SkLS accepts nullptr for pointer args, handles alpha accurately, has new GM

src/gpu/GrFragmentProcessor.cpp

Index: src/gpu/GrFragmentProcessor.cpp
diff --git a/src/gpu/GrFragmentProcessor.cpp b/src/gpu/GrFragmentProcessor.cpp
index bad7ebe0360cd046262d39b4fa639aeecb874445..c5bd637fa2ff27efa387b62ee17b6459f1a5abff 100644
--- a/src/gpu/GrFragmentProcessor.cpp
+++ b/src/gpu/GrFragmentProcessor.cpp
@@ -143,6 +143,45 @@ sk_sp<GrFragmentProcessor> GrFragmentProcessor::MulOutputByInputAlpha(
                                                              SkXfermode::kDstIn_Mode);
 }
 
+sk_sp<GrFragmentProcessor> GrFragmentProcessor::PremulInput(sk_sp<GrFragmentProcessor> fp) {
+
+    class PremulInputFragmentProcessor : public GrFragmentProcessor {
+    public:
+        PremulInputFragmentProcessor() {
+            this->initClassID<PremulInputFragmentProcessor>();
+        }
+
+        const char* name() const override { return "PremultiplyInput"; }
+
+    private:
+        GrGLSLFragmentProcessor* onCreateGLSLInstance() const override {
+            class GLFP : public GrGLSLFragmentProcessor {
+            public:
+                void emitCode(EmitArgs& args) override {
+                    GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
+
+                    fragBuilder->codeAppendf("%s = %s;", args.fOutputColor, args.fInputColor);
+                    fragBuilder->codeAppendf("%s.rgb *= %s.a;", args.fOutputColor, args.fInputColor);

[egdaniel, 2016/07/14 03:22:47]

100 chars

[dvonbeck, 2016/07/14 14:30:33]

This was fixed in patch set 6

+                }
+            };
+            return new GLFP;
+        }
+
+        void onGetGLSLProcessorKey(const GrGLSLCaps&, GrProcessorKeyBuilder*) const override {}
+
+        bool onIsEqual(const GrFragmentProcessor&) const override { return true; }
+
+        void onComputeInvariantOutput(GrInvariantOutput* inout) const override {
+            inout->mulByUnknownFourComponents();

[egdaniel, 2016/07/14 03:22:47]

This doesn't seem right. I feel like it should be able to tell some info if some
of the values are known. For example if we know the alpha is opaque then we
should do nothing to the inout. Knowing that the color stays opaque can
definitely be useful to us in our optimizations later on.

[dvonbeck, 2016/07/14 14:30:33]

Adding appropriate invariant option in separate CL.

+        }
+    };
+    if (!fp) {
+        return nullptr;
+    }
+    sk_sp<GrFragmentProcessor> fpPipeline[] = { sk_make_sp<PremulInputFragmentProcessor>(), fp};
+    return GrFragmentProcessor::RunInSeries(fpPipeline, 2);
+}
+
 sk_sp<GrFragmentProcessor> GrFragmentProcessor::MulOutputByInputUnpremulColor(
     sk_sp<GrFragmentProcessor> fp) {