Make swizzling in read/write pixel copy code more generic

src/gpu/effects/GrConfigConversionEffect.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrConfigConversionEffect_DEFINED
 #define GrConfigConversionEffect_DEFINED
 
 #include "GrSingleTextureEffect.h"
+#include "GrSwizzle.h"
 
 class GrInvariantOutput;
 
 /**
  * This class is used to perform config conversions. Clients may want to read/write data that is
- * unpremultiplied. Also on some systems reading/writing BGRA or RGBA is faster. In those cases we
- * read/write using the faster path and perform an R/B swap in the shader if the client data is in
- * the slower config.
+ * unpremultiplied. Additionally, the channels may also be swizzled for optimal readback/upload
+ * performance.
  */
 class GrConfigConversionEffect : public GrSingleTextureEffect {
 public:
     /**
      * The PM->UPM or UPM->PM conversions to apply.
      */
     enum PMConversion {
         kNone_PMConversion = 0,
         kMulByAlpha_RoundUp_PMConversion,
         kMulByAlpha_RoundDown_PMConversion,
         kDivByAlpha_RoundUp_PMConversion,
         kDivByAlpha_RoundDown_PMConversion,
 
         kPMConversionCnt
     };
 
-    static const GrFragmentProcessor* Create(GrTexture*, bool swapRedAndBlue, PMConversion,
+    static const GrFragmentProcessor* Create(GrTexture*, const GrSwizzle&, PMConversion,
                                              const SkMatrix&);
 
     const char* name() const override { return "Config Conversion"; }
 
-    bool swapsRedAndBlue() const { return fSwapRedAndBlue; }
+    const GrSwizzle& swizzle() const { return fSwizzle; }
     PMConversion  pmConversion() const { return fPMConversion; }
 
     // This function determines whether it is possible to choose PM->UPM and UPM->PM conversions
     // for which in any PM->UPM->PM->UPM sequence the two UPM values are the same. This means that
     // if pixels are read back to a UPM buffer, written back to PM to the GPU, and read back again
     // both reads will produce the same result. This test is quite expensive and should not be run
     // multiple times for a given context.
     static void TestForPreservingPMConversions(GrContext* context,
                                                PMConversion* PMToUPMRule,
                                                PMConversion* UPMToPMRule);
 
 private:
     GrConfigConversionEffect(GrTexture*,
-                             bool swapRedAndBlue,
+                             const GrSwizzle&,
                              PMConversion pmConversion,
                              const SkMatrix& matrix);
 
     GrGLSLFragmentProcessor* onCreateGLSLInstance() const override;
 
     void onGetGLSLProcessorKey(const GrGLSLCaps&, GrProcessorKeyBuilder*) const override;
 
     bool onIsEqual(const GrFragmentProcessor&) const override;
 
     void onComputeInvariantOutput(GrInvariantOutput* inout) const override;
 
-    bool            fSwapRedAndBlue;
+    GrSwizzle       fSwizzle;
     PMConversion    fPMConversion;
 
     GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
 
     typedef GrSingleTextureEffect INHERITED;
 };
 
 #endif