Refactor shadow rendering logic.

Source/core/platform/graphics/DrawLooper.cpp

Index: Source/core/platform/graphics/DrawLooper.cpp
diff --git a/Source/core/platform/graphics/DrawLooper.cpp b/Source/core/platform/graphics/DrawLooper.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..81cb211e9ae6bdfd30ea4fe8850494948f511860
--- /dev/null
+++ b/Source/core/platform/graphics/DrawLooper.cpp
@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2013 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "core/platform/graphics/DrawLooper.h"
+
+#include "core/platform/graphics/Color.h"
+#include "core/platform/graphics/FloatSize.h"
+#include "third_party/skia/include/core/SkColor.h"
+#include "third_party/skia/include/core/SkColorFilter.h"
+#include "third_party/skia/include/core/SkPaint.h"
+#include "third_party/skia/include/core/SkXfermode.h"
+#include "third_party/skia/include/effects/SkBlurMaskFilter.h"
+
+namespace WebCore {
+
+DrawLooper::DrawLooper() : m_skDrawLooper(new SkLayerDrawLooper) { }
+
+void DrawLooper::addUnmodifiedContent()
+{
+    skDrawLooper()->addLayer();
+}
+
+void DrawLooper::addShadow(const FloatSize& offset, float blur, const Color& color,
+    ShadowTransformMode shadowTransformMode, ShadowAlphaMode shadowAlphaMode)
+{
+    // Detect when there's no effective shadow.
+    if (!color.isValid() || !color.alpha())
+        return;
+
+    SkColor skColor;
+    if (color.isValid())
+        skColor = color.rgb();
+    else
+        skColor = SkColorSetARGB(0xFF / 3, 0, 0, 0); // "std" apple shadow color.
+
+    // TODO(tc): Should we have a max value for the blur? CG clamps at 1000.0
+    // for perf reasons.

[Stephen Chennney, 2013/05/17 15:35:34]

Take this out. We clearly haven't seen problems in the wild, so I don't see an y
reason to keep this TODO.

[jbroman, 2013/05/17 15:43:18]

Sure. I just migrated it from the old home of this code; didn't want to lose a
TODO I didn't know anything about.

+
+    SkLayerDrawLooper::LayerInfo info;
+
+    switch (shadowAlphaMode) {
+    case ShadowRespectsAlpha:
+        info.fColorMode = SkXfermode::kDst_Mode;
+        break;
+    case ShadowIgnoresAlpha:
+        info.fColorMode = SkXfermode::kSrc_Mode;
+        break;
+    default:
+        ASSERT_NOT_REACHED();
+    }
+
+    if (blur)
+        info.fPaintBits |= SkLayerDrawLooper::kMaskFilter_Bit; // our blur
+    info.fPaintBits |= SkLayerDrawLooper::kColorFilter_Bit;
+    info.fOffset.set(offset.width(), offset.height());
+    info.fPostTranslate = (shadowTransformMode == ShadowIgnoresTransforms);
+
+    SkPaint* paint = skDrawLooper()->addLayer(info);
+
+    if (blur) {
+        uint32_t mfFlags = SkBlurMaskFilter::kHighQuality_BlurFlag;
+        if (shadowTransformMode == ShadowIgnoresTransforms)
+            mfFlags |= SkBlurMaskFilter::kIgnoreTransform_BlurFlag;
+        SkMaskFilter* mf = SkBlurMaskFilter::Create((double)blur / 2.0,
+            SkBlurMaskFilter::kNormal_BlurStyle, mfFlags);
+        SkSafeUnref(paint->setMaskFilter(mf));
+    }
+
+    SkColorFilter* cf = SkColorFilter::CreateModeFilter(skColor, SkXfermode::kSrcIn_Mode);
+    SkSafeUnref(paint->setColorFilter(cf));
+}
+
+} // namespace WebCore