fix bloom viewport (bevyengine#6802)

# Objective

fix bloom when used on a camera with a viewport specified

## Solution

- pass viewport into the prefilter shader, and use it to read from the correct section of the original rendered screen
- don't apply viewport for the intermediate bloom passes, only for the final blend output

crates/bevy_core_pipeline/src/bloom/bloom.wgsl

@@ -5,6 +5,7 @@ struct BloomUniforms {
     knee: f32,
     scale: f32,
     intensity: f32,
+    viewport: vec4<f32>,
 };
 
 @group(0) @binding(0)
@@ -87,7 +88,8 @@ fn sample_original_3x3_tent(uv: vec2<f32>, scale: vec2<f32>) -> vec4<f32> {
 }
 
 @fragment
-fn downsample_prefilter(@location(0) uv: vec2<f32>) -> @location(0) vec4<f32> {
+fn downsample_prefilter(@location(0) output_uv: vec2<f32>) -> @location(0) vec4<f32> {
+    let sample_uv = uniforms.viewport.xy + output_uv * uniforms.viewport.zw;
     let texel_size = 1.0 / vec2<f32>(textureDimensions(original));
 
     let scale = texel_size;
@@ -98,7 +100,7 @@ fn downsample_prefilter(@location(0) uv: vec2<f32>) -> @location(0) vec4<f32> {
         0.25 / uniforms.knee,
     );
 
-    var o: vec4<f32> = sample_13_tap(uv, scale);
+    var o: vec4<f32> = sample_13_tap(sample_uv, scale);
 
     o = quadratic_threshold(o, uniforms.threshold, curve);
     o = max(o, vec4<f32>(0.00001));

crates/bevy_core_pipeline/src/bloom/mod.rs

@@ -7,7 +7,7 @@ use bevy_ecs::{
     system::{Commands, Query, Res, ResMut, Resource},
     world::{FromWorld, World},
 };
-use bevy_math::UVec2;
+use bevy_math::{UVec2, UVec4, Vec4};
 use bevy_reflect::{Reflect, TypeUuid};
 use bevy_render::{
     camera::ExtractedCamera,
@@ -152,18 +152,27 @@ impl ExtractComponent for BloomSettings {
             return None;
         }
 
-        camera.physical_viewport_size().map(|size| {
+        if let (Some((origin, _)), Some(size), Some(target_size)) = (
+            camera.physical_viewport_rect(),
+            camera.physical_viewport_size(),
+            camera.physical_target_size(),
+        ) {
             let min_view = size.x.min(size.y) / 2;
             let mip_count = calculate_mip_count(min_view);
             let scale = (min_view / 2u32.pow(mip_count)) as f32 / 8.0;
 
-            BloomUniform {
+            Some(BloomUniform {
                 threshold: settings.threshold,
                 knee: settings.knee,
                 scale: settings.scale * scale,
                 intensity: settings.intensity,
-            }
-        })
+                viewport: UVec4::new(origin.x, origin.y, size.x, size.y).as_vec4()
+                    / UVec4::new(target_size.x, target_size.y, target_size.x, target_size.y)
+                        .as_vec4(),
+            })
+        } else {
+            None
+        }
     }
 }
 
@@ -246,9 +255,6 @@ impl Node for BloomNode {
                 &bind_groups.prefilter_bind_group,
                 &[uniform_index.index()],
             );
-            if let Some(viewport) = camera.viewport.as_ref() {
-                prefilter_pass.set_camera_viewport(viewport);
-            }
             prefilter_pass.draw(0..3, 0..1);
         }
 
@@ -270,9 +276,6 @@ impl Node for BloomNode {
                 &bind_groups.downsampling_bind_groups[mip as usize - 1],
                 &[uniform_index.index()],
             );
-            if let Some(viewport) = camera.viewport.as_ref() {
-                downsampling_pass.set_camera_viewport(viewport);
-            }
             downsampling_pass.draw(0..3, 0..1);
         }
 
@@ -294,9 +297,6 @@ impl Node for BloomNode {
                 &bind_groups.upsampling_bind_groups[mip as usize - 1],
                 &[uniform_index.index()],
             );
-            if let Some(viewport) = camera.viewport.as_ref() {
-                upsampling_pass.set_camera_viewport(viewport);
-            }
             upsampling_pass.draw(0..3, 0..1);
         }
 
@@ -612,6 +612,7 @@ pub struct BloomUniform {
     knee: f32,
     scale: f32,
     intensity: f32,
+    viewport: Vec4,
 }
 
 #[derive(Component)]