Normally there's a front and a backbuffer.

the engine draws in the backbuffer and when that's finished it flips backbuffer
to front buffer and front to back. Then draw again.

d3d_triplebuffer adds one more buffer. let's call it middlebuffer

Draw to backbuffer

Switch back to middle, middle to front, front to back

goto Draw to backbuffer

So it takes 3 frames with d3d_triplebuffer

panel.visible=on;
wait(3);
//now the panel is visible;