Update GrFragmentProcessor::SwizzleOutput to use a child FP.

We are updating FPs to receive their input via a child FP where
possible, instead of relying on the input color.

This CL also adds a GM test for SwizzleOutput, since this did not appear
to be covered by existing unit tests.

Change-Id: I3d8176395bb42eab7ff471c9137597402b5b3a69
Bug: skia:10217
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/293884
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>

gm/swizzle.cpp

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2019 Google LLC.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm/gm.h"
+#include "include/core/SkCanvas.h"
+#include "include/core/SkImageInfo.h"
+#include "include/core/SkMatrix.h"
+#include "include/core/SkRect.h"
+#include "include/core/SkTypes.h"
+#include "include/gpu/GrContext.h"
+#include "src/gpu/GrBitmapTextureMaker.h"
+#include "src/gpu/GrContextPriv.h"
+#include "src/gpu/GrFragmentProcessor.h"
+#include "src/gpu/GrRenderTargetContext.h"
+#include "src/gpu/GrRenderTargetContextPriv.h"
+#include "src/gpu/ops/GrFillRectOp.h"
+#include "tools/Resources.h"
+#include "tools/ToolUtils.h"
+
+DEF_SIMPLE_GPU_GM(swizzle, ctx, rtCtx, canvas, 512, 512) {
+    SkRect bounds = SkRect::MakeIWH(512, 512);
+
+    SkBitmap bmp;
+    GetResourceAsBitmap("images/mandrill_512_q075.jpg", &bmp);
+    GrBitmapTextureMaker maker(ctx, bmp, GrImageTexGenPolicy::kDraw);
+    auto view = maker.view(GrMipMapped::kNo);
+    if (!view) {
+        return;
+    }
+    std::unique_ptr<GrFragmentProcessor> imgFP =
+        GrTextureEffect::Make(std::move(view), bmp.alphaType(), SkMatrix());
+    auto fp = GrFragmentProcessor::SwizzleOutput(std::move(imgFP), GrSwizzle("grb1"));
+
+    GrPaint grPaint;
+    grPaint.addColorFragmentProcessor(std::move(fp));
+
+    rtCtx->priv().testingOnly_addDrawOp(
+        GrFillRectOp::MakeNonAARect(ctx, std::move(grPaint), SkMatrix(), bounds));
+}

gn/gm.gni

@@ -349,6 +349,7 @@ gm_sources = [
   "$_gm/stroketext.cpp",
   "$_gm/subsetshader.cpp",
   "$_gm/surface.cpp",
+  "$_gm/swizzle.cpp",
   "$_gm/tablecolorfilter.cpp",
   "$_gm/tallstretchedbitmaps.cpp",
   "$_gm/tessellation.cpp",

src/gpu/GrFragmentProcessor.cpp

@@ -188,30 +188,38 @@ std::unique_ptr<GrFragmentProcessor> GrFragmentProcessor::SwizzleOutput(
         std::unique_ptr<GrFragmentProcessor> fp, const GrSwizzle& swizzle) {
     class SwizzleFragmentProcessor : public GrFragmentProcessor {
     public:
-        static std::unique_ptr<GrFragmentProcessor> Make(const GrSwizzle& swizzle) {
-            return std::unique_ptr<GrFragmentProcessor>(new SwizzleFragmentProcessor(swizzle));
+        static std::unique_ptr<GrFragmentProcessor> Make(std::unique_ptr<GrFragmentProcessor> fp,
+                                                         const GrSwizzle& swizzle) {
+            return std::unique_ptr<GrFragmentProcessor>(
+                new SwizzleFragmentProcessor(std::move(fp), swizzle));
         }
 
         const char* name() const override { return "Swizzle"; }
         const GrSwizzle& swizzle() const { return fSwizzle; }
 
-        std::unique_ptr<GrFragmentProcessor> clone() const override { return Make(fSwizzle); }
+        std::unique_ptr<GrFragmentProcessor> clone() const override {
+            return Make(this->childProcessor(0).clone(), fSwizzle);
+        }
 
     private:
-        SwizzleFragmentProcessor(const GrSwizzle& swizzle)
-                : INHERITED(kSwizzleFragmentProcessor_ClassID, kAll_OptimizationFlags)
-                , fSwizzle(swizzle) {}
+        SwizzleFragmentProcessor(std::unique_ptr<GrFragmentProcessor> fp, const GrSwizzle& swizzle)
+                : INHERITED(kSwizzleFragmentProcessor_ClassID, ProcessorOptimizationFlags(fp.get()))
+                , fSwizzle(swizzle) {
+            this->registerChildProcessor(std::move(fp));
+        }
 
         GrGLSLFragmentProcessor* onCreateGLSLInstance() const override {
             class GLFP : public GrGLSLFragmentProcessor {
             public:
                 void emitCode(EmitArgs& args) override {
+                    SkString childColor = this->invokeChild(0, args);
+
                     const SwizzleFragmentProcessor& sfp = args.fFp.cast<SwizzleFragmentProcessor>();
                     const GrSwizzle& swizzle = sfp.swizzle();
                     GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
 
                     fragBuilder->codeAppendf("%s = %s.%s;",
-                            args.fOutputColor, args.fInputColor, swizzle.asString().c_str());
+                            args.fOutputColor, childColor.c_str(), swizzle.asString().c_str());
                 }
             };
             return new GLFP;
@@ -241,9 +249,7 @@ std::unique_ptr<GrFragmentProcessor> GrFragmentProcessor::SwizzleOutput(
     if (GrSwizzle::RGBA() == swizzle) {
         return fp;
     }
-    std::unique_ptr<GrFragmentProcessor> fpPipeline[] = { std::move(fp),
-                                                          SwizzleFragmentProcessor::Make(swizzle) };
-    return GrFragmentProcessor::RunInSeries(fpPipeline, 2);
+    return SwizzleFragmentProcessor::Make(std::move(fp), swizzle);
 }
 
 std::unique_ptr<GrFragmentProcessor> GrFragmentProcessor::MakeInputPremulAndMulByOutput(