Temporarily allow linear interpolation of 2-color vertical gradients to be

turned off. With a Chromium gyp change to add
SK_SIMPLE_TWOCOLOR_VERTICAL_GRADIENTS, this reduces the rebaselining from
r3073 from ~200 to ~20.

codereview.appspot.com/5558055/

git-svn-id: http://skia.googlecode.com/svn/trunk@3077 2bbb7eff-a529-9590-31e7-b0007b416f81

diff --git a/src/effects/SkGradientShader.cpp b/src/effects/SkGradientShader.cpp
index 8c6bcfb..240a7a4 100644 (file)
--- a/src/effects/SkGradientShader.cpp
+++ b/src/effects/SkGradientShader.cpp
@@ -896,9 +896,26 @@ typedef void (*LinearShadeProc)(TileProc proc, SkFixed dx, SkFixed fx,
                                 SkPMColor* dstC, const SkPMColor* cache,
                                 int toggle, int count);
 
-// lerp is unnecessary if there are no sharp discontinuities in the
-// gradient - which must be true if there are only 2 colors - but for
-// vertical gradients it's so cheap we do it anyway.
+// This function is deprecated, and will be replaced by 
+// shadeSpan_linear_vertical_lerp() once Chrome has been weaned off of it.
+void shadeSpan_linear_vertical(TileProc proc, SkFixed dx, SkFixed fx,
+                               SkPMColor* SK_RESTRICT dstC,
+                               const SkPMColor* SK_RESTRICT cache,
+                               int toggle, int count) {
+    // We're a vertical gradient, so no change in a span.
+    // If colors change sharply across the gradient, dithering is
+    // insufficient (it subsamples the color space) and we need to lerp.
+    unsigned fullIndex = proc(fx);
+    unsigned fi = fullIndex >> (16 - Gradient_Shader::kCache32Bits);
+    sk_memset32_dither(dstC,
+            cache[toggle + fi],
+            cache[(toggle ^ Gradient_Shader::kDitherStride32) + fi],
+            count);
+}
+
+// Linear interpolation (lerp) is unnecessary if there are no sharp
+// discontinuities in the gradient - which must be true if there are
+// only 2 colors - but it's cheap.
 void shadeSpan_linear_vertical_lerp(TileProc proc, SkFixed dx, SkFixed fx,
                                     SkPMColor* SK_RESTRICT dstC,
                                     const SkPMColor* SK_RESTRICT cache,
@@ -1015,7 +1032,15 @@ void Linear_Gradient::shadeSpan(int x, int y, SkPMColor* SK_RESTRICT dstC,
 
         LinearShadeProc shadeProc = shadeSpan_linear_repeat;
         if (SkFixedNearlyZero(dx)) {
+#ifdef SK_SIMPLE_TWOCOLOR_VERTICAL_GRADIENTS
+            if (fColorCount > 2) {
+                shadeProc = shadeSpan_linear_vertical_lerp;
+            } else {
+                shadeProc = shadeSpan_linear_vertical;
+            }
+#else
             shadeProc = shadeSpan_linear_vertical_lerp;
+#endif
         } else if (proc == clamp_tileproc) {
             shadeProc = shadeSpan_linear_clamp;
         } else if (proc == mirror_tileproc) {