fix general-pespective for conical gradient bug=1744

src/effects/gradients/SkTwoPointConicalGradient.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 "SkTwoPointConicalGradient.h"
 
 static int valid_divide(float numer, float denom, float* ratio) {
@@ skipping 218 matching lines @@
             dy = SkFixedToScalar(fixedY);
         } else {
             SkASSERT(fDstToIndexClass == kLinear_MatrixClass);
             dx = fDstToIndex.getScaleX();
             dy = fDstToIndex.getSkewY();
         }
 
         fRec.setup(fx, fy, dx, dy);
         (*shadeProc)(&fRec, dstC, cache, toggle, count);
     } else {    // perspective case
-        SkScalar dstX = SkIntToScalar(x);
-        SkScalar dstY = SkIntToScalar(y);
+        SkScalar dstX = SkIntToScalar(x) + SK_ScalarHalf;
+        SkScalar dstY = SkIntToScalar(y) + SK_ScalarHalf;
         for (; count > 0; --count) {
             SkPoint srcPt;
             dstProc(fDstToIndex, dstX, dstY, &srcPt);
-            dstX += SK_Scalar1;
-
             fRec.setup(srcPt.fX, srcPt.fY, 0, 0);
             (*shadeProc)(&fRec, dstC, cache, toggle, 1);
+
+            dstX += SK_Scalar1;
             toggle = next_dither_toggle(toggle);
+            dstC += 1;
         }
     }
 }
 
 bool SkTwoPointConicalGradient::setContext(const SkBitmap& device,
                                            const SkPaint& paint,
                                            const SkMatrix& matrix) {
     if (!this->INHERITED::setContext(device, paint, matrix)) {
         return false;
     }
@@ skipping 468 matching lines @@
     str->appendScalar(fCenter2.fY);
     str->append(") radius2: ");
     str->appendScalar(fRadius2);
     str->append(" ");
 
     this->INHERITED::toString(str);
 
     str->append(")");
 }
 #endif