Fix example game of life (#12897)

# Objective

- Example `compute_shader_game_of_life` is random and not following the
rules of the game of life: at each steps, it randomly reads some pixel
of the current step and some of the previous step instead of only from
the previous step
- Fixes #9353 

## Solution

- Adopted from #9678 
- Added a switch of the texture displayed every frame otherwise the game
of life looks wrong
- Added a way to display the texture bigger so that I could manually
check everything was right

---------

Co-authored-by: Sludge <96552222+SludgePhD@users.noreply.github.com>
Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>

assets/shaders/game_of_life.wgsl

@@ -1,4 +1,12 @@
-@group(0) @binding(0) var texture: texture_storage_2d<r32float, read_write>;
+// The shader reads the previous frame's state from the `input` texture, and writes the new state of
+// each pixel to the `output` texture. The textures are flipped each step to progress the
+// simulation.
+// Two textures are needed for the game of life as each pixel of step N depends on the state of its
+// neighbors at step N-1.
+
+@group(0) @binding(0) var input: texture_storage_2d<r32float, read>;
+
+@group(0) @binding(1) var output: texture_storage_2d<r32float, write>;
 
 fn hash(value: u32) -> u32 {
     var state = value;
@@ -19,15 +27,15 @@ fn randomFloat(value: u32) -> f32 {
 fn init(@builtin(global_invocation_id) invocation_id: vec3<u32>, @builtin(num_workgroups) num_workgroups: vec3<u32>) {
     let location = vec2<i32>(i32(invocation_id.x), i32(invocation_id.y));
 
-    let randomNumber = randomFloat(invocation_id.y * num_workgroups.x + invocation_id.x);
+    let randomNumber = randomFloat(invocation_id.y << 16u | invocation_id.x);
     let alive = randomNumber > 0.9;
     let color = vec4<f32>(f32(alive));
 
-    textureStore(texture, location, color);
+    textureStore(output, location, color);
 }
 
 fn is_alive(location: vec2<i32>, offset_x: i32, offset_y: i32) -> i32 {
-    let value: vec4<f32> = textureLoad(texture, location + vec2<i32>(offset_x, offset_y));
+    let value: vec4<f32> = textureLoad(input, location + vec2<i32>(offset_x, offset_y));
     return i32(value.x);
 }
 
@@ -59,7 +67,5 @@ fn update(@builtin(global_invocation_id) invocation_id: vec3<u32>) {
     }
     let color = vec4<f32>(f32(alive));
 
-    storageBarrier();
-
-    textureStore(texture, location, color);
+    textureStore(output, location, color);
 }

examples/shader/compute_shader_game_of_life.rs

@@ -7,34 +7,42 @@ use bevy::{
     prelude::*,
     render::{
         extract_resource::{ExtractResource, ExtractResourcePlugin},
-        render_asset::RenderAssetUsages,
-        render_asset::RenderAssets,
+        render_asset::{RenderAssetUsages, RenderAssets},
         render_graph::{self, RenderGraph, RenderLabel},
-        render_resource::*,
+        render_resource::{binding_types::texture_storage_2d, *},
         renderer::{RenderContext, RenderDevice},
         Render, RenderApp, RenderSet,
     },
 };
 use std::borrow::Cow;
 
-const SIZE: (u32, u32) = (1280, 720);
+const DISPLAY_FACTOR: u32 = 4;
+const SIZE: (u32, u32) = (1280 / DISPLAY_FACTOR, 720 / DISPLAY_FACTOR);
 const WORKGROUP_SIZE: u32 = 8;
 
 fn main() {
     App::new()
         .insert_resource(ClearColor(Color::BLACK))
         .add_plugins((
-            DefaultPlugins.set(WindowPlugin {
-                primary_window: Some(Window {
-                    // uncomment for unthrottled FPS
-                    // present_mode: bevy::window::PresentMode::AutoNoVsync,
+            DefaultPlugins
+                .set(WindowPlugin {
+                    primary_window: Some(Window {
+                        resolution: (
+                            (SIZE.0 * DISPLAY_FACTOR) as f32,
+                            (SIZE.1 * DISPLAY_FACTOR) as f32,
+                        )
+                            .into(),
+                        // uncomment for unthrottled FPS
+                        // present_mode: bevy::window::PresentMode::AutoNoVsync,
+                        ..default()
+                    }),
                     ..default()
-                }),
-                ..default()
-            }),
+                })
+                .set(ImagePlugin::default_nearest()),
             GameOfLifeComputePlugin,
         ))
         .add_systems(Startup, setup)
+        .add_systems(Update, switch_textures)
         .run();
 }
 
