Proposed fix for small bug in gpu conical gradients

src/effects/gradients/SkTwoPointConicalGradient_gpu.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 "SkTwoPointConicalGradient_gpu.h"
 
@@ skipping 767 matching lines @@
     matrix.mapPoints(&centerEndTrans, &centerEnd, 1);
 
     SkScalar A = centerEndTrans.fX * centerEndTrans.fX + centerEndTrans.fY * centerEndTrans.fY
                  - radiusEnd * radiusEnd + 2 * radiusEnd - 1;
 
     // Check to see if start circle is inside end circle with edges touching.
     // If touching we return that it is of kEdge_ConicalType, and leave the matrix setting
     // to the edge shader. kEdgeErrorTol = 5 * kErrorTol was picked after manual testing
     // so that C = 1 / A is stable, and the linear approximation used in the Edge shader is
     // still accurate.
-    if (SkScalarAbs(A) < kEdgeErrorTol) {
+    if (SkScalarAbs(SkScalarAbs(shader.getDiffRadius()) - shader.getCenterX1()) <

[egdaniel, 2014/09/22 13:59:35]

can we do "SkScalarAbs(||centerEndTrans|| - (radiusEnd -1)) < kErrorTol"?

It involves the exact same math as your version and we only have to worry about
the radius scaling of error in the shader instead of both places.

+            kEdgeErrorTol * shader.getStartRadius()) {
         return kEdge_ConicalType;
     }
 
     SkScalar C = 1.f / A;
     SkScalar B = (radiusEnd - 1.f) * C;
 
     matrix.postScale(C, C);
 
     invLMatrix->postConcat(matrix);
 
@@ skipping 518 matching lines @@
         return CircleInside2PtConicalEffect::Create(ctx, shader, matrix, tm, info);
     } else if (type == kEdge_ConicalType) {
         set_matrix_edge_conical(shader, &matrix);
         return Edge2PtConicalEffect::Create(ctx, shader, matrix, tm);
     } else {
         return CircleOutside2PtConicalEffect::Create(ctx, shader, matrix, tm, info);
     }
 }
 
 #endif