Golang程序
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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.
// Package png implements a PNG image decoder and encoder.
//
// The PNG specification is at https://www.w3.org/TR/PNG/.
package png
import (
"compress/zlib"
"encoding/binary"
"fmt"
"hash"
"hash/crc32"
"image"
"image/color"
"io"
)
// 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
cbG1
cbG2
cbG4
cbG8
cbGA8
cbTC8
cbP1
cbP2
cbP4
cbP8
cbTCA8
cbG16
cbGA16
cbTC16
cbTCA16
)
func cbPaletted(cb int) bool {
return cbP1 <= cb && cb <= cbP8
}
// Filter type, as per the PNG spec.
const (
ftNone = 0
ftSub = 1
ftUp = 2
ftAverage = 3
ftPaeth = 4
nFilter = 5
)
// Interlace type.
const (
itNone = 0
itAdam7 = 1
)
// interlaceScan defines the placement and size of a pass for Adam7 interlacing.
type interlaceScan struct {
xFactor, yFactor, xOffset, yOffset int
}
// interlacing defines Adam7 interlacing, with 7 passes of reduced images.
// See https://www.w3.org/TR/PNG/#8Interlace
var interlacing = []interlaceScan{
{8, 8, 0, 0},
{8, 8, 4, 0},
{4, 8, 0, 4},
{4, 4, 2, 0},
{2, 4, 0, 2},
{2, 2, 1, 0},
{1, 2, 0, 1},
}
// Decoding stage.
// The PNG specification says that the IHDR, PLTE (if present), tRNS (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).
// https://www.w3.org/TR/PNG/#5ChunkOrdering
const (
dsStart = iota
dsSeenIHDR
dsSeenPLTE
dsSeentRNS
dsSeenIDAT
dsSeenIEND
)
const pngHeader = "\x89PNG\r\n\x1a\n"
type decoder struct {
r io.Reader
img image.Image
crc hash.Hash32
width, height int
depth int
palette color.Palette
cb int
stage int
idatLength uint32
tmp [3 * 256]byte
interlace int
// useTransparent and transparent are used for grayscale and truecolor
// transparency, as opposed to palette transparency.
useTransparent bool
transparent [6]byte
}
// A FormatError reports that the input is not a valid PNG.
type FormatError string
func (e FormatError) Error() string { return "png: invalid format: " + string(e) }
var chunkOrderError = FormatError("chunk out of order")
// An UnsupportedError reports that the input uses a valid but unimplemented PNG feature.
type UnsupportedError string
func (e UnsupportedError) Error() string { return "png: unsupported feature: " + string(e) }
func min(a, b int) int {
if a < b {
return a
}
return b
}
func (d *decoder) parseIHDR(length uint32) error {
if length != 13 {
return FormatError("bad IHDR length")
}
if _, err := io.ReadFull(d.r, d.tmp[:13]); err != nil {
return err
}
d.crc.Write(d.tmp[:13])
if d.tmp[10] != 0 {
return UnsupportedError("compression method")
}
if d.tmp[11] != 0 {
return UnsupportedError("filter method")
}
if d.tmp[12] != itNone && d.tmp[12] != itAdam7 {
return FormatError("invalid interlace method")
}
d.interlace = int(d.tmp[12])
w := int32(binary.BigEndian.Uint32(d.tmp[0:4]))
h := int32(binary.BigEndian.Uint32(d.tmp[4:8]))
if w <= 0 || h <= 0 {
return FormatError("non-positive dimension")
}
nPixels := int64(w) * int64(h)
if nPixels != int64(int(nPixels)) {
return UnsupportedError("dimension overflow")
}
// There can be up to 8 bytes per pixel, for 16 bits per channel RGBA.
