From 37da2899f40661e3e9631e497da8dc59b971cbd0 Mon Sep 17 00:00:00 2001
From: "Charles.Forsyth" <devnull@localhost>
Date: Fri, 22 Dec 2006 17:07:39 +0000
Subject: 20060303a

---
 appl/lib/writegif.b | 362 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 362 insertions(+)
 create mode 100644 appl/lib/writegif.b

(limited to 'appl/lib/writegif.b')

diff --git a/appl/lib/writegif.b b/appl/lib/writegif.b
new file mode 100644
index 00000000..3990ed63
--- /dev/null
+++ b/appl/lib/writegif.b
@@ -0,0 +1,362 @@
+implement WImagefile;
+
+include "sys.m";
+	sys: Sys;
+
+include "draw.m";
+	draw: Draw;
+	Chans, Display, Image, Rect: import draw;
+
+include "bufio.m";
+	bufio: Bufio;
+	Iobuf: import bufio;
+
+include "imagefile.m";
+
+Nhash: con 4001;
+
+Entry: adt
+{
+	index: int;
+	prefix: int;
+	exten: int;
+	next:	cyclic ref Entry;
+};
+
+IO: adt
+{
+	fd:	ref Iobuf;
+	buf:	array of byte;
+	i:	int;
+	nbits:	int;	 # bits in right side of shift register
+	sreg:	int;	# shift register
+};
+
+tbl: array of ref Entry;
+
+colormap: array of array of byte;
+log2 := array[] of {1 => 0, 2 => 1, 4 => 2, 8 => 3, * => -1};
+
+init(iomod: Bufio)
+{
+	if(sys == nil){
+		sys = load Sys Sys->PATH;
+		draw = load Draw Draw->PATH;
+	}
+	bufio = iomod;
+}
+
+writeimage(fd: ref Iobuf, image: ref Image): string
+{
+	case image.chans.desc {
+	(Draw->GREY1).desc or (Draw->GREY2).desc or
+	(Draw->GREY4).desc or (Draw->GREY8).desc or
+	(Draw->CMAP8).desc =>
+		if(image.depth > 8 || (image.depth&(image.depth-1)) != 0)
+			return "inconsistent depth";
+	* =>
+		return "unsupported channel type";
+	}
+
+	inittbl();
+
+	writeheader(fd, image);
+	writedescriptor(fd, image);
+
+	err := writedata(fd, image);
+	if(err != nil)
+		return err;
+
+	writetrailer(fd);
+	fd.flush();
+	return err;
+}
+
+inittbl()
+{
+	tbl = array[4096] of ref Entry;
+	for(i:=0; i<len tbl; i++)
+		tbl[i] = ref Entry(i, -1, i, nil);
+}
+
+# Write header, logical screen descriptor, and color map
+writeheader(fd: ref Iobuf, image: ref Image): string
+{
+	# Header
+	fd.puts("GIF89a");
+
+	# Logical Screen Descriptor
+	put2(fd, image.r.dx());
+	put2(fd, image.r.dy());
+	# color table present, 4 bits per color (for RGBV best case), size of color map
+	fd.putb(byte ((1<<7)|(3<<4)|(image.depth-1)));
+	fd.putb(byte 0);	# white background (doesn't matter anyway)
+	fd.putb(byte 0);	# pixel aspect ratio - unused
+
+	# Global Color Table
+	getcolormap(image);
+	ldepth := log2[image.depth];
+	if(image.chans.eq(Draw->GREY8))
+		ldepth = 4;
+	fd.write(colormap[ldepth], len colormap[ldepth]);
+	return nil;
+}
+
+# Write image descriptor
+writedescriptor(fd: ref Iobuf, image: ref Image)
+{
+	# Image Separator
+	fd.putb(byte 16r2C);
+
+	# Left, top, width, height
+	put2(fd, 0);
+	put2(fd, 0);
+	put2(fd, image.r.dx());
+	put2(fd, image.r.dy());
+	# no special processing
+	fd.putb(byte 0);
+}
+
+# Write data
+writedata(fd: ref Iobuf, image: ref Image): string
+{
+	# LZW Minimum code size
+	if(image.depth == 1)
+		fd.putb(byte 2);
+
+	else
+		fd.putb(byte image.depth);
+
+	# Encode and emit the data
+	err := encode(fd, image);
+	if(err != nil)
+		return err;
+
+	# Block Terminator
+	fd.putb(byte 0);
+	return nil;
+}
+
+# Write data
+writetrailer(fd: ref Iobuf)
+{
+	fd.putb(byte 16r3B);
+}
+
+# Write little-endian 16-bit integer
+put2(fd: ref Iobuf, i: int)
+{
+	fd.putb(byte i);
+	fd.putb(byte (i>>8));
+}
+
+# Get color map for all ldepths, in format suitable for writing out
+getcolormap(image: ref Draw->Image)
+{
+	if(colormap != nil)
+		return;
+	colormap = array[5] of array of byte;
+	display := image.display;
+	colormap[4] = array[3*256] of byte;
+	colormap[3] = array[3*256] of byte;
+	colormap[2] = array[3*16] of byte;
+	colormap[1] = array[3*4] of byte;
+	colormap[0] = array[3*2] of byte;
+	c := colormap[4];
+	for(i:=0; i<256; i++){
+		c[3*i+0] = byte i;
+		c[3*i+1] = byte i;
+		c[3*i+2] = byte i;
+	}
+	c = colormap[3];
+	for(i=0; i<256; i++){
+		(r, g, b) := display.cmap2rgb(i);
+		c[3*i+0] = byte r;
