Use GrGammaEffect to support YUV conversion without sRGB write control

src/gpu/GrYUVProvider.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrContext.h"
 #include "GrDrawContext.h"
 #include "GrYUVProvider.h"
+#include "effects/GrGammaEffect.h"
 #include "effects/GrYUVEffect.h"
 
 #include "SkCachedData.h"
 #include "SkRefCnt.h"
 #include "SkResourceCache.h"
 #include "SkYUVPlanesCache.h"
 
 namespace {
 /**
  *  Helper class to manage the resources used for storing the YUV planar data. Depending on the
@@ skipping 92 matching lines @@
     }
 
     sk_sp<GrDrawContext> drawContext(ctx->newDrawContext(SkBackingFit::kExact,
                                                          desc.fWidth, desc.fHeight,
                                                          desc.fConfig, desc.fSampleCnt));
     if (!drawContext) {
         return nullptr;
     }
 
     GrPaint paint;
-    // We may be decoding an sRGB image, but the result of our linear math on the YUV planes
-    // is already in sRGB in that case. Don't convert (which will make the image too bright).
-    paint.setDisableOutputConversionToSRGB(true);
     SkAutoTUnref<const GrFragmentProcessor> yuvToRgbProcessor(
                                         GrYUVEffect::CreateYUVToRGB(yuvTextures[0],
                                                                     yuvTextures[1],
                                                                     yuvTextures[2],
                                                                     yuvInfo.fSizeInfo.fSizes,
                                                                     yuvInfo.fColorSpace));
     paint.addColorFragmentProcessor(yuvToRgbProcessor);
+
+    // If we're decoding an sRGB image, the result of our linear math on the YUV planes is already
+    // in sRGB. (The encoding is just math on bytes, with no concept of color spaces.) So, we need
+    // to output the results of that math directly to the buffer that we will then consider sRGB.
+    // If we have sRGB write control, we can just tell the HW not to do the Linear -> sRGB step.
+    // Otherwise, we do our shader math to go from YUV -> sRGB, manually convert sRGB -> Linear,
+    // then let the HW convert Linear -> sRGB.
+    if (GrPixelConfigIsSRGB(desc.fConfig)) {
+        if (ctx->caps()->srgbWriteControl()) {
+            paint.setDisableOutputConversionToSRGB(true);
+        } else {
+            paint.addColorFragmentProcessor(GrGammaEffect::Create(2.2f))->unref();
+        }
+    }
+
     paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
     const SkRect r = SkRect::MakeIWH(yuvInfo.fSizeInfo.fSizes[SkYUVSizeInfo::kY].fWidth,
             yuvInfo.fSizeInfo.fSizes[SkYUVSizeInfo::kY].fHeight);
 
     drawContext->drawRect(GrClip::WideOpen(), paint, SkMatrix::I(), r);
 
     return drawContext->asTexture();
 }