Subversion Repositories planix.SVN

#include <u.h>

#include <libc.h>

#include <draw.h>

#include <memdraw.h>

#include <memlayer.h>

/*

 * ellipse(dst, c, a, b, t, src, sp)

 *   draws an ellipse centered at c with semiaxes a,b>=0

 *   and semithickness t>=0, or filled if t<0.  point sp

 *   in src maps to c in dst

 *

 *   very thick skinny ellipses are brushed with circles (slow)

 *   others are approximated by filling between 2 ellipses

 *   criterion for very thick when b<a: t/b > 0.5*x/(1-x)

 *   where x = b/a

 */

typedef struct Param	Param;

typedef struct State	State;

static	void	bellipse(int, State*, Param*);

static	void	erect(int, int, int, int, Param*);

static	void	eline(int, int, int, int, Param*);

struct Param {

	Memimage	*dst;

	Memimage	*src;

	Point			c;

	int			t;

	Point			sp;

	Memimage	*disc;

	int			op;

};

/*

 * denote residual error by e(x,y) = b^2*x^2 + a^2*y^2 - a^2*b^2

 * e(x,y) = 0 on ellipse, e(x,y) < 0 inside, e(x,y) > 0 outside

 */

struct State {

	int	a;

	int	x;

	vlong	a2;	/* a^2 */

	vlong	b2;	/* b^2 */

	vlong	b2x;	/* b^2 * x */

	vlong	a2y;	/* a^2 * y */

	vlong	c1;

	vlong	c2;	/* test criteria */

	vlong	ee;	/* ee = e(x+1/2,y-1/2) - (a^2+b^2)/4 */

	vlong	dxe;

	vlong	dye;

	vlong	d2xe;

	vlong	d2ye;

};

static

State*

newstate(State *s, int a, int b)

{

	s->x = 0;

	s->a = a;

	s->a2 = (vlong)(a*a);

	s->b2 = (vlong)(b*b);

	s->b2x = (vlong)0;

	s->a2y = s->a2*(vlong)b;

	s->c1 = -((s->a2>>2) + (vlong)(a&1) + s->b2);

	s->c2 = -((s->b2>>2) + (vlong)(b&1));

	s->ee = -s->a2y;

	s->dxe = (vlong)0;

	s->dye = s->ee<<1;

	s->d2xe = s->b2<<1;

	s->d2ye = s->a2<<1;

	return s;

}

/*

 * return x coord of rightmost pixel on next scan line

 */

static

int

step(State *s)

{

	while(s->x < s->a) {

		if(s->ee+s->b2x <= s->c1 ||	/* e(x+1,y-1/2) <= 0 */

		   s->ee+s->a2y <= s->c2) {	/* e(x+1/2,y) <= 0 (rare) */

			s->dxe += s->d2xe;	  

			s->ee += s->dxe;	  

			s->b2x += s->b2;

			s->x++;	  

			continue;

		}

		s->dye += s->d2ye;	  

		s->ee += s->dye;	  

		s->a2y -= s->a2;

		if(s->ee-s->a2y <= s->c2) {	/* e(x+1/2,y-1) <= 0 */

			s->dxe += s->d2xe;	  

			s->ee += s->dxe;	  

			s->b2x += s->b2;

			return s->x++;

		}

		break;

	}

	return s->x;	  

}

void

memellipse(Memimage *dst, Point c, int a, int b, int t, Memimage *src, Point sp, int op)

{

	State in, out;

	int y, inb, inx, outx, u;

	Param p;

	if(a < 0)

		a = -a;

	if(b < 0)

		b = -b;

	p.dst = dst;

	p.src = src;

	p.c = c;

	p.t = t;

	p.sp = subpt(sp, c);

	p.disc = nil;

	p.op = op;

	u = (t<<1)*(a-b);

	if((b<a && u>b*b) || (a<b && -u>a*a)) {

/*	if(b<a&&(t<<1)>b*b/a || a<b&&(t<<1)>a*a/b)	# very thick */

		bellipse(b, newstate(&in, a, b), &p);

		return;

	}

	if(t < 0) {

		inb = -1;

		newstate(&out, a, y = b);

	} else {	

		inb = b - t;

		newstate(&out, a+t, y = b+t);

	}

	if(t > 0)

		newstate(&in, a-t, inb);

	inx = 0;

	for( ; y>=0; y--) {

		outx = step(&out);

		if(y > inb) {

			erect(-outx, y, outx, y, &p);

			if(y != 0)

				erect(-outx, -y, outx, -y, &p);

			continue;

		}

		if(t > 0) {

			inx = step(&in);

			if(y == inb)

				inx = 0;

		} else if(inx > outx)

			inx = outx;

		erect(inx, y, outx, y, &p);

		if(y != 0)

			erect(inx, -y, outx, -y, &p);

		erect(-outx, y, -inx, y, &p);

		if(y != 0)

			erect(-outx, -y, -inx, -y, &p);

		inx = outx + 1;

	}

}

static Point p00 = {0, 0};

/*

 * a brushed ellipse

 */

static

void

bellipse(int y, State *s, Param *p)

{

	int t, ox, oy, x, nx;

	t = p->t;

	p->disc = allocmemimage(Rect(-t,-t,t+1,t+1), GREY1);

	if(p->disc == nil)

		return;

	memfillcolor(p->disc, DTransparent);

	memellipse(p->disc, p00, t, t, -1, memopaque, p00, p->op);

	oy = y;

	ox = 0;

	nx = x = step(s);

	do {

		while(nx==x && y-->0)

			nx = step(s);

		y++;

		eline(-x,-oy,-ox, -y, p);

		eline(ox,-oy,  x, -y, p);

		eline(-x,  y,-ox, oy, p);

		eline(ox,  y,  x, oy, p);

		ox = x+1;

		x = nx;

		y--;

		oy = y;

	} while(oy > 0);

}

/*

 * a rectangle with closed (not half-open) coordinates expressed

 * relative to the center of the ellipse

 */

static

void

erect(int x0, int y0, int x1, int y1, Param *p)

{

	Rectangle r;

/*	print("R %d,%d %d,%d\n", x0, y0, x1, y1); */

	r = Rect(p->c.x+x0, p->c.y+y0, p->c.x+x1+1, p->c.y+y1+1);

	memdraw(p->dst, r, p->src, addpt(p->sp, r.min), memopaque, p00, p->op);

}

/*

 * a brushed point similarly specified

 */

static

void

epoint(int x, int y, Param *p)

{

	Point p0;

	Rectangle r;

/*	print("P%d %d,%d\n", p->t, x, y);	*/

	p0 = Pt(p->c.x+x, p->c.y+y);

	r = Rpt(addpt(p0, p->disc->r.min), addpt(p0, p->disc->r.max));

	memdraw(p->dst, r, p->src, addpt(p->sp, r.min), p->disc, p->disc->r.min, p->op);

}

/* 

 * a brushed horizontal or vertical line similarly specified

 */

static

void

eline(int x0, int y0, int x1, int y1, Param *p)

{

/*	print("L%d %d,%d %d,%d\n", p->t, x0, y0, x1, y1); */

	if(x1 > x0+1)

		erect(x0+1, y0-p->t, x1-1, y1+p->t, p);

	else if(y1 > y0+1)

		erect(x0-p->t, y0+1, x1+p->t, y1-1, p);

	epoint(x0, y0, p);

	if(x1-x0 || y1-y0)

		epoint(x1, y1, p);

}