+		c[3*i+1] = byte g;
+		c[3*i+2] = byte b;
+	}
+	c = colormap[2];
+	for(i=0; i<16; i++){
+		col := (i<<4)|i;
+		(r, g, b) := display.cmap2rgb(col);
+		c[3*i+0] = byte r;
+		c[3*i+1] = byte g;
+		c[3*i+2] = byte b;
+	}
+	c = colormap[1];
+	for(i=0; i<4; i++){
+		col := (i<<6)|(i<<4)|(i<<2)|i;
+		(r, g, b) := display.cmap2rgb(col);
+		c[3*i+0] = byte r;
+		c[3*i+1] = byte g;
+		c[3*i+2] = byte b;
+	}
+	c = colormap[0];
+	for(i=0; i<2; i++){
+		if(i == 0)
+			col := 0;
+		else
+			col = 16rFF;
+		(r, g, b) := display.cmap2rgb(col);
+		c[3*i+0] = byte r;
+		c[3*i+1] = byte g;
+		c[3*i+2] = byte b;
+	}
+}
+
+# Put n bits of c into output at io.buf[i];
+output(io: ref IO, c, n: int)
+{
+	if(c < 0){
+		if(io.nbits != 0)
+			io.buf[io.i++] = byte io.sreg;
+		io.fd.putb(byte io.i);
+		io.fd.write(io.buf, io.i);
+		io.nbits = 0;
+		return;
+	}
+
+	if(io.nbits+n >= 31){
+		sys->print("panic: WriteGIF sr overflow\n");
+		exit;
+	}
+	io.sreg |= c<<io.nbits;
+	io.nbits += n;
+
+	while(io.nbits >= 8){
+		io.buf[io.i++] = byte io.sreg;
+		io.sreg >>= 8;
+		io.nbits -= 8;
+	}
+
+	if(io.i >= 255){
+		io.fd.putb(byte 255);
+		io.fd.write(io.buf, 255);
+		io.buf[0:] = io.buf[255:io.i];
+		io.i -= 255;
+	}
+}
+
+# LZW encoder
+encode(fd: ref Iobuf, image: ref Image): string
+{
+	c, h, csize, prefix: int;
+	e, oe: ref Entry;
+
+	first := 1;
+	ld := log2[image.depth];
+	# ldepth 0 must generate codesize 2 with values 0 and 1 (see the spec.)
+	ld0 := ld;
+	if(ld0 == 0)
+		ld0 = 1;
+	codesize := (1<<ld0);
+	CTM := 1<<codesize;
+	EOD := CTM+1;
+
+	io := ref IO (fd, array[300] of byte, 0, 0, 0);
+	sreg := 0;
+	nbits := 0;
+	bitsperpixel := 1<<ld;
+	pm := (1<<bitsperpixel)-1;
+
+	# Read image data into memory
+	# potentially one extra byte on each end of each scan line
+	data := array[image.r.dy()*(2+(image.r.dx()>>(3-log2[image.depth])))] of byte;
+	ndata := image.readpixels(image.r, data);
+	if(ndata < 0)
+		return sys->sprint("WriteGIF: readpixels: %r");
+	datai := 0;
+	x := image.r.min.x;
+
+Init:
+	for(;;){
+		csize = codesize+1;
+		nentry := EOD+1;
+		maxentry := (1<<csize);
+		hash := array[Nhash] of ref Entry;
+		for(i := 0; i<nentry; i++){
+			e = tbl[i];
+			h = (e.prefix<<24) | (e.exten<<8);
+			h %= Nhash;
+			if(h < 0)
+				h += Nhash;
+			e.next = hash[h];
+			hash[h] = e;
+		}
+		prefix = -1;
+		if(first)
+			output(io, CTM, csize);
+		first = 0;
+
+		# Scan over pixels.  Because of partially filled bytes on ends of scan lines,
+		# which must be ignored in the data stream passed to GIF, this is more
+		# complex than we'd like
+	Next:
+		for(;;){
+			if(ld != 3){
+				# beginning of scan line is difficult; prime the shift register
+				if(x == image.r.min.x){
+					if(datai == ndata)
+						break;
+					sreg = int data[datai++];
+					nbits = 8-((x&(7>>ld))<<ld);
+				}
+				x++;
+				if(x == image.r.max.x)
+					x = image.r.min.x;
+			}
+			if(nbits == 0){
+				if(datai == ndata)
+					break;
+				sreg = int data[datai++];
+				nbits = 8;
+			}
+			nbits -= bitsperpixel;
+			c = sreg>>nbits & pm;
+			h = prefix<<24 | c<<8;
+			h %= Nhash;
+			if(h < 0)
+				h += Nhash;
+			oe = nil;
+			for(e = hash[h]; e!=nil; e=e.next){
+				if(e.prefix == prefix && e.exten == c){
+					if(oe != nil){
+						oe.next = e.next;
+						e.next = hash[h];
+						hash[h] = e;
+					}
+					prefix = e.index;
+					continue Next;
+				}
+				oe = e;
+			}
+
+			output(io, prefix, csize);
+			early:=0; # peculiar tiff feature here for reference
+			if(nentry == maxentry-early){
+				if(csize == 12){
+					nbits += codesize;	# unget pixel
+					x--;
+					output(io, CTM, csize);
+					continue Init;
+				}
+				csize++;
+				maxentry = (1<<csize);
+			}
+
+			e = tbl[nentry];
+			e.prefix = prefix;
+			e.exten = c;
+			e.next = hash[h];
+			hash[h] = e;
+
+			prefix = c;
+			nentry++;
+		}
+		break Init;
+	}
+	output(io, prefix, csize);
+	output(io, EOD, csize);
+	output(io, -1, csize);
+	return nil;
+}
-- 
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