if nPixels != (nPixels*8)/8 {
return UnsupportedError("dimension overflow")
}
d.cb = cbInvalid
d.depth = int(d.tmp[8])
switch d.depth {
case 1:
switch d.tmp[9] {
case ctGrayscale:
d.cb = cbG1
case ctPaletted:
d.cb = cbP1
}
case 2:
switch d.tmp[9] {
case ctGrayscale:
d.cb = cbG2
case ctPaletted:
d.cb = cbP2
}
case 4:
switch d.tmp[9] {
case ctGrayscale:
d.cb = cbG4
case ctPaletted:
d.cb = cbP4
}
case 8:
switch d.tmp[9] {
case ctGrayscale:
d.cb = cbG8
case ctTrueColor:
d.cb = cbTC8
case ctPaletted:
d.cb = cbP8
case ctGrayscaleAlpha:
d.cb = cbGA8
case ctTrueColorAlpha:
d.cb = cbTCA8
}
case 16:
switch d.tmp[9] {
case ctGrayscale:
d.cb = cbG16
case ctTrueColor:
d.cb = cbTC16
case ctGrayscaleAlpha:
d.cb = cbGA16
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 d.verifyChecksum()
}
func (d *decoder) parsePLTE(length uint32) error {
np := int(length / 3) // The number of palette entries.
if length%3 != 0 || np <= 0 || np > 256 || np > 1<<uint(d.depth) {
return FormatError("bad PLTE length")
}
n, err := io.ReadFull(d.r, d.tmp[:3*np])
if err != nil {
return err
}
d.crc.Write(d.tmp[:n])
switch d.cb {
case cbP1, cbP2, cbP4, cbP8:
d.palette = make(color.Palette, 256)
for i := 0; i < np; i++ {
d.palette[i] = color.RGBA{d.tmp[3*i+0], d.tmp[3*i+1], d.tmp[3*i+2], 0xff}
}
for i := np; i < 256; i++ {
// Initialize the rest of the palette to opaque black. The spec (section
// 11.2.3) says that "any out-of-range pixel value found in the image data
// is an error", but some real-world PNG files have out-of-range pixel
// values. We fall back to opaque black, the same as libpng 1.5.13;
// ImageMagick 6.5.7 returns an error.
d.palette[i] = color.RGBA{0x00, 0x00, 0x00, 0xff}
}
d.palette = d.palette[:np]
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 d.verifyChecksum()
}
func (d *decoder) parsetRNS(length uint32) error {
switch d.cb {
case cbG1, cbG2, cbG4, cbG8, cbG16:
if length != 2 {
return FormatError("bad tRNS length")
}
n, err := io.ReadFull(d.r, d.tmp[:length])
if err != nil {
return err
}
d.crc.Write(d.tmp[:n])
copy(d.transparent[:], d.tmp[:length])
switch d.cb {
case cbG1:
d.transparent[1] *= 0xff
case cbG2:
d.transparent[1] *= 0x55
case cbG4:
d.transparent[1] *= 0x11
}
d.useTransparent = true
case cbTC8, cbTC16:
if length != 6 {
return FormatError("bad tRNS length")
}
n, err := io.ReadFull(d.r, d.tmp[:length])
if err != nil {
return err
}
d.crc.Write(d.tmp[:n])
copy(d.transparent[:], d.tmp[:length])
d.useTransparent = true
case cbP1, cbP2, cbP4, cbP8:
if length > 256 {
return FormatError("bad tRNS length")
}
n, err := io.ReadFull(d.r, d.tmp[:length])
if err != nil {
return err
}
d.crc.Write(d.tmp[:n])
if len(d.palette) < n {
d.palette = d.palette[:n]
}
for i := 0; i < n; i++ {
rgba := d.palette[i].(color.RGBA)
d.palette[i] = color.NRGBA{rgba.R, rgba.G, rgba.B, d.tmp[i]}
}
default:
return FormatError("tRNS, color type mismatch")
}
return d.verifyChecksum()
}
// Read presents one or more IDAT chunks as one continuous stream (minus the
// intermediate chunk headers and footers). If the PNG data looked like:
// ... len0 IDAT xxx crc0 len1 IDAT yy crc1 len2 IEND crc2
// then this reader presents xxxyy. For well-formed PNG data, the decoder state
// immediately before the first Read call is that d.r is positioned between the
// first IDAT and xxx, and the decoder state immediately after the last Read
// call is that d.r is positioned between yy and crc1.