@@ -52,19 +60,34 @@ fn setup(mut commands: Commands, mut images: ResMut<Assets<Image>>) {
     );
     image.texture_descriptor.usage =
         TextureUsages::COPY_DST | TextureUsages::STORAGE_BINDING | TextureUsages::TEXTURE_BINDING;
-    let image = images.add(image);
+    let image0 = images.add(image.clone());
+    let image1 = images.add(image);
 
     commands.spawn(SpriteBundle {
         sprite: Sprite {
             custom_size: Some(Vec2::new(SIZE.0 as f32, SIZE.1 as f32)),
             ..default()
         },
-        texture: image.clone(),
+        texture: image0.clone(),
+        transform: Transform::from_scale(Vec3::splat(DISPLAY_FACTOR as f32)),
         ..default()
     });
     commands.spawn(Camera2dBundle::default());
 
-    commands.insert_resource(GameOfLifeImage { texture: image });
+    commands.insert_resource(GameOfLifeImages {
+        texture_a: image0,
+        texture_b: image1,
+    });
+}
+
+// Switch texture to display every frame to show the one that was written to most recently.
+fn switch_textures(images: Res<GameOfLifeImages>, mut displayed: Query<&mut Handle<Image>>) {
+    let mut displayed = displayed.single_mut();
+    if *displayed == images.texture_a {
+        *displayed = images.texture_b.clone_weak();
+    } else {
+        *displayed = images.texture_a.clone_weak();
+    }
 }
 
 struct GameOfLifeComputePlugin;
@@ -76,7 +99,7 @@ impl Plugin for GameOfLifeComputePlugin {
     fn build(&self, app: &mut App) {
         // Extract the game of life image resource from the main world into the render world
         // for operation on by the compute shader and display on the sprite.
-        app.add_plugins(ExtractResourcePlugin::<GameOfLifeImage>::default());
+        app.add_plugins(ExtractResourcePlugin::<GameOfLifeImages>::default());
         let render_app = app.sub_app_mut(RenderApp);
         render_app.add_systems(
             Render,
@@ -94,29 +117,35 @@ impl Plugin for GameOfLifeComputePlugin {
     }
 }
 
-#[derive(Resource, Clone, Deref, ExtractResource, AsBindGroup)]
-struct GameOfLifeImage {
-    #[storage_texture(0, image_format = R32Float, access = ReadWrite)]
-    texture: Handle<Image>,
+#[derive(Resource, Clone, ExtractResource)]
+struct GameOfLifeImages {
+    texture_a: Handle<Image>,
+    texture_b: Handle<Image>,
 }
 
 #[derive(Resource)]
-struct GameOfLifeImageBindGroup(BindGroup);
+struct GameOfLifeImageBindGroups([BindGroup; 2]);
 
 fn prepare_bind_group(
     mut commands: Commands,
     pipeline: Res<GameOfLifePipeline>,
     gpu_images: Res<RenderAssets<Image>>,
-    game_of_life_image: Res<GameOfLifeImage>,
+    game_of_life_images: Res<GameOfLifeImages>,
     render_device: Res<RenderDevice>,
 ) {
-    let view = gpu_images.get(&game_of_life_image.texture).unwrap();
-    let bind_group = render_device.create_bind_group(
+    let view_a = gpu_images.get(&game_of_life_images.texture_a).unwrap();
+    let view_b = gpu_images.get(&game_of_life_images.texture_b).unwrap();
+    let bind_group_0 = render_device.create_bind_group(
         None,
         &pipeline.texture_bind_group_layout,
-        &BindGroupEntries::single(&view.texture_view),
+        &BindGroupEntries::sequential((&view_a.texture_view, &view_b.texture_view)),
     );
-    commands.insert_resource(GameOfLifeImageBindGroup(bind_group));
+    let bind_group_1 = render_device.create_bind_group(
+        None,
+        &pipeline.texture_bind_group_layout,
+        &BindGroupEntries::sequential((&view_b.texture_view, &view_a.texture_view)),
+    );
+    commands.insert_resource(GameOfLifeImageBindGroups([bind_group_0, bind_group_1]));
 }
 
