implement RImagefile; include "sys.m";	sys: Sys; include "draw.m"; include "bufio.m";	bufio: Bufio;	Iobuf: import bufio; include "imagefile.m"; Header: adt{	fd: ref Iobuf;	buf: array of byte;	vers: string;	screenw: int;	screenh: int;	fields: int;	bgrnd: int;	aspect: int;	transp: int;	trindex: byte;}; Entry: adt{	prefix: int;	exten: int;}; tbl: array of Entry; init(iomod: Bufio){	if(sys == nil)		sys = load Sys Sys->PATH;	bufio = iomod;}read(fd: ref Iobuf): (ref Rawimage, string){	(a, err) := readarray(fd, 0);	if(a != nil)		return (a[0], err);	return (nil, err);} readmulti(fd: ref Iobuf): (array of ref Rawimage, string){	return readarray(fd, 1);} readarray(fd: ref Iobuf, multi: int): (array of ref Rawimage, string){	inittbl(); 	buf := array[3*256] of byte; 	(header, err) := readheader(fd, buf);	if(header == nil)		return (nil, err); 	globalcmap: array of byte;	if(header.fields & 16r80){		(globalcmap, err) = readcmap(header, (header.fields&7)+1);		if(globalcmap == nil)			return (nil, err);	} 	images: array of ref Rawimage;	new: ref Rawimage;     Loop:	for(;;){		case c := fd.getb(){		Bufio->EOF =>			if(err == "")				err = "ReadGIF: premature EOF";			break Loop;		Bufio->ERROR =>			err = sys->sprint("ReadGIF: read error: %r");			return (nil, err);		16r21 =>	# Extension (ignored)			err = skipextension(header);			if(err != nil)				return (nil, err); 		16r2C =>	# Image Descriptor			if(!multi && images!=nil)	# why read the rest?				break Loop;			(new, err) = readimage(header);			if(new == nil)				return (nil ,err);			if(new.fields & 16r80){				(new.cmap, err) = readcmap(header, (new.fields&7)+1);				if(new.cmap == nil)					return (nil, err);			}else				new.cmap = globalcmap;			(new.chans[0], err) = decode(header, new);			if(new.chans[0] == nil)				return (nil, err);			if(new.fields & 16r40)				interlace(new);			new.transp = header.transp;			new.trindex = header.trindex;			nimages := array[len images+1] of ref Rawimage;			nimages[0:] = images[0:];			nimages[len images] = new;			images = nimages; 		16r3B =>	# Trailer			break Loop; 		* =>			err = sys->sprint("ReadGIF: unknown block type: %x", c);			break Loop;		}	} 	if(images==nil || images[0].chans[0] == nil){		if(err == nil)			err = "ReadGIF: no picture in file";		return (nil, err);	} 	return (images, err);} readheader(fd: ref Iobuf, buf: array of byte): (ref Header, string){	if(fd.read(buf, 13) != 13){		err := sys->sprint("ReadGIF: can't read header: %r");		return (nil, err);	}	h := ref Header;	h.vers = string buf[0:6];	if(h.vers!="GIF87a" && h.vers!="GIF89a"){		err := sys->sprint("ReadGIF: can't recognize format %s", h.vers);		return (nil, err);	}	h.screenw = int buf[6]+(int buf[7]<<8);	h.screenh = int buf[8]+(int buf[9]<<8);	h.fields = int buf[10];	h.bgrnd = int buf[11];	h.aspect = int buf[12];	h.fd = fd;	h.buf = buf;	h.transp = 0;	return (h, "");} readcmap(h: ref Header, size: int): (array of byte,string){	size = 3*(1<<size);	map := array[size] of byte;	if(h.fd.read(map, size) != size)		return (nil, "ReadGIF: short read on color map");	return (map, "");} readimage(h: ref Header): (ref Rawimage, string){	if(h.fd.read(h.buf, 9) != 9){		err := sys->sprint("ReadGIF: can't read image descriptor: %r");		return (nil, err);	}	i := ref Rawimage;	left := int h.buf[0]+(int h.buf[1]<<8);	top := int h.buf[2]+(int h.buf[3]<<8);	width := int h.buf[4]+(int h.buf[5]<<8);	height := int h.buf[6]+(int h.buf[7]<<8);	i.fields = int h.buf[8];	i.r.min.x = left;	i.r.min.y = top;	i.r.max.x = left+width;	i.r.max.y = top+height;	i.nchans = 1;	i.chans = array[1] of array of byte;	i.chandesc = CRGB1;	return (i, "");} readdata(h: ref Header, ch: chan of (array of byte, string)){	err: string; 	# send nil for error, buffer of length 0 for EOF	for(;;){		nbytes := h.fd.getb();		if(nbytes < 0){			err = sys->sprint("ReadGIF: can't read data: %r");			ch <-= (nil, err);			return;		}		d := array[nbytes] of byte;		if(nbytes == 0){			ch <-= (d, "");			return;		}		n := h.fd.read(d, nbytes);		if(n != nbytes){			if(n > 0){				ch <-= (d[0:n], nil);				ch <-= (d[0:0], "ReadGIF: short data subblock");			}else				ch <-= (nil, sys->sprint("ReadGIF: can't read data: %r"));			return;		}		ch <-= (d, "");	}} readerr: con "ReadGIF: can't read extension: %r"; skipextension(h: ref Header): string{	fmterr: con "ReadGIF: bad extension format"; 	hsize := 0;	hasdata := 0; 	case h.fd.getb(){	Bufio->ERROR or Bufio->EOF =>		return sys->sprint(readerr);	16r01 =>	# Plain Text Extension		hsize = 13;		hasdata = 1;	16rF9 =>	# Graphic Control Extension		return graphiccontrol(h);	16rFE =>	# Comment Extension		hasdata = 1;	16rFF =>	# Application Extension		hsize = h.fd.getb();		# standard says this must be 11, but Adobe likes to put out 10-byte ones,		# so we pay attention to the field.		