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..a911387f56d01d41d30778e7d6e521ed747147d2 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 +1225,156 @@ TEST(GraphicsContextTest, RecordingCanvas)
     context.endRecording();
 }
 
+TEST(GraphicsContextTest, BeginLayerDontAffectCanvasState)
+{
+    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::endLayer() must preserve current states.
+    EXPECT_EQ(0, context.getTotalMatrix().getTranslateX());
+
+    context.fillRect(rect, Color::lightGray);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::lightGray);
+}
+
+// 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, BeginLayerDontAffectPaintState)
+{
+    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::endLayer() must preserve current states.
+    EXPECT_EQ(CompositeSourceOver, context.compositeOperation());
+
+    context.fillRect(rect, Color::lightGray);
+    EXPECT_PIXELS_MATCH_COLOR(bitmap, rect, Color::lightGray);
+}
+
+// Cannot reuse SkClipStack::Element::operator==() because it checks save count.
+bool equal(const SkClipStack::Element* a, const SkClipStack::Element* b)
+{
+    if (a->getOp() != b->getOp() || a->getType() != b->getType() || a->isAA() != b->isAA()) {
+        return false;
+    }
+    switch (a->getType()) {
+    case SkClipStack::Element::kPath_Type:
+        return a->getPath() == b->getPath();
+    case SkClipStack::Element::kRRect_Type:
+        return a->getRRect() == b->getRRect();
+    case SkClipStack::Element::kRect_Type:
+        return a->getRect() == b->getRect();
+    case SkClipStack::Element::kEmpty_Type:
+        return true;
+    default:
+        ASSERT_NOT_REACHED();
+        return false;
+    }
+}
+
+// Cannot reuse SkClipStack::operator==() because it checks save count.
+bool equal(const SkClipStack* a, const SkClipStack* b)
+{
+    SkClipStack::B2TIter aIter(*a);
+    SkClipStack::B2TIter bIter(*b);
+    const SkClipStack::Element* aElement = aIter.next();
+    const SkClipStack::Element* bElement = bIter.next();
+
+    while (aElement && bElement) {
+        if (!equal(aElement, bElement)) {
+            return false;
+        }
+        aElement = aIter.next();
+        bElement = bIter.next();
+    }
+    return !aElement && !bElement;
+}
+
+TEST(GraphicsContextTest, BeginLayerDontAffectClipState)
+{
+    SkBitmap bitmap;
+    bitmap.allocN32Pixels(10, 10);
+    bitmap.eraseColor(0);
+    SkCanvas canvas(bitmap);
+    GraphicsContext context(&canvas);
+    // Reference to compare clip stack. It's needed because SkCanvas::saveLayer() can perform an additional clip op.
+    SkBitmap bitmapRef;
+    bitmapRef.allocN32Pixels(10, 10);
+    bitmapRef.eraseColor(0);
+    SkCanvas canvasRef(bitmapRef);
+    GraphicsContext contextRef(&canvasRef);
+
+    context.clip(IntRect(1, 1, 9, 9));
+    contextRef.clip(IntRect(1, 1, 9, 9));
+    context.save();
+    context.clip(IntRect(0, 0, 7, 7));
+    context.translate(1, 1);
+    context.clip(IntRect(0, 0, 7, 7));
+    contextRef.save();
+    contextRef.clip(IntRect(0, 0, 7, 7));
+    contextRef.translate(1, 1);
+    contextRef.clip(IntRect(0, 0, 7, 7));
+    EXPECT_TRUE(equal(canvasRef.getClipStack(), canvas.getClipStack()));
+
+    RoundedRect roundedClipRect(IntRect(20, 20, 70, 70), RoundedRect::Radii(IntSize(2, 3), IntSize(2, 3), IntSize(2, 3), IntSize(2, 3)));
+    context.beginLayer(1, CompositeSourceOver);
+    context.scale(0.1, 0.1);
+    context.clipRoundedRect(roundedClipRect);
+    context.clipOut(IntRect(40, 40, 10, 10));
+    context.endLayer();
+    contextRef.scale(0.1, 0.1);
+    contextRef.clipRoundedRect(roundedClipRect);
+    contextRef.clipOut(IntRect(40, 40, 10, 10));
+
+    // GraphicsContext::endLayer() must preserve clip state.
+    EXPECT_TRUE(equal(canvasRef.getClipStack(), canvas.getClipStack()));
+    context.restore();
+    contextRef.restore();
+}
+
 } // namespace