[Impeller] made plus an advanced blend

Author: gaaclarke

impeller/aiks/aiks_unittests.cc

@@ -1121,6 +1121,42 @@ TEST_P(AiksTest, BlendModePlusAlpha) {
   ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
 }
 
+// Bug: https://github.com/flutter/flutter/issues/142549
+TEST_P(AiksTest, BlendModePlusAlphaHalf) {
+  Canvas canvas;
+  canvas.Scale(GetContentScale());
+  canvas.DrawPaint({.color = Color(0.9, 1.0, 0.9, 1.0)});
+  canvas.DrawRect(Rect::MakeXYWH(0, 0, 300, 300),
+                  {.color = Color(1, 0, 0, 0.5)});
+  canvas.SaveLayer({});
+  Paint paint;
+  paint.blend_mode = BlendMode::kPlus;
+  paint.color = Color(0, 0, 1, 0.5);
+  canvas.DrawRect(Rect::MakeXYWH(0, 0, 150, 300), paint);
+  paint.color = Color(1, 0, 1, 1);
+  canvas.DrawRect(Rect::MakeXYWH(150, 0, 150, 300), paint);
+  canvas.Restore();
+  ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
+}
+
+TEST_P(AiksTest, BlendModePlusAlphaFoo) {
+  Canvas canvas;
+  canvas.Scale(GetContentScale());
+  canvas.DrawPaint({.color = Color(0.9, 1.0, 0.9, 1.0)});
+  canvas.DrawRect(Rect::MakeXYWH(0, 0, 300, 300), {.color = Color(1, 0, 0, 1)});
+  canvas.SaveLayer({});
+  Paint paint;
+  paint.blend_mode = BlendMode::kPlus;
+  paint.color = Color(0, 0, 1, 10.0 / 255.0);
+  for (int i = 0; i < 20; ++i) {
+    canvas.DrawRect(Rect::MakeXYWH(0, 0, 150, 300), paint);
+  }
+  paint.color = Color(0, 0, 1, 200.0 / 255.0);
+  canvas.DrawRect(Rect::MakeXYWH(150, 0, 150, 300), paint);
+  canvas.Restore();
+  ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
+}
+
 TEST_P(AiksTest, ColorWheel) {
   // Compare with https://fiddle.skia.org/c/@BlendModes
 

impeller/entity/contents/content_context.cc

@@ -128,15 +128,6 @@ void ContentContextOptions::ApplyToPipelineDescriptor(
       color0.src_alpha_blend_factor = BlendFactor::kOneMinusDestinationAlpha;
       color0.src_color_blend_factor = BlendFactor::kOneMinusDestinationAlpha;
       break;
-    case BlendMode::kPlus:
-      color0.dst_alpha_blend_factor =
-          IsAlphaClampedToOne(color_attachment_pixel_format)
-              ? BlendFactor::kOne
-              : BlendFactor::kOneMinusSourceAlpha;
-      color0.dst_color_blend_factor = BlendFactor::kOne;
-      color0.src_alpha_blend_factor = BlendFactor::kOne;
-      color0.src_color_blend_factor = BlendFactor::kOne;
-      break;
     case BlendMode::kModulate:
       color0.dst_alpha_blend_factor = BlendFactor::kSourceAlpha;
       color0.dst_color_blend_factor = BlendFactor::kSourceColor;
@@ -332,6 +323,9 @@ ContentContext::ContentContext(
     framebuffer_blend_lighten_pipelines_.CreateDefault(
         *context_, options_trianglestrip,
         {static_cast<Scalar>(BlendSelectValues::kLighten), supports_decal});
+    framebuffer_blend_plus_pipelines_.CreateDefault(
+        *context_, options_trianglestrip,
+        {static_cast<Scalar>(BlendSelectValues::kPlus), supports_decal});
     framebuffer_blend_luminosity_pipelines_.CreateDefault(
         *context_, options_trianglestrip,
         {static_cast<Scalar>(BlendSelectValues::kLuminosity), supports_decal});
@@ -379,6 +373,9 @@ ContentContext::ContentContext(
   blend_lighten_pipelines_.CreateDefault(
       *context_, options_trianglestrip,
       {static_cast<Scalar>(BlendSelectValues::kLighten), supports_decal});
+  blend_plus_pipelines_.CreateDefault(
+      *context_, options_trianglestrip,
+      {static_cast<Scalar>(BlendSelectValues::kPlus), supports_decal});
   blend_luminosity_pipelines_.CreateDefault(
       *context_, options_trianglestrip,
       {static_cast<Scalar>(BlendSelectValues::kLuminosity), supports_decal});

