PNG decoder now handles transparent paletted images.

Fixes #439.

R=r
CC=golang-dev
https://golang.org/cl/181087

diff --git a/src/pkg/image/png/reader.go b/src/pkg/image/png/reader.go
index 9176524c92c38ab8438b93feed0a1fa744b319f4..5db125eb3bbab6f49e3e90632dfb14e8f59a9a81 100644 (file)
--- a/src/pkg/image/png/reader.go
+++ b/src/pkg/image/png/reader.go
@@ -164,6 +164,33 @@ func (d *decoder) parsePLTE(r io.Reader, crc hash.Hash32, length uint32) os.Erro
        return nil
 }
 
+func (d *decoder) parsetRNS(r io.Reader, crc hash.Hash32, length uint32) os.Error {
+       if length > 256 {
+               return FormatError("bad tRNS length")
+       }
+       n, err := io.ReadFull(r, d.tmp[0:length])
+       if err != nil {
+               return err
+       }
+       crc.Write(d.tmp[0:n])
+       switch d.colorType {
+       case ctTrueColor:
+               return UnsupportedError("TrueColor transparency")
+       case ctPaletted:
+               p := d.image.(*image.Paletted).Palette
+               if n > len(p) {
+                       return FormatError("bad tRNS length")
+               }
+               for i := 0; i < n; i++ {
+                       rgba := p[i].(image.RGBAColor)
+                       p[i] = image.RGBAColor{rgba.R, rgba.G, rgba.B, d.tmp[i]}
+               }
+       case ctTrueColorAlpha:
+               return FormatError("tRNS, color type mismatch")
+       }
+       return nil
+}
+
 // The Paeth filter function, as per the PNG specification.
 func paeth(a, b, c uint8) uint8 {
        p := int(a) + int(b) - int(c)
@@ -353,6 +380,11 @@ func (d *decoder) parseChunk(r io.Reader) os.Error {
                }
                d.stage = dsSeenPLTE
                err = d.parsePLTE(r, crc, length)
+       case "tRNS":
+               if d.stage != dsSeenPLTE {
+                       return chunkOrderError
+               }
+               err = d.parsetRNS(r, crc, length)
        case "IDAT":
                if d.stage < dsSeenIHDR || d.stage > dsSeenIDAT || (d.colorType == ctPaletted && d.stage == dsSeenIHDR) {
                        return chunkOrderError