I just tried your approach and I think it works suprisingly well!

I wouldnt think the re-evaluation of the panels alpha while the blur is
enabled would be much of a problem, in fact it seems a good idea.

I havent experimented with other panels that have transparency, but if it
causes a noticable, bothersome problem on a prominent semi-transparent panel,
perhaps the affected panels' alpha transparency could be adjusted while the
blur is active?

I changed the set_motion_blur function in mine to fade the blur out when
you "turn it off" instead of it just ending abrubtly like this;

Code:

---

function set_motion_blur(newval)
{
  motion_blur=newval;

  if(newval==0) 
   {
    // No blur; shut off the panel:
    while(panel_motion_blur.alpha < 100)
     {
       panel_motion_blur.alpha += 3*time_step;
       wait(1);
     }
    panel_motion_blur.visible=0;
    camera.bmap = 0;
   }
  else 
   {
    // Blur is positive:
    panel_motion_blur.visible=1;
    camera.bmap = bitmap_motion_blur;
   }
}

---

You always come up with the most amazing stuff Ichiro! Thanks for sharing this.