SSBO, don't double-premultiply

Author: bdero

impeller/aiks/aiks_unittests.cc

@@ -395,6 +395,30 @@ TEST_P(AiksTest, CanRenderLinearGradientDecal) {
   CanRenderLinearGradient(this, Entity::TileMode::kDecal);
 }
 
+TEST_P(AiksTest, CanRenderLinearGradientDecalWithColorFilter) {
+  Canvas canvas;
+  canvas.Scale(GetContentScale());
+  Paint paint;
+  canvas.Translate({100.0f, 0, 0});
+
+  std::vector<Color> colors = {Color{0.9568, 0.2627, 0.2118, 1.0},
+                               Color{0.1294, 0.5882, 0.9529, 0.0}};
+  std::vector<Scalar> stops = {0.0, 1.0};
+
+  paint.color_source = ColorSource::MakeLinearGradient(
+      {0, 0}, {200, 200}, std::move(colors), std::move(stops),
+      Entity::TileMode::kDecal, {});
+  // Overlay the gradient with 50% green. This should appear as the entire
+  // rectangle being drawn with 50% green, including the border area outside the
+  // decal gradient.
+  paint.color_filter = ColorFilter::MakeBlend(BlendMode::kSourceOver,
+                                              Color::Green().WithAlpha(0.50));
+
+  paint.color = Color(1.0, 1.0, 1.0, 1.0);
+  canvas.DrawRect({0, 0, 600, 600}, paint);
+  ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
+}
+
 namespace {
 void CanRenderLinearGradientWithOverlappingStops(AiksTest* aiks_test,
                                                  Entity::TileMode tile_mode) {

impeller/entity/contents/conical_gradient_contents.cc

@@ -70,6 +70,7 @@ bool ConicalGradientContents::RenderSSBO(const ContentContext& renderer,
   frag_info.center = center_;
   frag_info.radius = radius_;
   frag_info.tile_mode = static_cast<Scalar>(tile_mode_);
+  frag_info.decal_border_color = decal_border_color_;
   frag_info.alpha = GetOpacity();
   if (focus_) {
     frag_info.focus = focus_.value();
@@ -140,7 +141,7 @@ bool ConicalGradientContents::RenderTexture(const ContentContext& renderer,
   frag_info.center = center_;
   frag_info.radius = radius_;
   frag_info.tile_mode = static_cast<Scalar>(tile_mode_);
-  frag_info.decal_border_color = decal_border_color_.Premultiply();
+  frag_info.decal_border_color = decal_border_color_;
   frag_info.texture_sampler_y_coord_scale = gradient_texture->GetYCoordScale();
   frag_info.alpha = GetOpacity();
   frag_info.half_texel = Vector2(0.5 / gradient_texture->GetSize().width,

impeller/entity/contents/linear_gradient_contents.cc

@@ -82,7 +82,7 @@ bool LinearGradientContents::RenderTexture(const ContentContext& renderer,
   frag_info.start_point = start_point_;
   frag_info.end_point = end_point_;
   frag_info.tile_mode = static_cast<Scalar>(tile_mode_);
-  frag_info.decal_border_color = decal_border_color_.Premultiply();
+  frag_info.decal_border_color = decal_border_color_;
   frag_info.texture_sampler_y_coord_scale = gradient_texture->GetYCoordScale();
   frag_info.alpha = GetOpacity();
   frag_info.half_texel = Vector2(0.5 / gradient_texture->GetSize().width,
@@ -139,6 +139,7 @@ bool LinearGradientContents::RenderSSBO(const ContentContext& renderer,
   frag_info.start_point = start_point_;
   frag_info.end_point = end_point_;
   frag_info.tile_mode = static_cast<Scalar>(tile_mode_);
+  frag_info.decal_border_color = decal_border_color_;
   frag_info.alpha = GetOpacity();
 
   auto& host_buffer = pass.GetTransientsBuffer();

impeller/entity/contents/radial_gradient_contents.cc

@@ -76,6 +76,7 @@ bool RadialGradientContents::RenderSSBO(const ContentContext& renderer,
   frag_info.center = center_;
   frag_info.radius = radius_;
   frag_info.tile_mode = static_cast<Scalar>(tile_mode_);
+  frag_info.decal_border_color = decal_border_color_;
   frag_info.alpha = GetOpacity();
 
