skia: Prevent GL_RED from being used with MESA

src/gpu/gl/GrGLCaps.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGLCaps.h"
 
@@ skipping 160 matching lines @@
         fTexStorageSupport = version >= GR_GL_VER(4,2) ||
                              ctxInfo.hasExtension("GL_ARB_texture_storage") ||
                              ctxInfo.hasExtension("GL_EXT_texture_storage");
     } else {
         // Qualcomm Adreno drivers appear to have issues with texture storage.
         fTexStorageSupport = (version >= GR_GL_VER(3,0) &&
                               kQualcomm_GrGLVendor != ctxInfo.vendor()) ||
                              ctxInfo.hasExtension("GL_EXT_texture_storage");
     }
 
-    // ARB_texture_rg is part of OpenGL 3.0, but mesa doesn't support it if
-    // it doesn't have ARB_texture_rg extension.
-    if (kGL_GrGLStandard == standard) {
-        if (ctxInfo.isMesa()) {
-            fTextureRedSupport = ctxInfo.hasExtension("GL_ARB_texture_rg");
-        } else {
+    // ARB_texture_rg is part of OpenGL 3.0, but mesa doesn't support GL_RED 
+    // and GL_RG on FBO textures.
+    if (!ctxInfo.isMesa()) {
+        if (kGL_GrGLStandard == standard) {
             fTextureRedSupport = version >= GR_GL_VER(3,0) ||
                                  ctxInfo.hasExtension("GL_ARB_texture_rg");
+        } else {
+            fTextureRedSupport =  version >= GR_GL_VER(3,0) ||
+                                  ctxInfo.hasExtension("GL_EXT_texture_rg");
         }
-    } else {
-        fTextureRedSupport =  version >= GR_GL_VER(3,0) ||
-                              ctxInfo.hasExtension("GL_EXT_texture_rg");
     }
-
     fImagingSupport = kGL_GrGLStandard == standard &&
                       ctxInfo.hasExtension("GL_ARB_imaging");
 
     // ES 2 only guarantees RGBA/uchar + one other format/type combo for
     // ReadPixels. The other format has to checked at run-time since it
     // can change based on which render target is bound
     fTwoFormatLimit = kGLES_GrGLStandard == standard;
 
     // Frag Coords Convention support is not part of ES
     // Known issue on at least some Intel platforms:
@@ skipping 667 matching lines @@
     r.appendf("Two Format Limit: %s\n", (fTwoFormatLimit ? "YES": "NO"));
     r.appendf("Fragment coord conventions support: %s\n",
              (fFragCoordsConventionSupport ? "YES": "NO"));
     r.appendf("Vertex array object support: %s\n", (fVertexArrayObjectSupport ? "YES": "NO"));
     r.appendf("Use non-VBO for dynamic data: %s\n",
              (fUseNonVBOVertexAndIndexDynamicData ? "YES" : "NO"));
     r.appendf("Full screen clear is free: %s\n", (fFullClearIsFree ? "YES" : "NO"));
     r.appendf("Drops tile on zero divide: %s\n", (fDropsTileOnZeroDivide ? "YES" : "NO"));
     return r;
 }