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Diffstat (limited to 'libgo/go/image/png/reader.go')
-rw-r--r--libgo/go/image/png/reader.go588
1 files changed, 588 insertions, 0 deletions
diff --git a/libgo/go/image/png/reader.go b/libgo/go/image/png/reader.go
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+++ b/libgo/go/image/png/reader.go
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+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The png package implements a PNG image decoder and encoder.
+//
+// The PNG specification is at http://www.libpng.org/pub/png/spec/1.2/PNG-Contents.html
+package png
+
+import (
+ "compress/zlib"
+ "fmt"
+ "hash"
+ "hash/crc32"
+ "image"
+ "io"
+ "os"
+)
+
+// Color type, as per the PNG spec.
+const (
+ ctGrayscale = 0
+ ctTrueColor = 2
+ ctPaletted = 3
+ ctGrayscaleAlpha = 4
+ ctTrueColorAlpha = 6
+)
+
+// A cb is a combination of color type and bit depth.
+const (
+ cbInvalid = iota
+ cbG8
+ cbTC8
+ cbP8
+ cbTCA8
+ cbG16
+ cbTC16
+ cbTCA16
+)
+
+// Filter type, as per the PNG spec.
+const (
+ ftNone = 0
+ ftSub = 1
+ ftUp = 2
+ ftAverage = 3
+ ftPaeth = 4
+ nFilter = 5
+)
+
+// Decoding stage.
+// The PNG specification says that the IHDR, PLTE (if present), IDAT and IEND
+// chunks must appear in that order. There may be multiple IDAT chunks, and
+// IDAT chunks must be sequential (i.e. they may not have any other chunks
+// between them).
+const (
+ dsStart = iota
+ dsSeenIHDR
+ dsSeenPLTE
+ dsSeenIDAT
+ dsSeenIEND
+)
+
+const pngHeader = "\x89PNG\r\n\x1a\n"
+
+type imgOrErr struct {
+ img image.Image
+ err os.Error
+}
+
+type decoder struct {
+ width, height int
+ palette image.PalettedColorModel
+ cb int
+ stage int
+ idatWriter io.WriteCloser
+ idatDone chan imgOrErr
+ tmp [3 * 256]byte
+}
+
+// A FormatError reports that the input is not a valid PNG.
+type FormatError string
+
+func (e FormatError) String() string { return "png: invalid format: " + string(e) }
+
+var chunkOrderError = FormatError("chunk out of order")
+
+// An IDATDecodingError wraps an inner error (such as a ZLIB decoding error) encountered while processing an IDAT chunk.
+type IDATDecodingError struct {
+ Err os.Error
+}
+
+func (e IDATDecodingError) String() string { return "png: IDAT decoding error: " + e.Err.String() }
+
+// An UnsupportedError reports that the input uses a valid but unimplemented PNG feature.
+type UnsupportedError string
+
+func (e UnsupportedError) String() string { return "png: unsupported feature: " + string(e) }
+
+// Big-endian.
+func parseUint32(b []uint8) uint32 {
+ return uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])
+}
+
+func abs(x int) int {
+ if x < 0 {
+ return -x
+ }
+ return x
+}
+
+func min(a, b int) int {
+ if a < b {
+ return a
+ }
+ return b
+}
+
+func (d *decoder) parseIHDR(r io.Reader, crc hash.Hash32, length uint32) os.Error {
+ if length != 13 {
+ return FormatError("bad IHDR length")
+ }
+ _, err := io.ReadFull(r, d.tmp[0:13])
+ if err != nil {
+ return err
+ }
+ crc.Write(d.tmp[0:13])
+ if d.tmp[10] != 0 || d.tmp[11] != 0 || d.tmp[12] != 0 {
+ return UnsupportedError("compression, filter or interlace method")
+ }
+ w := int32(parseUint32(d.tmp[0:4]))
+ h := int32(parseUint32(d.tmp[4:8]))
+ if w < 0 || h < 0 {
+ return FormatError("negative dimension")
+ }
+ nPixels := int64(w) * int64(h)
+ if nPixels != int64(int(nPixels)) {
+ return UnsupportedError("dimension overflow")
+ }
+ d.cb = cbInvalid
+ switch d.tmp[8] {
+ case 8:
+ switch d.tmp[9] {
+ case ctGrayscale:
+ d.cb = cbG8
+ case ctTrueColor:
+ d.cb = cbTC8
+ case ctPaletted:
+ d.cb = cbP8
+ case ctTrueColorAlpha:
+ d.cb = cbTCA8
+ }
+ case 16:
+ switch d.tmp[9] {
+ case ctGrayscale:
+ d.cb = cbG16
+ case ctTrueColor:
+ d.cb = cbTC16
+ case ctTrueColorAlpha:
+ d.cb = cbTCA16
+ }
+ }
+ if d.cb == cbInvalid {
+ return UnsupportedError(fmt.Sprintf("bit depth %d, color type %d", d.tmp[8], d.tmp[9]))
+ }
+ d.width, d.height = int(w), int(h)
+ return nil
+}
+
+func (d *decoder) parsePLTE(r io.Reader, crc hash.Hash32, length uint32) os.Error {
+ np := int(length / 3) // The number of palette entries.
