Bloom (#6397)

# Objective

- Adds a bloom pass for HDR-enabled Camera3ds.
- Supersedes (and all credit due to!) #3430 and #2876

![image](https://user-images.githubusercontent.com/47158642/198698783-228edc00-20b5-4218-a613-331ccd474f38.png)

## Solution

- A threshold is applied to isolate emissive samples, and then a series of downscale and upscaling passes are applied and composited together.
- Bloom is applied to 2d or 3d Cameras with hdr: true and a BloomSettings component.

---

## Changelog

- Added a `core_pipeline::bloom::BloomSettings` component.
- Added `BloomNode` that runs between the main pass and tonemapping.
- Added a `BloomPlugin` that is loaded as part of CorePipelinePlugin.
- Added a bloom example project.

Co-authored-by: JMS55 <[email protected]>
Co-authored-by: Carter Anderson <[email protected]>
Co-authored-by: DGriffin91 <[email protected]>

Cargo.toml

@@ -313,6 +313,10 @@ description = "Illustrates spot lights"
 category = "3D Rendering"
 wasm = true
 
+[[example]]
+name = "bloom"
+path = "examples/3d/bloom.rs"
+
 [[example]]
 name = "load_gltf"
 path = "examples/3d/load_gltf.rs"

crates/bevy_core_pipeline/Cargo.toml

@@ -25,6 +25,7 @@ bevy_ecs = { path = "../bevy_ecs", version = "0.9.0-dev" }
 bevy_reflect = { path = "../bevy_reflect", version = "0.9.0-dev" }
 bevy_render = { path = "../bevy_render", version = "0.9.0-dev" }
 bevy_transform = { path = "../bevy_transform", version = "0.9.0-dev" }
+bevy_math = { path = "../bevy_math", version = "0.9.0-dev" }
 bevy_utils = { path = "../bevy_utils", version = "0.9.0-dev" }
 