func (d *decoder) Read(p []byte) (int, error) {
if len(p) == 0 {
return 0, nil
}
for d.idatLength == 0 {
// We have exhausted an IDAT chunk. Verify the checksum of that chunk.
if err := d.verifyChecksum(); err != nil {
return 0, err
}
// Read the length and chunk type of the next chunk, and check that
// it is an IDAT chunk.
if _, err := io.ReadFull(d.r, d.tmp[:8]); err != nil {
return 0, err
}
d.idatLength = binary.BigEndian.Uint32(d.tmp[:4])
if string(d.tmp[4:8]) != "IDAT" {
return 0, FormatError("not enough pixel data")
}
d.crc.Reset()
d.crc.Write(d.tmp[4:8])
}
if int(d.idatLength) < 0 {
return 0, UnsupportedError("IDAT chunk length overflow")
}
n, err := d.r.Read(p[:min(len(p), int(d.idatLength))])
d.crc.Write(p[:n])
d.idatLength -= uint32(n)
return n, err
}
// decode decodes the IDAT data into an image.
func (d *decoder) decode() (image.Image, error) {
r, err := zlib.NewReader(d)
if err != nil {
return nil, err
}
defer r.Close()
var img image.Image
if d.interlace == itNone {
img, err = d.readImagePass(r, 0, false)
if err != nil {
return nil, err
}
} else if d.interlace == itAdam7 {
// Allocate a blank image of the full size.
img, err = d.readImagePass(nil, 0, true)
if err != nil {
return nil, err
}
for pass := 0; pass < 7; pass++ {
imagePass, err := d.readImagePass(r, pass, false)
if err != nil {
return nil, err
}
if imagePass != nil {
d.mergePassInto(img, imagePass, pass)
}
}
}
// Check for EOF, to verify the zlib checksum.
n := 0
for i := 0; n == 0 && err == nil; i++ {
if i == 100 {
return nil, io.ErrNoProgress
}
n, err = r.Read(d.tmp[:1])
}
if err != nil && err != io.EOF {
return nil, FormatError(err.Error())
}
if n != 0 || d.idatLength != 0 {
return nil, FormatError("too much pixel data")
}
return img, nil
}
// readImagePass reads a single image pass, sized according to the pass number.
func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image.Image, error) {
bitsPerPixel := 0
pixOffset := 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
)
width, height := d.width, d.height
if d.interlace == itAdam7 && !allocateOnly {
p := interlacing[pass]
// Add the multiplication factor and subtract one, effectively rounding up.
width = (width - p.xOffset + p.xFactor - 1) / p.xFactor
height = (height - p.yOffset + p.yFactor - 1) / p.yFactor
// A PNG image can't have zero width or height, but for an interlaced
// image, an individual pass might have zero width or height. If so, we
// shouldn't even read a per-row filter type byte, so return early.
if width == 0 || height == 0 {
return nil, nil
}
}
switch d.cb {
case cbG1, cbG2, cbG4, cbG8:
bitsPerPixel = d.depth
if d.useTransparent {
nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
img = nrgba
} else {
gray = image.NewGray(image.Rect(0, 0, width, height))
img = gray
}
case cbGA8:
bitsPerPixel = 16
nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
img = nrgba
case cbTC8:
bitsPerPixel = 24
if d.useTransparent {
nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
img = nrgba
} else {
rgba = image.NewRGBA(image.Rect(0, 0, width, height))
img = rgba
}
case cbP1, cbP2, cbP4, cbP8:
bitsPerPixel = d.depth
paletted = image.NewPaletted(image.Rect(0, 0, width, height), d.palette)
img = paletted
case cbTCA8:
bitsPerPixel = 32
nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
img = nrgba
case cbG16:
bitsPerPixel = 16
if d.useTransparent {
nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
img = nrgba64
} else {
gray16 = image.NewGray16(image.Rect(0, 0, width, height))
img = gray16
}
case cbGA16:
bitsPerPixel = 32
nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
img = nrgba64
case cbTC16:
bitsPerPixel = 48
if d.useTransparent {
nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
img = nrgba64
} else {
rgba64 = image.NewRGBA64(image.Rect(0, 0, width, height))
img = rgba64
}
case cbTCA16:
bitsPerPixel = 64
nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
img = nrgba64
}
if allocateOnly {
return img, nil
}
bytesPerPixel := (bitsPerPixel + 7) / 8
// The +1 is for the per-row filter type, which is at cr[0].
