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decoder.go
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decoder.go
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// Package pcx implements a PCX image decoder and encoder.
//
// Specification: http://web.archive.org/web/20030111010058/http://www.nist.fss.ru/hr/doc/spec/pcx.htm
//
// Sample files: http://samples.ffmpeg.org/image-samples/pcx/
package pcx
import (
"bufio"
"errors"
"fmt"
"image"
"image/color"
"io"
)
// Version:
// 0 = Version 2.5 of PC Paintbrush
// 2 = Version 2.8 w/palette information
// 3 = Version 2.8 w/o palette information
// 4 = PC Paintbrush for Windows(Plus for
// Windows uses Ver 5)
// 5 = Version 3.0 and > of PC Paintbrush
// and PC Paintbrush +, includes
// Publisher's Paintbrush . Includes
// 24-bit .PCX files
const (
magic = 0x0a
paletteMagic = 0x0c
)
type decoder struct {
r io.Reader
version int
rle bool
bpp int
bounds image.Rectangle
horizDpi int
vertDpi int
horizSize int
vertSize int
colormap [48]byte
nplanes int
bytesPerLine int
bytesPerScanline int
grayscale bool
pb4 bool
colorModel color.Model
}
// A FormatError reports that the input is not a valid PCX.
type FormatError string
func (e FormatError) Error() string {
return "pcx: invalid format: " + string(e)
}
// An UnsupportedError reports that the input uses a valid but unimplemented PCX feature.
type UnsupportedError string
func (e UnsupportedError) Error() string {
return "pcx: unsupported variant: " + string(e)
}
var cga16ColorPalette = [16]color.Color{
color.RGBA{0x00, 0x00, 0x00, 0xff}, // 0 black
color.RGBA{0x00, 0x00, 0xaa, 0xff}, // 1 blue
color.RGBA{0x00, 0xaa, 0x00, 0xff}, // 2 green
color.RGBA{0x00, 0xaa, 0xaa, 0xff}, // 3 cyan
color.RGBA{0xaa, 0x00, 0x00, 0xff}, // 4 red
color.RGBA{0xaa, 0x00, 0xaa, 0xff}, // 5 magenta
color.RGBA{0xaa, 0x55, 0x00, 0xff}, // 6 brown
color.RGBA{0xaa, 0xaa, 0xaa, 0xff}, // 7 light gray
color.RGBA{0x55, 0x55, 0x55, 0xff}, // 8 gray
color.RGBA{0x55, 0x55, 0xff, 0xff}, // 9 light blue
color.RGBA{0x55, 0xff, 0x55, 0xff}, // 10 light green
color.RGBA{0x55, 0xff, 0xff, 0xff}, // 11 light cyan
color.RGBA{0xff, 0x55, 0x55, 0xff}, // 12 light red
color.RGBA{0xff, 0x55, 0xff, 0xff}, // 13 light magenta
color.RGBA{0xff, 0xff, 0x55, 0xff}, // 14 yellow
color.RGBA{0xff, 0xff, 0xff, 0xff}, // 15 white
}
var cga4ColorPalettes = [8][]color.Color{
{cga16ColorPalette[2], cga16ColorPalette[4], cga16ColorPalette[6]}, // green, red, brown
{cga16ColorPalette[10], cga16ColorPalette[12], cga16ColorPalette[14]}, // light green, light red, yellow
{cga16ColorPalette[3], cga16ColorPalette[5], cga16ColorPalette[7]}, // cyan, magenta, light gray
{cga16ColorPalette[11], cga16ColorPalette[13], cga16ColorPalette[15]}, // light cyan, light magenta, white
{cga16ColorPalette[3], cga16ColorPalette[4], cga16ColorPalette[7]}, // cyan, red, light gray
{cga16ColorPalette[11], cga16ColorPalette[12], cga16ColorPalette[15]}, // light cyan, light red, white
{cga16ColorPalette[3], cga16ColorPalette[4], cga16ColorPalette[7]}, // cyan, red, light gray
{cga16ColorPalette[11], cga16ColorPalette[12], cga16ColorPalette[15]}, // light cyan, light red, white
}
func init() {
// The magic also matches the RLE bit to make sure it's set
image.RegisterFormat("pcx", "\x0a?\x01", Decode, DecodeConfig)
}
// Decode reads a PCX image from r and returns it as an image.Image.
