Make readback of alpha channel work for RGBA.

src/gpu/gl/GrGLProgramDesc.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "GrGLProgramDesc.h"
 
 #include "GrProcessor.h"
 #include "GrGLGpu.h"
@@ skipping 24 matching lines @@
 /**
  * A function which emits a meta key into the key builder.  This is required because shader code may
  * be dependent on properties of the effect that the effect itself doesn't use
  * in its key (e.g. the pixel format of textures used). So we create a meta-key for
  * every effect using this function. It is also responsible for inserting the effect's class ID
  * which must be different for every GrProcessor subclass. It can fail if an effect uses too many
  * transforms, etc, for the space allotted in the meta-key.  NOTE, both FPs and GPs share this
  * function because it is hairy, though FPs do not have attribs, and GPs do not have transforms
  */
 static bool gen_meta_key(const GrProcessor& proc,
-                         const GrGLCaps& caps,
+                         const GrGLSLCaps& glslCaps,
                          uint32_t transformKey,
                          GrProcessorKeyBuilder* b) {
     size_t processorKeySize = b->size();
     uint32_t classID = proc.classID();
 
     // Currently we allow 16 bits for the class id and the overall processor key size.
     static const uint32_t kMetaKeyInvalidMask = ~((uint32_t) SK_MaxU16);
     if ((processorKeySize | classID) & kMetaKeyInvalidMask) {
         return false;
     }
 
-    add_texture_key(b, proc, *caps.glslCaps());
+    add_texture_key(b, proc, glslCaps);
 
     uint32_t* key = b->add32n(2);
     key[0] = (classID << 16) | SkToU32(processorKeySize);
     key[1] = transformKey;
     return true;
 }
 
 static bool gen_frag_proc_and_meta_keys(const GrPrimitiveProcessor& primProc,
                                         const GrFragmentProcessor& fp,
                                         const GrGLCaps& caps,
                                         GrProcessorKeyBuilder* b) {
     for (int i = 0; i < fp.numChildProcessors(); ++i) {
         if (!gen_frag_proc_and_meta_keys(primProc, fp.childProcessor(i), caps, b)) {
             return false;
         }
     }
 
     fp.getGLSLProcessorKey(*caps.glslCaps(), b);
 
     //**** use glslCaps here?
-    return gen_meta_key(fp, caps, primProc.getTransformKey(fp.coordTransforms(),
+    return gen_meta_key(fp, *caps.glslCaps(), primProc.getTransformKey(fp.coordTransforms(),
                                                            fp.numTransformsExclChildren()), b);
 }
 
 bool GrGLProgramDescBuilder::Build(GrProgramDesc* desc,
                                    const GrPrimitiveProcessor& primProc,
                                    const GrPipeline& pipeline,
                                    const GrGLGpu* gpu) {
+    const GrGLSLCaps& glslCaps = *gpu->glCaps().glslCaps();
+
     // The descriptor is used as a cache key. Thus when a field of the
     // descriptor will not affect program generation (because of the attribute
     // bindings in use or other descriptor field settings) it should be set
     // to a canonical value to avoid duplicate programs with different keys.
 
     GrGLProgramDesc* glDesc = (GrGLProgramDesc*) desc;
 
     GR_STATIC_ASSERT(0 == kProcessorKeysOffset % sizeof(uint32_t));
     // Make room for everything up to the effect keys.
     glDesc->key().reset();
     glDesc->key().push_back_n(kProcessorKeysOffset);
 
     GrProcessorKeyBuilder b(&glDesc->key());
 
-    primProc.getGLSLProcessorKey(*gpu->glCaps().glslCaps(), &b);
-    //**** use glslCaps here?
-    if (!gen_meta_key(primProc, gpu->glCaps(), 0, &b)) {
+    primProc.getGLSLProcessorKey(glslCaps, &b);
+    if (!gen_meta_key(primProc, glslCaps, 0, &b)) {
         glDesc->key().reset();
         return false;
     }
 
     for (int i = 0; i < pipeline.numFragmentProcessors(); ++i) {
         const GrFragmentProcessor& fp = pipeline.getFragmentProcessor(i);
         if (!gen_frag_proc_and_meta_keys(primProc, fp, gpu->glCaps(), &b)) {
             glDesc->key().reset();
             return false;
         }
     }
 
     const GrXferProcessor& xp = pipeline.getXferProcessor();
     xp.getGLSLProcessorKey(*gpu->glCaps().glslCaps(), &b);
     //**** use glslCaps here?
-    if (!gen_meta_key(xp, gpu->glCaps(), 0, &b)) {
+    if (!gen_meta_key(xp, glslCaps, 0, &b)) {
         glDesc->key().reset();
         return false;
     }
 
     // --------DO NOT MOVE HEADER ABOVE THIS LINE--------------------------------------------------
     // Because header is a pointer into the dynamic array, we can't push any new data into the key
     // below here.
     KeyHeader* header = glDesc->atOffset<KeyHeader, kHeaderOffset>();
 
     // make sure any padding in the header is zeroed.
     memset(header, 0, kHeaderSize);
 
+    header->fOutputSwizzle =
+        glslCaps.configOutputSwizzle(pipeline.getRenderTarget()->config()).asKey();
+
     if (pipeline.readsFragPosition()) {
         header->fFragPosKey =
                 GrGLSLFragmentShaderBuilder::KeyForFragmentPosition(pipeline.getRenderTarget());
     } else {
         header->fFragPosKey = 0;
     }
 
     if (pipeline.ignoresCoverage()) {
         header->fIgnoresCoverage = 1;
     } else {
         header->fIgnoresCoverage = 0;
     }
 
     header->fSnapVerticesToPixelCenters = pipeline.snapVerticesToPixelCenters();
     header->fColorEffectCnt = pipeline.numColorFragmentProcessors();
     header->fCoverageEffectCnt = pipeline.numCoverageFragmentProcessors();
     glDesc->finalize();
     return true;
 }