From: Nigel Tao <nigeltao@golang.org>
Date: Sun, 1 Aug 2010 23:52:15 +0000 (+1000)
Subject: image/png: use image-specific methods for checking opacity.
X-Git-Tag: weekly.2010-08-04~34
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=55badd474b628de0c6c2144fe925eded1c7652b3;p=gostls13.git

image/png: use image-specific methods for checking opacity.

R=rsc
CC=golang-dev, mpl
https://golang.org/cl/1894047
---

diff --git a/src/pkg/image/png/writer.go b/src/pkg/image/png/writer.go
index e186ca819b..323e66f114 100644
--- a/src/pkg/image/png/writer.go
+++ b/src/pkg/image/png/writer.go
@@ -32,8 +32,15 @@ func writeUint32(b []uint8, u uint32) {
 	b[3] = uint8(u >> 0)
 }
 
+type opaquer interface {
+	Opaque() bool
+}
+
 // Returns whether or not the image is fully opaque.
 func opaque(m image.Image) bool {
+	if o, ok := m.(opaquer); ok {
+		return o.Opaque()
+	}
 	for y := 0; y < m.Height(); y++ {
 		for x := 0; x < m.Width(); x++ {
 			_, _, _, a := m.At(x, y).RGBA()