#include <u.h>#include <libc.h>#include <libg.h>#include <layer.h> voidsegment(Bitmap *db, Point pt1, Point pt2, int v, Fcode c){	Layer *dl, *cover;	Rectangle r, rc;	Point t1, t2;	int fits; 	dl = (Layer*)db;	if(dl->cache == 0){    Easy:		_segment(db, pt1, pt2, v, c);		return;	}	/* this is clumsy but safe */	r = rcanon(Rpt(pt1, pt2));	if(pt2.x > pt1.x)		r.max.x++;	if(pt2.y > pt1.y)		r.max.y++;	fits = rectinrect(r, dl->clipr);	if(fits && dl->vis==Visible)		/*		 * Look for a Bitmap we can write on instead of a Layer.		 * r is known to fit within dl->clipr.  As long as we have		 * only Visible covering layers, we know that r will		 * therefore fit within their cliprs and no more clipping		 * is required.		 */		for(cover=dl->cover->layer; ; cover=cover->cover->layer){			if(cover->cache == 0){				db = cover;				goto Easy;			}			if(cover->vis != Visible)				break;		}	/*	 * Either dl or one of the covering layers is not Visible.	 * Do the operation in the cache and restore as necessary.	 * If dl is Visible, r is contained within cover->clipr and	 * the cache must be restored from the cover; otherwise the	 * cache is up to date but the restoration of the screen may	 * require clipping.	 *	 * First we must do real line clipping; if we were lucky we	 * avoided it altogether and didn't even get here.	 */	t1 = pt1;	t2 = pt2;	if(!clipline(dl->clipr, &t1, &t2))		return;	r = rcanon(Rpt(t1, t2));	r.max.x++;	r.max.y++;	if(!fits && !rectclip(&r, dl->clipr))		return;	/* r is now bbox of the portion of dl that will be modified */	cover = dl->cover->layer;	if(dl->vis == Visible)		bitblt(dl->cache, r.min, cover, r, S);	if(!fits){		rc = dl->cache->clipr;		clipr(dl->cache, r);	}	_segment(dl->cache, pt1, pt2, v, c);	if(!fits)		clipr(dl->cache, rc);	if(dl->vis == Visible)		bitblt(cover, r.min, dl->cache, r, S);	else if(dl->vis==Obscured)		layerop(lupdate, r, dl, (void *)0);} void_segment(Bitmap *d, Point p1, Point p2, int v, Fcode f){	uchar *buf; 	buf = bneed(22);	buf[0] = 'l';	BPSHORT(buf+1, d->id);	BPLONG(buf+3, p1.x);	BPLONG(buf+7, p1.y);	BPLONG(buf+11, p2.x);	BPLONG(buf+15, p2.y);	buf[19] = v;	BPSHORT(buf+20, f);}