Sprite change image (#3207)

# Objective

- Changing the underlying image would not update a sprite

## Solution

- 'Detect' if the underlying image changes to update the sprite

Currently, we don't support change detection on `RenderAssets`, so we have to manually check it. 
This method at least maintains the bind groups when the image isn't changing. They were cached, so I assume that's important.

This gives us correct behaviour here.

Co-authored-by: Carter Anderson <mcanders1@gmail.com>

pipelined/bevy_render2/src/render_asset.rs

@@ -102,9 +102,8 @@ fn extract_render_asset<A: RenderAsset>(
                 changed_assets.insert(handle);
             }
             AssetEvent::Removed { handle } => {
-                if !changed_assets.remove(handle) {
+                changed_assets.remove(handle);
-                    removed.push(handle.clone_weak());
+                removed.push(handle.clone_weak());
-                }
             }
         }
     }

pipelined/bevy_sprite2/src/lib.rs

@@ -43,7 +43,9 @@ impl Plugin for SpritePlugin {
             .init_resource::<SpecializedPipelines<SpritePipeline>>()
             .init_resource::<SpriteMeta>()
             .init_resource::<ExtractedSprites>()
+            .init_resource::<SpriteAssetEvents>()
             .add_system_to_stage(RenderStage::Extract, render::extract_sprites)
+            .add_system_to_stage(RenderStage::Extract, render::extract_sprite_events)
             .add_system_to_stage(RenderStage::Prepare, render::prepare_sprites)
             .add_system_to_stage(RenderStage::Queue, queue_sprites);
 

pipelined/bevy_sprite2/src/render/mod.rs

@@ -4,7 +4,7 @@ use crate::{
     texture_atlas::{TextureAtlas, TextureAtlasSprite},
     Rect, Sprite, SPRITE_SHADER_HANDLE,
 };
-use bevy_asset::{Assets, Handle};
+use bevy_asset::{AssetEvent, Assets, Handle};
 use bevy_core::FloatOrd;
 use bevy_core_pipeline::Transparent2d;
 use bevy_ecs::{
@@ -172,6 +172,37 @@ pub struct ExtractedSprites {
     sprites: Vec<ExtractedSprite>,
 }
 
+#[derive(Default)]
+pub struct SpriteAssetEvents {
+    images: Vec<AssetEvent<Image>>,
+}
+
+pub fn extract_sprite_events(
+    mut render_world: ResMut<RenderWorld>,
+    mut image_events: EventReader<AssetEvent<Image>>,
+) {
+    let mut events = render_world
+        .get_resource_mut::<SpriteAssetEvents>()
+        .unwrap();
+    let SpriteAssetEvents { ref mut images } = *events;
+    images.clear();
+
+    for image in image_events.iter() {
+        // AssetEvent: !Clone
+        images.push(match image {
+            AssetEvent::Created { handle } => AssetEvent::Created {
+                handle: handle.clone_weak(),
+            },
+            AssetEvent::Modified { handle } => AssetEvent::Modified {
+                handle: handle.clone_weak(),
+            },
+            AssetEvent::Removed { handle } => AssetEvent::Removed {
+                handle: handle.clone_weak(),
+            },
+        });
+    }
+}
+
 pub fn extract_sprites(
     mut render_world: ResMut<RenderWorld>,
     images: Res<Assets<Image>>,
@@ -453,7 +484,17 @@ pub fn queue_sprites(
     gpu_images: Res<RenderAssets<Image>>,
     mut sprite_batches: Query<(Entity, &SpriteBatch)>,
     mut views: Query<&mut RenderPhase<Transparent2d>>,
+    events: Res<SpriteAssetEvents>,
 ) {
+    // If an image has changed, the GpuImage has (probably) changed
+    for event in &events.images {
+        match event {
+            AssetEvent::Created { .. } => None,
+            AssetEvent::Modified { handle } => image_bind_groups.values.remove(handle),
+            AssetEvent::Removed { handle } => image_bind_groups.values.remove(handle),
+        };
+    }
+
     if let Some(view_binding) = view_uniforms.uniforms.binding() {
         sprite_meta.view_bind_group = Some(render_device.create_bind_group(&BindGroupDescriptor {
             entries: &[BindGroupEntry {