image/png: tRNS chunk is *non*-alpha-premultiplied.

R=r
CC=golang-dev
https://golang.org/cl/6446062

diff --git a/src/pkg/image/png/reader.go b/src/pkg/image/png/reader.go
index 6962926c8a39d517fb853d2fc4baa45c8bf798ff..b3901b2adf944e62b203de9d5781745c7bc2f50c 100644 (file)
--- a/src/pkg/image/png/reader.go
+++ b/src/pkg/image/png/reader.go
@@ -226,7 +226,7 @@ func (d *decoder) parsetRNS(length uint32) error {
                }
                for i := 0; i < n; i++ {
                        rgba := d.palette[i].(color.RGBA)
-                       d.palette[i] = color.RGBA{rgba.R, rgba.G, rgba.B, d.tmp[i]}
+                       d.palette[i] = color.NRGBA{rgba.R, rgba.G, rgba.B, d.tmp[i]}
                }
        case cbGA8, cbGA16, cbTCA8, cbTCA16:
                return FormatError("tRNS, color type mismatch")

diff --git a/src/pkg/image/png/reader_test.go b/src/pkg/image/png/reader_test.go
index 0d8c1d9cb9a0f3582a72e8723a89805c105a4822..8223f521cc377bc412c56029703d54b55dfeb6ac 100644 (file)
--- a/src/pkg/image/png/reader_test.go
+++ b/src/pkg/image/png/reader_test.go
@@ -107,13 +107,18 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
                lastAlpha := -1
                io.WriteString(w, "PLTE {\n")
                for i, c := range cpm {
-                       r, g, b, a := c.RGBA()
-                       if a != 0xffff {
+                       var r, g, b, a uint8
+                       switch c := c.(type) {
+                       case color.RGBA:
+                               r, g, b, a = c.R, c.G, c.B, 0xff
+                       case color.NRGBA:
+                               r, g, b, a = c.R, c.G, c.B, c.A
+                       default:
+                               panic("unknown palette color type")
+                       }
+                       if a != 0xff {
                                lastAlpha = i
                        }
-                       r >>= 8
-                       g >>= 8
-                       b >>= 8
                        fmt.Fprintf(w, "    (%3d,%3d,%3d)     # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
                }
                io.WriteString(w, "}\n")

diff --git a/src/pkg/image/png/writer.go b/src/pkg/image/png/writer.go
index 57c03792b59dc835969f9421d66ff8e3fdc8d107..88683a937b4e291139d6db54d3b56b436be3c485 100644 (file)
--- a/src/pkg/image/png/writer.go
+++ b/src/pkg/image/png/writer.go
@@ -21,7 +21,7 @@ type encoder struct {
        err    error
        header [8]byte
        footer [4]byte
-       tmp    [3 * 256]byte
+       tmp    [4 * 256]byte
 }
 
 // Big-endian.
@@ -70,7 +70,7 @@ func (e *encoder) writeChunk(b []byte, name string) {
                e.err = UnsupportedError(name + " chunk is too large: " + strconv.Itoa(len(b)))
                return
        }
-       writeUint32(e.header[0:4], n)
+       writeUint32(e.header[:4], n)
        e.header[4] = name[0]
        e.header[5] = name[1]
        e.header[6] = name[2]
@@ -78,9 +78,9 @@ func (e *encoder) writeChunk(b []byte, name string) {
        crc := crc32.NewIEEE()
        crc.Write(e.header[4:8])
        crc.Write(b)
-       writeUint32(e.footer[0:4], crc.Sum32())
+       writeUint32(e.footer[:4], crc.Sum32())
 
-       _, e.err = e.w.Write(e.header[0:8])
+       _, e.err = e.w.Write(e.header[:8])
        if e.err != nil {
                return
        }
@@ -88,7 +88,7 @@ func (e *encoder) writeChunk(b []byte, name string) {
        if e.err != nil {
                return
        }
-       _, e.err = e.w.Write(e.footer[0:4])
+       _, e.err = e.w.Write(e.footer[:4])
 }
 
 func (e *encoder) writeIHDR() {
@@ -122,36 +122,29 @@ func (e *encoder) writeIHDR() {
        e.tmp[10] = 0 // default compression method
        e.tmp[11] = 0 // default filter method
        e.tmp[12] = 0 // non-interlaced
-       e.writeChunk(e.tmp[0:13], "IHDR")
+       e.writeChunk(e.tmp[:13], "IHDR")
 }
 
-func (e *encoder) writePLTE(p color.Palette) {
+func (e *encoder) writePLTEAndTRNS(p color.Palette) {
        if len(p) < 1 || len(p) > 256 {
                e.err = FormatError("bad palette length: " + strconv.Itoa(len(p)))
                return
        }
-       for i, c := range p {
-               r, g, b, _ := c.RGBA()
-               e.tmp[3*i+0] = uint8(r >> 8)
-               e.tmp[3*i+1] = uint8(g >> 8)
-               e.tmp[3*i+2] = uint8(b >> 8)
-       }
-       e.writeChunk(e.tmp[0:3*len(p)], "PLTE")
-}
-
-func (e *encoder) maybeWritetRNS(p color.Palette) {
        last := -1
        for i, c := range p {
-               _, _, _, a := c.RGBA()
-               if a != 0xffff {
+               c1 := color.NRGBAModel.Convert(c).(color.NRGBA)
+               e.tmp[3*i+0] = c1.R
+               e.tmp[3*i+1] = c1.G
+               e.tmp[3*i+2] = c1.B
+               if c1.A != 0xff {
                        last = i
                }
-               e.tmp[i] = uint8(a >> 8)
+               e.tmp[3*256+i] = c1.A
        }
-       if last == -1 {
-               return
+       e.writeChunk(e.tmp[:3*len(p)], "PLTE")
+       if last != -1 {
+               e.writeChunk(e.tmp[3*256:3*256+1+last], "tRNS")
        }
-       e.writeChunk(e.tmp[:last+1], "tRNS")
 }
 
 // An encoder is an io.Writer that satisfies writes by writing PNG IDAT chunks,
@@ -412,7 +405,7 @@ func (e *encoder) writeIDATs() {
        e.err = bw.Flush()
 }
 
-func (e *encoder) writeIEND() { e.writeChunk(e.tmp[0:0], "IEND") }
+func (e *encoder) writeIEND() { e.writeChunk(nil, "IEND") }
 
 // Encode writes the Image m to w in PNG format. Any Image may be encoded, but
 // images that are not image.NRGBA might be encoded lossily.
@@ -460,8 +453,7 @@ func Encode(w io.Writer, m image.Image) error {
        _, e.err = io.WriteString(w, pngHeader)
        e.writeIHDR()
        if pal != nil {
-               e.writePLTE(pal)
-               e.maybeWritetRNS(pal)
+               e.writePLTEAndTRNS(pal)
        }
        e.writeIDATs()
        e.writeIEND()