rowSize := 1 + (bitsPerPixel*width+7)/8
// cr and pr are the bytes for the current and previous row.
cr := make([]uint8, rowSize)
pr := make([]uint8, rowSize)
for y := 0; y < height; y++ {
// Read the decompressed bytes.
_, err := io.ReadFull(r, cr)
if err != nil {
if err == io.EOF || err == io.ErrUnexpectedEOF {
return nil, FormatError("not enough pixel data")
}
return nil, err
}
// Apply the filter.
cdat := cr[1:]
pdat := pr[1:]
switch cr[0] {
case ftNone:
// No-op.
case ftSub:
for i := bytesPerPixel; i < len(cdat); i++ {
cdat[i] += cdat[i-bytesPerPixel]
}
case ftUp:
for i, p := range pdat {
cdat[i] += p
}
case ftAverage:
// The first column has no column to the left of it, so it is a
// special case. We know that the first column exists because we
// check above that width != 0, and so len(cdat) != 0.
for i := 0; i < bytesPerPixel; i++ {
cdat[i] += pdat[i] / 2
}
for i := bytesPerPixel; i < len(cdat); i++ {
cdat[i] += uint8((int(cdat[i-bytesPerPixel]) + int(pdat[i])) / 2)
}
case ftPaeth:
filterPaeth(cdat, pdat, bytesPerPixel)
default:
return nil, FormatError("bad filter type")
}
// Convert from bytes to colors.
switch d.cb {
case cbG1:
if d.useTransparent {
ty := d.transparent[1]
for x := 0; x < width; x += 8 {
b := cdat[x/8]
for x2 := 0; x2 < 8 && x+x2 < width; x2++ {
ycol := (b >> 7) * 0xff
acol := uint8(0xff)
if ycol == ty {
acol = 0x00
}
nrgba.SetNRGBA(x+x2, y, color.NRGBA{ycol, ycol, ycol, acol})
b <<= 1
}
}
} else {
for x := 0; x < width; x += 8 {
b := cdat[x/8]
for x2 := 0; x2 < 8 && x+x2 < width; x2++ {
gray.SetGray(x+x2, y, color.Gray{(b >> 7) * 0xff})
b <<= 1
}
}
}
case cbG2:
if d.useTransparent {
ty := d.transparent[1]
for x := 0; x < width; x += 4 {
b := cdat[x/4]
for x2 := 0; x2 < 4 && x+x2 < width; x2++ {
ycol := (b >> 6) * 0x55
acol := uint8(0xff)
if ycol == ty {
acol = 0x00
}
nrgba.SetNRGBA(x+x2, y, color.NRGBA{ycol, ycol, ycol, acol})
b <<= 2
}
}
} else {
for x := 0; x < width; x += 4 {
b := cdat[x/4]
for x2 := 0; x2 < 4 && x+x2 < width; x2++ {
gray.SetGray(x+x2, y, color.Gray{(b >> 6) * 0x55})
b <<= 2
}
}
}
case cbG4:
if d.useTransparent {
ty := d.transparent[1]
for x := 0; x < width; x += 2 {
b := cdat[x/2]
for x2 := 0; x2 < 2 && x+x2 < width; x2++ {
ycol := (b >> 4) * 0x11
acol := uint8(0xff)
if ycol == ty {
acol = 0x00
}
nrgba.SetNRGBA(x+x2, y, color.NRGBA{ycol, ycol, ycol, acol})
b <<= 4
}
}
} else {
for x := 0; x < width; x += 2 {
b := cdat[x/2]
for x2 := 0; x2 < 2 && x+x2 < width; x2++ {
gray.SetGray(x+x2, y, color.Gray{(b >> 4) * 0x11})
b <<= 4
}
}
}
case cbG8:
if d.useTransparent {
ty := d.transparent[1]
for x := 0; x < width; x++ {
ycol := cdat[x]
acol := uint8(0xff)
if ycol == ty {
acol = 0x00
}
nrgba.SetNRGBA(x, y, color.NRGBA{ycol, ycol, ycol, acol})
}
} else {
copy(gray.Pix[pixOffset:], cdat)
pixOffset += gray.Stride
}
case cbGA8:
for x := 0; x < width; x++ {
ycol := cdat[2*x+0]
nrgba.SetNRGBA(x, y, color.NRGBA{ycol, ycol, ycol, cdat[2*x+1]})
}
case cbTC8:
if d.useTransparent {
pix, i, j := nrgba.Pix, pixOffset, 0
