sRGB support in Ganesh. Several pieces:

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 1379 matching lines @@
                 fConfigTable[kBGRA_8888_GrPixelConfig].fFlags |=
                     ConfigInfo::kRenderableWithMSAA_Flag;
             }
         }
     }
     if (texStorageSupported) {
         fConfigTable[kBGRA_8888_GrPixelConfig].fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
     }
     fConfigTable[kBGRA_8888_GrPixelConfig].fSwizzle = GrSwizzle::RGBA();
 
-    // We only enable srgb support if both textures and FBOs support srgb.
-    bool srgbSupport = false;
+    // We only enable srgb support if both textures and FBOs support srgb,
+    // *and* we can disable sRGB decode-on-read, to support "legacy" mode.
     if (kGL_GrGLStandard == standard) {
         if (ctxInfo.version() >= GR_GL_VER(3,0)) {
-            srgbSupport = true;
+            fSRGBSupport = true;
         } else if (ctxInfo.hasExtension("GL_EXT_texture_sRGB")) {
             if (ctxInfo.hasExtension("GL_ARB_framebuffer_sRGB") ||
                 ctxInfo.hasExtension("GL_EXT_framebuffer_sRGB")) {
-                srgbSupport = true;
+                fSRGBSupport = true;
             }
         }
         // All the above srgb extensions support toggling srgb writes
-        fSRGBWriteControl = srgbSupport;
+        fSRGBWriteControl = fSRGBSupport;
     } else {
         // See https://bug.skia.org/4148 for PowerVR issue.
-        srgbSupport = kPowerVRRogue_GrGLRenderer != ctxInfo.renderer() &&
+        fSRGBSupport = kPowerVRRogue_GrGLRenderer != ctxInfo.renderer() &&
             (ctxInfo.version() >= GR_GL_VER(3,0) || ctxInfo.hasExtension("GL_EXT_sRGB"));
         // ES through 3.1 requires EXT_srgb_write_control to support toggling
         // sRGB writing for destinations.
         fSRGBWriteControl = ctxInfo.hasExtension("GL_EXT_sRGB_write_control");
     }
+    if (!ctxInfo.hasExtension("GL_EXT_texture_sRGB_decode")) {
+        // To support "legacy" L32 mode, we require the ability to turn off sRGB decode:
+        fSRGBSupport = false;
+    }
     fConfigTable[kSRGBA_8888_GrPixelConfig].fFormats.fBaseInternalFormat = GR_GL_SRGB_ALPHA;
     fConfigTable[kSRGBA_8888_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_SRGB8_ALPHA8;
     // GL does not do srgb<->rgb conversions when transferring between cpu and gpu. Thus, the
     // external format is GL_RGBA. See below for note about ES2.0 and glTex[Sub]Image.
     fConfigTable[kSRGBA_8888_GrPixelConfig].fFormats.fExternalFormat[kOther_ExternalFormatUsage] =
         GR_GL_RGBA;
     fConfigTable[kSRGBA_8888_GrPixelConfig].fFormats.fExternalType = GR_GL_UNSIGNED_BYTE;
     fConfigTable[kSRGBA_8888_GrPixelConfig].fFormatType = kNormalizedFixedPoint_FormatType;
-    if (srgbSupport) {
+    if (fSRGBSupport) {
         fConfigTable[kSRGBA_8888_GrPixelConfig].fFlags = ConfigInfo::kTextureable_Flag |
                                                          allRenderFlags;
     }
     if (texStorageSupported) {
         fConfigTable[kSRGBA_8888_GrPixelConfig].fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
     }
     fConfigTable[kSRGBA_8888_GrPixelConfig].fSwizzle = GrSwizzle::RGBA();
 
