Tiling support for GrGradientEffect kTwo_ColorType/kThree_ColorType

(re-land of https://skia-review.googlesource.com/c/30780)

Currently only the hard-stop specializations support tiling.

Consolidate the tiling code and expand to kTwo_ColorType,
kThree_ColorType also.

BUG=6925
Change-Id: I017b4accba30e87367e139333e96246cb362b6a4
Reviewed-on: https://skia-review.googlesource.com/31422
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index 6ca9d632ee..04559c3dbd 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -892,10 +892,14 @@ void GrGLCaps::initGLSL(const GrGLContextInfo& ctxInfo) {
         shaderCaps->fVertexIDSupport = ctxInfo.glslGeneration() >= k330_GrGLSLGeneration;
     }
 
-    // The Tegra3 compiler will sometimes never return if we have min(abs(x), 1.0), so we must do
-    // the abs first in a separate expression.
     if (kTegra3_GrGLRenderer == ctxInfo.renderer()) {
+        // The Tegra3 compiler will sometimes never return if we have min(abs(x), 1.0),
+        // so we must do the abs first in a separate expression.
         shaderCaps->fCanUseMinAndAbsTogether = false;
+
+        // Tegra3 fract() seems to trigger undefined behavior for negative values, so we
+        // must avoid this condition.
+        shaderCaps->fCanUseFractForNegativeValues = false;
     }
 
     // On Intel GPU there is an issue where it reads the second argument to atan "- %s.x" as an int