Increase precision in GrSRGBEffect

Allows ApplyGammaTest to pass on Bifrost, which uses fp16 for mediump.

Change-Id: Icd04001939a2cb7e1789132ab035ca498c92112a
Reviewed-on: https://skia-review.googlesource.com/118162
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/src/gpu/effects/GrSRGBEffect.cpp b/src/gpu/effects/GrSRGBEffect.cpp
index 7e823eaae7..6ca975919d 100644
--- a/src/gpu/effects/GrSRGBEffect.cpp
+++ b/src/gpu/effects/GrSRGBEffect.cpp
@@ -47,7 +47,9 @@ public:
             args.fInputColor = "half4(1)";
         }
 
-        fragBuilder->codeAppendf("half4 color = %s;", args.fInputColor);
+        // Mali Bifrost uses fp16 for mediump. Making the intermediate color variable highp causes
+        // calculations to be performed with sufficient precision.
+        fragBuilder->codeAppendf("float4 color = %s;", args.fInputColor);
         if (srgbe.alpha() == GrSRGBEffect::Alpha::kPremul) {
             fragBuilder->codeAppendf("half nonZeroAlpha = max(color.a, 0.00001);");
             fragBuilder->codeAppendf("color = half4(color.rgb / nonZeroAlpha, color.a);");