Delay color premultiplication until RenderContext to keep intermediat…

…e colors unpremultiplied. (#425)

src/core/Canvas.cpp

@@ -54,10 +54,10 @@ static FillStyle CreateFillStyle(const Paint& paint) {
   Color color = {};
   if (shader && shader->asColor(&color)) {
     color.alpha *= paint.getAlpha();
-    style.color = color.premultiply();
+    style.color = color;
     shader = nullptr;
   } else {
-    style.color = paint.getColor().premultiply();
+    style.color = paint.getColor();
   }
   style.shader = shader;
   style.antiAlias = paint.isAntiAlias();
@@ -504,7 +504,7 @@ void Canvas::drawAtlas(std::shared_ptr<Image> atlas, const Matrix matrix[], cons
     state.matrix.preTranslate(-rect.x(), -rect.y());
     auto glyphStyle = style;
     if (colors) {
-      glyphStyle.color = colors[i].premultiply();
+      glyphStyle.color = colors[i];
     }
     if (rect == atlasRect) {
       drawContext->drawImage(atlas, sampling, state, glyphStyle);

src/core/FillStyle.h

@@ -33,7 +33,7 @@ class FillStyle {
   bool antiAlias = true;
 
   /**
-   * The input color, premultiplied, as four floating point values.
+   * The input color, unpremultiplied, as four floating point values.
    */
   Color color = Color::White();
 

src/gpu/RenderContext.cpp

@@ -99,7 +99,7 @@ void RenderContext::drawRect(const Rect& rect, const MCState& state, const FillS
   if (localBounds.isEmpty()) {
     return;
   }
-  auto drawOp = RectDrawOp::Make(style.color, localBounds, state.matrix);
+  auto drawOp = RectDrawOp::Make(style.color.premultiply(), localBounds, state.matrix);
   addDrawOp(std::move(drawOp), localBounds, state, style);
 }
 
@@ -111,7 +111,7 @@ bool RenderContext::drawAsClear(const Rect& rect, const MCState& state, const Fi
   if (!HasColorOnly(style) || !style.isOpaque() || !state.matrix.rectStaysRect()) {
     return false;
   }
-  auto color = style.color;
+  auto color = style.color.premultiply();
   auto bounds = rect;
   state.matrix.mapRect(&bounds);
   auto [clipRect, useScissor] = getClipRect(state.clip, &bounds);
@@ -136,7 +136,7 @@ void RenderContext::drawRRect(const RRect& rRect, const MCState& state, const Fi
   if (localBounds.isEmpty()) {
     return;
   }
-  auto drawOp = RRectDrawOp::Make(style.color, rRect, state.matrix);
+  auto drawOp = RRectDrawOp::Make(style.color.premultiply(), rRect, state.matrix);
   addDrawOp(std::move(drawOp), localBounds, state, style);
 }
 
@@ -153,7 +153,8 @@ void RenderContext::drawShape(std::shared_ptr<Shape> shape, const MCState& state
     return;
   }
   auto clipBounds = getClipBounds(state.clip);
-  auto drawOp = ShapeDrawOp::Make(style.color, std::move(shape), state.matrix, clipBounds);
+  auto drawOp =
+      ShapeDrawOp::Make(style.color.premultiply(), std::move(shape), state.matrix, clipBounds);
   addDrawOp(std::move(drawOp), localBounds, state, style);
 }
 
@@ -184,7 +185,7 @@ void RenderContext::drawImageRect(std::shared_ptr<Image> image, const Rect& rect
   if (processor == nullptr) {
     return;
   }
-  auto drawOp = RectDrawOp::Make(style.color, localBounds, state.matrix, uvMatrix);
+  auto drawOp = RectDrawOp::Make(style.color.premultiply(), localBounds, state.matrix, uvMatrix);
   drawOp->addColorFP(std::move(processor));
   addDrawOp(std::move(drawOp), localBounds, state, style);
 }
@@ -224,7 +225,7 @@ void RenderContext::drawGlyphRunList(std::shared_ptr<GlyphRunList> glyphRunList,
   if (processor == nullptr) {
     return;
   }
-  auto drawOp = RectDrawOp::Make(style.color, localBounds, state.matrix);
+  auto drawOp = RectDrawOp::Make(style.color.premultiply(), localBounds, state.matrix);
   drawOp->addCoverageFP(std::move(processor));
   addDrawOp(std::move(drawOp), localBounds, state, style);
 }

test/baseline/version.json

@@ -20,7 +20,7 @@
         "Path_addArc_reversed7": "4802e56",
         "Path_addArc_reversed8": "4802e56",
         "Path_complex": "e031f25",
-        "Picture": "b062b9a",
+        "Picture": "002c391",
         "PictureImage": "c28a93c",
         "PictureImage_Path": "2212c4e",
         "PictureImage_Text": "b062b9a",
@@ -100,7 +100,7 @@
         "DropShadowStyle-stroke-behindLayer": "002c391",
         "DropShadowStyle-stroke-blur": "002c391",
         "DropShadowStyle-stroke-blur-behindLayer": "002c391",
-        "DropShadowStyle2": "19dcc4d",
+        "DropShadowStyle2": "7a9c80a",
         "InnerShadowStyle": "19dcc4d",
         "Layer_hitTestPoint": "50c58e6",
         "Layer_hitTestPointNested": "b062b9a",

test/src/SVGExportTest.cpp

@@ -105,13 +105,13 @@ TGFX_TEST(SVGExportTest, OpacityColor) {
   std::string compareString =
       "<?xml version=\"1.0\" encoding=\"utf-8\" ?><svg xmlns=\"http://www.w3.org/2000/svg\" "
       "xmlns:xlink=\"http://www.w3.org/1999/xlink\" width=\"200\" height=\"200\"><circle "
-      "fill=\"#00007F\" fill-opacity=\"0.5\" cx=\"100\" cy=\"100\" r=\"100\"/></svg>";
+      "fill=\"#00F\" fill-opacity=\"0.5\" cx=\"100\" cy=\"100\" r=\"100\"/></svg>";
 
   ContextScope scope;
   auto* context = scope.getContext();
   ASSERT_TRUE(context != nullptr);
 
-  tgfx::Paint paint;
+  Paint paint;
   paint.setColor(Color::Blue());
   paint.setAlpha(0.5f);
 
@@ -131,7 +131,7 @@ TGFX_TEST(SVGExportTest, OpacityColorFile) {
   std::string compareString =
       "<?xml version=\"1.0\" encoding=\"utf-8\" ?><svg xmlns=\"http://www.w3.org/2000/svg\" "
       "xmlns:xlink=\"http://www.w3.org/1999/xlink\" width=\"200\" height=\"200\"><circle "
-      "fill=\"#00007F\" fill-opacity=\"0.5\" cx=\"100\" cy=\"100\" r=\"100\"/></svg>";
+      "fill=\"#00F\" fill-opacity=\"0.5\" cx=\"100\" cy=\"100\" r=\"100\"/></svg>";
 
   ContextScope scope;
   auto* context = scope.getContext();
@@ -156,7 +156,7 @@ TGFX_TEST(SVGExportTest, OpacityColorFile) {
 
   auto readStream = Stream::MakeFromFile(path);
   EXPECT_TRUE(readStream != nullptr);
-  EXPECT_EQ(readStream->size(), 222U);
+  EXPECT_EQ(readStream->size(), 219U);
   Buffer buffer(readStream->size());
   readStream->read(buffer.data(), buffer.size());
   EXPECT_EQ(std::string((char*)buffer.data(), buffer.size()), compareString);