line.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

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

enum
{
	Arrow1 = 8,
	Arrow2 = 10,
	Arrow3 = 3,
};

static
int
lmin(int a, int b)
{
	if(a < b)
		return a;
	return b;
}

static
int
lmax(int a, int b)
{
	if(a > b)
		return a;
	return b;
}

#ifdef NOTUSED
/*
 * Rather than line clip, we run the Bresenham loop over the full line,
 * and clip on each pixel.  This is more expensive but means that
 * lines look the same regardless of how the windowing has tiled them.
 * For speed, we check for clipping outside the loop and make the
 * test easy when possible.
 */

static
void
horline1(Memimage *dst, Point p0, Point p1, int srcval, Rectangle clipr)
{
	int x, y, dy, deltay, deltax, maxx;
	int dd, easy, e, bpp, m, m0;
	uchar *d;

	deltax = p1.x - p0.x;
	deltay = p1.y - p0.y;
	dd = dst->width*sizeof(ulong);
	dy = 1;
	if(deltay < 0){
		dd = -dd;
		deltay = -deltay;
		dy = -1;
	}
	maxx = lmin(p1.x, clipr.max.x-1);
	bpp = dst->depth;
	m0 = 0xFF^(0xFF>>bpp);
	m = m0 >> (p0.x&(7/dst->depth))*bpp;
	easy = ptinrect(p0, clipr) && ptinrect(p1, clipr);
	e = 2*deltay - deltax;
	y = p0.y;
	d = byteaddr(dst, p0);
	deltay *= 2;
	deltax = deltay - 2*deltax;
	for(x=p0.x; x<=maxx; x++){
		if(easy || (clipr.min.x<=x && clipr.min.y<=y && y<clipr.max.y))
			*d ^= (*d^srcval) & m;
		if(e > 0){
			y += dy;
			d += dd;
			e += deltax;
		}else
			e += deltay;
		d++;
		m >>= bpp;
		if(m == 0)
			m = m0;
	}
}

static
void
verline1(Memimage *dst, Point p0, Point p1, int srcval, Rectangle clipr)
{
	int x, y, deltay, deltax, maxy;
	int easy, e, bpp, m, m0, dd;
	uchar *d;

	deltax = p1.x - p0.x;
	deltay = p1.y - p0.y;
	dd = 1;
	if(deltax < 0){
		dd = -1;
		deltax = -deltax;
	}
	maxy = lmin(p1.y, clipr.max.y-1);
	bpp = dst->depth;
	m0 = 0xFF^(0xFF>>bpp);
	m = m0 >> (p0.x&(7/dst->depth))*bpp;
	easy = ptinrect(p0, clipr) && ptinrect(p1, clipr);
	e = 2*deltax - deltay;
	x = p0.x;
	d = byteaddr(dst, p0);
	deltax *= 2;
	deltay = deltax - 2*deltay;
	for(y=p0.y; y<=maxy; y++){
		if(easy || (clipr.min.y<=y && clipr.min.x<=x && x<clipr.max.x))
			*d ^= (*d^srcval) & m;
		if(e > 0){
			x += dd;
			d += dd;
			e += deltay;
		}else
			e += deltax;
		d += dst->width*sizeof(ulong);
		m >>= bpp;
		if(m == 0)
			m = m0;
	}
}

static
void
horliner(Memimage *dst, Point p0, Point p1, Memimage *src, Point dsrc, Rectangle clipr)
{
	int x, y, sx, sy, deltay, deltax, minx, maxx;
	int bpp, m, m0;
	uchar *d, *s;

	deltax = p1.x - p0.x;
	deltay = p1.y - p0.y;
	sx = drawreplxy(src->r.min.x, src->r.max.x, p0.x+dsrc.x);
	minx = lmax(p0.x, clipr.min.x);
	maxx = lmin(p1.x, clipr.max.x-1);
	bpp = dst->depth;
	m0 = 0xFF^(0xFF>>bpp);
	m = m0 >> (minx&(7/dst->depth))*bpp;
	for(x=minx; x<=maxx; x++){
		y = p0.y + (deltay*(x-p0.x)+deltax/2)/deltax;
		if(clipr.min.y<=y && y<clipr.max.y){
			d = byteaddr(dst, Pt(x, y));
			sy = drawreplxy(src->r.min.y, src->r.max.y, y+dsrc.y);
			s = byteaddr(src, Pt(sx, sy));
			*d ^= (*d^*s) & m;
		}
		if(++sx >= src->r.max.x)
			sx = src->r.min.x;
		m >>= bpp;
		if(m == 0)
			m = m0;
	}
}