tr, tg, tb := d.transparent[1], d.transparent[3], d.transparent[5]
for x := 0; x < width; x++ {
r := cdat[j+0]
g := cdat[j+1]
b := cdat[j+2]
a := uint8(0xff)
if r == tr && g == tg && b == tb {
a = 0x00
}
pix[i+0] = r
pix[i+1] = g
pix[i+2] = b
pix[i+3] = a
i += 4
j += 3
}
pixOffset += nrgba.Stride
} else {
pix, i, j := rgba.Pix, pixOffset, 0
for x := 0; x < width; x++ {
pix[i+0] = cdat[j+0]
pix[i+1] = cdat[j+1]
pix[i+2] = cdat[j+2]
pix[i+3] = 0xff
i += 4
j += 3
}
pixOffset += rgba.Stride
}
case cbP1:
for x := 0; x < width; x += 8 {
b := cdat[x/8]
for x2 := 0; x2 < 8 && x+x2 < width; x2++ {
idx := b >> 7
if len(paletted.Palette) <= int(idx) {
paletted.Palette = paletted.Palette[:int(idx)+1]
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 1
}
}
case cbP2:
for x := 0; x < width; x += 4 {
b := cdat[x/4]
for x2 := 0; x2 < 4 && x+x2 < width; x2++ {
idx := b >> 6
if len(paletted.Palette) <= int(idx) {
paletted.Palette = paletted.Palette[:int(idx)+1]
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 2
}
}
case cbP4:
for x := 0; x < width; x += 2 {
b := cdat[x/2]
for x2 := 0; x2 < 2 && x+x2 < width; x2++ {
idx := b >> 4
if len(paletted.Palette) <= int(idx) {
paletted.Palette = paletted.Palette[:int(idx)+1]
}
paletted.SetColorIndex(x+x2, y, idx)
b <<= 4
}
}
case cbP8:
if len(paletted.Palette) != 255 {
for x := 0; x < width; x++ {
if len(paletted.Palette) <= int(cdat[x]) {
paletted.Palette = paletted.Palette[:int(cdat[x])+1]
}
}
}
copy(paletted.Pix[pixOffset:], cdat)
pixOffset += paletted.Stride
case cbTCA8:
copy(nrgba.Pix[pixOffset:], cdat)
pixOffset += nrgba.Stride
case cbG16:
if d.useTransparent {
ty := uint16(d.transparent[0])<<8 | uint16(d.transparent[1])
for x := 0; x < width; x++ {
ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
acol := uint16(0xffff)
if ycol == ty {
acol = 0x0000
}
nrgba64.SetNRGBA64(x, y, color.NRGBA64{ycol, ycol, ycol, acol})
}
} else {
for x := 0; x < width; x++ {
ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
gray16.SetGray16(x, y, color.Gray16{ycol})
}
}
case cbGA16:
for x := 0; x < width; x++ {
ycol := uint16(cdat[4*x+0])<<8 | uint16(cdat[4*x+1])
acol := uint16(cdat[4*x+2])<<8 | uint16(cdat[4*x+3])
nrgba64.SetNRGBA64(x, y, color.NRGBA64{ycol, ycol, ycol, acol})
}
case cbTC16:
if d.useTransparent {
tr := uint16(d.transparent[0])<<8 | uint16(d.transparent[1])
tg := uint16(d.transparent[2])<<8 | uint16(d.transparent[3])
tb := uint16(d.transparent[4])<<8 | uint16(d.transparent[5])
for x := 0; x < 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])
acol := uint16(0xffff)
if rcol == tr && gcol == tg && bcol == tb {
acol = 0x0000
}
nrgba64.SetNRGBA64(x, y, color.NRGBA64{rcol, gcol, bcol, acol})
}
} else {
for x := 0; x < 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.SetRGBA64(x, y, color.RGBA64{rcol, gcol, bcol, 0xffff})
}
}
case cbTCA16:
for x := 0; x < 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.SetNRGBA64(x, y, color.NRGBA64{rcol, gcol, bcol, acol})
}
}
// The current row for y is the previous row for y+1.
