Revert of Create swizzle table inside of glsl caps (patchset #12 id:210001 of https://codereview.chromium.org/1420033005/ )

Reason for revert:
Breaking gm's on nexus7 and s3

Original issue's description:
> Create swizzle table inside of glsl caps
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/4036674952f341dab0695c3b054fefa5bb8cdec1

TBR=bsalomon@google.com,robertphillips@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1426653008

1 files changed, 19 insertions, 6 deletions

diff --git a/src/gpu/gl/GrGLProgramDesc.cpp b/src/gpu/gl/GrGLProgramDesc.cpp
index 8ff25575c6..a232a63514 100644
--- a/src/gpu/gl/GrGLProgramDesc.cpp
+++ b/src/gpu/gl/GrGLProgramDesc.cpp
@@ -18,14 +18,26 @@
  * present in the texture's config. swizzleComponentMask indicates the channels present in the
  * shader swizzle.
  */
-static bool swizzle_requires_alpha_remapping(const GrGLSLCaps& caps, GrPixelConfig config) {
-    if (!caps.mustSwizzleInShader()) {
+static bool swizzle_requires_alpha_remapping(const GrGLCaps& caps,
+                                             uint32_t configComponentMask,
+                                             uint32_t swizzleComponentMask) {
+    if (caps.textureSwizzleSupport()) {
         // Any remapping is handled using texture swizzling not shader modifications.
         return false;
     }
-    const char* swizzleMap = caps.getSwizzleMap(config);
-    
-    return SkToBool(memcmp(swizzleMap, "rgba", 4));
+    // check if the texture is alpha-only
+    if (kA_GrColorComponentFlag == configComponentMask) {
+        if (caps.textureRedSupport() && (kA_GrColorComponentFlag & swizzleComponentMask)) {
+            // we must map the swizzle 'a's to 'r'.
+            return true;
+        }
+        if (kRGB_GrColorComponentFlags & swizzleComponentMask) {
+            // The 'r', 'g', and/or 'b's must be mapped to 'a' according to our semantics that
+            // alpha-only textures smear alpha across all four channels when read.
+            return true;
+        }
+    }
+    return false;
 }
 
 static uint32_t gen_texture_key(const GrProcessor& proc, const GrGLCaps& caps) {
@@ -33,7 +45,8 @@ static uint32_t gen_texture_key(const GrProcessor& proc, const GrGLCaps& caps) {
     int numTextures = proc.numTextures();
     for (int t = 0; t < numTextures; ++t) {
         const GrTextureAccess& access = proc.textureAccess(t);
-        if (swizzle_requires_alpha_remapping(*caps.glslCaps(), access.getTexture()->config())) {
+        uint32_t configComponentMask = GrPixelConfigComponentMask(access.getTexture()->config());
+        if (swizzle_requires_alpha_remapping(caps, configComponentMask, access.swizzleMask())) {
             key |= 1 << t;
         }
     }