[ISOMETRIC] [BEVY] Replace MeshPickingPlugin with Rapier raycast hover detection

[h0lybyte]

Summary

The isometric game uses a two-stage render pipeline (scene camera renders to an offscreen texture, not the window). Bevy's built-in MeshPickingPlugin doesn't work with this setup — hover events never fire.

This replaces it with a custom Rapier raycast-based hover system that casts rays from the orthographic scene camera through the cursor position.

Changes

main.rs

• Remove MeshPickingPlugin

object_registry.rs

• Remove per-entity .observe(on_pointer_over) / .observe(on_pointer_out) from all object spawns

scene_objects.rs

• Remove on_pointer_over / on_pointer_out event handlers
• Add raycast_hover_detection system using Rapier cast_ray through the orthographic camera
• Fix update_occlusion to query IsometricCamera instead of Camera3d

Diff

diff --git a/apps/kbve/isometric/src-tauri/src/game/object_registry.rs b/apps/kbve/isometric/src-tauri/src/game/object_registry.rs
index 4c2ef8d42..0d529f564 100644
--- a/apps/kbve/isometric/src-tauri/src/game/object_registry.rs
+++ b/apps/kbve/isometric/src-tauri/src/game/object_registry.rs
@@ -11,8 +11,7 @@ use std::sync::LazyLock;
 use bevy_rapier3d::prelude::*;
 
 use super::scene_objects::{
-    AnimatedCrystal, HoverOutline, Occludable, OriginalEmissive, RotatingBox, on_pointer_out,
-    on_pointer_over,
+    AnimatedCrystal, HoverOutline, Occludable, OriginalEmissive, RotatingBox,
 };
 use super::terrain::TerrainMap;
 
@@ -339,8 +338,6 @@ fn spawn_object_entity(
                         half_extents: Vec3::splat(half),
                     },
                 ))
-                .observe(on_pointer_over)
-                .observe(on_pointer_out)
                 .id()
         }
         ObjectKind::DarkCrate => {
@@ -367,8 +364,6 @@ fn spawn_object_entity(
                         half_extents: Vec3::splat(half),
                     },
                 ))
-                .observe(on_pointer_over)
-                .observe(on_pointer_out)
                 .id()
         }
         ObjectKind::Crystal => {
@@ -393,8 +388,6 @@ fn spawn_object_entity(
                         half_extents: Vec3::splat(1.0),
                     },
                 ))
-                .observe(on_pointer_over)
-                .observe(on_pointer_out)
                 .id()
         }
         ObjectKind::Pillar => commands
@@ -417,8 +410,6 @@ fn spawn_object_entity(
                     half_extents: Vec3::new(0.4, 2.0, 0.4),
                 },
             ))
-            .observe(on_pointer_over)
-            .observe(on_pointer_out)
             .id(),
         ObjectKind::MetallicSphere => {
             let radius = 0.8;
@@ -442,8 +433,6 @@ fn spawn_object_entity(
                         half_extents: Vec3::splat(radius),
                     },
                 ))
-                .observe(on_pointer_over)
-                .observe(on_pointer_out)
                 .id()
         }
         ObjectKind::SpotLight => commands
diff --git a/apps/kbve/isometric/src-tauri/src/game/scene_objects.rs b/apps/kbve/isometric/src-tauri/src/game/scene_objects.rs
index 39c1af598..98345160a 100644
--- a/apps/kbve/isometric/src-tauri/src/game/scene_objects.rs
+++ b/apps/kbve/isometric/src-tauri/src/game/scene_objects.rs
@@ -1,11 +1,10 @@
-use bevy::picking::events::{Out, Over, Pointer};
 use bevy::prelude::*;
+use bevy::window::PrimaryWindow;
+use bevy_rapier3d::prelude::*;
 
+use super::camera::IsometricCamera;
 use super::player::Player;
 
-// Re-export EntityEvent so event_target() is available
-use bevy::ecs::event::EntityEvent;
-
 /// Marker for objects that become semi-transparent when occluding the player.
 #[derive(Component)]
 pub struct Occludable;
@@ -39,6 +38,7 @@ impl Plugin for SceneObjectsPlugin {
         app.add_systems(
             Update,
             (
+                raycast_hover_detection,
                 animate_crystal,
                 rotate_boxes,
                 update_occlusion,
@@ -49,12 +49,81 @@ impl Plugin for SceneObjectsPlugin {
     }
 }
 
