ref: fba5f2f124a6aeb04ae27ff67d43739b0caeaf92
dir: /sys/src/cmd/plot/libplot/disk.c/
#include "mplot.h"
void plotdisc(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);
fillellipse(screen, p, rad, rad, getcolor(e1->foregr), ZP);
}