Why not?

src/cmd/jpg/writegif.c

@@ -0,0 +1,568 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+#include <memdraw.h>
+#include <bio.h>
+#include "imagefile.h"
+
+enum
+{
+	Nhash	= 4001,
+	Nbuf		= 300,
+};
+
+typedef struct Entry Entry;
+typedef struct IO IO;
+
+
+struct Entry
+{
+	int		index;
+	int		prefix;
+	int		exten;
+	Entry	*next;
+};
+
+struct IO
+{
+	Biobuf	*fd;
+	uchar	buf[Nbuf];
+	int		i;
+	int		nbits;	/* bits in right side of shift register */
+	int		sreg;		/* shift register */
+};
+
+static Rectangle	mainrect;
+static Entry	tbl[4096];
+static uchar	*colormap[5];	/* one for each ldepth: GREY1 GREY2 GREY4 CMAP8=rgbv plus GREY8 */
+#define	GREYMAP	4
+static int		colormapsize[] = { 2, 4, 16, 256, 256 };	/* 2 for zero is an odd property of GIF */
+
+static void		writeheader(Biobuf*, Rectangle, int, ulong, int);
+static void		writedescriptor(Biobuf*, Rectangle);
+static char*	writedata(Biobuf*, Image*, Memimage*);
+static void		writecomment(Biobuf *fd, char*);
+static void		writegraphiccontrol(Biobuf *fd, int, int);
+static void*	gifmalloc(ulong);
+static void		encode(Biobuf*, Rectangle, int, uchar*, uint);
+
+static
+char*
+startgif0(Biobuf *fd, ulong chan, Rectangle r, int depth, int loopcount)
+{
+	int i;
+
+	for(i=0; i<nelem(tbl); i++)
+		tbl[i] = (Entry){i, -1, i, nil};
+
+	switch(chan){
+	case GREY1:
+	case GREY2:
+	case GREY4:
+	case CMAP8:
+	case GREY8:
+		break;
+	default:
+		return "WriteGIF: can't handle channel type";
+	}
+
+	mainrect = r;
+	writeheader(fd, r, depth, chan, loopcount);
+	return nil;
+}
+
+char*
+startgif(Biobuf *fd, Image *image, int loopcount)
+{
+	return startgif0(fd, image->chan, image->r, image->depth, loopcount);
+}
+
+char*
+memstartgif(Biobuf *fd, Memimage *memimage, int loopcount)
+{
+	return startgif0(fd, memimage->chan, memimage->r, memimage->depth, loopcount);
+}
+
+static
+char*
+writegif0(Biobuf *fd, Image *image, Memimage *memimage, ulong chan, Rectangle r, char *comment, int dt, int trans)
+{
+	char *err;
+
+	switch(chan){
+	case GREY1:
+	case GREY2:
+	case GREY4:
+	case CMAP8:
+	case GREY8:
+		break;
+	default:
+		return "WriteGIF: can't handle channel type";
+	}
+
+	writecomment(fd, comment);
+	writegraphiccontrol(fd, dt, trans);
+	writedescriptor(fd, r);
+
+	err = writedata(fd, image, memimage);
+	if(err != nil)
+		return err;
+
+	return nil;
+}
+
+char*
+writegif(Biobuf *fd, Image *image, char *comment, int dt, int trans)
+{
+	return writegif0(fd, image, nil, image->chan, image->r, comment, dt, trans);
+}
+
+char*
+memwritegif(Biobuf *fd, Memimage *memimage, char *comment, int dt, int trans)
+{
+	return writegif0(fd, nil, memimage, memimage->chan, memimage->r, comment, dt, trans);
+}
+
+/*
+ * Write little-endian 16-bit integer
+ */
+static
+void
+put2(Biobuf *fd, int i)
+{
+	Bputc(fd, i);
+	Bputc(fd, i>>8);
+}
+
+/*
+ * Get color map for all ldepths, in format suitable for writing out
+ */
+static
+void
+getcolormap(void)
+{
+	int i, col;
+	ulong rgb;
+	uchar *c;
+
+	if(colormap[0] != nil)
+		return;
+	for(i=0; i<nelem(colormap); i++)
+		colormap[i] = gifmalloc(3* colormapsize[i]);
+	c = colormap[GREYMAP];	/* GREY8 */
+	for(i=0; i<256; i++){
+		c[3*i+0] = i;	/* red */
+		c[3*i+1] = i;	/* green */
+		c[3*i+2] = i;	/* blue */
+	}
+	c = colormap[3];	/* RGBV */
+	for(i=0; i<256; i++){
+		rgb = cmap2rgb(i);
+		c[3*i+0] = (rgb>>16) & 0xFF;	/* red */
+		c[3*i+1] = (rgb>> 8) & 0xFF;	/* green */
+		c[3*i+2] = (rgb>> 0) & 0xFF;	/* blue */
+	}
