Bug 1573886 - Fix backdrop-filter blur errors due to incorrect scaling r=kvark

Differential Revision: https://phabricator.services.mozilla.com/D42013

--HG--
extra : moz-landing-system : lando

gfx/wr/webrender/res/cs_blur.glsl

@@ -25,6 +25,7 @@ in int aBlurDirection;
 struct BlurTask {
     RenderTaskCommonData common_data;
     float blur_radius;
+    vec2 blur_region;
 };
 
 BlurTask fetch_blur_task(int address) {
@@ -32,7 +33,8 @@ BlurTask fetch_blur_task(int address) {
 
     BlurTask task = BlurTask(
         task_data.common_data,
-        task_data.user_data.x
+        task_data.user_data.x,
+        task_data.user_data.yz
     );
 
     return task;
@@ -72,7 +74,7 @@ void main(void) {
     }
 
     vUvRect = vec4(src_rect.p0 + vec2(0.5),
-                   src_rect.p0 + src_rect.size - vec2(0.5));
+                   src_rect.p0 + blur_task.blur_region - vec2(0.5));
     vUvRect /= texture_size.xyxy;
 
     vec2 pos = target_rect.p0 + target_rect.size * aPosition.xy;

gfx/wr/webrender/src/picture.rs

@@ -2563,7 +2563,7 @@ impl PicturePrimitive {
                             blur_std_deviation * scale_factors.0,
                             blur_std_deviation * scale_factors.1
                         );
-                        let device_rect = if self.options.inflate_if_required {
+                        let mut device_rect = if self.options.inflate_if_required {
                             let inflation_factor = frame_state.surfaces[raster_config.surface_index.0].inflation_factor;
                             let inflation_factor = (inflation_factor * device_pixel_scale.0).ceil();
 
@@ -2582,26 +2582,26 @@ impl PicturePrimitive {
                                 .intersection(&unclipped)
                                 .unwrap();
 
-                            let mut device_rect = match device_rect.try_cast::<i32>() {
+                            match device_rect.try_cast::<i32>() {
                                 Some(rect) => rect,
                                 None => {
                                     return None
                                 }
-                            };
-
-                            // 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.
-                            device_rect.size = RenderTask::adjusted_blur_source_size(
-                                device_rect.size,
-                                blur_std_deviation,
-                            );
-
-                            device_rect
+                            }
                         } else {
                             clipped
                         };
 
+                        let original_size = device_rect.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.
+                        device_rect.size = RenderTask::adjusted_blur_source_size(
+                            device_rect.size,
+                            blur_std_deviation,
+                        );
+
                         let uv_rect_kind = calculate_uv_rect_kind(
                             &pic_rect,
                             &transform,
@@ -2630,6 +2630,7 @@ impl PicturePrimitive {
                             RenderTargetKind::Color,
                             ClearMode::Transparent,
                             None,
+                            original_size,
                         );
 
                         Some((blur_render_task_id, picture_task_id))
@@ -2701,6 +2702,7 @@ impl PicturePrimitive {
                                 RenderTargetKind::Color,
                                 ClearMode::Transparent,
                                 Some(&mut blur_tasks),
+                                device_rect.size,
                             );
                         }
 

gfx/wr/webrender/src/render_task.rs

@@ -559,6 +559,7 @@ pub struct BlurTask {
     pub blur_std_deviation: f32,
     pub target_kind: RenderTargetKind,
     pub uv_rect_handle: GpuCacheHandle,
+    pub blur_region: DeviceIntSize,
     uv_rect_kind: UvRectKind,
 }
 
@@ -975,6 +976,7 @@ impl RenderTask {
                                 RenderTargetKind::Alpha,
                                 ClearMode::Zero,
                                 None,
+                                cache_size,
                             )
                         }
                     ));
@@ -1086,6 +1088,7 @@ impl RenderTask {
         target_kind: RenderTargetKind,
         clear_mode: ClearMode,
         mut blur_cache: Option<&mut BlurTaskCache>,
+        blur_region: DeviceIntSize,
     ) -> RenderTaskId {
         // Adjust large std deviation value.
         let mut adjusted_blur_std_deviation = blur_std_deviation;
@@ -1137,6 +1140,8 @@ impl RenderTask {
             None => None,
         };
 
+        let blur_region = blur_region / (scale_factor as i32);
+
         let blur_task_id = cached_task.unwrap_or_else(|| {
             let blur_task_v = RenderTask::with_dynamic_location(
                 adjusted_blur_target_size,
@@ -1145,6 +1150,7 @@ impl RenderTask {
                     blur_std_deviation: adjusted_blur_std_deviation.height,
                     target_kind,
                     uv_rect_handle: GpuCacheHandle::new(),
+                    blur_region,
                     uv_rect_kind,
                 }),
                 clear_mode,
@@ -1159,6 +1165,7 @@ impl RenderTask {
                     blur_std_deviation: adjusted_blur_std_deviation.width,
                     target_kind,
                     uv_rect_handle: GpuCacheHandle::new(),
+                    blur_region,
                     uv_rect_kind,
                 }),
                 clear_mode,
@@ -1363,6 +1370,7 @@ impl RenderTask {
                         RenderTargetKind::Color,
                         ClearMode::Transparent,
                         None,
+                        content_size,
                     )
                 }
                 FilterPrimitiveKind::Opacity(ref opacity) => {
@@ -1432,6 +1440,7 @@ impl RenderTask {
                         RenderTargetKind::Color,
                         ClearMode::Transparent,
                         None,
+                        content_size,
                     );
 
                     let task = RenderTask::new_svg_filter_primitive(
@@ -1585,8 +1594,8 @@ impl RenderTask {
             RenderTaskKind::HorizontalBlur(ref task) => {
                 [
                     task.blur_std_deviation,
-                    0.0,
-                    0.0,
+                    task.blur_region.width as f32,
+                    task.blur_region.height as f32,
                 ]
             }
             RenderTaskKind::Readback(..) |