ref: a04fd342727c329584a9f443092caf21e3884bdf
dir: /sys/src/libmemdraw/arc.c/
#include <u.h>
#include <libc.h>
#include <draw.h>
#include <memdraw.h>
#include <memlayer.h>
/*
* elarc(dst,c,a,b,t,src,sp,alpha,phi)
* draws the part of an ellipse between rays at angles alpha and alpha+phi
* measured counterclockwise from the positive x axis. other
* arguments are as for ellipse(dst,c,a,b,t,src,sp)
*/
enum
{
R, T, L, B /* right, top, left, bottom */
};
static
Point corners[] = {
{1,1},
{-1,1},
{-1,-1},
{1,-1}
};
/*
* make a "wedge" mask covering the desired angle and contained in
* a surrounding square; draw a full ellipse; intersect that with the
* wedge to make a mask through which to copy src to dst.
*/
void
memarc(Memimage *dst, Point c, int a, int b, int t, Memimage *src, Point sp, int alpha, int phi, int op)
{
int i, w, beta, tmp, c1, c2, m, m1;
Rectangle rect;
Point p, bnd[8];
Memimage *wedge, *figure, *mask;
if(phi == 0)
return;
if(phi <= -360 || phi >= 360){
memellipse(dst, c, a, b, t, src, sp, op);
return;
}
alpha %= 360;
alpha = -alpha; /* compensate for upside-down coords */
phi = -phi;
beta = alpha + phi;
if(phi < 0){
tmp = alpha;
alpha = beta;
beta = tmp;
phi = -phi;
}
while(alpha < 0)
alpha += 360;
while(beta < 0)
beta += 360;
c1 = alpha/90 & 3; /* number of nearest corner */
c2 = beta/90 & 3;
/*
* icossin returns point at radius ICOSSCALE.
* multiplying by m1 moves it outside the ellipse
*/
if(a < 0)
a = -a;
if(b < 0)
b = -b;
w = t;
if(w < 0)
w = 0;
rect = Rect(-a-w, -b-w, a+w+1, b+w+1);
m = rect.max.x; /* inradius of bounding square */
if(m < rect.max.y)
m = rect.max.y;
m1 = (m+ICOSSCALE-1) >> 10;
m = m1 << 10; /* assure m1*cossin is inside */
i = 0;
bnd[i++] = Pt(0,0);
icossin(alpha, &p.x, &p.y);
bnd[i++] = mulpt(p, m1);
for(;;) {
bnd[i++] = mulpt(corners[c1], m);
if(c1==c2 && phi<180)
break;
c1 = (c1+1) & 3;
phi -= 90;
}
icossin(beta, &p.x, &p.y);
bnd[i++] = mulpt(p, m1);
figure = nil;
mask = nil;
wedge = allocmemimage(rect, GREY1);
if(wedge == nil)
goto Return;
memfillcolor(wedge, DTransparent);
memfillpoly(wedge, bnd, i, ~0, memopaque, ZP, S);
figure = allocmemimage(rect, GREY1);
if(figure == nil)
goto Return;
memfillcolor(figure, DTransparent);
memellipse(figure, ZP, a, b, t, memopaque, ZP, S);
mask = allocmemimage(rect, GREY1);
if(mask == nil)
goto Return;
memfillcolor(mask, DTransparent);
memimagedraw(mask, rect, figure, rect.min, wedge, rect.min, S);
c = subpt(c, dst->r.min);
memdraw(dst, dst->r, src, subpt(sp, c), mask, subpt(ZP, c), op);
Return:
freememimage(wedge);
freememimage(figure);
freememimage(mask);
}