func Decode(r io.Reader) (img image.Image, er error) {
/* Reading the whole file in may be inefficient, but libjpeg wants callbacks
* to functions to read in more data, and that is a nightmare to implement. We
* don't want to read the entire stream, however, which means pulling the header.
* We may be able to read enough to call jpeg_read_header with a [10]byte, but
* I'll change it later if need be, since this probably doesn't play nicely
* with a non-closing io.Reader */
var wholeFile []byte
if wholeFile, er = ioutil.ReadAll(r); er != nil {
return
}
var cinfo C.struct_jpeg_decompress_struct
var jerr C.struct_jpeg_error_mgr
cinfo.err = C.jpeg_std_error(&jerr)
C.jpeg_CreateDecompress(&cinfo, C.JPEG_LIB_VERSION, C.size_t(unsafe.Sizeof(cinfo)))
C.jpeg_mem_src(&cinfo, (*C.uchar)(unsafe.Pointer(&wholeFile[0])), C.ulong(len(wholeFile)))
if C.jpeg_read_header(&cinfo, C.TRUE) == C.JPEG_HEADER_OK {
C.jpeg_start_decompress(&cinfo)
if cinfo.num_components == 1 {
img = decodeGrayscale(&cinfo)
} else if cinfo.num_components == 3 {
img = decodeRGB(&cinfo)
} else if cinfo.num_components == 4 {
img = decodeCMYK(&cinfo)
} else {
er = fmt.Errorf("Invalid number of components (%d)", cinfo.num_components)
}
if er == nil {
C.jpeg_finish_decompress(&cinfo)
}
}
C.jpeg_destroy_decompress(&cinfo)
return
}
