void showHelp() {
    fill(dblue); pushMatrix(); translate(20,20);
     text("REALTIME 2D VISIBILITY by Jarek Rossignac",0,0); translate(0,20);
     text(" --------------------------------------- ",0,0); translate(0,20);
     text("  ",0,0); translate(0,20);
     text("First click in the window to activate it ",0,0); translate(0,20);
     text("Press SPACE to show/hide this help text and 'M' to show/hide (for pictures) the menu-bar on the right ",0,0); translate(0,20);
     text("Click and drag viewpoint (red point) or the view direction (tip of red arrow)",0,0); translate(0,20);
     text("Keep 'c' pressed and click and drag disk to move it",0,0); translate(0,20);
     text("Press 'd' to redistribute disk so that they do not overlap",0,0); translate(0,20);
     text("Use menu buttons to change number of disks and change settings ",0,0); translate(0,20);
     text("Press 'X' top snap a picture of the window (only when running Processing, not in an applet)",0,0); translate(0,20);
     popMatrix(); noFill();
   }