+ if length%3 != 0 || np <= 0 || np > 256 {
+ return FormatError("bad PLTE length")
+ }
+ n, err := io.ReadFull(r, d.tmp[0:3*np])
+ if err != nil {
+ return err
+ }
+ crc.Write(d.tmp[0:n])
+ switch d.cb {
+ case cbP8:
+ d.palette = image.PalettedColorModel(make([]image.Color, np))
+ for i := 0; i < np; i++ {
+ d.palette[i] = image.RGBAColor{d.tmp[3*i+0], d.tmp[3*i+1], d.tmp[3*i+2], 0xff}
+ }
+ case cbTC8, cbTCA8, cbTC16, cbTCA16:
+ // As per the PNG spec, a PLTE chunk is optional (and for practical purposes,
+ // ignorable) for the ctTrueColor and ctTrueColorAlpha color types (section 4.1.2).
+ default:
+ return FormatError("PLTE, color type mismatch")
+ }
+ 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.cb {
+ case cbG8, cbG16:
+ return UnsupportedError("grayscale transparency")
+ case cbTC8, cbTC16:
+ return UnsupportedError("truecolor transparency")
+ case cbP8:
+ if n > len(d.palette) {
+ return FormatError("bad tRNS length")
+ }
+ for i := 0; i < n; i++ {
+ rgba := d.palette[i].(image.RGBAColor)
+ d.palette[i] = image.RGBAColor{rgba.R, rgba.G, rgba.B, d.tmp[i]}
+ }
+ case cbTCA8, cbTCA16:
+ 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)
+ pa := abs(p - int(a))
+ pb := abs(p - int(b))
+ pc := abs(p - int(c))
+ if pa <= pb && pa <= pc {
+ return a
+ } else if pb <= pc {
+ return b
+ }
+ return c
+}
+
+func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
+ r, err := zlib.NewReader(idat)
+ if err != nil {
+ return nil, err
+ }
+ defer r.Close()
+ bpp := 0 // Bytes per pixel.
+ maxPalette := uint8(0)
+ var (
+ gray *image.Gray
+ rgba *image.RGBA
+ paletted *image.Paletted
+ nrgba *image.NRGBA
+ gray16 *image.Gray16
+ rgba64 *image.RGBA64
+ nrgba64 *image.NRGBA64
+ img image.Image
+ )
+ switch d.cb {
+ case cbG8:
+ bpp = 1
+ gray = image.NewGray(d.width, d.height)
+ img = gray
+ case cbTC8:
+ bpp = 3
+ rgba = image.NewRGBA(d.width, d.height)
+ img = rgba
+ case cbP8:
+ bpp = 1
+ paletted = image.NewPaletted(d.width, d.height, d.palette)
+ img = paletted
+ maxPalette = uint8(len(d.palette) - 1)
+ case cbTCA8:
+ bpp = 4
+ nrgba = image.NewNRGBA(d.width, d.height)
+ img = nrgba
+ case cbG16:
+ bpp = 2
+ gray16 = image.NewGray16(d.width, d.height)
+ img = gray16
+ case cbTC16:
+ bpp = 6
+ rgba64 = image.NewRGBA64(d.width, d.height)
+ img = rgba64
+ case cbTCA16:
+ bpp = 8
+ nrgba64 = image.NewNRGBA64(d.width, d.height)
+ img = nrgba64
+ }
+ // cr and pr are the bytes for the current and previous row.
+ // The +1 is for the per-row filter type, which is at cr[0].
+ cr := make([]uint8, 1+bpp*d.width)
+ pr := make([]uint8, 1+bpp*d.width)
+
+ for y := 0; y < d.height; y++ {
+ // Read the decompressed bytes.
+ _, err := io.ReadFull(r, cr)
+ if err != nil {
+ return nil, err
+ }
+
+ // Apply the filter.
+ cdat := cr[1:]
+ pdat := pr[1:]
+ switch cr[0] {
+ case ftNone:
+ // No-op.
