commit 4ffbc6172403ee38fc70608377ce78c9db00394a
author Mike Reed <reed@google.com> Fri Mar 12 14:22:51 2010 -0500
committer Mike Reed <reed@google.com> Fri Mar 12 14:22:51 2010 -0500
tree d04eb3706773a2a56e58d8942a35e3915fd02e9a
parent d7d0da62bf31ccc5550f526fc10c01cd24f81af9

improve precision of blend

fixes http://b/issue?id=2136225

Change-Id: Ifa01a04406e1b53ffbd12a29a81445eeb60f0e60

src/effects/SkAvoidXfermode.cpp

diff --git a/src/effects/SkAvoidXfermode.cpp b/src/effects/SkAvoidXfermode.cpp
index d26039c..97bfeae 100644
--- a/src/effects/SkAvoidXfermode.cpp
+++ b/src/effects/SkAvoidXfermode.cpp
@@ -116,6 +116,10 @@
     return SkPackARGB32(a, r, g, b);
 }
 
+static inline unsigned Accurate255To256(unsigned x) {
+    return x + (x >> 7);
+}
+
 void SkAvoidXfermode::xfer32(SkPMColor dst[], const SkPMColor src[], int count,
                              const SkAlpha aa[])
 {
@@ -140,14 +144,14 @@
         // now reverse d if we need to
         d = MAX + (d ^ mask) - mask;
         SkASSERT((unsigned)d <= 255);
-        d = SkAlpha255To256(d);
+        d = Accurate255To256(d);
         
         d = scale_dist_14(d, mul, sub);
         SkASSERT(d <= 256);
         
         if (d > 0) {
             if (NULL != aa) {
-                d = SkAlphaMul(d, SkAlpha255To256(*aa++));
+                d = SkAlphaMul(d, Accurate255To256(*aa++));
                 if (0 == d) {
                     continue;
                 }
@@ -198,7 +202,7 @@
 
         if (d > 0) {
             if (NULL != aa) {
-                d = SkAlphaMul(d, SkAlpha255To256(*aa++));
+                d = SkAlphaMul(d, Accurate255To256(*aa++));
                 if (0 == d) {
                     continue;
                 }
@@ -239,7 +243,7 @@
         
         if (d > 0) {
             if (NULL != aa) {
-                d = SkAlphaMul(d, SkAlpha255To256(*aa++));
+                d = SkAlphaMul(d, Accurate255To256(*aa++));
                 if (0 == d) {
                     continue;
                 }