impeller/entity/contents/content_context.h

@@ -197,6 +197,8 @@ using BlendHuePipeline =
     RenderPipelineT<AdvancedBlendVertexShader, AdvancedBlendFragmentShader>;
 using BlendLightenPipeline =
     RenderPipelineT<AdvancedBlendVertexShader, AdvancedBlendFragmentShader>;
+using BlendPlusPipeline =
+    RenderPipelineT<AdvancedBlendVertexShader, AdvancedBlendFragmentShader>;
 using BlendLuminosityPipeline =
     RenderPipelineT<AdvancedBlendVertexShader, AdvancedBlendFragmentShader>;
 using BlendMultiplyPipeline =
@@ -237,6 +239,9 @@ using FramebufferBlendHuePipeline =
 using FramebufferBlendLightenPipeline =
     RenderPipelineT<FramebufferBlendVertexShader,
                     FramebufferBlendFragmentShader>;
+using FramebufferBlendPlusPipeline =
+    RenderPipelineT<FramebufferBlendVertexShader,
+                    FramebufferBlendFragmentShader>;
 using FramebufferBlendLuminosityPipeline =
     RenderPipelineT<FramebufferBlendVertexShader,
                     FramebufferBlendFragmentShader>;
@@ -640,6 +645,11 @@ class ContentContext {
     return GetPipeline(blend_lighten_pipelines_, opts);
   }
 
+  std::shared_ptr<Pipeline<PipelineDescriptor>> GetBlendPlusPipeline(
+      ContentContextOptions opts) const {
+    return GetPipeline(blend_plus_pipelines_, opts);
+  }
+
   std::shared_ptr<Pipeline<PipelineDescriptor>> GetBlendLuminosityPipeline(
       ContentContextOptions opts) const {
     return GetPipeline(blend_luminosity_pipelines_, opts);
@@ -725,6 +735,12 @@ class ContentContext {
     return GetPipeline(framebuffer_blend_lighten_pipelines_, opts);
   }
 
+  std::shared_ptr<Pipeline<PipelineDescriptor>> GetFramebufferBlendPlusPipeline(
+      ContentContextOptions opts) const {
+    FML_DCHECK(GetDeviceCapabilities().SupportsFramebufferFetch());
+    return GetPipeline(framebuffer_blend_plus_pipelines_, opts);
+  }
+
   std::shared_ptr<Pipeline<PipelineDescriptor>>
   GetFramebufferBlendLuminosityPipeline(ContentContextOptions opts) const {
     FML_DCHECK(GetDeviceCapabilities().SupportsFramebufferFetch());
@@ -993,6 +1009,7 @@ class ContentContext {
   mutable Variants<BlendHardLightPipeline> blend_hardlight_pipelines_;
   mutable Variants<BlendHuePipeline> blend_hue_pipelines_;
   mutable Variants<BlendLightenPipeline> blend_lighten_pipelines_;
+  mutable Variants<BlendPlusPipeline> blend_plus_pipelines_;
   mutable Variants<BlendLuminosityPipeline> blend_luminosity_pipelines_;
   mutable Variants<BlendMultiplyPipeline> blend_multiply_pipelines_;
   mutable Variants<BlendOverlayPipeline> blend_overlay_pipelines_;
@@ -1018,6 +1035,8 @@ class ContentContext {
       framebuffer_blend_hue_pipelines_;
   mutable Variants<FramebufferBlendLightenPipeline>
       framebuffer_blend_lighten_pipelines_;
+  mutable Variants<FramebufferBlendPlusPipeline>
+      framebuffer_blend_plus_pipelines_;
   mutable Variants<FramebufferBlendLuminosityPipeline>
       framebuffer_blend_luminosity_pipelines_;
   mutable Variants<FramebufferBlendMultiplyPipeline>

impeller/entity/contents/filters/blend_filter_contents.cc

@@ -338,6 +338,9 @@ std::optional<Entity> BlendFilterContents::CreateForegroundAdvancedBlend(
       case BlendMode::kColor:
         pass.SetPipeline(renderer.GetBlendColorPipeline(options));
         break;
+      case BlendMode::kPlus:
+        pass.SetPipeline(renderer.GetBlendPlusPipeline(options));
+        break;
       case BlendMode::kLuminosity:
         pass.SetPipeline(renderer.GetBlendLuminosityPipeline(options));
         break;

