline`]; the renderer calls it at fixed
+//! points of a world frame and draws vanilla's way wherever it doesn't answer. With none set
+//! (`Renderer::set_external_pipeline`), each point is one `Option` test.
+//!
+//! Workspace-internal: the trait names the engine's frame, its mesh format and its pass order,
+//! has one implementer in this workspace, carries no stability promise and is never exposed to
+//! mods. A mesher or pass change updates its implementer in the same PR. HDR output
+//! (`output.rs`, `frame_policy`) is not an implementer: it stays the one output stage after the
+//! frame, and a pipeline draws into the frame it gives.
+//!
+//! Shadows are an engine frame point, on request: a pipeline that wants a shadow pass answers
+//! [`ShadowView`], the engine culls the sections from it ([`ShadowCull`]) and hands back the
+//! terrain seen from the light. Vanilla's path never asks, so it never computes shadow
+//! visibility.
+
+use glam::{Mat4, Vec3, Vec4};
+
+use super::{Cull, EffectiveOutput, Frame, Frustum, Sides, facing_runs, frustum};
+
+/// What a world frame gives an external pipeline at its points: the frame's own values, and
+/// the display's from the renderer's one output snapshot (`EffectiveOutput`: whether HDR is on,
+/// paper white, peak), never worked out again, so each split-screen window keeps its own.
+pub struct FrameState<'a> {
+    pub frame: &'a Frame<'a>,
+    pub output: &'a EffectiveOutput,
+}
+
+/// An external shader pipeline, called by the renderer at fixed points of a world frame (not
+/// title frames). Every method has a default that leaves vanilla's way in place.
+pub trait ExternalPipeline: Send {
+    /// A world frame starts, before culling.
+    fn begin_frame(&mut self, _state: &FrameState<'_>) {}
+    /// The shadow pass this frame wants; `None` draws none.
+    fn shadow_request(&self, _state: &FrameState<'_>) -> Option<ShadowView> {
+        None
+    }
+    /// The window's drawable size changed.
+    fn resize(&mut self, _size: [u32; 2]) {}
+    /// Forget what was kept from earlier frames: the next is drawn as a fresh pipeline's first.
+    fn reset_history(&mut self) {}
+}
+
+/// What the shadow camera sees of the terrain, for the game's draw lists: its view and
+/// projection in wgpu's clip space, the direction toward the light, and how far from the camera
+/// terrain is drawn (`shadowDistanceRenderMul`).
+pub struct ShadowView {
+    pub cull: glam::Mat4,
+    pub light: glam::Vec3,
+    pub distance: Option<f32>,
+    /// Draw everything, every face, within this many blocks (`shadow.culling=false|reversed`):
+    /// packs that voxelize the world in their shadow pass need all of it.
+    pub unculled: Option<f32>,
+    /// Every face of the drawn sections, not only those that can face the light. Iris 1.11.7's
+    /// shadow map holds the faces turned away from the light too (#9033): under a hill at low sun
+    /// a cave's ceiling, which faces away, is often all that shadows the cave.
+    pub every_face: bool,
+    /// Only the sections whose shadow can fall into the camera's view: those the camera's
+    /// frustum, stretched toward the light, takes in (`shadow_casters`). Our probes' Iris 1.11.7
+    /// maps fit keeping only those with `shadow.culling` unset (#8464): under a noon sun, only
+    /// the terrain above the ground the camera sees; with a low sun ahead, none behind the camera.
+    pub view_casters: bool,
+    /// Whether the projection's near and far planes in `cull` drop sections too. Our probes'
+    /// Iris 1.11.7 maps hold the terrain at every depth we put it along the light (from 535 blocks
+    /// beyond the shadow camera to about 120 before it), whatever `shadowNearPlane` and
+    /// `shadowFarPlane` the pack sets, or none (#10403): only its sides cull.
+    pub depth_planes: bool,
+}
+
+/// A shader pack's shadow camera's box, and with `casters` only what can shade the camera's view
+/// (`shadow_casters`): a box must meet all of them.
+#[derive(Clone, Copy, Debug)]
+pub struct ShadowCull {
+    pub light: Frustum,
+    pub casters: Option<[Frustum; 2]>,
+    /// `shadowDistance × shadowDistanceRenderMul`: only what lies within this many blocks of the
+    /// camera along each axis, a cube around it. Our probe's Iris 1.11.7 maps keep the sections
+    /// whose box, grown by `SHADOW_CASTER_MARGIN` as for the casters, meets that cube (#8464):
+    /// out to its corners, and a section 1 block past its side but not one 1.5 blocks past.