// The type of Image returned depends on the PCX contents.
func Decode(r io.Reader) (image.Image, error) {
d, err := newDecoder(r)
if err != nil {
return nil, err
}
img, err := d.decode()
if err != nil {
return nil, err
}
return img, nil
}
// DecodeConfig returns the color model and dimensions of a PCX image
// without decoding the entire image.
func DecodeConfig(r io.Reader) (image.Config, error) {
d, err := newDecoder(r)
if err != nil {
return image.Config{}, err
}
return image.Config{
ColorModel: d.colorModel,
Width: d.bounds.Dx(),
Height: d.bounds.Dy(),
}, nil
}
func newDecoder(r io.Reader) (*decoder, error) {
d := &decoder{
r: r,
}
if err := d.readHeader(); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return nil, err
}
return d, nil
}
func (d *decoder) readHeader() error {
var buf [128]byte
_, err := io.ReadFull(d.r, buf[:128])
if err != nil {
return err
}
if buf[0] != magic {
return FormatError("not a PCX file")
}
d.version = int(buf[1])
d.rle = buf[2] == 1
d.bpp = int(buf[3])
if d.bpp < 1 || d.bpp > 8 {
return FormatError(fmt.Sprintf("unsupported bpp (%d)", d.bpp))
}
var dim [4]int
for i := 0; i < 4; i++ {
dim[i] = int(buf[4+i*2]) | (int(buf[5+i*2]) << 8)
}
d.bounds = image.Rect(
int(buf[4])|(int(buf[5])<<8),
int(buf[6])|(int(buf[7])<<8),
int(buf[8])|(int(buf[9])<<8)+1,
int(buf[10])|(int(buf[11])<<8)+1)
d.horizDpi = int(buf[12]) | (int(buf[13]) << 8)
d.vertDpi = int(buf[14]) | (int(buf[15]) << 8)
copy(d.colormap[:48], buf[16:16+48])
d.nplanes = int(buf[65])
d.bytesPerLine = int(buf[66]) | (int(buf[67]) << 8)
d.bytesPerScanline = d.bytesPerLine * d.nplanes
d.grayscale = buf[68] == 2
d.pb4 = buf[68] != 0
d.horizSize = int(buf[70]) | (int(buf[71]) << 8)
d.vertSize = int(buf[72]) | (int(buf[73]) << 8)
if d.bytesPerScanline < (d.bounds.Dx()*d.bpp*d.nplanes+7)/8 {
return FormatError("corrupt image")
}
if d.grayscale {
d.colorModel = color.GrayModel
} else {
d.colorModel = color.RGBAModel
}
return nil
}
func (d *decoder) decode() (image.Image, error) {
if !d.rle {
return nil, UnsupportedError("non-RLE")
}
switch {
case d.colorModel == color.GrayModel:
if d.bpp == 8 {
return d.decodeGrayscale()
}
return nil, UnsupportedError("grayscale only supported with 8bpp")
case d.nplanes == 1:
if d.bpp == 8 {
return d.decodeRGBPaletted()
}
return d.decodePaletted()
case d.bpp == 8 && (d.nplanes == 3 || d.nplanes == 4):
return d.decodeRGB()
case d.bpp == 1 && (d.nplanes >= 2 && d.nplanes <= 4):
return d.decodePlanar()
}
return nil, UnsupportedError(fmt.Sprintf("version %d with %d planes %d bpp", d.version, d.nplanes, d.bpp))
}
func (d *decoder) decodeGrayscale() (image.Image, error) {
bufR := bufio.NewReader(d.r)
img := image.NewGray(d.bounds)
height := d.bounds.Dy()
for y := 0; y < height; y++ {
if err := d.rleDecode(bufR, img.Pix[y*img.Stride:]); err != nil {
return img, err
}
}
return img, nil
}
func (d *decoder) decodeRGB() (image.Image, error) {
bufR := bufio.NewReader(d.r)
img := image.NewRGBA(d.bounds)
width := d.bounds.Dx()
height := d.bounds.Dy()
offset := 0
buf := make([]byte, d.bytesPerScanline)
for y := 0; y < height; y++ {
if err := d.rleDecode(bufR, buf); err != nil {
return img, err
}
for x := 0; x < width; x++ {
img.Pix[offset] = buf[x]
img.Pix[offset+1] = buf[x+d.bytesPerLine]
img.Pix[offset+2] = buf[x+2*d.bytesPerLine]
