Add support for transfer functions to GrColorSpaceXform

With this change, untagged sources (eg N32) are treated as
sRGB data, which causes a huge number of GMs to render more
correctly in GPU sRGB/F16/etc... configs. Also, because the
sources are treated as having a color space, we actually do
gamut conversion for wide or narrow gamut outputs.

This change also applies the transfer function math to
individual colors in the case of gradient stops and color
shaders. (The CPU backend doesn't do this yet, but I think
we've decided there's no reason not to support it).

Bug: skia:
Change-Id: If76e9e4a268f9f74110ff4bbe4fe189ba5d19d9f
Reviewed-on: https://skia-review.googlesource.com/64100
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/shaders/gradients/SkGradientShader.cpp b/src/shaders/gradients/SkGradientShader.cpp
index 7d31e50f84..279491b177 100644
--- a/src/shaders/gradients/SkGradientShader.cpp
+++ b/src/shaders/gradients/SkGradientShader.cpp
@@ -184,6 +184,7 @@ SkGradientShaderBase::SkGradientShaderBase(const Descriptor& desc, const SkMatri
         fColorSpace = SkColorSpace::MakeSRGBLinear();
     } else {
         // The color space refers to the float colors, so it must be linear gamma
+        // TODO: GPU code no longer requires this (see GrGradientEffect). Remove this restriction?
         SkASSERT(desc.fColorSpace->gammaIsLinear());
         fColorSpace = desc.fColorSpace;
     }
@@ -1260,8 +1261,11 @@ GrGradientEffect::GrGradientEffect(ClassID classID, const CreateArgs& args, bool
             fPremulType = kAfterInterp_PremulType;
         }
 
-        // Convert input colors to GrColor4f, possibly premul, and apply color space xform
+        // Convert input colors to GrColor4f, possibly premul, and apply color space xform.
+        // The xform is constructed assuming floats as input, but the color space can have a
+        // transfer function on it, which will be applied below.
         auto colorSpaceXform = GrColorSpaceXform::Make(shader.fColorSpace.get(),
+                                                       kRGBA_float_GrPixelConfig,
                                                        args.fDstColorSpace);
         SkASSERT(shader.fOrigColors && shader.fOrigColors4f);
         fColors4f.setCount(shader.fColorCount);