Bart Krekelberg wrote:
> I have an application that needs to draw the same (moving) image to two
> separate OpenGL windows.
>
> I cannot call the drawing code itself twice; because it would take too long,
> but also because that code has side effects that should not happen twice.
>
> The solution would seem to be to create an OpenGL Display list,
> make the normal window current , execute the display list, then make the
> other window (called 'mirror') current and execute it again. This worked in a
> GLUT-based version of my application but not in FLTK.
In fltk there's only one time you can draw into a window,
from that window's draw() method.
So don't try to draw into a window outside of that
window's draw() method. This would include using one
window's draw() method to draw into the other.
To trigger the draws, I'd recommend using a timer running
at the frame rate you want to update the drawlist, and then
tell fltk to schedule both windows to redraw themselves by
calling redraw() for both windows:
// YOUR TIMER'S CALLBACK
YourTimer_CB(void*) {
UpdateDisplayList();
window->redraw();
mirror->redraw();
}
When your callback returns, FLTK will handle invoking
the draw() methods for the two windows, which can then
both access the mainDisplayList.
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