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, 14 insertions, 0 deletions

diff --git a/include/core/SkColorSpace.h b/include/core/SkColorSpace.h
index 5b2d86b175..962253243d 100644
--- a/include/core/SkColorSpace.h
+++ b/include/core/SkColorSpace.h
@@ -54,6 +54,20 @@ struct SK_API SkColorSpaceTransferFn {
      * this one.
      */
     SkColorSpaceTransferFn invert() const;
+
+    /**
+     * Transform a single float by this transfer function.
+     * For negative inputs, returns sign(x) * f(abs(x)).
+     */
+    float operator()(float x) {
+        SkScalar s = SkScalarSignAsScalar(x);
+        x = sk_float_abs(x);
+        if (x >= fD) {
+            return s * (powf(fA * x + fB, fG) + fE);
+        } else {
+            return s * (fC * x + fF);
+        }
+    }
 };
 
 class SK_API SkColorSpace : public SkRefCnt {