Function: plotrpoint
Section: graphic
C-Name: plotrpoint
Prototype: vLGG
Help: plotrpoint(w,dx,dy): draw a point (and move cursor) at position dx,dy
 relative to present position of the cursor in rectwindow w.
Doc: draw the point $(x1+dx,y1+dy)$ on the rectwindow $w$ (if it is inside
 $w$), where $(x1,y1)$ is the current position of the cursor, and in any case
 move the virtual cursor to position $(x1+dx,y1+dy)$.

 If you draw few points in the rectwindow, they will be hard to see; in
 this case, you can use filled boxes instead. Compare:
 \bprog
 ? plotinit(0, 100,100); plotrpoint(0, 50,50); plotrpoint(0, 10,10);
 ? plotdraw(0)

 ? thickpoint(w,x,y)= plotmove(w,x-2,y-2); plotrbox(w,4,4,1);
 ? plotinit(1, 100,100); thickpoint(1, 50,50); thickpoint(1, 60,60);
 ? plotdraw(1)
 @eprog
