ref: f02c92a5fb2d18e1248a67b15cd2ec7dcea2b4d7
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);
m_circ(p, rad, e1->foregr);
}