   auto& host_buffer = pass.GetTransientsBuffer();
@@ -139,7 +140,7 @@ bool RadialGradientContents::RenderTexture(const ContentContext& renderer,
   frag_info.center = center_;
   frag_info.radius = radius_;
   frag_info.tile_mode = static_cast<Scalar>(tile_mode_);
-  frag_info.decal_border_color = decal_border_color_.Premultiply();
+  frag_info.decal_border_color = decal_border_color_;
   frag_info.texture_sampler_y_coord_scale = gradient_texture->GetYCoordScale();
   frag_info.alpha = GetOpacity();
   frag_info.half_texel = Vector2(0.5 / gradient_texture->GetSize().width,

impeller/entity/contents/sweep_gradient_contents.cc

@@ -82,6 +82,7 @@ bool SweepGradientContents::RenderSSBO(const ContentContext& renderer,
   frag_info.bias = bias_;
   frag_info.scale = scale_;
   frag_info.tile_mode = static_cast<Scalar>(tile_mode_);
+  frag_info.decal_border_color = decal_border_color_;
   frag_info.alpha = GetOpacity();
 
   auto& host_buffer = pass.GetTransientsBuffer();
@@ -147,7 +148,7 @@ bool SweepGradientContents::RenderTexture(const ContentContext& renderer,
   frag_info.scale = scale_;
   frag_info.texture_sampler_y_coord_scale = gradient_texture->GetYCoordScale();
   frag_info.tile_mode = static_cast<Scalar>(tile_mode_);
-  frag_info.decal_border_color = decal_border_color_.Premultiply();
+  frag_info.decal_border_color = decal_border_color_;
   frag_info.alpha = GetOpacity();
   frag_info.half_texel = Vector2(0.5 / gradient_texture->GetSize().width,
                                  0.5 / gradient_texture->GetSize().height);

impeller/entity/shaders/conical_gradient_fill.frag

@@ -4,6 +4,7 @@
 
 precision mediump float;
 
+#include <impeller/color.glsl>
 #include <impeller/gradient.glsl>
 #include <impeller/texture.glsl>
 #include <impeller/types.glsl>
@@ -43,6 +44,5 @@ void main() {
                                  frag_info.half_texel,                     //
                                  frag_info.tile_mode,                      //
                                  frag_info.decal_border_color);
-  frag_color =
-      vec4(frag_color.xyz * frag_color.a, frag_color.a) * frag_info.alpha;
+  frag_color = IPPremultiply(frag_color) * frag_info.alpha;
 }

impeller/entity/shaders/conical_gradient_ssbo_fill.frag

@@ -4,6 +4,7 @@
 
 precision mediump float;
 
+#include <impeller/color.glsl>
 #include <impeller/gradient.glsl>
 #include <impeller/texture.glsl>
 #include <impeller/types.glsl>
@@ -22,6 +23,7 @@ uniform FragInfo {
   highp vec2 center;
   float radius;
   float tile_mode;
+  vec4 decal_border_color;
   float alpha;
   int colors_length;
   vec2 focus;
@@ -36,33 +38,29 @@ out vec4 frag_color;
 void main() {
   vec2 res = IPComputeConicalT(frag_info.focus, frag_info.focus_radius,
                                frag_info.center, frag_info.radius, v_position);
-  if (res.y < 0.0) {
-    frag_color = vec4(0);
-    return;
-  }
 
   float t = res.x;
-  if ((t < 0.0 || t > 1.0) && frag_info.tile_mode == kTileModeDecal) {
-    frag_color = vec4(0);
-    return;
-  }
-  t = IPFloatTile(t, frag_info.tile_mode);
+  if (res.y < 0.0 ||
+      ((t < 0.0 || t > 1.0) && frag_info.tile_mode == kTileModeDecal)) {
+    frag_color = frag_info.decal_border_color;
+  } else {
+    t = IPFloatTile(t, frag_info.tile_mode);
 