 serde = { version = "1", features = ["derive"] }

crates/bevy_core_pipeline/src/bloom/bloom.wgsl

@@ -0,0 +1,136 @@
+#import bevy_core_pipeline::fullscreen_vertex_shader
+
+struct BloomUniforms {
+    threshold: f32,
+    knee: f32,
+    scale: f32,
+    intensity: f32,
+};
+
+@group(0) @binding(0)
+var original: texture_2d<f32>;
+@group(0) @binding(1)
+var original_sampler: sampler;
+@group(0) @binding(2)
+var<uniform> uniforms: BloomUniforms;
+@group(0) @binding(3)
+var up: texture_2d<f32>;
+
+fn quadratic_threshold(color: vec4<f32>, threshold: f32, curve: vec3<f32>) -> vec4<f32> {
+    let br = max(max(color.r, color.g), color.b);
+
+    var rq: f32 = clamp(br - curve.x, 0.0, curve.y);
+    rq = curve.z * rq * rq;
+
+    return color * max(rq, br - threshold) / max(br, 0.0001);
+}
+
+// Samples original around the supplied uv using a filter.
+//
+// o   o   o
+//   o   o
+// o   o   o
+//   o   o
+// o   o   o
+//
+// This is used because it has a number of advantages that
+// outweigh the cost of 13 samples that basically boil down
+// to it looking better.
+//
+// These advantages are outlined in a youtube video by the Cherno:
+//   https://www.youtube.com/watch?v=tI70-HIc5ro
+fn sample_13_tap(uv: vec2<f32>, scale: vec2<f32>) -> vec4<f32> {
+    let a = textureSample(original, original_sampler, uv + vec2<f32>(-1.0, -1.0) * scale);
+    let b = textureSample(original, original_sampler, uv + vec2<f32>(0.0, -1.0) * scale);
+    let c = textureSample(original, original_sampler, uv + vec2<f32>(1.0, -1.0) * scale);
+    let d = textureSample(original, original_sampler, uv + vec2<f32>(-0.5, -0.5) * scale);
+    let e = textureSample(original, original_sampler, uv + vec2<f32>(0.5, -0.5) * scale);
+    let f = textureSample(original, original_sampler, uv + vec2<f32>(-1.0, 0.0) * scale);
+    let g = textureSample(original, original_sampler, uv + vec2<f32>(0.0, 0.0) * scale);
+    let h = textureSample(original, original_sampler, uv + vec2<f32>(1.0, 0.0) * scale);
+    let i = textureSample(original, original_sampler, uv + vec2<f32>(-0.5, 0.5) * scale);
+    let j = textureSample(original, original_sampler, uv + vec2<f32>(0.5, 0.5) * scale);
+    let k = textureSample(original, original_sampler, uv + vec2<f32>(-1.0, 1.0) * scale);
+    let l = textureSample(original, original_sampler, uv + vec2<f32>(0.0, 1.0) * scale);
+    let m = textureSample(original, original_sampler, uv + vec2<f32>(1.0, 1.0) * scale);
+
+    let div = (1.0 / 4.0) * vec2<f32>(0.5, 0.125);
+
+    var o: vec4<f32> = (d + e + i + j) * div.x;
+    o = o + (a + b + g + f) * div.y;
+    o = o + (b + c + h + g) * div.y;
+    o = o + (f + g + l + k) * div.y;
+    o = o + (g + h + m + l) * div.y;
+
+    return o;
+}
+
+// Samples original using a 3x3 tent filter.
+//
+// NOTE: Use a 2x2 filter for better perf, but 3x3 looks better.
+fn sample_original_3x3_tent(uv: vec2<f32>, scale: vec2<f32>) -> vec4<f32> {
+    let d = vec4<f32>(1.0, 1.0, -1.0, 0.0);
+
+    var s: vec4<f32> = textureSample(original, original_sampler, uv - d.xy * scale);
+    s = s + textureSample(original, original_sampler, uv - d.wy * scale) * 2.0;
+    s = s + textureSample(original, original_sampler, uv - d.zy * scale);
+
+    s = s + textureSample(original, original_sampler, uv + d.zw * scale) * 2.0;
+    s = s + textureSample(original, original_sampler, uv) * 4.0;
+    s = s + textureSample(original, original_sampler, uv + d.xw * scale) * 2.0;
+
+    s = s + textureSample(original, original_sampler, uv + d.zy * scale);
+    s = s + textureSample(original, original_sampler, uv + d.wy * scale) * 2.0;
+    s = s + textureSample(original, original_sampler, uv + d.xy * scale);
+
+    return s / 16.0;
+}
+
+@fragment
+fn downsample_prefilter(@location(0) uv: vec2<f32>) -> @location(0) vec4<f32> {
+    let texel_size = 1.0 / vec2<f32>(textureDimensions(original));
+
+    let scale = texel_size;
+
+    let curve = vec3<f32>(
+        uniforms.threshold - uniforms.knee,
+        uniforms.knee * 2.0,
+        0.25 / uniforms.knee,
+    );
+
+    var o: vec4<f32> = sample_13_tap(uv, scale);
+
+    o = quadratic_threshold(o, uniforms.threshold, curve);
+    o = max(o, vec4<f32>(0.00001));
+
+    return o;
+}
+
+@fragment
+fn downsample(@location(0) uv: vec2<f32>) -> @location(0) vec4<f32> {
+    let texel_size = 1.0 / vec2<f32>(textureDimensions(original));
+
+    let scale = texel_size;
+
+    return sample_13_tap(uv, scale);
+}
+
+@fragment
+fn upsample(@location(0) uv: vec2<f32>) -> @location(0) vec4<f32> {
+    let texel_size = 1.0 / vec2<f32>(textureDimensions(original));
+
+    let upsample = sample_original_3x3_tent(uv, texel_size * uniforms.scale);
+    var color: vec4<f32> = textureSample(up, original_sampler, uv);
+    color = vec4<f32>(color.rgb + upsample.rgb, upsample.a);
+
+    return color;
+}
+
+@fragment
+fn upsample_final(@location(0) uv: vec2<f32>) -> @location(0) vec4<f32> {
+    let texel_size = 1.0 / vec2<f32>(textureDimensions(original));
+
+    let upsample = sample_original_3x3_tent(uv, texel_size * uniforms.scale);
+
+    return vec4<f32>(upsample.rgb * uniforms.intensity, upsample.a);
+}