static
void
verliner(Memimage *dst, Point p0, Point p1, Memimage *src, Point dsrc, Rectangle clipr)
{
	int x, y, sx, sy, deltay, deltax, miny, maxy;
	int bpp, m, m0;
	uchar *d, *s;

	deltax = p1.x - p0.x;
	deltay = p1.y - p0.y;
	sy = drawreplxy(src->r.min.y, src->r.max.y, p0.y+dsrc.y);
	miny = lmax(p0.y, clipr.min.y);
	maxy = lmin(p1.y, clipr.max.y-1);
	bpp = dst->depth;
	m0 = 0xFF^(0xFF>>bpp);
	for(y=miny; y<=maxy; y++){
		if(deltay == 0)	/* degenerate line */
			x = p0.x;
		else
			x = p0.x + (deltax*(y-p0.y)+deltay/2)/deltay;
		if(clipr.min.x<=x && x<clipr.max.x){
			m = m0 >> (x&(7/dst->depth))*bpp;
			d = byteaddr(dst, Pt(x, y));
			sx = drawreplxy(src->r.min.x, src->r.max.x, x+dsrc.x);
			s = byteaddr(src, Pt(sx, sy));
			*d ^= (*d^*s) & m;
		}
		if(++sy >= src->r.max.y)
			sy = src->r.min.y;
	}
}

static
void
horline(Memimage *dst, Point p0, Point p1, Memimage *src, Point dsrc, Rectangle clipr)
{
	int x, y, deltay, deltax, minx, maxx;
	int bpp, m, m0;
	uchar *d, *s;

	deltax = p1.x - p0.x;
	deltay = p1.y - p0.y;
	minx = lmax(p0.x, clipr.min.x);
	maxx = lmin(p1.x, clipr.max.x-1);
	bpp = dst->depth;
	m0 = 0xFF^(0xFF>>bpp);
	m = m0 >> (minx&(7/dst->depth))*bpp;
	for(x=minx; x<=maxx; x++){
		y = p0.y + (deltay*(x-p0.x)+deltay/2)/deltax;
		if(clipr.min.y<=y && y<clipr.max.y){
			d = byteaddr(dst, Pt(x, y));
			s = byteaddr(src, addpt(dsrc, Pt(x, y)));
			*d ^= (*d^*s) & m;
		}
		m >>= bpp;
		if(m == 0)
			m = m0;
	}
}

static
void
verline(Memimage *dst, Point p0, Point p1, Memimage *src, Point dsrc, Rectangle clipr)
{
	int x, y, deltay, deltax, miny, maxy;
	int bpp, m, m0;
	uchar *d, *s;

	deltax = p1.x - p0.x;
	deltay = p1.y - p0.y;
	miny = lmax(p0.y, clipr.min.y);
	maxy = lmin(p1.y, clipr.max.y-1);
	bpp = dst->depth;
	m0 = 0xFF^(0xFF>>bpp);
	for(y=miny; y<=maxy; y++){
		if(deltay == 0)	/* degenerate line */
			x = p0.x;
		else
			x = p0.x + deltax*(y-p0.y)/deltay;
		if(clipr.min.x<=x && x<clipr.max.x){
			m = m0 >> (x&(7/dst->depth))*bpp;
			d = byteaddr(dst, Pt(x, y));
			s = byteaddr(src, addpt(dsrc, Pt(x, y)));
			*d ^= (*d^*s) & m;
		}
	}
}
#endif /* NOTUSED */

static Memimage*
membrush(int radius)
{
	static Memimage *brush;
	static int brushradius;