pr, cr = cr, pr
}
return img, nil
}
// mergePassInto merges a single pass into a full sized image.
func (d *decoder) mergePassInto(dst image.Image, src image.Image, pass int) {
p := interlacing[pass]
var (
srcPix []uint8
dstPix []uint8
stride int
rect image.Rectangle
bytesPerPixel int
)
switch target := dst.(type) {
case *image.Alpha:
srcPix = src.(*image.Alpha).Pix
dstPix, stride, rect = target.Pix, target.Stride, target.Rect
bytesPerPixel = 1
case *image.Alpha16:
srcPix = src.(*image.Alpha16).Pix
dstPix, stride, rect = target.Pix, target.Stride, target.Rect
bytesPerPixel = 2
case *image.Gray:
srcPix = src.(*image.Gray).Pix
dstPix, stride, rect = target.Pix, target.Stride, target.Rect
bytesPerPixel = 1
case *image.Gray16:
srcPix = src.(*image.Gray16).Pix
dstPix, stride, rect = target.Pix, target.Stride, target.Rect
bytesPerPixel = 2
case *image.NRGBA:
srcPix = src.(*image.NRGBA).Pix
dstPix, stride, rect = target.Pix, target.Stride, target.Rect
bytesPerPixel = 4
case *image.NRGBA64:
srcPix = src.(*image.NRGBA64).Pix
dstPix, stride, rect = target.Pix, target.Stride, target.Rect
bytesPerPixel = 8
case *image.Paletted:
srcPix = src.(*image.Paletted).Pix
dstPix, stride, rect = target.Pix, target.Stride, target.Rect
bytesPerPixel = 1
case *image.RGBA:
srcPix = src.(*image.RGBA).Pix
dstPix, stride, rect = target.Pix, target.Stride, target.Rect
bytesPerPixel = 4
case *image.RGBA64:
srcPix = src.(*image.RGBA64).Pix
dstPix, stride, rect = target.Pix, target.Stride, target.Rect
bytesPerPixel = 8
}
s, bounds := 0, src.Bounds()
for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
dBase := (y*p.yFactor+p.yOffset-rect.Min.Y)*stride + (p.xOffset-rect.Min.X)*bytesPerPixel
for x := bounds.Min.X; x < bounds.Max.X; x++ {
d := dBase + x*p.xFactor*bytesPerPixel
copy(dstPix[d:], srcPix[s:s+bytesPerPixel])
s += bytesPerPixel
}
}
}
func (d *decoder) parseIDAT(length uint32) (err error) {
d.idatLength = length
d.img, err = d.decode()
if err != nil {
return err
}
return d.verifyChecksum()
}
func (d *decoder) parseIEND(length uint32) error {
if length != 0 {
return FormatError("bad IEND length")
}
return d.verifyChecksum()
}
func (d *decoder) parseChunk() error {
// Read the length and chunk type.
