Analytic AntiAlias for Convex Shapes

include/private/SkFixed.h

Index: include/private/SkFixed.h
diff --git a/include/private/SkFixed.h b/include/private/SkFixed.h
index be3bb5d6045d9b24fd98096295b3385be409d5d3..083d02394176e92647189be4c1d4f2efbcb9bdd9 100644
--- a/include/private/SkFixed.h
+++ b/include/private/SkFixed.h
@@ -88,6 +88,10 @@ inline SkFixed SkFixedMul_longlong(SkFixed a, SkFixed b) {
 }
 #define SkFixedMul(a,b)     SkFixedMul_longlong(a,b)
 
+inline SkFixed SkFixedMul_lowprec(SkFixed a, SkFixed b) {

[reed1, 2016/08/18 20:31:00]

is this referenced from several files? wondering if we need to add it to this
shared header.

Also, can we add asserts that it never overflows?

e.g.
    if debug mode, compute the answer as int64_t and assert that that fits in
32bits

[liyuqian, 2016/08/22 15:30:48]

It's used in SkEdge.h, SkEdge.cpp (SkAnalyticEdge.cpp in the future), and
SkScan_AAAPath.cpp. I can move it SkEdge.h which is private. I'll also add the
overflow check.

+    return (a >> 8) * (b >> 8);
+}
+
 
 #if defined(SK_CPU_ARM32)
     /* This guy does not handle NaN or other obscurities, but is faster than