Implement SkXfermode image filter

src/effects/SkXfermodeImageFilter.cpp

+/*
+ * Copyright 2013 The Android Open Source Project
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkXfermodeImageFilter.h"
+#include "SkCanvas.h"
+#include "SkColorPriv.h"
+#include "SkFlattenableBuffers.h"
+#include "SkXfermode.h"
+#if SK_SUPPORT_GPU
+#include "GrContext.h"
+#include "effects/GrSimpleTextureEffect.h"
+#include "SkGr.h"
+#include "SkImageFilterUtils.h"
+#endif
+
+///////////////////////////////////////////////////////////////////////////////
+
+SkXfermodeImageFilter::SkXfermodeImageFilter(SkXfermode* mode, SkImageFilter* background, SkImageFilter* foreground)
+  : INHERITED(background, foreground), fMode(mode)
+{
+    SkSafeRef(fMode);

[reed1, 2013/05/30 16:56:32]

What happens if mode is NULL? Is that ever useful? Should we change to a Factory
for this subclass, that returns NULL if it doesn't like its input, rather than a
constructor that has to handle this sort of case?

[Stephen White, 2013/05/30 17:24:20]

I don't think it's particularly useful, but it's not harmful (AsNewEffect.. will
handle it correctly). A factory seems like overkill in this case.

+}
+
+SkXfermodeImageFilter::~SkXfermodeImageFilter() {
+    SkSafeUnref(fMode);
+}
+
+SkXfermodeImageFilter::SkXfermodeImageFilter(SkFlattenableReadBuffer& buffer)
+  : INHERITED(buffer)
+{
+    fMode = buffer.readFlattenableT<SkXfermode>();
+}
+
+void SkXfermodeImageFilter::flatten(SkFlattenableWriteBuffer& buffer) const {
+    this->INHERITED::flatten(buffer);
+    buffer.writeFlattenable(fMode);
+}
+
+bool SkXfermodeImageFilter::onFilterImage(Proxy* proxy,
+                                            const SkBitmap& src,
+                                            const SkMatrix& ctm,
+                                            SkBitmap* dst,
+                                            SkIPoint* offset) {
+    SkBitmap background = src, foreground = src;
+    SkImageFilter* backgroundInput = getInput(0);
+    SkImageFilter* foregroundInput = getInput(1);
+    if (backgroundInput && !backgroundInput->filterImage(proxy, src, ctm, &background, offset)) {
+        return false;
+    }
+    if (foregroundInput && !foregroundInput->filterImage(proxy, src, ctm, &foreground, offset)) {
+        return false;
+    }
+    dst->setConfig(background.config(), background.width(), background.height());
+    dst->allocPixels();
+    SkCanvas canvas(*dst);
+    SkPaint paint;
+    paint.setXfermodeMode(SkXfermode::kSrc_Mode);
+    canvas.drawBitmap(background, 0, 0, &paint);
+    paint.setXfermode(fMode);
+    canvas.drawBitmap(foreground, 0, 0, &paint);
+    return true;
+}
+
+#if SK_SUPPORT_GPU
+
+bool SkXfermodeImageFilter::filterImageGPU(Proxy* proxy, const SkBitmap& src, SkBitmap* result) {
+    SkBitmap background;
+    if (!SkImageFilterUtils::GetInputResultGPU(getInput(0), proxy, src, &background)) {
+        return false;
+    }
+    GrTexture* backgroundTex = (GrTexture*) background.getTexture();
+    SkBitmap foreground;
+    if (!SkImageFilterUtils::GetInputResultGPU(getInput(1), proxy, src, &foreground)) {
+        return false;
+    }
+    GrTexture* foregroundTex = (GrTexture*) foreground.getTexture();
+    GrContext* context = foregroundTex->getContext();
+
+    GrEffectRef* xferEffect = NULL;
+
+    GrTextureDesc desc;
+    desc.fFlags = kRenderTarget_GrTextureFlagBit | kNoStencil_GrTextureFlagBit;
+    desc.fWidth = src.width();
+    desc.fHeight = src.height();
+    desc.fConfig = kSkia8888_GrPixelConfig;
+
+    GrAutoScratchTexture ast(context, desc);
+    SkAutoTUnref<GrTexture> dst(ast.detach());
+
+    GrContext::AutoRenderTarget art(context, dst->asRenderTarget());
+
+    SkXfermode::Coeff sm, dm;
+    if (!SkXfermode::AsNewEffectOrCoeff(fMode, context, &xferEffect, &sm, &dm, backgroundTex)) {
+        return false;
+    }
+
+    GrPaint paint;
+    SkRect srcRect;
+    src.getBounds(&srcRect);
+    if (NULL != xferEffect) {
+        paint.colorStage(0)->setEffect(
+            GrSimpleTextureEffect::Create(foregroundTex, GrEffect::MakeDivByTextureWHMatrix(foregroundTex)))->unref();
+        paint.colorStage(1)->setEffect(xferEffect);
+        context->drawRect(paint, srcRect);
+    } else {
+        paint.colorStage(0)->setEffect(
+            GrSimpleTextureEffect::Create(backgroundTex, GrEffect::MakeDivByTextureWHMatrix(backgroundTex)))->unref();
+        context->drawRect(paint, srcRect);
+        paint.setBlendFunc(sk_blend_to_grblend(sm), sk_blend_to_grblend(dm));
+        paint.colorStage(0)->setEffect(
+            GrSimpleTextureEffect::Create(foregroundTex, GrEffect::MakeDivByTextureWHMatrix(foregroundTex)))->unref();
+        context->drawRect(paint, srcRect);
+    }
+    return SkImageFilterUtils::WrapTexture(dst, src.width(), src.height(), result);
+}
+
+#endif