-pub(crate) fn on_pointer_over(trigger: On<Pointer<Over>>, mut commands: Commands) {
-    commands.entity(trigger.event_target()).insert(Hovered);
-}
+fn raycast_hover_detection(
+    windows: Query<&Window, With<PrimaryWindow>>,
+    camera_query: Query<(&GlobalTransform, &Projection), With<IsometricCamera>>,
+    rapier_context: ReadRapierContext,
+    occludable: Query<(), With<Occludable>>,
+    current_hovered: Query<Entity, With<Hovered>>,
+    player_query: Query<Entity, With<Player>>,
+    mut commands: Commands,
+) {
+    let Ok(window) = windows.single() else { return };
+    let Ok((cam_gt, projection)) = camera_query.single() else { return };
+
+    let Some(cursor_pos) = window.cursor_position() else {
+        for entity in &current_hovered {
+            commands.entity(entity).remove::<Hovered>();
+        }
+        return;
+    };
+
+    let Projection::Orthographic(ortho) = projection else { return };
+    let viewport_height = match ortho.scaling_mode {
+        bevy::camera::ScalingMode::FixedVertical { viewport_height } => viewport_height,
+        _ => return,
+    };
+    let half_h = viewport_height / 2.0;
+    let aspect = window.width() / window.height();
+    let half_w = half_h * aspect;
+
+    let ndc_x = (cursor_pos.x / window.width()) * 2.0 - 1.0;
+    let ndc_y = 1.0 - (cursor_pos.y / window.height()) * 2.0;
+
+    let cam_tf = cam_gt.compute_transform();
+    let right = cam_tf.right().as_vec3();
+    let up = cam_tf.up().as_vec3();
+    let forward = cam_tf.forward().as_vec3();
+
+    let ray_origin = cam_tf.translation + right * (ndc_x * half_w) + up * (ndc_y * half_h);
+    let ray_dir = forward;
+
+    let mut filter = QueryFilter::new();
+    if let Ok(player_entity) = player_query.single() {
+        filter = filter.exclude_rigid_body(player_entity);
+    }
+
+    let Ok(context) = rapier_context.single() else { return };
+    let new_hovered = context
+        .cast_ray(ray_origin, ray_dir, 1000.0, false, filter)
+        .and_then(|(entity, _)| {
+            if occludable.get(entity).is_ok() {
+                Some(entity)
+            } else {
+                None
+            }
+        });
 
-pub(crate) fn on_pointer_out(trigger: On<Pointer<Out>>, mut commands: Commands) {
-    commands.entity(trigger.event_target()).remove::<Hovered>();
+    for entity in &current_hovered {
+        if Some(entity) != new_hovered {
+            commands.entity(entity).remove::<Hovered>();
+        }
+    }
+    if let Some(entity) = new_hovered {
+        if current_hovered.get(entity).is_err() {
+            commands.entity(entity).insert(Hovered);
+        }
+    }
 }
 
 fn update_occlusion(
-    camera_query: Query<&GlobalTransform, With<Camera3d>>,
+    camera_query: Query<&GlobalTransform, With<IsometricCamera>>,
     player_query: Query<&GlobalTransform, With<Player>>,
diff --git a/apps/kbve/isometric/src-tauri/src/main.rs b/apps/kbve/isometric/src-tauri/src/main.rs
index 6000c145c..52deaaefa 100644
--- a/apps/kbve/isometric/src-tauri/src/main.rs
+++ b/apps/kbve/isometric/src-tauri/src/main.rs
@@ -3,7 +3,6 @@
 
 use bevy::DefaultPlugins;
 use bevy::app::App;
-use bevy::picking::mesh_picking::MeshPickingPlugin;
 use bevy::prelude::*;
 use bevy_rapier3d::prelude::*;
 
@@ -38,9 +37,6 @@ fn main() {
     }));
 
-    // Mesh picking backend for mouse hover detection on 3D objects
-    app.add_plugins(MeshPickingPlugin);
-
     // Rapier physics engine
     app.add_plugins(RapierPhysicsPlugin::<NoUserData>::default());

Context

Found in worktree kbve-isometric-ui-test during cleanup. Needs review against current feat/isometric-rocks branch before applying.