Draw map markers on the cartography table's preview

MapRenderer.render in a screen draws the map's decorations over its image,
all of them since the map isn't in an item frame.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Rx5M6NS763D2WVnb2HmcTH

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

@@ -116,12 +116,13 @@ impl Game<'_> {
             );
         };
         let preview = |batch: &mut HudBatch, game: &mut Self, x: f32, y: f32, scale: f32| {
-            if let Some(rect) = id
+            if let Some((id, rect)) = id
                 .filter(|_| state.is_some())
-                .and_then(|id| game.map_texture(id))
+                .and_then(|id| game.map_texture(id).map(|rect| (id, rect)))
             {
                 let size = 128.0 * scale;
                 batch.rect_uv(ox + x, oy + y, size, size, rect, u32::MAX);
+                game.draw_map_decorations(batch, id, ox + x, oy + y, scale);
             }
         };
         if scaling && !locked {
@@ -142,6 +143,40 @@ impl Game<'_> {
         }
     }
 }
+impl Game<'_> {
+    /// `MapRenderer.render` in a screen (`GuiGraphicsExtractor.map`): map
+    /// `id`'s decorations, all of them (not in an item frame), over its
+    /// image at `(x, y)` drawn `scale` GUI pixels per map pixel.
+    fn draw_map_decorations(&self, batch: &mut HudBatch, id: i32, x: f32, y: f32, scale: f32) {
+        let Some(map) = self.maps.data.get(&id) else {
+            return;
+        };
+        for d in &map.decorations {
+            let Some(s) = self.gui.atlas.sprites.get(d.sprite).copied() else {
+                continue;
+            };
+            batch.quad(
+                decoration_corners(d, x, y, scale),
+                [[s.u0, s.v0], [s.u1, s.v0], [s.u1, s.v1], [s.u0, s.v1]],
+                u32::MAX,
+            );
+        }
+    }
+}
+
+/// Decoration `d`'s corners on screen, for a map drawn at `(x, y)` with
+/// `scale` GUI pixels per map pixel: (-1, 1), (1, 1), (1, -1), (-1, -1)
+/// under `MapRenderer.render`'s pose.
+fn decoration_corners(d: &super::maps::Decoration, x: f32, y: f32, scale: f32) -> [[f32; 2]; 4] {
+    let m = glam::Mat4::from_translation(glam::Vec3::new(x, y, 0.0))
+        * glam::Mat4::from_scale(glam::Vec3::new(scale, scale, 1.0))
+        * super::maps::decoration_pose(d, 0.0);
+    [(-1.0, 1.0), (1.0, 1.0), (1.0, -1.0), (-1.0, -1.0)].map(|(cx, cy)| {
+        let p = m.transform_point3(glam::Vec3::new(cx, cy, 0.0));
+        [p.x, p.y]
+    })
+}
+
 impl MapData {
     /// `MapItemSavedData.scaled`: a fresh map one scale up around the same centre.
     pub(super) fn scaled(&self) -> MapData {
@@ -172,3 +207,50 @@ impl MapData {
         m
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::game::maps::Decoration;
+
+    fn close(a: [[f32; 2]; 4], b: [[f32; 2]; 4]) {
+        for (a, b) in a.iter().zip(&b) {
+            assert!(
+                (a[0] - b[0]).abs() < 1e-4 && (a[1] - b[1]).abs() < 1e-4,
+                "{a:?} {b:?}"
+            );
+        }
+    }
+
+    #[test]
+    fn map_markers_sit_on_the_preview_like_on_a_held_map() {
+        let player = |x, y, rot| Decoration {
+            sprite: "map/decorations/player",
+            x,
+            y,
+            rot,
+            holder: None,
+        };
+        // The centre, facing north: 8 map pixels wide, nudged by (-0.5, 0.5).
+        close(
+            decoration_corners(&player(0, 0, 0), 0.0, 0.0, 1.0),
+            [[59.5, 68.5], [67.5, 68.5], [67.5, 60.5], [59.5, 60.5]],
+        );
+        // A quarter turn (rotation 4 of 16) turns the quad about its marker.
+        close(
+            decoration_corners(&player(0, 0, 4), 0.0, 0.0, 1.0),
+            [[59.5, 59.5], [59.5, 67.5], [67.5, 67.5], [67.5, 59.5]],
+        );
+        // The preview's offset and scale apply after: the top-left corner
+        // marker on the 0.45 preview at (71, 17).
+        close(
+            decoration_corners(&player(-128, -128, 0), 71.0, 17.0, 0.45),
+            [
+                [71.0 - 4.5 * 0.45, 17.0 + 4.5 * 0.45],
+                [71.0 + 3.5 * 0.45, 17.0 + 4.5 * 0.45],
+                [71.0 + 3.5 * 0.45, 17.0 - 3.5 * 0.45],
+                [71.0 - 4.5 * 0.45, 17.0 - 3.5 * 0.45],
+            ],
+        );
+    }
+}

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

@@ -337,6 +337,17 @@ const DECORATION_TYPES: [(&str, &str); 24] = [
     ("ocean_ruin_warm", "map/decorations/warm_ocean_ruins"),
 ];
 /// `MapDecorationType.showOnItemFrame` is false for the player arrows and the two markers.
+/// `MapRenderer.render`'s pose for decoration `d` in map pixels (0..128,
+/// y down) at depth `z`: its quad is (-1, -1) to (1, 1) under it.
+pub(super) fn decoration_pose(d: &Decoration, z: f32) -> glam::Mat4 {
+    glam::Mat4::from_translation(glam::Vec3::new(
+        f32::from(d.x) / 2.0 + 64.0,
+        f32::from(d.y) / 2.0 + 64.0,
+        z,
+    )) * glam::Mat4::from_rotation_z((f32::from(d.rot) * 360.0 / 16.0).to_radians())
+        * glam::Mat4::from_scale(glam::Vec3::splat(4.0))
+        * glam::Mat4::from_translation(glam::Vec3::new(-0.125, 0.125, 0.0))
+}
 fn shown_on_frame(sprite: &str) -> bool {
     !matches!(
         decoration_type(sprite),
@@ -1277,14 +1288,7 @@ impl Game<'_> {
             let Some(s) = self.gui.atlas.sprites.get(d.sprite).copied() else {
                 continue;
             };
-            let dm = glam::Mat4::from_translation(glam::Vec3::new(
-                f32::from(d.x) / 2.0 + 64.0,
-                f32::from(d.y) / 2.0 + 64.0,
-                -0.02 - count as f32 * 0.001,
-            )) * glam::Mat4::from_rotation_z(
-                (f32::from(d.rot) * 360.0 / 16.0).to_radians(),
-            ) * glam::Mat4::from_scale(glam::Vec3::splat(4.0))
-                * glam::Mat4::from_translation(glam::Vec3::new(-0.125, 0.125, 0.0));
+            let dm = decoration_pose(d, -0.02 - count as f32 * 0.001);
             let p = |x: f32, y: f32| dm.transform_point3(glam::Vec3::new(x, y, 0.0)).to_array();
             let mut q = |corners: [[f32; 3]; 4], uv: [[f32; 2]; 4]| {
                 for (c, uv) in corners.into_iter().zip(uv) {