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

src/gpu/GrFragmentProcessor.cpp

 /*
 * Copyright 2015 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #include "GrFragmentProcessor.h"
 #include "GrCoordTransform.h"
 #include "GrInvariantOutput.h"
@@ skipping 125 matching lines @@
 
 sk_sp<GrFragmentProcessor> GrFragmentProcessor::MulOutputByInputAlpha(
     sk_sp<GrFragmentProcessor> fp) {
     if (!fp) {
         return nullptr;
     }
     return GrXfermodeFragmentProcessor::MakeFromDstProcessor(std::move(fp),
                                                              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);
+                }
+            };
+            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->premulFourChannelColor();
+        }
+    };
+    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) {
 
     class PremulFragmentProcessor : public GrFragmentProcessor {
     public:
         PremulFragmentProcessor(sk_sp<GrFragmentProcessor> processor) {
             this->initClassID<PremulFragmentProcessor>();
             this->registerChildProcessor(processor);
         }
 
@@ skipping 214 matching lines @@
     } else {
         series += firstIdx;
         cnt -= firstIdx;
     }
 
     if (1 == cnt) {
         return series[0];
     }
     return sk_sp<GrFragmentProcessor>(new SeriesFragmentProcessor(series, cnt));
 }