Clarify GraphicsContext::beginLayer()/endLayer() have unexpected behaviors.

Source/platform/graphics/GraphicsContextTest.cpp

Index: Source/platform/graphics/GraphicsContextTest.cpp
diff --git a/Source/platform/graphics/GraphicsContextTest.cpp b/Source/platform/graphics/GraphicsContextTest.cpp
index fe8b95e939a8b6b9ff9302c82b5914cec334658a..41a055128115685eba08407c6542f80bc7192ad3 100644
--- a/Source/platform/graphics/GraphicsContextTest.cpp
+++ b/Source/platform/graphics/GraphicsContextTest.cpp
@@ -66,6 +66,17 @@ namespace {
         } \
 }
 
+#define EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, color) \
+{ \
+    SkAutoLockPixels locker(bitmap); \
+    for (int y = rect.y(); y < rect.maxY(); ++y) { \
+        for (int x = rect.x(); x < rect.maxX(); ++x) { \
+            RGBA32 pixel = *bitmap.getAddr32(x, y); \
+            EXPECT_EQ(color, pixel); \
+        } \
+    } \
+}
+
 TEST(GraphicsContextTest, trackOpaqueTest)
 {
     SkBitmap bitmap;
@@ -1214,4 +1225,77 @@ TEST(GraphicsContextTest, RecordingCanvas)
     context.endRecording();
 }
 
+TEST(GraphicsContextTest, BeginLayerPreserveCanvasState)
+{
+    SkBitmap bitmap;
+    bitmap.allocN32Pixels(1, 1);
+    bitmap.eraseColor(0);
+    SkCanvas canvas(bitmap);
+    GraphicsContext context(&canvas);
+
+    IntRect rect(0, 0, 1, 1);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::transparent);
+    context.fillRect(rect, Color::gray);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::gray);
+
+    // Translate out of bound not to draw.
+    context.translate(1, 0);
+    context.fillRect(rect, Color::darkGray);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::gray);
+    EXPECT_EQ(SK_Scalar1, context.getTotalMatrix().getTranslateX());
+
+    context.beginLayer(1, CompositeSourceOver);
+    context.translate(-1, 0);
+    EXPECT_EQ(0, context.getTotalMatrix().getTranslateX());
+    context.fillRect(rect, Color::darkGray);
+    context.endLayer();
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::darkGray);
+
+    // GraphicsContext::beginLayer()/endLayer() behaves the same as save()/restore()
+    // so current transform is restored.
+    EXPECT_EQ(SK_Scalar1, context.getTotalMatrix().getTranslateX());
+
+    context.fillRect(rect, Color::lightGray);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::darkGray);
+}
+
+// Although this test looks like duplicated to BeginLayerPreserveCanvasState,
+// this is needed because GraphicsContext keeps a composite operator in SkPaint
+// while setting a transform to SkCanvas directly.
+TEST(GraphicsContextTest, BeginLayerPreservePaintState)
+{
+    SkBitmap bitmap;
+    bitmap.allocN32Pixels(1, 1);
+    bitmap.eraseColor(0);
+    SkCanvas canvas(bitmap);
+    GraphicsContext context(&canvas);
+
+    IntRect rect(0, 0, 1, 1);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::transparent);
+    EXPECT_EQ(CompositeSourceOver, context.compositeOperation());
+    context.fillRect(rect, Color::gray);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::gray);
+
+    // Set CompositeDestinationIn not to draw.
+    context.setCompositeOperation(CompositeDestinationIn);
+    context.fillRect(rect, Color::darkGray);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::gray);
+    EXPECT_EQ(CompositeDestinationIn, context.compositeOperation());
+
+    context.beginLayer(1, CompositeSourceIn);
+    EXPECT_EQ(CompositeDestinationIn, context.compositeOperation());
+    context.setCompositeOperation(CompositeSourceOver);
+    EXPECT_EQ(CompositeSourceOver, context.compositeOperation());
+    context.fillRect(rect, Color::darkGray);
+    context.endLayer();
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::darkGray);
+
+    // GraphicsContext::beginLayer()/endLayer() behaves the same as save()/restore()
+    // so current composite operator is restored.
+    EXPECT_EQ(CompositeDestinationIn, context.compositeOperation());

[dshwang, 2014/10/14 17:25:07]

Without this CL, this line and #1298 fail, while BeginLayerPreserveCanvasState
test succeeds.

+
+    context.fillRect(rect, Color::lightGray);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::darkGray);
+}
+
 } // namespace