ref: dab539cd14726de15932b0310532212f8da29bf7
dir: /sys/src/libmemdraw/read.c/
#include <u.h>
#include <libc.h>
#include <draw.h>
#include <memdraw.h>
Memimage*
readmemimage(int fd)
{
char hdr[5*12+1];
int dy;
ulong chan;
uint l, n;
int m, j;
int new, miny, maxy;
Rectangle r;
uchar *tmp;
int ldepth, chunk;
Memimage *i;
if(readn(fd, hdr, 11) != 11){
werrstr("readimage: short header");
return nil;
}
if(memcmp(hdr, "compressed\n", 11) == 0)
return creadmemimage(fd);
if(readn(fd, hdr+11, 5*12-11) != 5*12-11){
werrstr("readimage: short header (2)");
return nil;
}
/*
* distinguish new channel descriptor from old ldepth.
* channel descriptors have letters as well as numbers,
* while ldepths are a single digit formatted as %-11d.
*/
new = 0;
for(m=0; m<10; m++){
if(hdr[m] != ' '){
new = 1;
break;
}
}
if(hdr[11] != ' '){
werrstr("readimage: bad format");
return nil;
}
if(new){
hdr[11] = '\0';
if((chan = strtochan(hdr)) == 0){
werrstr("readimage: bad channel string %s", hdr);
return nil;
}
}else{
ldepth = ((int)hdr[10])-'0';
if(ldepth<0 || ldepth>3){
werrstr("readimage: bad ldepth %d", ldepth);
return nil;
}
chan = drawld2chan[ldepth];
}
r.min.x = atoi(hdr+1*12);
r.min.y = atoi(hdr+2*12);
r.max.x = atoi(hdr+3*12);
r.max.y = atoi(hdr+4*12);
if(r.min.x>r.max.x || r.min.y>r.max.y){
werrstr("readimage: bad rectangle");
return nil;
}
miny = r.min.y;
maxy = r.max.y;
l = bytesperline(r, chantodepth(chan));
i = allocmemimage(r, chan);
if(i == nil)
return nil;
chunk = 32*1024;
if(chunk < l)
chunk = l;
tmp = malloc(chunk);
if(tmp == nil)
goto Err;
while(maxy > miny){
dy = maxy - miny;
if(dy*l > chunk)
dy = chunk/l;
n = dy*l;
m = readn(fd, tmp, n);
if(m != n){
werrstr("readmemimage: read count %d not %d: %r", m, n);
Err:
freememimage(i);
free(tmp);
return nil;
}
if(!new) /* an old image: must flip all the bits */
for(j=0; j<chunk; j++)
tmp[j] ^= 0xFF;
if(loadmemimage(i, Rect(r.min.x, miny, r.max.x, miny+dy), tmp, chunk) <= 0)
goto Err;
miny += dy;
}
free(tmp);
return i;
}