	if(brush==nil || brushradius!=radius){
		freememimage(brush);
		brush = allocmemimage(Rect(0, 0, 2*radius+1, 2*radius+1), memopaque->chan);
		if(brush != nil){
			memfillcolor(brush, DTransparent);	/* zeros */
			memellipse(brush, Pt(radius, radius), radius, radius, -1, memopaque, Pt(radius, radius), S);
		}
		brushradius = radius;
	}
	return brush;
}

static
void
discend(Point p, int radius, Memimage *dst, Memimage *src, Point dsrc, int op)
{
	Memimage *disc;
	Rectangle r;

	disc = membrush(radius);
	if(disc != nil){
		r.min.x = p.x - radius;
		r.min.y = p.y - radius;
		r.max.x = p.x + radius+1;
		r.max.y = p.y + radius+1;
		memdraw(dst, r, src, addpt(r.min, dsrc), disc, Pt(0,0), op);
	}
}

static
void
arrowend(Point tip, Point *pp, int end, int sin, int cos, int radius)
{
	int x1, x2, x3;

	/* before rotation */
	if(end == Endarrow){
		x1 = Arrow1;
		x2 = Arrow2;
		x3 = Arrow3;
	}else{
		x1 = (end>>5) & 0x1FF;	/* distance along line from end of line to tip */
		x2 = (end>>14) & 0x1FF;	/* distance along line from barb to tip */
		x3 = (end>>23) & 0x1FF;	/* distance perpendicular from edge of line to barb */
	}

	/* comments follow track of right-facing arrowhead */
	pp->x = tip.x+((2*radius+1)*sin/2-x1*cos);		/* upper side of shaft */
	pp->y = tip.y-((2*radius+1)*cos/2+x1*sin);
	pp++;
	pp->x = tip.x+((2*radius+2*x3+1)*sin/2-x2*cos);		/* upper barb */
	pp->y = tip.y-((2*radius+2*x3+1)*cos/2+x2*sin);
	pp++;
	pp->x = tip.x;
	pp->y = tip.y;
	pp++;
	pp->x = tip.x+(-(2*radius+2*x3+1)*sin/2-x2*cos);	/* lower barb */
	pp->y = tip.y-(-(2*radius+2*x3+1)*cos/2+x2*sin);
	pp++;
	pp->x = tip.x+(-(2*radius+1)*sin/2-x1*cos);		/* lower side of shaft */
	pp->y = tip.y+((2*radius+1)*cos/2-x1*sin);
}

void
_memimageline(Memimage *dst, Point p0, Point p1, int end0, int end1, int radius, Memimage *src, Point sp, Rectangle clipr, int op)
{
	/*
	 * BUG: We should really really pick off purely horizontal and purely
	 * vertical lines and handle them separately with calls to memimagedraw
	 * on rectangles.
	 */

	int hor;
	int sin, cos, dx, dy, t;
	Rectangle oclipr, r;
	Point q, pts[10], *pp, d;

	if(radius < 0)
		return;
	if(rectclip(&clipr, dst->r) == 0)
		return;
	if(rectclip(&clipr, dst->clipr) == 0)
		return;
	d = subpt(sp, p0);
	if(rectclip(&clipr, rectsubpt(src->clipr, d)) == 0)
		return;
	if((src->flags&Frepl)==0 && rectclip(&clipr, rectsubpt(src->r, d))==0)
		return;
	/* this means that only verline() handles degenerate lines (p0==p1) */
	hor = (abs(p1.x-p0.x) > abs(p1.y-p0.y));
	/*
	 * Clipping is a little peculiar.  We can't use Sutherland-Cohen
	 * clipping because lines are wide.  But this is probably just fine:
	 * we do all math with the original p0 and p1, but clip when deciding
	 * what pixels to draw.  This means the layer code can call this routine,
	 * using clipr to define the region being written, and get the same set
	 * of pixels regardless of the dicing.
	 */
	if((hor && p0.x>p1.x) || (!hor && p0.y>p1.y)){
		q = p0;
		p0 = p1;
		p1 = q;
		t = end0;
		end0 = end1;
		end1 = t;
	}

	if((p0.x == p1.x || p0.y == p1.y) && (end0&0x1F) == Endsquare && (end1&0x1F) == Endsquare){
		r.min = p0;
		r.max = p1;
		if(p0.x == p1.x){
			r.min.x -= radius;
			r.max.x += radius+1;
		}
		else{
			r.min.y -= radius;
			r.max.y += radius+1;
		}
		oclipr = dst->clipr;
		sp = addpt(r.min, d);
		dst->clipr = clipr;
		memimagedraw(dst, r, src, sp, memopaque, sp, op);
		dst->clipr = oclipr;
		return;
	}