+ case ftSub:
+ for i := bpp; i < len(cdat); i++ {
+ cdat[i] += cdat[i-bpp]
+ }
+ case ftUp:
+ for i := 0; i < len(cdat); i++ {
+ cdat[i] += pdat[i]
+ }
+ case ftAverage:
+ for i := 0; i < bpp; i++ {
+ cdat[i] += pdat[i] / 2
+ }
+ for i := bpp; i < len(cdat); i++ {
+ cdat[i] += uint8((int(cdat[i-bpp]) + int(pdat[i])) / 2)
+ }
+ case ftPaeth:
+ for i := 0; i < bpp; i++ {
+ cdat[i] += paeth(0, pdat[i], 0)
+ }
+ for i := bpp; i < len(cdat); i++ {
+ cdat[i] += paeth(cdat[i-bpp], pdat[i], pdat[i-bpp])
+ }
+ default:
+ return nil, FormatError("bad filter type")
+ }
+
+ // Convert from bytes to colors.
+ switch d.cb {
+ case cbG8:
+ for x := 0; x < d.width; x++ {
+ gray.Set(x, y, image.GrayColor{cdat[x]})
+ }
+ case cbTC8:
+ for x := 0; x < d.width; x++ {
+ rgba.Set(x, y, image.RGBAColor{cdat[3*x+0], cdat[3*x+1], cdat[3*x+2], 0xff})
+ }
+ case cbP8:
+ for x := 0; x < d.width; x++ {
+ if cdat[x] > maxPalette {
+ return nil, FormatError("palette index out of range")
+ }
+ paletted.SetColorIndex(x, y, cdat[x])
+ }
+ case cbTCA8:
+ for x := 0; x < d.width; x++ {
+ nrgba.Set(x, y, image.NRGBAColor{cdat[4*x+0], cdat[4*x+1], cdat[4*x+2], cdat[4*x+3]})
+ }
+ case cbG16:
+ for x := 0; x < d.width; x++ {
+ ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
+ gray16.Set(x, y, image.Gray16Color{ycol})
+ }
+ case cbTC16:
+ for x := 0; x < d.width; x++ {
+ rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
+ gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
+ bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
+ rgba64.Set(x, y, image.RGBA64Color{rcol, gcol, bcol, 0xffff})
+ }
+ case cbTCA16:
+ for x := 0; x < d.width; x++ {
+ rcol := uint16(cdat[8*x+0])<<8 | uint16(cdat[8*x+1])
+ gcol := uint16(cdat[8*x+2])<<8 | uint16(cdat[8*x+3])
+ bcol := uint16(cdat[8*x+4])<<8 | uint16(cdat[8*x+5])
+ acol := uint16(cdat[8*x+6])<<8 | uint16(cdat[8*x+7])
+ nrgba64.Set(x, y, image.NRGBA64Color{rcol, gcol, bcol, acol})
+ }
+ }
+
+ // The current row for y is the previous row for y+1.
+ pr, cr = cr, pr
+ }
+ return img, nil
+}
+
+func (d *decoder) parseIDAT(r io.Reader, crc hash.Hash32, length uint32) os.Error {
+ // There may be more than one IDAT chunk, but their contents must be
+ // treated as if it was one continuous stream (to the zlib decoder).
+ // We bring up an io.Pipe and write the IDAT chunks into the pipe as
+ // we see them, and decode the stream in a separate go-routine, which
+ // signals its completion (successful or not) via a channel.
+ if d.idatWriter == nil {
+ pr, pw := io.Pipe()
+ d.idatWriter = pw
+ d.idatDone = make(chan imgOrErr)
+ go func() {
+ img, err := d.idatReader(pr)
+ if err == os.EOF {
+ err = FormatError("too little IDAT")
+ }
+ pr.CloseWithError(FormatError("too much IDAT"))
+ d.idatDone <- imgOrErr{img, err}
+ }()
+ }
+ var buf [4096]byte
+ for length > 0 {
+ n, err1 := r.Read(buf[0:min(len(buf), int(length))])
+ // We delay checking err1. It is possible to get n bytes and an error,
+ // but if the n bytes themselves contain a FormatError, for example, we
+ // want to report that error, and not the one that made the Read stop.
+ n, err2 := d.idatWriter.Write(buf[0:n])
+ if err2 != nil {
+ return err2
+ }
+ if err1 != nil {
+ return err1
+ }
+ crc.Write(buf[0:n])
+ length -= uint32(n)
+ }
+ return nil
+}
+
+func (d *decoder) parseIEND(r io.Reader, crc hash.Hash32, length uint32) os.Error {
+ if length != 0 {
+ return FormatError("bad IEND length")
+ }
+ return nil
+}
+
+func (d *decoder) parseChunk(r io.Reader) os.Error {
+ // Read the length.
