Perspective interpolation fix for brush_blend

webrender/res/brush_blend.glsl

@@ -32,7 +32,10 @@ void brush_vs(
     vec2 uv = snap_device_pos(vi) +
         src_task.common_data.task_rect.p0 -
         src_task.content_origin;
-    vUv = vec3(uv / texture_size, src_task.common_data.texture_layer_index);
+    vUv = vec3(
+        uv * gl_Position.w / texture_size, // multiply by W to compensate for perspective interpolation
+        src_task.common_data.texture_layer_index
+    );
 
     vec2 uv0 = src_task.common_data.task_rect.p0;
     vec2 uv1 = uv0 + src_task.common_data.task_rect.size;
@@ -124,7 +127,8 @@ vec3 Brightness(vec3 Cs, float amount) {
 }
 
 Fragment brush_fs() {
-    vec4 Cs = texture(sColor0, vUv);
+    vec2 base_uv = vUv.xy * gl_FragCoord.w;
+    vec4 Cs = texture(sColor0, vec3(base_uv, vUv.z));
 
     if (Cs.a == 0.0) {
         return Fragment(vec4(0.0)); // could also `discard`
@@ -155,7 +159,7 @@ Fragment brush_fs() {
 
     // Fail-safe to ensure that we don't sample outside the rendered
     // portion of a blend source.
-    alpha *= point_inside_rect(vUv.xy, vUvClipBounds.xy, vUvClipBounds.zw);
+    alpha *= point_inside_rect(base_uv, vUvClipBounds.xy, vUvClipBounds.zw);
 
     // Pre-multiply the alpha into the output value.
     return Fragment(alpha * vec4(color, 1.0));

webrender/src/batch.rs

@@ -829,6 +829,7 @@ impl AlphaBatchBuilder {
                                                 );
 
                                                 let filter_mode = match filter {
+                                                    FilterOp::Identity => 1, // matches `Contrast(1)`
                                                     FilterOp::Blur(..) => 0,
                                                     FilterOp::Contrast(..) => 1,
                                                     FilterOp::Grayscale(..) => 2,
@@ -843,6 +844,7 @@ impl AlphaBatchBuilder {
                                                 };
 
                                                 let user_data = match filter {
+                                                    FilterOp::Identity => 0x10000i32, // matches `Contrast(1)`
                                                     FilterOp::Contrast(amount) |
                                                     FilterOp::Grayscale(amount) |
                                                     FilterOp::Invert(amount) |

webrender/src/scene.rs

@@ -201,6 +201,7 @@ pub trait FilterOpHelpers {
 impl FilterOpHelpers for FilterOp {
     fn is_visible(&self) -> bool {
         match *self {
+            FilterOp::Identity |
             FilterOp::Blur(..) |
             FilterOp::Brightness(..) |
             FilterOp::Contrast(..) |
@@ -219,6 +220,7 @@ impl FilterOpHelpers for FilterOp {
 
     fn is_noop(&self) -> bool {
         match *self {
+            FilterOp::Identity => false, // this is intentional
             FilterOp::Blur(length) => length == 0.0,
             FilterOp::Brightness(amount) => amount == 1.0,
             FilterOp::Contrast(amount) => amount == 1.0,

webrender_api/src/display_item.rs

@@ -543,6 +543,9 @@ pub enum MixBlendMode {
 
 #[derive(Clone, Copy, Debug, PartialEq, Deserialize, Serialize)]
 pub enum FilterOp {
+    /// Filter that does no transformation of the colors, needed for
+    /// debug purposes only.
+    Identity,
     Blur(f32),
     Brightness(f32),
     Contrast(f32),

wrench/reftests/transforms/reftest.list

@@ -13,7 +13,8 @@ platform(linux,mac) == content-offset.yaml content-offset.png
 platform(linux,mac) == coord-system.yaml coord-system.png
 platform(linux,mac) zoom(4) == border-zoom.yaml border-zoom.png
 platform(linux) fuzzy(1,520) == perspective-origin.yaml perspective-origin.png
-platform(linux,mac) color_targets(1) alpha_targets(0) fuzzy(1,180) == screen-space-blit.yaml screen-space-blit.png
+platform(linux,mac) color_targets(2) alpha_targets(0) fuzzy(1,180) == screen-space-blit.yaml screen-space-blit.png
+platform(linux,mac) color_targets(1) alpha_targets(0) fuzzy(128,800) == screen-space-blit-trivial.yaml screen-space-blit.png
 platform(linux) fuzzy(11,4592) == screen-space-blur.yaml screen-space-blur.png
 platform(linux,mac) == nested-rotate-x.yaml nested-rotate-x.png
 platform(linux,mac) == nested-preserve-3d.yaml nested-preserve-3d.png

wrench/reftests/transforms/screen-space-blit-trivial.yaml

@@ -0,0 +1,22 @@
+# This test is similar to "screen-space-blit" but without filters,
+# so the implementation doesn't attempt to bake the contents
+# into a separate render target.
+---
+root:
+  items:
+    - type: "stacking-context"
+      perspective: 100
+      perspective-origin: 100 100
+      items:
+        - type: "stacking-context"
+          transform-origin: 235 235
+          transform: rotate-x(15)
+          items:
+            - image: checkerboard(2, 16, 16)
+              bounds: [100, 100, 260, 260]
+    - type: "stacking-context"
+      transform-origin: 635 235
+      transform: rotate-z(45)
+      items:
+        - image: checkerboard(2, 16, 16)
+          bounds: [500, 100, 260, 260]

wrench/reftests/transforms/screen-space-blit.yaml

@@ -1,3 +1,6 @@
+# This test uses `identity` filter on a preserve3D context to test how
+# filters mix up with the SC's baking for preserve3d.
+---
 root:
   items:
     - type: "stacking-context"
@@ -7,14 +10,13 @@ root:
         - type: "stacking-context"
           transform-origin: 235 235
           transform: rotate-x(15)
-          filters: opacity(0.5)
+          filters: identity
           items:
             - image: checkerboard(2, 16, 16)
               bounds: [100, 100, 260, 260]
     - type: "stacking-context"
       transform-origin: 635 235
       transform: rotate-z(45)
-      filters: opacity(0.5)
       items:
         - image: checkerboard(2, 16, 16)
           bounds: [500, 100, 260, 260]

wrench/src/yaml_frame_writer.rs

@@ -228,6 +228,7 @@ fn write_stacking_context(
     let mut filters = vec![];
     for filter in filter_iter {
         match filter {
+            FilterOp::Identity => { filters.push(Yaml::String("identity".into())) }
             FilterOp::Blur(x) => { filters.push(Yaml::String(format!("blur({})", x))) }
             FilterOp::Brightness(x) => { filters.push(Yaml::String(format!("brightness({})", x))) }
             FilterOp::Contrast(x) => { filters.push(Yaml::String(format!("contrast({})", x))) }

wrench/src/yaml_helper.rs

@@ -544,6 +544,9 @@ impl YamlHelper for Yaml {
     fn as_filter_op(&self) -> Option<FilterOp> {
         if let Some(s) = self.as_str() {
             match parse_function(s) {
+                ("identity", _, _) => {
+                    Some(FilterOp::Identity)
+                }
                 ("blur", ref args, _) if args.len() == 1 => {
                     Some(FilterOp::Blur(args[0].parse().unwrap()))
                 }