Fix alpha computation in SkArithmeticMode.

Note: this will require new baselines for the arithmode GM.

R=reed@google.com

Review URL: https://codereview.chromium.org/15917010

git-svn-id: http://skia.googlecode.com/svn/trunk@9302 2bbb7eff-a529-9590-31e7-b0007b416f81

diff --git a/gm/arithmode.cpp b/gm/arithmode.cpp
index f5e1091..2a97eca 100644 (file)
--- a/gm/arithmode.cpp
+++ b/gm/arithmode.cpp
@@ -29,8 +29,8 @@ static SkBitmap make_src() {
     SkPaint paint;
     SkPoint pts[] = { {0, 0}, {SkIntToScalar(WW), SkIntToScalar(HH)} };
     SkColor colors[] = {
-        SK_ColorBLACK, SK_ColorGREEN, SK_ColorCYAN,
-        SK_ColorRED, SK_ColorMAGENTA, SK_ColorWHITE
+        SK_ColorTRANSPARENT, SK_ColorGREEN, SK_ColorCYAN,
+        SK_ColorRED, SK_ColorMAGENTA, SK_ColorWHITE,
     };
     SkShader* s = SkGradientShader::CreateLinear(pts, colors, NULL, SK_ARRAY_COUNT(colors),
                                                  SkShader::kClamp_TileMode);

diff --git a/src/effects/SkArithmeticMode.cpp b/src/effects/SkArithmeticMode.cpp
index 7492cce..5bc48f1 100644 (file)
--- a/src/effects/SkArithmeticMode.cpp
+++ b/src/effects/SkArithmeticMode.cpp
@@ -73,12 +73,12 @@ void SkArithmeticMode_scalar::xfer32(SkPMColor dst[], const SkPMColor src[],
             int da = SkGetPackedA32(dc);
 
             int srcNeedsUnpremul = needsUnpremul(sa);
-            int dstNeedsUnpremul = needsUnpremul(sa);
+            int dstNeedsUnpremul = needsUnpremul(da);
 
             int a, r, g, b;
 
             if (!srcNeedsUnpremul && !dstNeedsUnpremul) {
-                a = arith(k1, k2, k3, k4, sa, sa);
+                a = arith(k1, k2, k3, k4, sa, da);
                 r = arith(k1, k2, k3, k4, SkGetPackedR32(sc), SkGetPackedR32(dc));
                 g = arith(k1, k2, k3, k4, SkGetPackedG32(sc), SkGetPackedG32(dc));
                 b = arith(k1, k2, k3, k4, SkGetPackedB32(sc), SkGetPackedB32(dc));
@@ -103,7 +103,7 @@ void SkArithmeticMode_scalar::xfer32(SkPMColor dst[], const SkPMColor src[],
                     db = SkUnPreMultiply::ApplyScale(scale, db);
                 }
 
-                a = arith(k1, k2, k3, k4, sa, sa);
+                a = arith(k1, k2, k3, k4, sa, da);
                 r = arith(k1, k2, k3, k4, sr, dr);
                 g = arith(k1, k2, k3, k4, sg, dg);
                 b = arith(k1, k2, k3, k4, sb, db);