+ n, err := io.ReadFull(r, d.tmp[0:4])
+ if err == os.EOF {
+ return io.ErrUnexpectedEOF
+ }
+ if err != nil {
+ return err
+ }
+ length := parseUint32(d.tmp[0:4])
+
+ // Read the chunk type.
+ n, err = io.ReadFull(r, d.tmp[0:4])
+ if err == os.EOF {
+ return io.ErrUnexpectedEOF
+ }
+ if err != nil {
+ return err
+ }
+ crc := crc32.NewIEEE()
+ crc.Write(d.tmp[0:4])
+
+ // Read the chunk data.
+ switch string(d.tmp[0:4]) {
+ case "IHDR":
+ if d.stage != dsStart {
+ return chunkOrderError
+ }
+ d.stage = dsSeenIHDR
+ err = d.parseIHDR(r, crc, length)
+ case "PLTE":
+ if d.stage != dsSeenIHDR {
+ return chunkOrderError
+ }
+ 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.cb == cbP8 && d.stage == dsSeenIHDR) {
+ return chunkOrderError
+ }
+ d.stage = dsSeenIDAT
+ err = d.parseIDAT(r, crc, length)
+ case "IEND":
+ if d.stage != dsSeenIDAT {
+ return chunkOrderError
+ }
+ d.stage = dsSeenIEND
+ err = d.parseIEND(r, crc, length)
+ default:
+ // Ignore this chunk (of a known length).
+ var ignored [4096]byte
+ for length > 0 {
+ n, err = io.ReadFull(r, ignored[0:min(len(ignored), int(length))])
+ if err != nil {
+ return err
+ }
+ crc.Write(ignored[0:n])
+ length -= uint32(n)
+ }
+ }
+ if err != nil {
+ return err
+ }
+
+ // Read the checksum.
+ n, err = io.ReadFull(r, d.tmp[0:4])
+ if err == os.EOF {
+ return io.ErrUnexpectedEOF
+ }
+ if err != nil {
+ return err
+ }
+ if parseUint32(d.tmp[0:4]) != crc.Sum32() {
+ return FormatError("invalid checksum")
+ }
+ return nil
+}
+
+func (d *decoder) checkHeader(r io.Reader) os.Error {
+ _, err := io.ReadFull(r, d.tmp[0:8])
+ if err != nil {
+ return err
+ }
+ if string(d.tmp[0:8]) != pngHeader {
+ return FormatError("not a PNG file")
+ }
+ return nil
+}
+
+// Decode reads a PNG image from r and returns it as an image.Image.
+// The type of Image returned depends on the PNG contents.
+func Decode(r io.Reader) (image.Image, os.Error) {
+ var d decoder
+ err := d.checkHeader(r)
+ if err != nil {
+ return nil, err
+ }
+ for d.stage != dsSeenIEND {
+ err = d.parseChunk(r)
+ if err != nil {
+ break
+ }
+ }
+ var img image.Image
+ if d.idatWriter != nil {
+ d.idatWriter.Close()
+ ie := <-d.idatDone
+ if err == nil {
+ img, err = ie.img, ie.err
+ }
+ }
+ if err != nil {
+ return nil, err
+ }
+ return img, nil
+}
+
+// DecodeConfig returns the color model and dimensions of a PNG image without
+// decoding the entire image.
+func DecodeConfig(r io.Reader) (image.Config, os.Error) {
+ var d decoder
+ err := d.checkHeader(r)
+ if err != nil {
+ return image.Config{}, err
+ }
+ for {
+ err = d.parseChunk(r)
+ if err != nil {
+ return image.Config{}, err
+ }
+ if d.stage == dsSeenIHDR && d.cb != cbP8 {
+ break
+ }
+ if d.stage == dsSeenPLTE && d.cb == cbP8 {
+ break
+ }
+ }
+ var cm image.ColorModel
+ switch d.cb {
+ case cbG8:
+ cm = image.GrayColorModel
+ case cbTC8:
+ cm = image.RGBAColorModel
+ case cbP8:
+ cm = d.palette
+ case cbTCA8:
+ cm = image.NRGBAColorModel
+ case cbG16:
+ cm = image.Gray16ColorModel
+ case cbTC16:
+ cm = image.RGBA64ColorModel
+ case cbTCA16:
+ cm = image.NRGBA64ColorModel
+ }
+ return image.Config{cm, d.width, d.height}, nil
+}
+
+func init() {
+ image.RegisterFormat("png", pngHeader, Decode, DecodeConfig)
+}
generated by cgit v1.2.3 (git 2.25.1) at 2024-06-02 07:16:15 +0000