Expose max_mip_dimension and uv_offset in BloomSettings. (#14512)

# Objective

By default, Bevy's bloom effect shows square artifacts on small bright
particles due to a low max mip resolution. This PR makes this
configurable via BloomSettings so users can customize these parameters
instead of having them in private module constants.

## Solution

Expose max_mip_dimension and uv_offset in BloomSettings.

## Testing

I tested these changes by running the Bloom 2D / 3D examples.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

crates/bevy_core_pipeline/src/bloom/bloom.wgsl

@@ -10,6 +10,7 @@ struct BloomUniforms {
     threshold_precomputations: vec4<f32>,
     viewport: vec4<f32>,
     aspect: f32,
+    uv_offset: f32
 };
 
 @group(0) @binding(0) var input_texture: texture_2d<f32>;
@@ -94,9 +95,9 @@ fn sample_input_13_tap(uv: vec2<f32>) -> vec3<f32> {
 
 // [COD] slide 162
 fn sample_input_3x3_tent(uv: vec2<f32>) -> vec3<f32> {
-    // Radius. Empirically chosen by and tweaked from the LearnOpenGL article.
-    let x = 0.004 / uniforms.aspect;
-    let y = 0.004;
+    // UV offsets configured from uniforms.
+    let x = uniforms.uv_offset / uniforms.aspect;
+    let y = uniforms.uv_offset;
 
     let a = textureSample(input_texture, s, vec2<f32>(uv.x - x, uv.y + y)).rgb;
     let b = textureSample(input_texture, s, vec2<f32>(uv.x, uv.y + y)).rgb;

crates/bevy_core_pipeline/src/bloom/downsampling_pipeline.rs

@@ -41,6 +41,7 @@ pub struct BloomUniforms {
     pub threshold_precomputations: Vec4,
     pub viewport: Vec4,
     pub aspect: f32,
+    pub uv_offset: f32,
 }
 
 impl FromWorld for BloomDownsamplingPipeline {

crates/bevy_core_pipeline/src/bloom/mod.rs

@@ -38,10 +38,6 @@ const BLOOM_SHADER_HANDLE: Handle<Shader> = Handle::weak_from_u128(9295994769239
 
 const BLOOM_TEXTURE_FORMAT: TextureFormat = TextureFormat::Rg11b10Float;
 
-// Maximum size of each dimension for the largest mipchain texture used in downscaling/upscaling.
-// 512 behaves well with the UV offset of 0.004 used in bloom.wgsl
-const MAX_MIP_DIMENSION: u32 = 512;
-
 pub struct BloomPlugin;
 
 impl Plugin for BloomPlugin {
@@ -328,18 +324,18 @@ fn prepare_bloom_textures(
     mut commands: Commands,
     mut texture_cache: ResMut<TextureCache>,
     render_device: Res<RenderDevice>,
-    views: Query<(Entity, &ExtractedCamera), With<BloomSettings>>,
+    views: Query<(Entity, &ExtractedCamera, &BloomSettings)>,
 ) {
-    for (entity, camera) in &views {
+    for (entity, camera, settings) in &views {
         if let Some(UVec2 {
             x: width,
             y: height,
         }) = camera.physical_viewport_size
         {
             // How many times we can halve the resolution minus one so we don't go unnecessarily low
-            let mip_count = MAX_MIP_DIMENSION.ilog2().max(2) - 1;
+            let mip_count = settings.max_mip_dimension.ilog2().max(2) - 1;
             let mip_height_ratio = if height != 0 {
-                MAX_MIP_DIMENSION as f32 / height as f32
+                settings.max_mip_dimension as f32 / height as f32
             } else {
                 0.
             };

crates/bevy_core_pipeline/src/bloom/settings.rs

@@ -102,9 +102,20 @@ pub struct BloomSettings {
     /// configured in a non-energy-conserving way,
     /// otherwise set to [`BloomCompositeMode::EnergyConserving`].
     pub composite_mode: BloomCompositeMode,
+
+    /// Maximum size of each dimension for the largest mipchain texture used in downscaling/upscaling.
+    /// Only tweak if you are seeing visual artifacts.
+    pub max_mip_dimension: u32,
+
+    /// UV offset for bloom shader. Ideally close to 2.0 / `max_mip_dimension`.
+    /// Only tweak if you are seeing visual artifacts.
+    pub uv_offset: f32,
 }
 
 impl BloomSettings {
+    const DEFAULT_MAX_MIP_DIMENSION: u32 = 512;
+    const DEFAULT_UV_OFFSET: f32 = 0.004;
+
     /// The default bloom preset.
     ///
     /// This uses the [`EnergyConserving`](BloomCompositeMode::EnergyConserving) composite mode.
@@ -118,6 +129,8 @@ impl BloomSettings {
             threshold_softness: 0.0,
         },
         composite_mode: BloomCompositeMode::EnergyConserving,
+        max_mip_dimension: Self::DEFAULT_MAX_MIP_DIMENSION,
+        uv_offset: Self::DEFAULT_UV_OFFSET,
     };
 
     /// A preset that's similar to how older games did bloom.
@@ -131,6 +144,8 @@ impl BloomSettings {
             threshold_softness: 0.2,
         },
         composite_mode: BloomCompositeMode::Additive,
+        max_mip_dimension: Self::DEFAULT_MAX_MIP_DIMENSION,
+        uv_offset: Self::DEFAULT_UV_OFFSET,
     };
 
     /// A preset that applies a very strong bloom, and blurs the whole screen.
@@ -144,6 +159,8 @@ impl BloomSettings {
             threshold_softness: 0.0,
         },
         composite_mode: BloomCompositeMode::EnergyConserving,
+        max_mip_dimension: Self::DEFAULT_MAX_MIP_DIMENSION,
+        uv_offset: Self::DEFAULT_UV_OFFSET,
     };
 }
 
@@ -213,6 +230,7 @@ impl ExtractComponent for BloomSettings {
                         / UVec4::new(target_size.x, target_size.y, target_size.x, target_size.y)
                             .as_vec4(),
                     aspect: AspectRatio::from_pixels(size.x, size.y).into(),
+                    uv_offset: settings.uv_offset,
                 };
 
                 Some((settings.clone(), uniform))