ggiCopyBox - Copy a rectangular area
int ggiCopyBox(ggi_visual_t vis, int x, int y, int w, int h, int nx ,int ny);
This is a area-to-area-blit, all in the same visual. Copy the box
described by x, y, w, h to the new location nx, ny. This automatically
takes care of overlaps and optimizes for the given visual (e.g. uses
HW-accel or intermediate buffers as appropriate).
ggiCopyBox will transfer an area between frames when the read frame is
not the same as the write frame.
0 for OK, otherwise a ggi-error(3) code.