Flip back buffer to front, making changes visible on screen.
void CL_DisplayWindow::flip( int interval = -1);
Detailed description:
The parameter interval specifies the minimum number of video frames that are displayed before a buffer swap will occur.
If interval is set to a value of 0, buffer swaps are not synchronized to a video frame.
If interval is set to a value of -1 (the default), then it will use the buffer swap used for previous flip. If its the first flip, it will use the system default.