improve precision of gradients

src/effects/gradients/SkClampRange.h

Index: src/effects/gradients/SkClampRange.h
diff --git a/src/effects/gradients/SkClampRange.h b/src/effects/gradients/SkClampRange.h
index 09386d7e71bb7e9bf37c2eaede1f83885e35463f..a71009d65436aa72d82a3c2f3a88ea5faf29da00 100644
--- a/src/effects/gradients/SkClampRange.h
+++ b/src/effects/gradients/SkClampRange.h
@@ -1,4 +1,3 @@
-
 /*
  * Copyright 2011 Google Inc.
  *
@@ -6,14 +5,30 @@
  * found in the LICENSE file.
  */
 
-
 #ifndef SkClampRange_DEFINED
 #define SkClampRange_DEFINED
 
 #include "SkFixed.h"
+#include "SkScalar.h"
+
+#define SK_SUPPORT_LEGACY_GRADIENT_PRECISION
+
+#ifdef SK_SUPPORT_LEGACY_GRADIENT_PRECISION
+    #define SkGradFixed             SkFixed
+    #define SkScalarToGradFixed     SkScalarToFixed
+    #define SkFixedToGradFixed(x)   (x)
+    #define SkGradFixedToFixed(x)   (x)
+    #define kFracMax_SkGradFixed    0xFFFF
+#else
+    #define SkGradFixed             SkFixed3232
+    #define SkScalarToGradFixed     SkScalarToFixed3232
+    #define SkFixedToGradFixed      SkFixedToFixed3232
+    #define SkGradFixedToFixed(x)   (SkFixed)((x) >> 16)
+    #define kFracMax_SkGradFixed    0xFFFFFFFFLL
+#endif
 
 /**
- *  Iteration fixed fx by dx, clamping as you go to [0..0xFFFF], this class
+ *  Iteration fixed fx by dx, clamping as you go to [0..kFracMax_SkGradFixed], this class
  *  computes the (up to) 3 spans there are:
  *
  *  range0: use constant value V0
@@ -24,14 +39,14 @@ struct SkClampRange {
     int fCount0;    // count for fV0
     int fCount1;    // count for interpolating (fV0...fV1)
     int fCount2;    // count for fV1
-    SkFixed fFx1;   // initial fx value for the fCount1 range.
+    SkGradFixed fFx1;   // initial fx value for the fCount1 range.
                     // only valid if fCount1 > 0
     int fV0, fV1;
 
-    void init(SkFixed fx, SkFixed dx, int count, int v0, int v1);
+    void init(SkGradFixed fx, SkGradFixed dx, int count, int v0, int v1);
 
 private:
-    void initFor1(SkFixed fx);
+    void initFor1(SkGradFixed fx);
 };
 
 #endif