Fix elliptical rrect clip shaders for large radii on devices with mediump

src/gpu/effects/GrRRectEffect.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrRRectEffect.h"
 
 #include "GrConvexPolyEffect.h"
@@ skipping 491 matching lines @@
     GrGLFragmentBuilder* fsBuilder = args.fBuilder->getFragmentShaderBuilder();
     const char* fragmentPos = fsBuilder->fragmentPosition();
     // At each quarter-ellipse corner we compute a vector that is the offset of the fragment pos
     // to the ellipse center. The vector is pinned in x and y to be in the quarter-plane relevant
     // to that corner. This means that points near the interior near the rrect top edge will have
     // a vector that points straight up for both the TL left and TR corners. Computing an
     // alpha from this vector at either the TR or TL corner will give the correct result. Similarly,
     // fragments near the other three edges will get the correct AA. Fragments in the interior of
     // the rrect will have a (0,0) vector at all four corners. So long as the radii > 0.5 they will
     // correctly produce an alpha value of 1 at all four corners. We take the min of all the alphas.
+    //
     // The code below is a simplified version of the above that performs maxs on the vector
     // components before computing distances and alpha values so that only one distance computation
     // need be computed to determine the min alpha.
     fsBuilder->codeAppendf("\t\tvec2 dxy0 = %s.xy - %s.xy;\n", rectName, fragmentPos);
     fsBuilder->codeAppendf("\t\tvec2 dxy1 = %s.xy - %s.zw;\n", fragmentPos, rectName);
+    // The uniforms with the inv squared radii are highp to prevent underflow.
     switch (erre.getRRect().getType()) {
         case SkRRect::kSimple_Type: {
             const char *invRadiiXYSqdName;
             fInvRadiiSqdUniform = args.fBuilder->addUniform(GrGLProgramBuilder::kFragment_Visibility,
-                                                      kVec2f_GrSLType, kDefault_GrSLPrecision,
+                                                      kVec2f_GrSLType, kHigh_GrSLPrecision,
                                                       "invRadiiXY",
                                                       &invRadiiXYSqdName);
             fsBuilder->codeAppend("\t\tvec2 dxy = max(max(dxy0, dxy1), 0.0);\n");
             // Z is the x/y offsets divided by squared radii.
             fsBuilder->codeAppendf("\t\tvec2 Z = dxy * %s;\n", invRadiiXYSqdName);
             break;
         }
         case SkRRect::kNinePatch_Type: {
             const char *invRadiiLTRBSqdName;
             fInvRadiiSqdUniform = args.fBuilder->addUniform(GrGLProgramBuilder::kFragment_Visibility,
-                                                      kVec4f_GrSLType, kDefault_GrSLPrecision,
+                                                      kVec4f_GrSLType, kHigh_GrSLPrecision,
                                                       "invRadiiLTRB",
                                                       &invRadiiLTRBSqdName);
             fsBuilder->codeAppend("\t\tvec2 dxy = max(max(dxy0, dxy1), 0.0);\n");
             // Z is the x/y offsets divided by squared radii. We only care about the (at most) one
             // corner where both the x and y offsets are positive, hence the maxes. (The inverse
             // squared radii will always be positive.)
             fsBuilder->codeAppendf("\t\tvec2 Z = max(max(dxy0 * %s.xy, dxy1 * %s.zw), 0.0);\n",
                                    invRadiiLTRBSqdName, invRadiiLTRBSqdName);
             break;
         }
@@ skipping 164 matching lines @@
                 if (rrect.isNinePatch()) {
                     return EllipticalRRectEffect::Create(edgeType, rrect);
                 }
                 return NULL;
             }
         }
     }
 
     return NULL;
 }