+    pub reach: Option<f32>,
+}
+impl ShadowCull {
+    /// Whether the camera-relative box `min..max`, grown by the margin, meets (`whole`: lies
+    /// within) `reach`'s cube.
+    fn within_reach(&self, min: Vec3, max: Vec3, whole: bool) -> bool {
+        let (min, max) = (min - SHADOW_CASTER_MARGIN, max + SHADOW_CASTER_MARGIN);
+        self.reach.is_none_or(|d| {
+            if whole {
+                min.cmpge(Vec3::splat(-d)).all() && max.cmple(Vec3::splat(d)).all()
+            } else {
+                max.cmpge(Vec3::splat(-d)).all() && min.cmple(Vec3::splat(d)).all()
+            }
+        })
+    }
+}
+/// How far past a section's 16 blocks the shadow pass looks for what can shade the view: our
+/// probes' Iris 1.11.7 maps keep the sections whose box, grown by this much on every side, meets
+/// `shadow_casters`' shape. Over 76 scenes at fields of view 30 to 110, Iris keeps every section
+/// that needs up to 1.1224 blocks and drops every one that needs 1.1252 or more (#8464): one
+/// growth, whatever the field of view, of 9/8 (a fit, not Iris's code). Without it the edges of
+/// the wedge lose a column of terrain.
+const SHADOW_CASTER_MARGIN: f32 = 1.125;
+impl Cull for ShadowCull {
+    fn intersects(&self, min: Vec3, max: Vec3) -> bool {
+        let (grown_min, grown_max) = (min - SHADOW_CASTER_MARGIN, max + SHADOW_CASTER_MARGIN);
+        self.within_reach(min, max, false)
+            && self.light.intersects(min, max)
+            && self
+                .casters
+                .is_none_or(|c| c.iter().all(|f| f.intersects(grown_min, grown_max)))
+    }
+    fn contains(&self, min: Vec3, max: Vec3) -> bool {
+        let (grown_min, grown_max) = (min - SHADOW_CASTER_MARGIN, max + SHADOW_CASTER_MARGIN);
+        self.within_reach(min, max, true)
+            && self.light.contains(min, max)
+            && self
+                .casters
+                .is_none_or(|c| c.iter().all(|f| f.contains(grown_min, grown_max)))
+    }
+    /// Our probe's Iris 1.11.7 maps fit testing the casters' whole sections (a guess that matched).
+    fn tight(&self) -> bool {
+        self.casters.is_none()
+    }
+}
+/// The shadow camera's box that the shadow pass draws terrain in: the sides of `view.cull`, and
+/// its near and far planes only with `depth_planes`.
+pub(super) fn shadow_box(view: &ShadowView) -> Frustum {
+    let mut planes = frustum(view.cull);
+    if !view.depth_planes {
+        // `frustum`'s faces at depth 0 and 1 take in everything.
+        planes[4] = Vec4::W;
+        planes[5] = Vec4::W;
+    }
+    Frustum { planes }
+}
+
+/// The runs of a section's solid quads the shadow pass draws: every face within the unculled
+/// distance, or everywhere for `every_face`; else the quads that can face the light.
+pub(super) fn shadow_runs(
+    sides: &Sides,
+    view: &ShadowView,
+    origin: [f32; 3],
+    draw: impl FnMut(u32, u32),
+) {
+    let unculled = view.unculled.is_some_and(|d| {
+        let o = Vec3::from(origin) + 8.0;
+        o.x.abs().max(o.z.abs()) <= d + 8.0
+    });
+    let toward = (!unculled && !view.every_face).then_some(view.light * 1.0e5);
+    facing_runs(sides, toward, origin, draw);
+}
+
+/// The camera's view `view_proj` (wgpu depth, reversed or not) stretched without end toward
+/// `light` (a direction): the boxes whose shadow, cast away from the light, can fall into the
+/// view. Its planes are the view's faces turned toward the light, and through each edge between
+/// such a face and one turned away, the plane along the light; unused ones take in everything.
