Fix BGRA/RGBA readback conversions on mac

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 35 matching lines @@
     fUseNonVBOVertexAndIndexDynamicData = false;
     fIsCoreProfile = false;
     fBindFragDataLocationSupport = false;
     fExternalTextureSupport = false;
     fRectangleTextureSupport = false;
     fTextureSwizzleSupport = false;
     fSRGBWriteControl = false;
     fRGBA8888PixelsOpsAreSlow = false;
     fPartialFBOReadIsSlow = false;
     fMipMapLevelAndLodControlSupport = false;
+    fRGBAToBGRAReadbackConversionsAreSlow = false;
 
     fBlitFramebufferSupport = kNone_BlitFramebufferSupport;
 
     fShaderCaps.reset(new GrGLSLCaps(contextOptions));
 
     this->init(contextOptions, ctxInfo, glInterface);
 }
 
 void GrGLCaps::init(const GrContextOptions& contextOptions,
                     const GrGLContextInfo& ctxInfo,
@@ skipping 193 matching lines @@
     // We're assuming that on Windows Chromium we're using ANGLE.
     bool isANGLE = kANGLE_GrGLDriver == ctxInfo.driver() ||
                    kChromium_GrGLDriver == ctxInfo.driver();
     // Angle has slow read/write pixel paths for 32bit RGBA (but fast for BGRA). 
     fRGBA8888PixelsOpsAreSlow = isANGLE;
     // On DX9 ANGLE reading a partial FBO is slow. TODO: Check whether this is still true and
     // check DX11 ANGLE.
     fPartialFBOReadIsSlow = isANGLE;
 #endif
 
+    bool isMESA = kMesa_GrGLDriver == ctxInfo.driver();
+    bool isMAC = false;
+#ifdef SK_BUILD_FOR_MAC
+    isMAC = true;
+#endif
+
+    // Both mesa and mac have reduced performance if reading back an RGBA framebuffer as BGRA or
+    // vis-versa.
+    fRGBAToBGRAReadbackConversionsAreSlow = isMESA || isMAC;
+
     /**************************************************************************
     * GrShaderCaps fields
     **************************************************************************/
 
     // This must be called after fCoreProfile is set on the GrGLCaps
     this->initGLSL(ctxInfo);
     GrGLSLCaps* glslCaps = static_cast<GrGLSLCaps*>(fShaderCaps.get());
 
     glslCaps->fPathRenderingSupport = this->hasPathRenderingSupport(ctxInfo, gli);
 
@@ skipping 766 matching lines @@
     r.appendf("Base instance support: %s\n", (fBaseInstanceSupport ? "YES" : "NO"));
     r.appendf("Use non-VBO for dynamic data: %s\n",
              (fUseNonVBOVertexAndIndexDynamicData ? "YES" : "NO"));
     r.appendf("SRGB write contol: %s\n", (fSRGBWriteControl ? "YES" : "NO"));
     r.appendf("RGBA 8888 pixel ops are slow: %s\n", (fRGBA8888PixelsOpsAreSlow ? "YES" : "NO"));
     r.appendf("Partial FBO read is slow: %s\n", (fPartialFBOReadIsSlow ? "YES" : "NO"));
     r.appendf("Bind uniform location support: %s\n", (fBindUniformLocationSupport ? "YES" : "NO"));
     r.appendf("External texture support: %s\n", (fExternalTextureSupport ? "YES" : "NO"));
     r.appendf("Rectangle texture support: %s\n", (fRectangleTextureSupport? "YES" : "NO"));
     r.appendf("Texture swizzle support: %s\n", (fTextureSwizzleSupport ? "YES" : "NO"));
+    r.appendf("BGRA to RGBA readback conversions are slow: %s\n", 
+              (fRGBAToBGRAReadbackConversionsAreSlow ? "YES" : "NO"));
 
     r.append("Configs\n-------\n");
     for (int i = 0; i < kGrPixelConfigCnt; ++i) {
         r.appendf("  cfg: %d flags: 0x%04x, b_internal: 0x%08x s_internal: 0x%08x, e_format: "
                   "0x%08x, e_format_teximage: 0x%08x, e_type: 0x%08x, i_for_teximage: 0x%08x, "
                   "i_for_renderbuffer: 0x%08x\n",
                   i,
                   fConfigTable[i].fFlags,
                   fConfigTable[i].fFormats.fBaseInternalFormat,
                   fConfigTable[i].fFormats.fSizedInternalFormat,
@@ skipping 737 matching lines @@
         for (int j = 0; j < kExternalFormatUsageCnt; ++j) {
             SkASSERT(defaultEntry.fFormats.fExternalFormat[j] !=
                      fConfigTable[i].fFormats.fExternalFormat[j]);
         }
         SkASSERT(defaultEntry.fFormats.fExternalType != fConfigTable[i].fFormats.fExternalType);
     }
 #endif
 }
 
 void GrGLCaps::onApplyOptionsOverrides(const GrContextOptions& options) {}