Simulations always result in some time delay between input and result. Consequently real time calculations would be ideal. Many functions can already be performed in real time. Often, however, the technical progress also involves higher representation requirements, which results in speed reduction. The real-time technology is inspired by computer games, where interaction directly modifies the image sequence. Computer game users benefit from elaborate preliminary calculations that are uncommon in architectural simulations. The solutions developed by the manufacturers of rendering programs depend on the hardware functions of powerful graphics cards.