hasdata = 1;	* =>		return "ReadGIF: unknown extension";	}	if(hsize>0 && h.fd.read(h.buf, hsize) != hsize)		return sys->sprint(readerr);	if(!hasdata){		if(int h.buf[hsize-1] != 0)			return fmterr;	}else{		ch := chan of (array of byte, string);		spawn readdata(h, ch);		for(;;){			(data, err) := <-ch;			if(data == nil)				return err;			if(len data == 0)				break;		}	}	return "";} graphiccontrol(h: ref Header): string{	if(h.fd.read(h.buf, 5+1) != 5+1)		return sys->sprint(readerr);	if(int h.buf[1] & 1){		h.transp = 1;		h.trindex = h.buf[4];	}	return "";} inittbl(){	tbl = array[4096] of Entry;	for(i:=0; i<258; i++) {		tbl[i].prefix = -1;		tbl[i].exten = i;	}} decode(h: ref Header, i: ref Rawimage): (array of byte, string){	c, incode: int; 	err := "";	if(h.fd.read(h.buf, 1) != 1){		err = sys->sprint("ReadGIF: can't read data: %r");		return (nil, err);	}	codesize := int h.buf[0];	if(codesize>8 || 0>codesize){		err = sys->sprint("ReadGIF: can't handle codesize %d", codesize);		return (nil, err);	}	err1 := "";	if(i.cmap!=nil && len i.cmap!=3*(1<<codesize)	  && (codesize!=2 || len i.cmap!=3*2)) # peculiar GIF bitmap files...		err1 = sys->sprint("ReadGIF: codesize %d doesn't match color map 3*%d", codesize, len i.cmap/3); 	ch := chan of (array of byte, string); 	spawn readdata(h, ch); 	CTM :=1<<codesize;	EOD := CTM+1; 	pic := array[(i.r.max.x-i.r.min.x)*(i.r.max.y-i.r.min.y)] of byte;	pici := 0;	data := array[0] of byte;	datai := 0; 	nbits := 0;	sreg := 0;	stack := array[4096] of byte;	stacki: int;	fc := 0; Init:	for(;;){		csize := codesize+1;		nentry := EOD+1;		maxentry := (1<<csize)-1;		first := 1;		ocode := -1; 		for(;; ocode = incode) {			while(nbits < csize) {				if(datai == len data){					(data, err) = <-ch;					if(data == nil)						return (nil, err);					if(err!="" && err1=="")						err1 = err;					if(len data == 0)						break Init;					datai = 0;				}				c = int data[datai++];				sreg |= c<<nbits;				nbits += 8;			}			code := sreg & ((1<<csize) - 1);			sreg >>= csize;			nbits -= csize; 			if(code == EOD){				(data, err) = <-ch;				if(len data != 0)					err = "ReadGIF: unexpected data past EOD";				if(err!="" && err1=="")					err1 = err;				break Init;			} 			if(code == CTM)				continue Init; 			stacki = len stack-1; 			incode = code; 			# special case for KwKwK 			if(code == nentry) {				stack[stacki--] = byte fc;				code = ocode;			} 			if(code > nentry) {				err = sys->sprint("ReadGIF: bad code %x %x", code, nentry);				return (nil, err);			}					for(c=code; c>=0; c=tbl[c].prefix)				stack[stacki--] = byte tbl[c].exten; 			nb := len stack-(stacki+1);			if(pici+nb > len pic){				if(err1 == "")					err1 = "ReadGIF: data overflows picture";			}else{				pic[pici:] = stack[stacki+1:];				pici += nb;			} 			fc = int stack[stacki+1]; 			if(first){				first = 0;				continue;			}			early:=0; # peculiar tiff feature here for reference			if(nentry == maxentry-early) {				if(csize >= 12)					continue;				csize++;				maxentry = (1<<csize);				if(csize < 12)					maxentry--;			}			tbl[nentry].prefix = ocode;			tbl[nentry].exten = fc;			nentry++;		}	}	return (pic, err1);} interlace(image: ref Rawimage){	pic := image.chans[0];	r := image.r;	dx := r.max.x-r.min.x;	ipic := array[dx*(r.max.y-r.min.y)] of byte; 	# Group 1: every 8th row, starting with row 0	yy := 0;	for(y:=r.min.y; y<r.max.y; y+=8){		ipic[y*dx:] = pic[yy*dx:(yy+1)*dx];		yy++;	} 	# Group 2: every 8th row, starting with row 4	for(y=r.min.y+4; y<r.max.y; y+=8){		ipic[y*dx:] = pic[yy*dx:(yy+1)*dx];		yy++;	} 	# Group 3: every 4th row, starting with row 2	for(y=r.min.y+2; y<r.max.y; y+=4){		ipic[y*dx:] = pic[yy*dx:(yy+1)*dx];		yy++;	} 	# Group 4: every 2nd row, starting with row 1	for(y=r.min.y+1; y<r.max.y; y+=2){		ipic[y*dx:] = pic[yy*dx:(yy+1)*dx];		yy++;	} 	image.chans[0] = ipic;}