Make GrGammaEffect have explicit sRGB modes, plus exponential mode.

src/gpu/GrContext.cpp

Index: src/gpu/GrContext.cpp
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index 443494073af596a9ac0f9fee05d49be897d7478c..4235ae85524ab36d9ffc4426d0e00a3d4548aa33 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -550,12 +550,9 @@ bool GrContext::applyGamma(GrRenderTarget* dst, GrTexture* src, SkScalar gamma){
     }
 
     GrPaint paint;
-    if (SkScalarNearlyEqual(gamma, 1.0f)) {
-        paint.addColorTextureProcessor(src, GrCoordTransform::MakeDivByTextureWHMatrix(src));
-    } else {
-        SkAutoTUnref<const GrFragmentProcessor> fp;
-        fp.reset(GrGammaEffect::Create(src, gamma));
-        paint.addColorFragmentProcessor(fp);
+    paint.addColorTextureProcessor(src, GrCoordTransform::MakeDivByTextureWHMatrix(src));

[bsalomon, 2016/05/11 02:15:01]

I may have asked this before, but I'll ask again anyway just in case :) Should
we check if the src texture happens to be sRGB and the dst happens to be linear
and the gamma happens to be 2.2? (Or the reverse transformation).

[Brian Osman, 2016/05/11 02:49:20]

Perhaps, although right now I'm picturing that this is only going to be used
when we know that we need it (because the automatic behavior wouldn't be
correct). I don't picture external code ever injecting these, and I think that
we're going to want a higher level check? Maybe not - perhaps we end up always
inserting a "conversion" effect after texture read that's actually a no-op in
those cases...

+    if (!SkScalarNearlyEqual(gamma, 1.0f)) {
+        paint.addColorFragmentProcessor(GrGammaEffect::Create(gamma))->unref();
     }
     paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
     paint.setGammaCorrect(true);