ref: 1cfe7fded39233cf93f110b0c63b9c5c9f2e7f3e dir: /sys/src/cmd/plot/libplot/rvec.c/
#include "mplot.h" void rvec(double xx, double yy){ e1->copyx += xx; e1->copyy += yy; vec(e1->copyx, e1->copyy); }