#include <u.h>
#include <libc.h>
#include <draw.h>
#include <memdraw.h>

static void
resample(Memimage *dst, Rectangle r, Memimage *src, Rectangle sr, int bilinear)
{
	Point sp, dp;
	Point _sp, qp;
	Point ssize, dsize;
	uchar *pdst0, *pdst, *psrc0, *psrc;
	ulong s00, s01, s10, s11;
	int tx, ty, b, bpp, bpl;

	ssize = subpt(subpt(sr.max, sr.min), Pt(1,1));
	dsize = subpt(subpt(r.max, r.min), Pt(1,1));
	pdst0 = byteaddr(dst, r.min);
	bpp = src->depth/8;
	bpl = src->width*sizeof(int);

	qp.x = (ssize.x<<12)/dsize.x;
	qp.y = (ssize.y<<12)/dsize.y;
	_sp.y = sr.min.y<<12;
	for(dp.y=0; dp.y<=dsize.y; dp.y++){
		sp.y = _sp.y>>12;
		ty = _sp.y&0xFFF;
		if(!bilinear && ty >= 0x800)
			sp.y++;
		pdst = pdst0;
		sp.x = sr.min.x;
		psrc0 = byteaddr(src, sp);
		_sp.x = 0;
		for(dp.x=0; dp.x<=dsize.x; dp.x++){
			sp.x = _sp.x>>12;
			tx = _sp.x&0xFFF;
			psrc = psrc0 + sp.x*bpp;
			if(!bilinear){
				if(tx >= 0x800)
					psrc += bpp;
				for(b=0; b<bpp; b++)
					pdst[b] = psrc[b];
			}else{
				s00 = (0x1000-tx)*(0x1000-ty);
				s01 = tx*(0x1000-ty);
				s10 = (0x1000-tx)*ty;
				s11 = tx*ty;
				for(b=0; b<bpp; b++){
					pdst[b] = ( s11*psrc[bpl+bpp+b]
							   +s10*psrc[bpl+b]
							   +s01*psrc[bpp+b]
							   +s00*psrc[b]
							  ) >>24;
				}
			}
			pdst += bpp;
			_sp.x += qp.x;
		}
		pdst0 += dst->width*sizeof(int);
		_sp.y += qp.y;
	}
}

void
usage(void)
{
	sysfatal("Usage: %s -s width height [-b] [image]\n", argv0);
}

void
main(int argc, char **argv)
{
	Memimage *im, *nim;
	Rectangle r = {0, 0, 0, 0};
	int bilinear=  0;

	ARGBEGIN{
	case 'b':
		bilinear++;
		break;
	case 's':
		r.max.x = atoi(EARGF(usage()));
		r.max.y = atoi(EARGF(usage()));
		break;
	default:
		usage();
	}ARGEND
	if(argc != 0 && argc != 1)
		usage();
	memimageinit();
	im = readmemimage(open(argv[0]? argv[0] : "/fd/0", OREAD));
	nim = allocmemimage(r, im->chan);
	resample(nim, r, im, im->r, bilinear);
	writememimage(1, nim);
	exits(0);
}