ref: e55cb65c247a9cdfa0528d34dec70d435898d098
dir: /sys/src/cmd/scat/dssread.c/
#include <u.h> #include <libc.h> #include <bio.h> #include "sky.h" static void dodecode(Biobuf*, Pix*, int, int, uchar*); static long getlong(uchar*); int debug; Img* dssread(char *file) { int nx, ny, scale, sumall; Pix *p, *pend; uchar buf[21]; Biobuf *bp; Img *ip; if(debug) Bprint(&bout, "reading %s\n", file); bp = Bopen(file, OREAD); if(bp == 0) return 0; if(Bread(bp, buf, sizeof(buf)) != sizeof(buf) || buf[0] != 0xdd || buf[1] != 0x99){ werrstr("bad format"); return 0; } nx = getlong(buf+2); ny = getlong(buf+6); scale = getlong(buf+10); sumall = getlong(buf+14); if(debug) fprint(2, "%s: nx=%d, ny=%d, scale=%d, sumall=%d, nbitplanes=%d,%d,%d\n", file, nx, ny, scale, sumall, buf[18], buf[19], buf[20]); ip = malloc(sizeof(Img) + (nx*ny-1)*sizeof(int)); if(ip == 0){ Bterm(bp); werrstr("no memory"); return 0; } ip->nx = nx; ip->ny = ny; dodecode(bp, ip->a, nx, ny, buf+18); ip->a[0] = sumall; /* sum of all pixels */ Bterm(bp); if(scale > 1){ p = ip->a; pend = &ip->a[nx*ny]; while(p < pend) *p++ *= scale; } hinv(ip->a, nx, ny); return ip; } static void dodecode(Biobuf *infile, Pix *a, int nx, int ny, uchar *nbitplanes) { int nel, nx2, ny2, bits, mask; Pix *aend, px; nel = nx*ny; nx2 = (nx+1)/2; ny2 = (ny+1)/2; memset(a, 0, nel*sizeof(*a)); /* * Initialize bit input */ start_inputing_bits(); /* * read bit planes for each quadrant */ qtree_decode(infile, &a[0], ny, nx2, ny2, nbitplanes[0]); qtree_decode(infile, &a[ny2], ny, nx2, ny/2, nbitplanes[1]); qtree_decode(infile, &a[ny*nx2], ny, nx/2, ny2, nbitplanes[1]); qtree_decode(infile, &a[ny*nx2+ny2], ny, nx/2, ny/2, nbitplanes[2]); /* * make sure there is an EOF symbol (nybble=0) at end */ if(input_nybble(infile) != 0){ fprint(2, "dodecode: bad bit plane values\n"); exits("format"); } /* * get the sign bits */ aend = &a[nel]; mask = 0; bits = 0;; for(; a<aend; a++) { if(px = *a) { if(mask == 0) { mask = 0x80; bits = Bgetc(infile); } if(mask & bits) *a = -px; mask >>= 1; } } } static long getlong(uchar *p) { return (p[0]<<24) | (p[1]<<16) | (p[2]<<8) | p[3]; }