Fix sRGB textures that must be copied (for NPOT tiling, etc...)

src/gpu/GrTextureParamsAdjuster.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 "GrTextureParamsAdjuster.h"
 
 #include "GrCaps.h"
@@ skipping 54 matching lines @@
 
     SkAutoTUnref<GrTexture> copy(context->textureProvider()->createTexture(rtDesc,
                                                                            SkBudgeted::kYes));
     if (!copy) {
         return nullptr;
     }
 
     // TODO: If no scaling is being performed then use copySurface.
 
     GrPaint paint;
+    paint.setGammaCorrect(true);

[egdaniel, 2016/05/11 22:04:46]

so you have no conditional around this, so we always want to setGammaCorrect for
true here. If we want all our copies to be gamma correct is this also true for
generic GrPaints? If so why do we need to set this instead of it just being an
implicit property.

[Brian Osman, 2016/05/12 01:01:35]

This sets two flags on the paint (one that basically allows sRGB inputs, and one
for sRGB output). Normally, those are configured from the drawContext when we
convert an SkPaint to GrPaint. I made the defaults be as "safe" as possible,
such that we would never accidentally break "Legacy" mode (and we would have to
opt-in to being gamma-correct as we discovered locations where it's necessary).
In other places, it could alter the outcome and produce different results.

Here, we're really just copying a texture to another texture with the same
format, so as long as the paint causes the resulting draw operation to be
equivalent to a memcpy, we're good. Unfortunately, the default values on GrPaint
don't do that (allowSRGBInputs is false, so we don't accidentally decode an sRGB
texture in the legacy pipeline, but allowSRGBOutput is true, because you want
that 99.9% of the time, and it's not "dangerous" to the legacy pipeline - it
only affects sRGB render targets which are - by definition - gamma correct).

 
     // TODO: Initializing these values for no reason cause the compiler is complaining
     SkScalar sx = 0.f;
     SkScalar sy = 0.f;
     if (subset) {
         sx = 1.f / inputTexture->width();
         sy = 1.f / inputTexture->height();
     }
 
     if (copyParams.fFilter != GrTextureParams::kNone_FilterMode && subset &&
@@ skipping 421 matching lines @@
 }
 
 GrTexture* GrTextureMaker::generateTextureForParams(const CopyParams& copyParams,
                                                     bool willBeMipped) {
     SkAutoTUnref<GrTexture> original(this->refOriginalTexture(willBeMipped));
     if (!original) {
         return nullptr;
     }
     return copy_on_gpu(original, nullptr, copyParams);
 }