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(centerEndTrans.length() - (radiusEnd - 1)) < kEdgeErrorTol) {
         return kEdge_ConicalType;
     }
 
     SkScalar C = 1.f / A;
     SkScalar B = (radiusEnd - 1.f) * C;
 
     matrix.postScale(C, C);
 
     invLMatrix->postConcat(matrix);
 
@@ skipping 111 matching lines @@
     SkPoint center1 = {random->nextUScalar1(), random->nextUScalar1()};
     SkScalar radius1 = random->nextUScalar1() + 0.0001f; // make sure radius1 != 0
     SkPoint center2;
     SkScalar radius2;
     do {
         center2.set(random->nextUScalar1(), random->nextUScalar1());
         // Below makes sure that circle one is contained within circle two
         SkScalar increase = random->nextUScalar1();
         SkPoint diff = center2 - center1;
         SkScalar diffLen = diff.length();
         radius2 = radius1 + diffLen + increase;

[egdaniel, 2014/09/22 14:57:01]

radius2 = radius1 + diffLen + increase + radius1 * kEdgeErrorTol;

         // If the circles are identical the factory will give us an empty shader.
     } while (radius1 == radius2 && center1 == center2);
 
     SkColor colors[kMaxRandomGradientColors];
     SkScalar stopsArray[kMaxRandomGradientColors];
     SkScalar* stops = stopsArray;
     SkShader::TileMode tm;
     int colorCount = RandomGradientParams(random, colors, &stops, &tm);
     SkAutoTUnref<SkShader> shader(SkGradientShader::CreateTwoPointConical(center1, radius1,
                                                                           center2, radius2,
@@ skipping 214 matching lines @@
     SkScalar radius2;
     SkScalar diffLen;
     do {
         center2.set(random->nextUScalar1(), random->nextUScalar1());
         // If the circles share a center than we can't be in the outside case
     } while (center1 == center2);
         SkPoint diff = center2 - center1;
         diffLen = diff.length();
         // Below makes sure that circle one is not contained within circle two
         // and have radius2 >= radius to match sorting on cpu side
         radius2 = radius1 + random->nextRangeF(0.f, diffLen);

[egdaniel, 2014/09/22 14:57:01]

can we change this to:

radius2 = radius1 + random->nextRangeF(0.f, diffLen - radius1 * kEdgeErrorTol);

This way we can never create an edge case during our outside test create.

 
     SkColor colors[kMaxRandomGradientColors];
     SkScalar stopsArray[kMaxRandomGradientColors];
     SkScalar* stops = stopsArray;
     SkShader::TileMode tm;
     int colorCount = RandomGradientParams(random, colors, &stops, &tm);
     SkAutoTUnref<SkShader> shader(SkGradientShader::CreateTwoPointConical(center1, radius1,
                                                                           center2, radius2,
                                                                           colors, stops, colorCount,
                                                                           tm));
@@ skipping 151 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