/*    Hard: */
	/* draw thick line using polygon fill */
	icossin2(p1.x-p0.x, p1.y-p0.y, &cos, &sin);
	dx = (sin*(2*radius+1))/2;
	dy = (cos*(2*radius+1))/2;
	pp = pts;
	oclipr = dst->clipr;
	dst->clipr = clipr;
	q.x = ICOSSCALE*p0.x+ICOSSCALE/2-cos/2;
	q.y = ICOSSCALE*p0.y+ICOSSCALE/2-sin/2;
	switch(end0 & 0x1F){
	case Enddisc:
		discend(p0, radius, dst, src, d, op);
		/* fall through */
	case Endsquare:
	default:
		pp->x = q.x-dx;
		pp->y = q.y+dy;
		pp++;
		pp->x = q.x+dx;
		pp->y = q.y-dy;
		pp++;
		break;
	case Endarrow:
		arrowend(q, pp, end0, -sin, -cos, radius);
		_memfillpolysc(dst, pts, 5, ~0, src, addpt(pts[0], mulpt(d, ICOSSCALE)), 1, 10, 1, op);
		pp[1] = pp[4];
		pp += 2;
	}
	q.x = ICOSSCALE*p1.x+ICOSSCALE/2+cos/2;
	q.y = ICOSSCALE*p1.y+ICOSSCALE/2+sin/2;
	switch(end1 & 0x1F){
	case Enddisc:
		discend(p1, radius, dst, src, d, op);
		/* fall through */
	case Endsquare:
	default:
		pp->x = q.x+dx;
		pp->y = q.y-dy;
		pp++;
		pp->x = q.x-dx;
		pp->y = q.y+dy;
		pp++;
		break;
	case Endarrow:
		arrowend(q, pp, end1, sin, cos, radius);
		_memfillpolysc(dst, pp, 5, ~0, src, addpt(pp[0], mulpt(d, ICOSSCALE)), 1, 10, 1, op);
		pp[1] = pp[4];
		pp += 2;
	}
	_memfillpolysc(dst, pts, pp-pts, ~0, src, addpt(pts[0], mulpt(d, ICOSSCALE)), 0, 10, 1, op);
	dst->clipr = oclipr;
	return;
}

void
memimageline(Memimage *dst, Point p0, Point p1, int end0, int end1, int radius, Memimage *src, Point sp, int op)
{
	_memimageline(dst, p0, p1, end0, end1, radius, src, sp, dst->clipr, op);
}

/*
 * Simple-minded conservative code to compute bounding box of line.
 * Result is probably a little larger than it needs to be.
 */
static
void
addbbox(Rectangle *r, Point p)
{
	if(r->min.x > p.x)
		r->min.x = p.x;
	if(r->min.y > p.y)
		r->min.y = p.y;
	if(r->max.x < p.x+1)
		r->max.x = p.x+1;
	if(r->max.y < p.y+1)
		r->max.y = p.y+1;
}

int
memlineendsize(int end)
{
	int x3;

	if((end&0x3F) != Endarrow)
		return 0;
	if(end == Endarrow)
		x3 = Arrow3;
	else
		x3 = (end>>23) & 0x1FF;
	return x3;
}

Rectangle
memlinebbox(Point p0, Point p1, int end0, int end1, int radius)
{
	Rectangle r, r1;
	int extra;

	r.min.x = 10000000;
	r.min.y = 10000000;
	r.max.x = -10000000;
	r.max.y = -10000000;
	extra = lmax(memlineendsize(end0), memlineendsize(end1));
	r1 = insetrect(canonrect(Rpt(p0, p1)), -(radius+extra));
	addbbox(&r, r1.min);
	addbbox(&r, r1.max);
	return r;
}