+pub(super) fn shadow_casters(view_proj: Mat4, light: Vec3) -> [Frustum; 2] {
+    let faces = frustum(view_proj);
+    let toward = faces.map(|p| p.truncate().dot(light) >= 0.0);
+    let inverse = view_proj.inverse();
+    // Corner (x, y, z) of clip space's box; `frustum`'s faces at x -1 and 1 are 0 and 1, at
+    // y -1 and 1 are 2 and 3, at depth 0 and 1 are 4 and 5.
+    let corner = |c: [usize; 3]| {
+        inverse.project_point3(Vec3::new(
+            c[0] as f32 * 2.0 - 1.0,
+            c[1] as f32 * 2.0 - 1.0,
+            c[2] as f32,
+        ))
+    };
+    let corners: Vec<[usize; 3]> = (0..8).map(|i| [i & 1, (i >> 1) & 1, i >> 2]).collect();
+    let centre = corners.iter().map(|&c| corner(c)).sum::<Vec3>() / 8.0;
+    let mut planes = [Vec4::W; 12];
+    let mut n = 0;
+    for (k, &face) in faces.iter().enumerate() {
+        if toward[k] {
+            planes[n] = face;
+            n += 1;
+        }
+    }
+    for a in &corners {
+        for axis in 0..3 {
+            if a[axis] == 1 {
+                continue;
+            }
+            let mut b = *a;
+            b[axis] = 1;
+            // The edge from a to b lies on the faces of the two other axes.
+            let [f, g] = [(axis + 1) % 3, (axis + 2) % 3].map(|o| o * 2 + a[o]);
+            if toward[f] == toward[g] {
+                continue;
+            }
+            let (p, q) = (corner(*a), corner(b));
+            let normal = (q - p).cross(light);
+            if normal.length_squared() < 1e-12 {
+                continue;
+            }
+            let normal = normal.normalize();
+            let side = if normal.dot(centre - p) < 0.0 {
+                -1.0
+            } else {
+                1.0
+            };
+            // At most six such edges with at most four faces toward the light: 12 planes.
+            if let Some(plane) = planes.get_mut(n) {
+                *plane = (normal * side).extend(-normal.dot(p) * side);
+                n += 1;
+            }
+        }
+    }
+    let [a, b] = [0, 6].map(|i| Frustum {
+        planes: planes[i..i + 6].try_into().expect("six planes"),
+    });
+    [a, b]
+}

crates/horizon-client-render/src/gfx/pack_post.rs

@@ -1201,31 +1201,7 @@ pub(super) type TerrainDraw<'a> = dyn FnMut(
         Option<(u32, &wgpu::BindGroupLayout)>,
     ) + 'a;
 
-/// What the shadow camera sees of the terrain, for the game's draw lists: its view and
-/// projection in wgpu's clip space, the direction toward the light, and how far from the camera
-/// terrain is drawn (`shadowDistanceRenderMul`).
-pub(super) struct ShadowView {
-    pub cull: glam::Mat4,
-    pub light: glam::Vec3,
-    pub distance: Option<f32>,
-    /// Draw everything, every face, within this many blocks (`shadow.culling=false|reversed`):
-    /// packs that voxelize the world in their shadow pass need all of it.
-    pub unculled: Option<f32>,
-    /// Every face of the drawn sections, not only those that can face the light. Iris 1.11.7's
-    /// shadow map holds the faces turned away from the light too (#9033): under a hill at low sun
-    /// a cave's ceiling, which faces away, is often all that shadows the cave.
-    pub every_face: bool,
-    /// Only the sections whose shadow can fall into the camera's view: those the camera's
-    /// frustum, stretched toward the light, takes in (`shadow_casters`). Our probes' Iris 1.11.7
-    /// maps fit keeping only those with `shadow.culling` unset (#8464): under a noon sun, only
-    /// the terrain above the ground the camera sees; with a low sun ahead, none behind the camera.
-    pub view_casters: bool,
-    /// Whether the projection's near and far planes in `cull` drop sections too. Our probes'
-    /// Iris 1.11.7 maps hold the terrain at every depth we put it along the light (from 535 blocks
-    /// beyond the shadow camera to about 120 before it), whatever `shadowNearPlane` and
-    /// `shadowFarPlane` the pack sets, or none (#10403): only its sides cull.
-    pub depth_planes: bool,
-}
+pub(super) use super::external::ShadowView;
 
 /// An arena page's key, native vertices and optional per-quad source records.
 pub(super) type TerrainPage = (u32, wgpu::Buffer, Option<wgpu::Buffer>);