-  vec4 result_color = vec4(0);
-  for (int i = 1; i < frag_info.colors_length; i++) {
-    ColorPoint prev_point = color_data.colors[i - 1];
-    ColorPoint current_point = color_data.colors[i];
-    if (t >= prev_point.stop && t <= current_point.stop) {
-      float delta = (current_point.stop - prev_point.stop);
-      if (delta < 0.001) {
-        result_color = current_point.color;
-      } else {
-        float ratio = (t - prev_point.stop) / delta;
-        result_color = mix(prev_point.color, current_point.color, ratio);
+    vec4 result_color = vec4(0);
+    for (int i = 1; i < frag_info.colors_length; i++) {
+      ColorPoint prev_point = color_data.colors[i - 1];
+      ColorPoint current_point = color_data.colors[i];
+      if (t >= prev_point.stop && t <= current_point.stop) {
+        float delta = (current_point.stop - prev_point.stop);
+        if (delta < 0.001) {
+          result_color = current_point.color;
+        } else {
+          float ratio = (t - prev_point.stop) / delta;
+          result_color = mix(prev_point.color, current_point.color, ratio);
+        }
+        break;
       }
-      break;
     }
   }
-  frag_color =
-      vec4(result_color.xyz * result_color.a, result_color.a) * frag_info.alpha;
+  frag_color = IPPremultiply(frag_color) * frag_info.alpha;
 }

impeller/entity/shaders/linear_gradient_fill.frag

@@ -4,6 +4,7 @@
 
 precision mediump float;
 
+#include <impeller/color.glsl>
 #include <impeller/texture.glsl>
 #include <impeller/types.glsl>
 
@@ -36,6 +37,5 @@ void main() {
                                  frag_info.half_texel,                     //
                                  frag_info.tile_mode,                      //
                                  frag_info.decal_border_color);
-  frag_color =
-      vec4(frag_color.xyz * frag_color.a, frag_color.a) * frag_info.alpha;
+  frag_color = IPPremultiply(frag_color) * frag_info.alpha;
 }

impeller/entity/shaders/linear_gradient_ssbo_fill.frag

@@ -4,6 +4,7 @@
 
 precision mediump float;
 
+#include <impeller/color.glsl>
 #include <impeller/texture.glsl>
 #include <impeller/types.glsl>
 
@@ -22,6 +23,7 @@ uniform FragInfo {
   highp vec2 end_point;
   float alpha;
   float tile_mode;
+  vec4 decal_border_color;
   int colors_length;
 }
 frag_info;
@@ -37,25 +39,24 @@ void main() {
       dot(start_to_position, start_to_end) / dot(start_to_end, start_to_end);
 
   if ((t < 0.0 || t > 1.0) && frag_info.tile_mode == kTileModeDecal) {
-    frag_color = vec4(0);
-    return;
-  }
-  t = IPFloatTile(t, frag_info.tile_mode);
-
-  for (int i = 1; i < frag_info.colors_length; i++) {
-    ColorPoint prev_point = color_data.colors[i - 1];
-    ColorPoint current_point = color_data.colors[i];
-    if (t >= prev_point.stop && t <= current_point.stop) {
-      float delta = (current_point.stop - prev_point.stop);
-      if (delta < 0.001) {
-        frag_color = current_point.color;
-      } else {
-        float ratio = (t - prev_point.stop) / delta;
-        frag_color = mix(prev_point.color, current_point.color, ratio);
+    frag_color = frag_info.decal_border_color;
+  } else {
+    t = IPFloatTile(t, frag_info.tile_mode);
+
+    for (int i = 1; i < frag_info.colors_length; i++) {
+      ColorPoint prev_point = color_data.colors[i - 1];
+      ColorPoint current_point = color_data.colors[i];
+      if (t >= prev_point.stop && t <= current_point.stop) {
+        float delta = (current_point.stop - prev_point.stop);
+        if (delta < 0.001) {
+          frag_color = current_point.color;
+        } else {
+          float ratio = (t - prev_point.stop) / delta;
+          frag_color = mix(prev_point.color, current_point.color, ratio);
+        }
+        break;
       }
-      break;
     }
   }
-  frag_color =
-      vec4(frag_color.xyz * frag_color.a, frag_color.a) * frag_info.alpha;
+  frag_color = IPPremultiply(frag_color) * frag_info.alpha;
 }

impeller/entity/shaders/radial_gradient_fill.frag

@@ -4,6 +4,7 @@
 
 precision mediump float;
 
+#include <impeller/color.glsl>
 #include <impeller/texture.glsl>
 #include <impeller/types.glsl>
 
@@ -34,6 +35,5 @@ void main() {
                                  frag_info.half_texel,                     //
                                  frag_info.tile_mode,                      //
                                  frag_info.decal_border_color);
-  frag_color =
-      vec4(frag_color.xyz * frag_color.a, frag_color.a) * frag_info.alpha;
+  frag_color = IPPremultiply(frag_color) * frag_info.alpha;
 }