Saves the framebuffer to the file fileName using one of the image file formats supported by Qt.
Writes vector data supported by gl2ps. The corresponding format types are "EPS","PS"or "PDF". If zlib has been configured this will be extended by "EPS_GZ" and "PS_GZ". Beware: BSPSORT turns out to behave very slowly and memory consuming, especially in cases where many polygons appear. It is still more exact than SIMPLESORT.