/
decoder.go
158 lines (120 loc) · 2.75 KB
/
decoder.go
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package im8f
import (
"encoding/binary"
"fmt"
"image"
"io"
"github.com/superloach/im8"
"github.com/superloach/im8/col8"
)
// Decoder holds the data that is read in im8f format.
type Decoder struct {
header []byte
config *image.Config
img *im8.Im8
}
// NewDecoder returns an empty Decoder, ready for use.
// &Decoder{} also works fine for this.
func NewDecoder() *Decoder {
return &Decoder{}
}
func (d *Decoder) readHeader(r io.Reader) (int, error) {
n := 0
ohdr := []byte(Magic)
if d.header == nil {
hdr := make([]byte, len(ohdr))
m, err := r.Read(hdr)
n += m
if err != nil {
return n, fmt.Errorf("read hdr: %w", err)
}
d.header = hdr
}
for i, b := range d.header {
if ohdr[i] != b {
return n, MagicMismatchError{i, b}
}
}
return n, nil
}
func (d *Decoder) readConfig(r io.Reader) (int, error) {
n, err := d.readHeader(r)
if err != nil {
return n, fmt.Errorf("read header: %w", err)
}
if d.config != nil {
return n, nil
}
conf := image.Config{
ColorModel: col8.Col8Model,
}
w := uint64(0)
err = binary.Read(r, binary.BigEndian, &w)
n += 8
if err != nil {
return n, fmt.Errorf("read w: %w", err)
}
conf.Width = int(w)
h := uint64(0)
err = binary.Read(r, binary.BigEndian, &h)
n += 8
if err != nil {
return n, fmt.Errorf("read h: %w", err)
}
conf.Height = int(h)
d.config = &conf
return n, nil
}
// Config reads an image.Config from r in im8f format.
func (d *Decoder) Config(r io.Reader) (image.Config, error) {
if d.config != nil {
return *d.config, nil
}
_, err := d.readConfig(r)
if err != nil {
return image.Config{}, fmt.Errorf("read config: %w", err)
}
return *d.config, nil
}
func (d *Decoder) readImage(r io.Reader) (int, error) {
n, err := d.readConfig(r)
if err != nil {
return n, fmt.Errorf("read config: %w", err)
}
if d.img != nil {
return n, nil
}
img := &im8.Im8{}
img.Pix = make([]uint8, d.config.Width*d.config.Height)
img.Stride = d.config.Width
img.Rect = image.Rect(0, 0, d.config.Width, d.config.Height)
m, err := r.Read(img.Pix)
n += m
if err != nil {
return n, fmt.Errorf("read pix: %w", err)
}
d.img = img
return n, nil
}
// Image reads an image.Image from r in im8f format.
func (d *Decoder) Image(r io.Reader) (image.Image, error) {
if d.img != nil {
return d.img, nil
}
_, err := d.readImage(r)
if err != nil {
return nil, fmt.Errorf("read image: %w", err)
}
return d.img, nil
}
// Decode reads an image.Image from r in im8f format.
func Decode(r io.Reader) (image.Image, error) {
return NewDecoder().Image(r)
}
// DecodeConfig reads an image.Config from r in im8f format.
func DecodeConfig(r io.Reader) (image.Config, error) {
return NewDecoder().Config(r)
}
func init() {
image.RegisterFormat("im8f", Magic, Decode, DecodeConfig)
}