ref: d5e2fd9028687dfc18c0ac1b249ccec38ab075f6
dir: /sys/src/cmd/jpg/writepng.c/
/*
* See PNG 1.2 spec, also RFC 2083.
*/
#include <u.h>
#include <libc.h>
#include <draw.h>
#include <memdraw.h>
#include <ctype.h>
#include <bio.h>
#include <flate.h>
#include "imagefile.h"
enum
{
IDATSIZE = 20000,
FilterNone = 0,
};
typedef struct ZlibR ZlibR;
typedef struct ZlibW ZlibW;
struct ZlibR
{
uchar *data;
int width;
int dx;
int dy;
int x;
int y;
int pixwid;
};
struct ZlibW
{
Biobuf *io;
uchar *buf;
uchar *b;
uchar *e;
};
static ulong *crctab;
static uchar PNGmagic[] = { 137, 'P', 'N', 'G', '\r', '\n', 26, '\n'};
static void
put4(uchar *a, ulong v)
{
a[0] = v>>24;
a[1] = v>>16;
a[2] = v>>8;
a[3] = v;
}
static void
chunk(Biobuf *bo, char *type, uchar *d, int n)
{
uchar buf[4];
ulong crc = 0;
if(strlen(type) != 4)
return;
put4(buf, n);
Bwrite(bo, buf, 4);
Bwrite(bo, type, 4);
Bwrite(bo, d, n);
crc = blockcrc(crctab, crc, type, 4);
crc = blockcrc(crctab, crc, d, n);
put4(buf, crc);
Bwrite(bo, buf, 4);
}
static int
zread(void *va, void *buf, int n)
{
int a, i, pixels, pixwid;
uchar *b, *e, *img;
ZlibR *z;
z = va;
pixwid = z->pixwid;
b = buf;
e = b+n;
while(b+pixwid < e){ /* one less for filter alg byte */
if(z->y >= z->dy)
break;
if(z->x == 0)
*b++ = FilterNone;
pixels = (e-b)/pixwid;
if(pixels > z->dx - z->x)
pixels = z->dx - z->x;
img = z->data + z->width*z->y + pixwid*z->x;
memmove(b, img, pixwid*pixels);
if(pixwid == 4){
/*
* Convert to non-premultiplied alpha.
*/
for(i=0; i<pixels; i++, b+=4){
a = b[3];
if(a == 0)
b[0] = b[1] = b[2] = 0;
else if(a != 255){
if(b[0] >= a)
b[0] = a;
b[0] = (b[0]*255)/a;
if(b[1] >= a)
b[1] = a;
b[1] = (b[1]*255)/a;
if(b[2] >= a)
b[2] = a;
b[2] = (b[2]*255)/a;
}
}
}else
b += pixwid*pixels;
z->x += pixels;
if(z->x >= z->dx){
z->x = 0;
z->y++;
}
}
return b - (uchar*)buf;
}
static void
IDAT(ZlibW *z)
{
chunk(z->io, "IDAT", z->buf, z->b - z->buf);
z->b = z->buf;
}
static int
zwrite(void *va, void *buf, int n)
{
int m;
uchar *b, *e;
ZlibW *z;
z = va;
b = buf;
e = b+n;
while(b < e){
m = z->e - z->b;
if(m > e - b)
m = e - b;
memmove(z->b, b, m);
z->b += m;
b += m;
if(z->b >= z->e)
IDAT(z);
}
return n;
}
static Memimage*
memRGBA(Memimage *i)
{
Memimage *ni;
char buf[32];
ulong dst;
/*
* [A]BGR because we want R,G,B,[A] in big-endian order. Sigh.
*/
chantostr(buf, i->chan);
if(strchr(buf, 'a'))
dst = ABGR32;
else
dst = BGR24;
if(i->chan == dst)
return i;
ni = allocmemimage(i->r, dst);
if(ni == nil)
return ni;
memimagedraw(ni, ni->r, i, i->r.min, nil, i->r.min, S);
return ni;
}
char*
memwritepng(Biobuf *io, Memimage *m, ImageInfo *II)
{
int err, n;
uchar buf[200], *h;
ulong vgamma;
Tm *tm;
Memimage *rgb;
ZlibR zr;
ZlibW zw;
crctab = mkcrctab(0xedb88320);
if(crctab == nil)
sysfatal("mkcrctab error");
deflateinit();
rgb = memRGBA(m);
if(rgb == nil)
return "allocmemimage nil";
Bwrite(io, PNGmagic, sizeof PNGmagic);
/* IHDR chunk */
h = buf;
put4(h, Dx(m->r)); h += 4;
put4(h, Dy(m->r)); h += 4;
*h++ = 8; /* 8 bits per channel */
if(rgb->chan == BGR24)
*h++ = 2; /* RGB */
else
*h++ = 6; /* RGBA */
*h++ = 0; /* compression - deflate */
*h++ = 0; /* filter - none */
*h++ = 0; /* interlace - none */
chunk(io, "IHDR", buf, h-buf);
/* time - using now is suspect */
tm = gmtime(time(0));
h = buf;
*h++ = (tm->year + 1900)>>8;
*h++ = (tm->year + 1900)&0xff;
*h++ = tm->mon + 1;
*h++ = tm->mday;
*h++ = tm->hour;
*h++ = tm->min;
*h++ = tm->sec;
chunk(io, "tIME", buf, h-buf);
/* gamma */
if(II->fields_set & II_GAMMA){
vgamma = II->gamma*100000;
put4(buf, vgamma);
chunk(io, "gAMA", buf, 4);
}
/* comment */
if(II->fields_set & II_COMMENT){
strncpy((char*)buf, "Comment", sizeof buf);
n = strlen((char*)buf)+1; // leave null between Comment and text
strncpy((char*)(buf+n), II->comment, sizeof buf - n);
chunk(io, "tEXt", buf, n+strlen((char*)buf+n));
}
/* image data */
zr.dx = Dx(m->r);
zr.dy = Dy(m->r);
zr.width = rgb->width * sizeof(ulong);
zr.data = rgb->data->bdata;
zr.x = 0;
zr.y = 0;
zr.pixwid = chantodepth(rgb->chan)/8;
zw.io = io;
zw.buf = malloc(IDATSIZE);
if(zw.buf == nil)
sysfatal("malloc: %r");
zw.b = zw.buf;
zw.e = zw.b + IDATSIZE;
if((err=deflatezlib(&zw, zwrite, &zr, zread, 6, 0)) < 0)
sysfatal("deflatezlib %s", flateerr(err));
if(zw.b > zw.buf)
IDAT(&zw);
free(zw.buf);
chunk(io, "IEND", nil, 0);
if(m != rgb)
freememimage(rgb);
return nil;
}