n, err := io.ReadFull(d.r, d.tmp[:8])
if err != nil {
return err
}
length := binary.BigEndian.Uint32(d.tmp[:4])
d.crc.Reset()
d.crc.Write(d.tmp[4:8])
// Read the chunk data.
switch string(d.tmp[4:8]) {
case "IHDR":
if d.stage != dsStart {
return chunkOrderError
}
d.stage = dsSeenIHDR
return d.parseIHDR(length)
case "PLTE":
if d.stage != dsSeenIHDR {
return chunkOrderError
}
d.stage = dsSeenPLTE
return d.parsePLTE(length)
case "tRNS":
if cbPaletted(d.cb) {
if d.stage != dsSeenPLTE {
return chunkOrderError
}
} else if d.stage != dsSeenIHDR {
return chunkOrderError
}
d.stage = dsSeentRNS
return d.parsetRNS(length)
case "IDAT":
if d.stage < dsSeenIHDR || d.stage > dsSeenIDAT || (d.stage == dsSeenIHDR && cbPaletted(d.cb)) {
return chunkOrderError
} else if d.stage == dsSeenIDAT {
// Ignore trailing zero-length or garbage IDAT chunks.
//
// This does not affect valid PNG images that contain multiple IDAT
// chunks, since the first call to parseIDAT below will consume all
// consecutive IDAT chunks required for decoding the image.
break
}
d.stage = dsSeenIDAT
return d.parseIDAT(length)
case "IEND":
if d.stage != dsSeenIDAT {
return chunkOrderError
}
d.stage = dsSeenIEND
return d.parseIEND(length)
}
if length > 0x7fffffff {
return FormatError(fmt.Sprintf("Bad chunk length: %d", length))
}
// Ignore this chunk (of a known length).
var ignored [4096]byte
for length > 0 {
n, err = io.ReadFull(d.r, ignored[:min(len(ignored), int(length))])
if err != nil {
return err
}
d.crc.Write(ignored[:n])
length -= uint32(n)
}
return d.verifyChecksum()
}
func (d *decoder) verifyChecksum() error {
if _, err := io.ReadFull(d.r, d.tmp[:4]); err != nil {
return err
}
if binary.BigEndian.Uint32(d.tmp[:4]) != d.crc.Sum32() {
return FormatError("invalid checksum")
}
return nil
}
func (d *decoder) checkHeader() error {
_, err := io.ReadFull(d.r, d.tmp[:len(pngHeader)])
if err != nil {
return err
}
if string(d.tmp[:len(pngHeader)]) != 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, error) {
d := &decoder{
r: r,
crc: crc32.NewIEEE(),
}
if err := d.checkHeader(); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return nil, err
}
for d.stage != dsSeenIEND {
if err := d.parseChunk(); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return nil, err
}
}
return d.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, error) {
d := &decoder{
r: r,
crc: crc32.NewIEEE(),
}
if err := d.checkHeader(); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return image.Config{}, err
}
for {
if err := d.parseChunk(); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return image.Config{}, err
}
paletted := cbPaletted(d.cb)
if d.stage == dsSeenIHDR && !paletted {
break
}
if d.stage == dsSeenPLTE && paletted {
break
}
}
var cm color.Model
switch d.cb {
case cbG1, cbG2, cbG4, cbG8:
cm = color.GrayModel
case cbGA8:
cm = color.NRGBAModel
case cbTC8:
cm = color.RGBAModel
case cbP1, cbP2, cbP4, cbP8:
cm = d.palette
case cbTCA8:
cm = color.NRGBAModel
case cbG16:
cm = color.Gray16Model
case cbGA16:
cm = color.NRGBA64Model
case cbTC16:
cm = color.RGBA64Model
case cbTCA16:
cm = color.NRGBA64Model
}
return image.Config{
ColorModel: cm,
Width: d.width,
Height: d.height,
}, nil
}
func init() {
image.RegisterFormat("png", pngHeader, Decode, DecodeConfig)
}