+	c = colormap[2];	/* GREY4 */
+	for(i=0; i<16; i++){
+		col = (i<<4)|i;
+		rgb = cmap2rgb(col);
+		c[3*i+0] = (rgb>>16) & 0xFF;	/* red */
+		c[3*i+1] = (rgb>> 8) & 0xFF;	/* green */
+		c[3*i+2] = (rgb>> 0) & 0xFF;	/* blue */
+	}
+	c = colormap[1];	/* GREY2 */
+	for(i=0; i<4; i++){
+		col = (i<<6)|(i<<4)|(i<<2)|i;
+		rgb = cmap2rgb(col);
+		c[3*i+0] = (rgb>>16) & 0xFF;	/* red */
+		c[3*i+1] = (rgb>> 8) & 0xFF;	/* green */
+		c[3*i+2] = (rgb>> 0) & 0xFF;	/* blue */
+	}
+	c = colormap[0];	/* GREY1 */
+	for(i=0; i<2; i++){
+		if(i == 0)
+			col = 0;
+		else
+			col = 0xFF;
+		rgb = cmap2rgb(col);
+		c[3*i+0] = (rgb>>16) & 0xFF;	/* red */
+		c[3*i+1] = (rgb>> 8) & 0xFF;	/* green */
+		c[3*i+2] = (rgb>> 0) & 0xFF;	/* blue */
+	}
+}
+
+/*
+ * Write header, logical screen descriptor, and color map
+ */
+static
+void
+writeheader(Biobuf *fd, Rectangle r, int depth, ulong chan, int loopcount)
+{
+	/* Header */
+	Bprint(fd, "%s", "GIF89a");
+
+	/*  Logical Screen Descriptor */
+	put2(fd, Dx(r));
+	put2(fd, Dy(r));
+
+	/* Color table present, 4 bits per color (for RGBV best case), size of color map */
+	Bputc(fd, (1<<7)|(3<<4)|(depth-1));	/* not right for GREY8, but GIF doesn't let us specify enough bits */
+	Bputc(fd, 0xFF);	/* white background (doesn't matter anyway) */
+	Bputc(fd, 0);	/* pixel aspect ratio - unused */
+
+	/* Global Color Table */
+	getcolormap();
+	if(chan == GREY8)
+		depth = GREYMAP;
+	else
+		depth = drawlog2[depth];
+	Bwrite(fd, colormap[depth], 3*colormapsize[depth]);
+
+	if(loopcount >= 0){	/* hard-to-discover way to force cycled animation */
+		/* Application Extension with (1 loopcountlo loopcounthi) as data */
+		Bputc(fd, 0x21);
+		Bputc(fd, 0xFF);
+		Bputc(fd, 11);
+		Bwrite(fd, "NETSCAPE2.0", 11);
+		Bputc(fd, 3);
+		Bputc(fd, 1);
+		put2(fd, loopcount);
+		Bputc(fd, 0);
+	}
+}
+
+/*
+ * Write optional comment block
+ */
+static
+void
+writecomment(Biobuf *fd, char *comment)
+{
+	int n;
+
+	if(comment==nil || comment[0]=='\0')
+		return;
+
+	/* Comment extension and label */
+	Bputc(fd, 0x21);
+	Bputc(fd, 0xFE);
+
+	/* Comment data */
+	n = strlen(comment);
+	if(n > 255)
+		n = 255;
+	Bputc(fd, n);
+	Bwrite(fd, comment, n);
+
+	/* Block terminator */
+	Bputc(fd, 0x00);
+}
+
+/*
+ * Write optional control block (sets Delay Time)
+ */
+static
+void
+writegraphiccontrol(Biobuf *fd, int dt, int trans)
+{
+	if(dt < 0 && trans < 0)
+		return;
+
+	/* Comment extension and label and block size*/
+	Bputc(fd, 0x21);
+	Bputc(fd, 0xF9);
+	Bputc(fd, 0x04);
+
+	/* Disposal method and other flags (none) */
+	if(trans >= 0)
+		Bputc(fd, 0x01);
+	else
+		Bputc(fd, 0x00);
+	
+	/* Delay time, in centisec (argument is millisec for sanity) */
+	if(dt < 0)
+		dt = 0;
+	else if(dt < 10)
+		dt = 1;
+	else
+		dt = (dt+5)/10;
+	put2(fd, dt);
+
+	/* Transparency index */
+	if(trans < 0)
+		trans = 0;
+	Bputc(fd, trans);
+
+	/* Block terminator */
+	Bputc(fd, 0x00);
+}
+
+/*
+ * Write image descriptor
+ */
+static
+void
+writedescriptor(Biobuf *fd, Rectangle r)
+{
+	/* Image Separator */
+	Bputc(fd, 0x2C);
+
+	/* Left, top, width, height */
+	put2(fd, r.min.x-mainrect.min.x);
+	put2(fd, r.min.y-mainrect.min.y);
+	put2(fd, Dx(r));
+	put2(fd, Dy(r));
+	/* no special processing */
+	Bputc(fd, 0);
+}
+
+/*
+ * Write data
+ */
+static
+char*
+writedata(Biobuf *fd, Image *image, Memimage *memimage)
+{
+	char *err;
+	uchar *data;
+	int ndata, depth;
+	Rectangle r;
+
+	if(memimage != nil){
+		r = memimage->r;
