gif.go

package magick

// #include <stdlib.h>
// extern void * gif_encode(void *im, int single, int *size);
// #cgo LDFLAGS: -lgif
import "C"

import (
	"bytes"
	"errors"
	"fmt"
	"os/exec"
	"unsafe"
)

var (
	gifsicleCmd          string
	errNoGifsicle        = errors.New("error decoding GIF image: Corrupt data. Install gifsicle to try to fix it.")
	errCouldNotEncodeGif = errors.New("error encoding GIF")
	maxGifTries          = 1
)

func looksLikeGif(data []byte) bool {
	return bytes.HasPrefix(data, []byte{'G', 'I', 'F'})
}

func runGifsicle(data []byte, args []string) ([]byte, error) {
	cmd := exec.Command(gifsicleCmd, args...)
	cmd.Stdin = bytes.NewReader(data)
	var out bytes.Buffer
	cmd.Stdout = &out
	err := cmd.Run()
	if err != nil {
		return nil, fmt.Errorf("error running gifsicle: %s", err)
	}
	return out.Bytes(), nil
}

func fixAndDecodeGif(data []byte, try int) (*Image, error) {
	if gifsicleCmd == "" {
		return nil, errNoGifsicle
	}
	args := []string{"--careful", "--unoptimize", "--colors=256"}
	data, err := runGifsicle(data, args)
	if err != nil {
		return nil, err
	}
	return decodeData(data, try+1)
}

// GifEncode encodes the Image as GIF using giflib
// rather than ImageMagick or GraphicksMagick. While this
// will result in a lower quality GIF, encoding is 9-10x
// faster and produces files ~20% smaller.
func (im *Image) GifEncode() ([]byte, error) {
	if !im.coalesced {
		coalesced, err := im.Coalesce()
		if err != nil {
			return nil, err
		}
		coalesced.parent = im.parent
		defer coalesced.Dispose()
		im = coalesced
	}
	var size C.int
	var single C.int
	if im.parent != nil {
		single = 1
	}
	res := C.gif_encode(unsafe.Pointer(im.image), single, &size)
	if res != nil {
		p := unsafe.Pointer(res)
		b := C.GoBytes(p, size)
		C.free(p)
		return b, nil
	}
	return nil, errCouldNotEncodeGif
}

func init() {
	gifsicleCmd, _ = exec.LookPath("gifsicle")
}