Fix SkRadialGradient center discontinuity

src/effects/gradients/SkRadialGradient.cpp

 
 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkRadialGradient.h"
 #include "SkNx.h"
@@ skipping 93 matching lines @@
 void shadeSpan_radial_clamp2(SkScalar sfx, SkScalar sdx, SkScalar sfy, SkScalar sdy,
                              SkPMColor* SK_RESTRICT dstC, const SkPMColor* SK_RESTRICT cache,
                              int count, int toggle) {
     if (radial_completely_pinned(sfx, sdx, sfy, sdy)) {
         unsigned fi = SkGradientShaderBase::kCache32Count - 1;
         sk_memset32_dither(dstC,
                            cache[toggle + fi],
                            cache[next_dither_toggle(toggle) + fi],
                            count);
     } else {
+        const Sk4f min(SK_ScalarNearlyZero);
         const Sk4f max(255);
         const float scale = 255;
         sfx *= scale;
         sfy *= scale;
         sdx *= scale;
         sdy *= scale;
         const Sk4f fx4(sfx, sfx + sdx, sfx + 2*sdx, sfx + 3*sdx);
         const Sk4f fy4(sfy, sfy + sdy, sfy + 2*sdy, sfy + 3*sdy);
         const Sk4f dx4(sdx * 4);
         const Sk4f dy4(sdy * 4);
 
         Sk4f tmpxy = fx4 * dx4 + fy4 * dy4;
         Sk4f tmpdxdy = sum_squares(dx4, dy4);
-        Sk4f R = sum_squares(fx4, fy4);
+        Sk4f R = Sk4f::Max(sum_squares(fx4, fy4), min);
         Sk4f dR = tmpxy + tmpxy + tmpdxdy;
         const Sk4f ddR = tmpdxdy + tmpdxdy;
 
         for (int i = 0; i < (count >> 2); ++i) {
             Sk4f dist = Sk4f::Min(fast_sqrt(R), max);
-            R = R + dR;
+            R = Sk4f::Max(R + dR, min);
             dR = dR + ddR;
 
             uint8_t fi[4];
             SkNx_cast<uint8_t>(dist).store(fi);
 
             for (int i = 0; i < 4; i++) {
                 *dstC++ = cache[toggle + fi[i]];
                 toggle = next_dither_toggle(toggle);
             }
         }
@@ skipping 232 matching lines @@
     str->appendScalar(fCenter.fY);
     str->append(") radius: ");
     str->appendScalar(fRadius);
     str->append(" ");
 
     this->INHERITED::toString(str);
 
     str->append(")");
 }
 #endif