if d.nplanes == 4 {
img.Pix[offset+3] = buf[x+3*d.bytesPerLine]
} else {
img.Pix[offset+3] = 255
}
offset += 4
}
}
return img, nil
}
func (d *decoder) decodeRGBPaletted() (image.Image, error) {
bufR := bufio.NewReader(d.r)
pal := make([]color.Color, 256)
img := image.NewPaletted(d.bounds, pal)
height := d.bounds.Dy()
for y := 0; y < height; y++ {
if err := d.rleDecode(bufR, img.Pix[y*img.Stride:]); err != nil {
return img, err
}
}
// Read palette
palBytes := make([]byte, 3*256)
switch by, err := bufR.ReadByte(); {
case (err == nil && by != paletteMagic) || err == io.EOF:
return img, errors.New("pcx: missing extended palette")
case err != nil:
return img, err
}
if _, err := io.ReadFull(bufR, palBytes); err != nil {
return img, err
}
for i := 0; i < 256; i++ {
pal[i] = color.RGBA{R: palBytes[i*3], G: palBytes[i*3+1], B: palBytes[i*3+2], A: 255}
}
return img, nil
}
func (d *decoder) decodePaletted() (image.Image, error) {
bufR := bufio.NewReader(d.r)
pal := make([]color.Color, 1<<uint(d.bpp))
switch {
case d.bpp == 1: // B&W
pal[0] = color.Black
pal[1] = color.White
case d.bpp == 2 && d.bounds.Dx() == 320 && d.bounds.Dy() == 200: // CGA
pal[0] = cga16ColorPalette[d.colormap[0]>>4]
idx := int(d.colormap[3] >> 5)
if d.pb4 {
// PC Paintbush 4.0 encodes the CGA palettes differently than 3.0.
// Very thankful for the person that figured it out here:
// https://github.com/wjaguar/mtPaint/blob/master/src/png.c
i := 0
if d.colormap[5] >= d.colormap[4] {
i = 1
}
idx = i * 2
if d.colormap[4+i] > 200 {
idx++
}
}
copy(pal[1:], cga4ColorPalettes[idx])
default: // EGA
for i := 0; i < len(pal)*3; i += 3 {
pal[i/3] = color.RGBA{R: d.colormap[i], G: d.colormap[i+1], B: d.colormap[i+2], A: 255}
}
}
img := image.NewPaletted(d.bounds, pal)
width, height := d.bounds.Dx(), d.bounds.Dy()
buf := make([]byte, d.bytesPerScanline)
mask := byte((1 << uint(d.bpp)) - 1)
for y := 0; y < height; y++ {
if err := d.rleDecode(bufR, buf); err != nil {
return img, err
}
shift := byte(8 - d.bpp)
for x, o := 0, 0; x < width; x++ {
img.Pix[y*img.Stride+x] = (buf[o] >> shift) & mask
if shift == 0 {
o++
shift = byte(8 - d.bpp)
} else {
shift -= byte(d.bpp)
}
}
}
return img, nil
}
func (d *decoder) decodePlanar() (image.Image, error) {
pal := make([]color.Color, 1<<uint(d.nplanes))
for i := 0; i < len(pal)*3; i += 3 {
pal[i/3] = color.RGBA{R: d.colormap[i], G: d.colormap[i+1], B: d.colormap[i+2], A: 255}
}
img := image.NewPaletted(d.bounds, pal)
bufR := bufio.NewReader(d.r)
width := d.bounds.Dx()
height := d.bounds.Dy()
buf := make([]byte, d.bytesPerScanline)
for y := 0; y < height; y++ {
if err := d.rleDecode(bufR, buf); err != nil {
return nil, err
}
for x := 0; x < width; x++ {
v := byte(0)
for i := 0; i < d.nplanes; i++ {
v = (v >> 1) | ((buf[d.bytesPerLine*i+(x/8)] << (uint(x) & 7)) & 0x80)
}
v >>= uint(8 - d.nplanes)
img.Pix[y*img.Stride+x] = v
}
}
return img, nil
}
func (d *decoder) rleDecode(bufR *bufio.Reader, out []byte) error {
for off := 0; off < d.bytesPerScanline; {
val, err := bufR.ReadByte()
if err != nil {
return err
}
run := 1
if val >= 0xc0 {
run = int(val & 0x3f)
val, err = bufR.ReadByte()
if err != nil {
return err
}
}
for i := 0; i < run; i++ {
if off >= d.bytesPerScanline {
return errors.New("pcx: RLE overrun")
}
if off < len(out) {
out[off] = val
}
off++
}
}
return nil
}