+		depth = memimage->depth;
+	}else{
+		r = image->r;
+		depth = image->depth;
+	}
+
+	/* LZW Minimum code size */
+	if(depth == 1)
+		Bputc(fd, 2);
+	else
+		Bputc(fd, depth);
+
+	/* 
+	 * Read image data into memory
+	 * potentially one extra byte on each end of each scan line
+	 */
+	ndata = Dy(r)*(2+(Dx(r)>>(3-drawlog2[depth])));
+	data = gifmalloc(ndata);
+	if(memimage != nil)
+		ndata = unloadmemimage(memimage, r, data, ndata);
+	else
+		ndata = unloadimage(image, r, data, ndata);
+	if(ndata < 0){
+		err = gifmalloc(ERRMAX);
+		snprint(err, ERRMAX, "WriteGIF: %r");
+		free(data);
+		return err;
+	}
+
+	/* Encode and emit the data */
+	encode(fd, r, depth, data, ndata);
+	free(data);
+
+	/*  Block Terminator */
+	Bputc(fd, 0);
+	return nil;
+}
+
+/*
+ * Write trailer
+ */
+void
+endgif(Biobuf *fd)
+{
+	Bputc(fd, 0x3B);
+	Bflush(fd);
+}
+
+void
+memendgif(Biobuf *fd)
+{
+	endgif(fd);
+}
+
+/*
+ * Put n bits of c into output at io.buf[i];
+ */
+static
+void
+output(IO *io, int c, int n)
+{
+	if(c < 0){
+		if(io->nbits != 0)
+			io->buf[io->i++] = io->sreg;
+		Bputc(io->fd, io->i);
+		Bwrite(io->fd, io->buf, io->i);
+		io->nbits = 0;
+		return;
+	}
+
+	if(io->nbits+n >= 31){
+		fprint(2, "panic: WriteGIF sr overflow\n");
+		exits("WriteGIF panic");
+	}
+	io->sreg |= c<<io->nbits;
+	io->nbits += n;
+
+	while(io->nbits >= 8){
+		io->buf[io->i++] = io->sreg;
+		io->sreg >>= 8;
+		io->nbits -= 8;
+	}
+
+	if(io->i >= 255){
+		Bputc(io->fd, 255);
+		Bwrite(io->fd, io->buf, 255);
+		memmove(io->buf, io->buf+255, io->i-255);
+		io->i -= 255;
+	}
+}
+
+/*
+ * LZW encoder
+ */
+static
+void
+encode(Biobuf *fd, Rectangle r, int depth, uchar *data, uint ndata)
+{
+	int i, c, h, csize, prefix, first, sreg, nbits, bitsperpixel;
+	int CTM, EOD, codesize, ld0, datai, x, ld, pm;
+	int nentry, maxentry, early;
+	Entry *e, *oe;
+	IO *io;
+	Entry **hash;
+
+	first = 1;
+	ld = drawlog2[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 = gifmalloc(sizeof(IO));
+	io->fd = fd;
+	sreg = 0;
+	nbits = 0;
+	bitsperpixel = 1<<ld;
+	pm = (1<<bitsperpixel)-1;
+
+	datai = 0;
+	x = r.min.x;
+	hash = gifmalloc(Nhash*sizeof(Entry*));
+
+Init:
+	memset(hash, 0, Nhash*sizeof(Entry*));
+	csize = codesize+1;
+	nentry = EOD+1;
+	maxentry = (1<<csize);
+	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 == r.min.x){
+				if(datai == ndata)
+					break;
+				sreg = data[datai++];
+				nbits = 8-((x&(7>>ld))<<ld);
+			}
+			x++;
+			if(x == r.max.x)
+				x = r.min.x;
+		}
+		if(nbits == 0){
+			if(datai == ndata)
+				break;
+			sreg = 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;
+				goto Next;
+			}
+			oe = e;
+		}
+
+		output(io, prefix, csize);
+		early = 0; /* peculiar tiff feature here for reference */
+		if(nentry == maxentry-early){
+			if(csize == 12){
+				nbits += bitsperpixel;	/* unget pixel */
+				x--;
+				if(ld != 3 && x == r.min.x)
+					datai--;
+				output(io, CTM, csize);
+				goto Init;
+			}
+			csize++;
+			maxentry = (1<<csize);
+		}
+
+		e = &tbl[nentry];
+		e->prefix = prefix;
+		e->exten = c;
+		e->next = hash[h];
+		hash[h] = e;
+
+		prefix = c;
+		nentry++;
+	}
+
+	output(io, prefix, csize);
+	output(io, EOD, csize);
+	output(io, -1, csize);
+	free(io);
+	free(hash);
+}
+
+static
+void*
+gifmalloc(ulong sz)
+{
+	void *v;
+	v = malloc(sz);
+	if(v == nil) {
+		fprint(2, "WriteGIF: out of memory allocating %ld\n", sz);
+abort();
+		exits("mem");
+	}
+	memset(v, 0, sz);
+	return v;
+}