 #[derive(Resource)]
@@ -129,7 +158,16 @@ struct GameOfLifePipeline {
 impl FromWorld for GameOfLifePipeline {
     fn from_world(world: &mut World) -> Self {
         let render_device = world.resource::<RenderDevice>();
-        let texture_bind_group_layout = GameOfLifeImage::bind_group_layout(render_device);
+        let texture_bind_group_layout = render_device.create_bind_group_layout(
+            "GameOfLifeImages",
+            &BindGroupLayoutEntries::sequential(
+                ShaderStages::COMPUTE,
+                (
+                    texture_storage_2d(TextureFormat::R32Float, StorageTextureAccess::ReadOnly),
+                    texture_storage_2d(TextureFormat::R32Float, StorageTextureAccess::WriteOnly),
+                ),
+            ),
+        );
         let shader = world.load_asset("shaders/game_of_life.wgsl");
         let pipeline_cache = world.resource::<PipelineCache>();
         let init_pipeline = pipeline_cache.queue_compute_pipeline(ComputePipelineDescriptor {
@@ -160,7 +198,7 @@ impl FromWorld for GameOfLifePipeline {
 enum GameOfLifeState {
     Loading,
     Init,
-    Update,
+    Update(usize),
 }
 
 struct GameOfLifeNode {
@@ -193,10 +231,16 @@ impl render_graph::Node for GameOfLifeNode {
                 if let CachedPipelineState::Ok(_) =
                     pipeline_cache.get_compute_pipeline_state(pipeline.update_pipeline)
                 {
-                    self.state = GameOfLifeState::Update;
+                    self.state = GameOfLifeState::Update(1);
                 }
             }
-            GameOfLifeState::Update => {}
+            GameOfLifeState::Update(0) => {
+                self.state = GameOfLifeState::Update(1);
+            }
+            GameOfLifeState::Update(1) => {
+                self.state = GameOfLifeState::Update(0);
+            }
+            GameOfLifeState::Update(_) => unreachable!(),
         }
     }
 
@@ -206,7 +250,7 @@ impl render_graph::Node for GameOfLifeNode {
         render_context: &mut RenderContext,
         world: &World,
     ) -> Result<(), render_graph::NodeRunError> {
-        let texture_bind_group = &world.resource::<GameOfLifeImageBindGroup>().0;
+        let bind_groups = &world.resource::<GameOfLifeImageBindGroups>().0;
         let pipeline_cache = world.resource::<PipelineCache>();
         let pipeline = world.resource::<GameOfLifePipeline>();
 
@@ -214,8 +258,6 @@ impl render_graph::Node for GameOfLifeNode {
             .command_encoder()
             .begin_compute_pass(&ComputePassDescriptor::default());
 
-        pass.set_bind_group(0, texture_bind_group, &[]);
-
         // select the pipeline based on the current state
         match self.state {
             GameOfLifeState::Loading => {}
@@ -223,13 +265,15 @@ impl render_graph::Node for GameOfLifeNode {
                 let init_pipeline = pipeline_cache
                     .get_compute_pipeline(pipeline.init_pipeline)
                     .unwrap();
+                pass.set_bind_group(0, &bind_groups[0], &[]);
                 pass.set_pipeline(init_pipeline);
                 pass.dispatch_workgroups(SIZE.0 / WORKGROUP_SIZE, SIZE.1 / WORKGROUP_SIZE, 1);
             }
-            GameOfLifeState::Update => {
+            GameOfLifeState::Update(index) => {
                 let update_pipeline = pipeline_cache
                     .get_compute_pipeline(pipeline.update_pipeline)
                     .unwrap();
+                pass.set_bind_group(0, &bind_groups[index], &[]);
                 pass.set_pipeline(update_pipeline);
                 pass.dispatch_workgroups(SIZE.0 / WORKGROUP_SIZE, SIZE.1 / WORKGROUP_SIZE, 1);
             }