ref: ff938783a149a445fe8019cf5b31f4c49b8f0eef
dir: /sys/src/cmd/plot/libplot/circ.c/
#include "mplot.h"
void circ(double xc, double yc, double r){
Point p;
int rad;
p.x=SCX(xc);
p.y=SCY(yc);
if (r < 0)
rad=SCR(-r);
else
rad=SCR(r);
ellipse(screen, p, rad, rad, 0, getcolor(e1->foregr), ZP);
}