impeller/entity/contents/filters/blend_filter_contents.h

@@ -12,7 +12,7 @@
 
 namespace impeller {
 
-constexpr std::array<std::array<Scalar, 5>, 15> kPorterDuffCoefficients = {{
+constexpr std::array<std::array<Scalar, 5>, 14> kPorterDuffCoefficients = {{
     {0, 0, 0, 0, 0},    // Clear
     {1, 0, 0, 0, 0},    // Source
     {0, 0, 1, 0, 0},    // Destination
@@ -25,7 +25,6 @@ constexpr std::array<std::array<Scalar, 5>, 15> kPorterDuffCoefficients = {{
     {0, 1, 1, -1, 0},   // SourceATop
     {1, -1, 0, 1, 0},   // DestinationATop
     {1, -1, 1, -1, 0},  // Xor
-    {1, 0, 1, 0, 0},    // Plus
     {0, 0, 0, 0, 1},    // Modulate
     {0, 0, 1, 0, -1},   // Screen
 }};

impeller/entity/contents/framebuffer_blend_contents.cc

@@ -118,6 +118,9 @@ bool FramebufferBlendContents::Render(const ContentContext& renderer,
     case BlendMode::kColor:
       pass.SetPipeline(renderer.GetFramebufferBlendColorPipeline(options));
       break;
+    case BlendMode::kPlus:
+      pass.SetPipeline(renderer.GetFramebufferBlendPlusPipeline(options));
+      break;
     case BlendMode::kLuminosity:
       pass.SetPipeline(renderer.GetFramebufferBlendLuminosityPipeline(options));
       break;

impeller/entity/contents/framebuffer_blend_contents.h

@@ -27,6 +27,7 @@ enum class BlendSelectValues {
   kHue,
   kSaturation,
   kColor,
+  kPlus,
   kLuminosity,
 };
 

impeller/entity/shaders/blending/advanced_blend.frag

@@ -51,7 +51,16 @@ void main() {
     src.a *= blend_info.src_input_alpha;
   }
 
-  f16vec3 blend_result = AdvancedBlend(dst.rgb, src.rgb, int(blend_type));
+  int nblend_type = int(blend_type);
 
-  frag_color = IPApplyBlendedColor(dst, src, blend_result);
+  if (nblend_type == /*BlendSelectValues::kPlus*/ 14) {
+    f16vec4 plus = src + dst;
+    if (plus.a > 1.0hf) {
+      plus.a = 1.0hf;
+    }
+    frag_color = IPHalfPremultiply(plus);
+  } else {
+    f16vec3 blend_result = AdvancedBlend(dst.rgb, src.rgb, nblend_type);
+    frag_color = IPApplyBlendedColor(dst, src, blend_result);
+  }
 }

impeller/entity/shaders/blending/blend_select.glsl

@@ -20,6 +20,7 @@
 // kHue,
 // kSaturation,
 // kColor,
+// kPlus,
 // kLuminosity,
 // Note, this isn't a switch as GLSL ES 1.0 does not support them.
 f16vec3 AdvancedBlend(f16vec3 dst, f16vec3 src, int blend_type) {
@@ -65,7 +66,8 @@ f16vec3 AdvancedBlend(f16vec3 dst, f16vec3 src, int blend_type) {
   if (blend_type == 13) {
     return IPBlendColor(dst, src);
   }
-  if (blend_type == 14) {
+  // 14 is `plus`, it's handled in advanced_blend.frag.
+  if (blend_type == 15) {
     return IPBlendLuminosity(dst, src);
   }
   return f16vec3(0.0hf);

impeller/entity/shaders/blending/framebuffer_blend.frag

@@ -50,7 +50,16 @@ void main() {
                      )));
   src.a *= frag_info.src_input_alpha;
 
-  f16vec3 blend_result = AdvancedBlend(dst.rgb, src.rgb, int(blend_type));
+  int nblend_type = int(blend_type);
 
-  frag_color = IPApplyBlendedColor(dst, src, blend_result);
+  if (nblend_type == /*BlendSelectValues::kPlus*/ 14) {
+    f16vec4 plus = src + dst;
+    if (plus.a > 1.0hf) {
+      plus.a = 1.0hf;
+    }
+    frag_color = IPHalfPremultiply(plus);
+  } else {
+    f16vec3 blend_result = AdvancedBlend(dst.rgb, src.rgb, nblend_type);
+    frag_color = IPApplyBlendedColor(dst, src, blend_result);
+  }
 }