Upstreaming DropShadowImageFilter into skia, from Blink

src/effects/SkDropShadowImageFilter.cpp

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkDropShadowImageFilter.h"
+
+#include "SkBitmap.h"
+#include "SkBlurImageFilter.h"
+#include "SkCanvas.h"
+#include "SkColorMatrixFilter.h"
+#include "SkDevice.h"
+#include "SkFlattenableBuffers.h"
+
+SkDropShadowImageFilter::SkDropShadowImageFilter(SkScalar dx, SkScalar dy, SkScalar sigma, SkColor color, SkImageFilter* input)
+    : SkImageFilter(input)
+    , fDx(dx)
+    , fDy(dy)
+    , fSigma(sigma)
+    , fColor(color)
+{
+}
+
+SkDropShadowImageFilter::SkDropShadowImageFilter(SkFlattenableReadBuffer& buffer) : SkImageFilter(buffer)
+{
+    fDx = buffer.readScalar();
+    fDy = buffer.readScalar();
+    fSigma = buffer.readScalar();
+    fColor = buffer.readColor();
+}
+
+void SkDropShadowImageFilter::flatten(SkFlattenableWriteBuffer& buffer) const
+{
+    this->INHERITED::flatten(buffer);

[Justin Novosad, 2013/08/06 19:27:24]

FYI: This line was missing in the Blink version of the filter.

+    buffer.writeScalar(fDx);
+    buffer.writeScalar(fDy);
+    buffer.writeScalar(fSigma);
+    buffer.writeColor(fColor);
+}
+
+bool SkDropShadowImageFilter::onFilterImage(Proxy* proxy, const SkBitmap& source, const SkMatrix& matrix, SkBitmap* result, SkIPoint* loc)
+{
+    SkBitmap src = source;
+    if (getInput(0) && !getInput(0)->filterImage(proxy, source, matrix, &src, loc))
+        return false;
+
+    SkAutoTUnref<SkDevice> device(proxy->createDevice(src.width(), src.height()));
+    SkCanvas canvas(device.get());
+
+    SkAutoTUnref<SkImageFilter> blurFilter(new SkBlurImageFilter(fSigma, fSigma));
+    SkAutoTUnref<SkColorFilter> colorFilter(SkColorFilter::CreateModeFilter(fColor, SkXfermode::kSrcIn_Mode));
+    SkPaint paint;
+    paint.setImageFilter(blurFilter.get());
+    paint.setColorFilter(colorFilter.get());
+    paint.setXfermodeMode(SkXfermode::kSrcOver_Mode);
+    canvas.saveLayer(0, &paint);
+    canvas.drawBitmap(src, fDx, fDy);

[Stephen White, 2013/08/06 19:33:37]

You can use drawBitmap(src, fDx, fDy, &paint) directly here, and skip the
saveLayer() / restore().

+    canvas.restore();
+    canvas.drawBitmap(src, 0, 0);
+    *result = device.get()->accessBitmap(false);

[Stephen White, 2013/08/06 19:33:37]

Nit: I think you can just use device->accessBitmap(false) here; no need to
get().

+    return true;
+}
+