Bug 1768678 - Fix blur source size adjustment for downscaling r=gfx-reviewers,lsalzman

Differential Revision: https://phabricator.services.mozilla.com/D152243

gfx/wr/webrender/src/picture.rs

@@ -5351,27 +5351,25 @@ impl PicturePrimitive {
                             height_std_deviation,
                         );
 
-                        let mut device_rect = surface_rects.clipped;
-                        let original_size = device_rect.size();
+                        let original_size = surface_rects.clipped.size();
 
                         // Adjust the size to avoid introducing sampling errors during the down-scaling passes.
                         // what would be even better is to rasterize the picture at the down-scaled size
                         // directly.
                         let adjusted_size = BlurTask::adjusted_blur_source_size(
-                            device_rect.size(),
+                            original_size,
                             blur_std_deviation,
                         );
-                        device_rect.set_size(adjusted_size);
 
                         let cmd_buffer_index = frame_state.cmd_buffers.create_cmd_buffer();
 
                         let picture_task_id = frame_state.rg_builder.add().init(
                             RenderTask::new_dynamic(
-                                surface_rects.task_size,
+                                adjusted_size,
                                 RenderTaskKind::new_picture(
-                                    surface_rects.task_size,
+                                    adjusted_size,
                                     surface_rects.needs_scissor_rect,
-                                    device_rect.min,
+                                    surface_rects.clipped.min,
                                     surface_spatial_node_index,
                                     raster_spatial_node_index,
                                     device_pixel_scale,

gfx/wr/webrender/src/render_task.rs

@@ -232,7 +232,7 @@ impl BlurTask {
     // In order to do the blur down-scaling passes without introducing errors, we need the
     // source of each down-scale pass to be a multuple of two. If need be, this inflates
     // the source size so that each down-scale pass will sample correctly.
-    pub fn adjusted_blur_source_size(original_size: DeviceSize, mut std_dev: DeviceSize) -> DeviceSize {
+    pub fn adjusted_blur_source_size(original_size: DeviceSize, mut std_dev: DeviceSize) -> DeviceIntSize {
         let mut adjusted_size = original_size;
         let mut scale_factor = 1.0;
         while std_dev.width > MAX_BLUR_STD_DEVIATION && std_dev.height > MAX_BLUR_STD_DEVIATION {
@@ -245,7 +245,7 @@ impl BlurTask {
             adjusted_size = (original_size.to_f32() / scale_factor).ceil();
         }
 
-        adjusted_size * scale_factor
+        (adjusted_size * scale_factor).round().to_i32()
     }
 }
 

gfx/wr/wrench/reftests/filters/filter-blur-downscale-fractional.yaml

@@ -0,0 +1,11 @@
+# verify that we correctly size an image to a power of two when
+# using downscale passes to avoid blur artifacts
+---
+root:
+  items:
+    - type: stacking-context
+      bounds: [100, 100, 300, 300]
+      filters: blur(16.4, 16.4)
+      items:
+      - image: "firefox.png"
+        bounds: 20 20 200 200

gfx/wr/wrench/reftests/filters/reftest.list

@@ -1,5 +1,6 @@
 == filter-grayscale.yaml filter-grayscale-ref.yaml
 platform(linux,mac) == draw_calls(7) color_targets(7) alpha_targets(0) filter-blur.yaml filter-blur.png
+platform(linux,mac) == filter-blur-downscale-fractional.yaml filter-blur-downscale-fractional.png
 == isolated.yaml isolated-ref.yaml
 == invisible.yaml invisible-ref.yaml
 fuzzy-if(platform(swgl),1,10000) == opacity.yaml opacity-ref.yaml

testing/web-platform/meta/css/filter-effects/backdrop-filter-edge-clipping.html.ini

@@ -0,0 +1,2 @@
+[backdrop-filter-edge-clipping.html]
+  fuzzy: maxDifference=10-32;totalPixels=1750-2100