Support mask images for filter-based -webkit-box-reflect.

third_party/WebKit/Source/core/paint/BoxReflectionUtils.cpp

Index: third_party/WebKit/Source/core/paint/BoxReflectionUtils.cpp
diff --git a/third_party/WebKit/Source/core/paint/BoxReflectionUtils.cpp b/third_party/WebKit/Source/core/paint/BoxReflectionUtils.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..9f16886435a70a07a8cd7fda16959a8b6ee9b428
--- /dev/null
+++ b/third_party/WebKit/Source/core/paint/BoxReflectionUtils.cpp
@@ -0,0 +1,81 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/paint/BoxReflectionUtils.h"
+
+#include "core/layout/LayoutBox.h"
+#include "core/paint/NinePieceImagePainter.h"
+#include "core/paint/PaintLayer.h"
+#include "platform/LengthFunctions.h"
+#include "platform/geometry/FloatRect.h"
+#include "platform/geometry/LayoutPoint.h"
+#include "platform/geometry/LayoutRect.h"
+#include "platform/graphics/BoxReflection.h"
+#include "platform/graphics/paint/DrawingRecorder.h"
+#include "platform/graphics/paint/SkPictureBuilder.h"
+
+namespace blink {
+
+BoxReflection boxReflectionForPaintLayer(const PaintLayer& layer, const ComputedStyle& style)
+{
+    const auto* reflectStyle = style.boxReflect();

[Stephen White, 2016/04/20 21:33:56]

This might be personal style, but I find "auto" here hurts readability more than
it helps conciseness. What do you think about putting the actual type here?

[jbroman, 2016/04/21 16:52:05]

Alright. The type is "StyleReflection", so the line becomes the amusingly
repetitive "const StyleReflection* reflectStyle = style.boxReflect()";

+
+    LayoutRect frameLayoutRect = toLayoutBox(layer.layoutObject())->frameRect();
+    FloatRect frameRect(frameLayoutRect);
+    BoxReflection::ReflectionDirection direction = BoxReflection::VerticalReflection;
+    float offset = 0;
+    switch (reflectStyle->direction()) {
+    case ReflectionAbove:
+        direction = BoxReflection::VerticalReflection;
+        offset = -floatValueForLength(reflectStyle->offset(), frameRect.height());
+        break;
+    case ReflectionBelow:
+        direction = BoxReflection::VerticalReflection;
+        offset = 2 * frameRect.height() + floatValueForLength(reflectStyle->offset(), frameRect.height());
+        break;
+    case ReflectionLeft:
+        direction = BoxReflection::HorizontalReflection;
+        offset = -floatValueForLength(reflectStyle->offset(), frameRect.width());
+        break;
+    case ReflectionRight:
+        direction = BoxReflection::HorizontalReflection;
+        offset = 2 * frameRect.width() + floatValueForLength(reflectStyle->offset(), frameRect.width());
+        break;
+    }
+
+    // Since the filter origin is the corner of the input bounds, which may
+    // include visual overflow (e.g. due to box-shadow), we must adjust the
+    // offset to also account for this offset (this is equivalent to using
+    // SkLocalMatrixImageFilter, but simpler).
+    // The rect used here should match the one used in FilterPainter.
+    LayoutRect filterInputBounds = layer.physicalBoundingBoxIncludingReflectionAndStackingChildren(LayoutPoint());
+    offset -= 2 * (direction == BoxReflection::VerticalReflection ? filterInputBounds.y() : filterInputBounds.x()).toFloat();
+
+    RefPtr<SkPicture> mask;
+    const auto& maskNinePiece = reflectStyle->mask();

[Stephen White, 2016/04/20 21:33:56]

Same here.

[jbroman, 2016/04/21 16:52:05]

Done.

+    if (maskNinePiece.hasImage()) {
+        LayoutRect maskRect(LayoutPoint(), frameLayoutRect.size());
+        maskRect.moveBy(-filterInputBounds.location());
+
+        LayoutRect maskBoundingRect(maskRect);
+        maskBoundingRect.expand(style.imageOutsets(maskNinePiece));
+        FloatRect maskBoundingFloatRect(maskBoundingRect);
+
+        // TODO(jbroman): SkPictureBuilder + DrawingRecorder seems excessive.
+        // If NinePieceImagePainter operated on SkCanvas, we'd only need an
+        // SkPictureRecorder here.
+        SkPictureBuilder recorder(maskBoundingFloatRect);
+        {
+            GraphicsContext& context = recorder.context();
+            DrawingRecorder drawingRecorder(context, *layer.layoutObject(), DisplayItem::ReflectionMask, maskBoundingFloatRect);
+            NinePieceImagePainter(*layer.layoutObject()).paint(
+                recorder.context(), maskRect, style, maskNinePiece, SkXfermode::kSrcOver_Mode);
+        }
+        mask = recorder.endRecording();
+    }
+
+    return BoxReflection(direction, offset, mask);
+}
+
+} // namespace blink