+    // sBGRA is not a "real" thing in OpenGL, but GPUs support it, and on platforms where
+    // kN32 == BGRA, we need some way to work with it. (The default framebuffer on Windows
+    // is in this format, for example).
+    fConfigTable[kSBGRA_8888_GrPixelConfig].fFormats.fBaseInternalFormat = GR_GL_SRGB_ALPHA;
+    fConfigTable[kSBGRA_8888_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_SRGB8_ALPHA8;
+    // GL does not do srgb<->rgb conversions when transferring between cpu and gpu. Thus, the
+    // external format is GL_BGRA.
+    fConfigTable[kSBGRA_8888_GrPixelConfig].fFormats.fExternalFormat[kOther_ExternalFormatUsage] =
+        GR_GL_BGRA;
+    fConfigTable[kSBGRA_8888_GrPixelConfig].fFormats.fExternalType = GR_GL_UNSIGNED_BYTE;
+    fConfigTable[kSBGRA_8888_GrPixelConfig].fFormatType = kNormalizedFixedPoint_FormatType;
+    if (fSRGBSupport) {
+        fConfigTable[kSBGRA_8888_GrPixelConfig].fFlags = ConfigInfo::kTextureable_Flag |
+            allRenderFlags;
+    }
+    if (texStorageSupported) {
+        fConfigTable[kSBGRA_8888_GrPixelConfig].fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
+    }
+    fConfigTable[kSBGRA_8888_GrPixelConfig].fSwizzle = GrSwizzle::RGBA();
+
     fConfigTable[kRGB_565_GrPixelConfig].fFormats.fBaseInternalFormat = GR_GL_RGB;
     if (this->ES2CompatibilitySupport()) {
         fConfigTable[kRGB_565_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_RGB565;
     } else {
         fConfigTable[kRGB_565_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_RGB5;
     }
     fConfigTable[kRGB_565_GrPixelConfig].fFormats.fExternalFormat[kOther_ExternalFormatUsage] =
         GR_GL_RGB;
     fConfigTable[kRGB_565_GrPixelConfig].fFormats.fExternalType = GR_GL_UNSIGNED_SHORT_5_6_5;
     fConfigTable[kRGB_565_GrPixelConfig].fFormatType = kNormalizedFixedPoint_FormatType;
@@ skipping 299 matching lines @@
             fConfigTable[i].fFormats.fSizedInternalFormat :
             fConfigTable[i].fFormats.fBaseInternalFormat;
     }
     // OpenGL ES 2.0 + GL_EXT_sRGB allows GL_SRGB_ALPHA to be specified as the <format>
     // param to Tex(Sub)Image. ES 2.0 requires the <internalFormat> and <format> params to match.
     // Thus, on ES 2.0 we will use GL_SRGB_ALPHA as the <format> param.
     // On OpenGL and ES 3.0+ GL_SRGB_ALPHA does not work for the <format> param to glTexImage.
     if (ctxInfo.standard() == kGLES_GrGLStandard && ctxInfo.version() == GR_GL_VER(2,0)) {
         fConfigTable[kSRGBA_8888_GrPixelConfig].fFormats.fExternalFormat[kTexImage_ExternalFormatUsage] =
             GR_GL_SRGB_ALPHA;
+
+        // Additionally, because we had to "invent" sBGRA, there is no way to make it work
+        // in ES 2.0, because there is no <internalFormat> we can use. So just make that format

[bsalomon, 2016/03/11 23:16:20]

Not true on ES 3.0+?

[Brian Osman, 2016/03/17 14:32:06]

My reading of this is that it's allowed? ES2 forces the two formats to match,
but ES3 will let us do conversion at Tex[Sub]Image time?

+        // unsupported. (If we have no sRGB support at all, this will get overwritten below).
+        fConfigTable[kSBGRA_8888_GrPixelConfig].fFlags = 0;
     }
 
     // If BGRA is supported as an internal format it must always be specified to glTex[Sub]Image
     // as a base format.
     // GL_EXT_texture_format_BGRA8888:
     //      This extension GL_BGRA as an unsized internal format. However, it is written against ES
     //      2.0 and therefore doesn't define a value for GL_BGRA8 as ES 2.0 uses unsized internal
     //      formats.
     // GL_APPLE_texture_format_BGRA8888: 
     //     ES 2.0: the extension makes BGRA an external format but not an internal format.
     //     ES 3.0: the extension explicitly states GL_BGRA8 is not a valid internal format for
     //             glTexImage (just for glTexStorage).
     if (useSizedTexFormats && this->bgraIsInternalFormat())  {
         fConfigTable[kBGRA_8888_GrPixelConfig].fFormats.fInternalFormatTexImage = GR_GL_BGRA;
     }
 
+    // HACK: Various GL implementations won't have sRGB support at all, particularly with our
+    // requirements. It's easy for sRGB data to leak in, though (via decoded PNGs, etc...).
+    // Thus, we employ a giant hack to ensure that any non-sRGB-capable device will continue
+    // to function as it always has, where everything is treated as linear. This isn't the

[bsalomon, 2016/03/11 23:16:20]

Can we pass the caps to the ct/at/pt -> grpc conversion and avoid this hack?

[Brian Osman, 2016/03/17 14:32:05]

Done.

+    // best way to do this - code that does things like elevate to draw for conversion to/from
+    // sRGB will still make that decision, even though the formats are now identical.
+    if (!fSRGBSupport) {
+        fConfigTable[kSRGBA_8888_GrPixelConfig] = fConfigTable[kRGBA_8888_GrPixelConfig];
+        fConfigTable[kSBGRA_8888_GrPixelConfig] = fConfigTable[kBGRA_8888_GrPixelConfig];
+    }
+
     // If we don't have texture swizzle support then the shader generator must insert the
     // swizzle into shader code.
     if (!this->textureSwizzleSupport()) {
         for (int i = 0; i < kGrPixelConfigCnt; ++i) {
             glslCaps->fConfigTextureSwizzle[i] = fConfigTable[i].fSwizzle;
         }
     }
 
     // Shader output swizzles will default to RGBA. When we've use GL_RED instead of GL_ALPHA to
     // implement kAlpha_8_GrPixelConfig we need to swizzle the shader outputs so the alpha channel
@@ skipping 19 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) {}