fix general-pespective for conical gradient bug=1744

src/effects/gradients/SkTwoPointConicalGradient.cpp

Index: src/effects/gradients/SkTwoPointConicalGradient.cpp
diff --git a/src/effects/gradients/SkTwoPointConicalGradient.cpp b/src/effects/gradients/SkTwoPointConicalGradient.cpp
index 2a822e48292108ce7f31380ed9fc631923ba1715..a9bd1c276274f1ba952f8fd544e6fefb1f6f6190 100644
--- a/src/effects/gradients/SkTwoPointConicalGradient.cpp
+++ b/src/effects/gradients/SkTwoPointConicalGradient.cpp
@@ -236,16 +236,17 @@ void SkTwoPointConicalGradient::shadeSpan(int x, int y, SkPMColor* dstCParam,
         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;
         }
     }
 }