Alter SkXfermode's asFragmentProcessor & asXPFactory contracts

src/effects/SkXfermodeImageFilter.cpp

Index: src/effects/SkXfermodeImageFilter.cpp
diff --git a/src/effects/SkXfermodeImageFilter.cpp b/src/effects/SkXfermodeImageFilter.cpp
index 5f88240481b316c7e0c6b7d57f0a22ed815d004a..1e3544159e670b2055846c653990d01b5ad2d630 100644
--- a/src/effects/SkXfermodeImageFilter.cpp
+++ b/src/effects/SkXfermodeImageFilter.cpp
@@ -25,12 +25,8 @@
 SkXfermodeImageFilter::SkXfermodeImageFilter(SkXfermode* mode,
                                              SkImageFilter* inputs[2],
                                              const CropRect* cropRect)
-  : INHERITED(2, inputs, cropRect), fMode(mode) {
-    SkSafeRef(fMode);
-}
-
-SkXfermodeImageFilter::~SkXfermodeImageFilter() {
-    SkSafeUnref(fMode);
+    : INHERITED(2, inputs, cropRect)
+    , fMode(SkSafeRef(mode)) {
 }
 
 SkFlattenable* SkXfermodeImageFilter::CreateProc(SkReadBuffer& buffer) {
@@ -45,10 +41,10 @@ void SkXfermodeImageFilter::flatten(SkWriteBuffer& buffer) const {
 }
 
 bool SkXfermodeImageFilter::onFilterImage(Proxy* proxy,
-                                            const SkBitmap& src,
-                                            const Context& ctx,
-                                            SkBitmap* dst,
-                                            SkIPoint* offset) const {
+                                          const SkBitmap& src,
+                                          const Context& ctx,
+                                          SkBitmap* dst,
+                                          SkIPoint* offset) const {
     SkBitmap background = src, foreground = src;
     SkIPoint backgroundOffset = SkIPoint::Make(0, 0);
     if (!this->filterInput(0, proxy, src, ctx, &background, &backgroundOffset)) {
@@ -120,9 +116,11 @@ void SkXfermodeImageFilter::toString(SkString* str) const {
 #if SK_SUPPORT_GPU
 
 bool SkXfermodeImageFilter::canFilterImageGPU() const {
-    return fMode && fMode->asFragmentProcessor(nullptr, nullptr) && !cropRectIsSet();
+    return !this->cropRectIsSet();
 }
 
+#include "SkXfermode_proccoeff.h"
+
 bool SkXfermodeImageFilter::filterImageGPU(Proxy* proxy,
                                            const SkBitmap& src,
                                            const Context& ctx,
@@ -153,8 +151,6 @@ bool SkXfermodeImageFilter::filterImageGPU(Proxy* proxy,
         return false;
     }
 
-    const GrFragmentProcessor* xferFP = nullptr;
-
     GrSurfaceDesc desc;
     desc.fFlags = kRenderTarget_GrSurfaceFlag;
     desc.fWidth = bounds.width();
@@ -176,18 +172,27 @@ bool SkXfermodeImageFilter::filterImageGPU(Proxy* proxy,
         GrTextureDomain::kDecal_Mode,
         GrTextureParams::kNone_FilterMode)
     );
-    if (!fMode || !fMode->asFragmentProcessor(&xferFP, bgFP)) {
-        // canFilterImageGPU() should've taken care of this
-        SkASSERT(false);
-        return false;
+
+    // A null fMode is interpreted to mean kSrcOver_Mode (to match raster).
+    SkAutoTUnref<SkXfermode> mode(SkSafeRef(fMode.get()));
+    if (!mode) {
+        // It would be awesome to use SkXfermode::Create here but it knows better
+        // than us and won't return a kSrcOver_Mode SkXfermode. That means we
+        // have to get one the hard way.
+        struct ProcCoeff rec;
+        rec.fProc = SkXfermode::GetProc(SkXfermode::kSrcOver_Mode);
+        SkXfermode::ModeAsCoeff(SkXfermode::kSrcOver_Mode, &rec.fSC, &rec.fDC);
+
+        mode.reset(new SkProcCoeffXfermode(rec, SkXfermode::kSrcOver_Mode));
     }
 
+    SkAutoTUnref<const GrFragmentProcessor> xferFP(mode->asFragmentProcessor(bgFP));
+
     SkMatrix foregroundMatrix;
     foregroundMatrix.setIDiv(foregroundTex->width(), foregroundTex->height());
     foregroundMatrix.preTranslate(SkIntToScalar(-foregroundOffset.fX),
                                   SkIntToScalar(-foregroundOffset.fY));
 
-
     SkAutoTUnref<const GrFragmentProcessor> foregroundFP(GrTextureDomainEffect::Create(
         foregroundTex, foregroundMatrix,
         GrTextureDomain::MakeTexelDomain(foregroundTex, foreground.bounds()),
@@ -196,8 +201,9 @@ bool SkXfermodeImageFilter::filterImageGPU(Proxy* proxy,
     );
 
     paint.addColorFragmentProcessor(foregroundFP.get());
+    // A null 'xferFP' here means kSrc_Mode was used in which case we can just proceed
     if (xferFP) {
-        paint.addColorFragmentProcessor(xferFP)->unref();
+        paint.addColorFragmentProcessor(xferFP);
     }
     paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);