VEGAS provides sophisticated compositing including green screen, masking, and keyframe animation. Prana Studios provided work on visual effects, animation and compositing. The short features techniques such as photorealistic lighting, shading, and compositing. Alpha compositing, color gradients, and 3D rendering are also affected by this issue. Compiz and KWin are compositing window managers for systems using the X Window System. Among other things, After Effects can be used for keying, tracking, compositing, and animation. Chroma key compositing was only used for background pieces. Updated features include GPGPU acceleration of video decoding, effects, playback, compositing, pan/crop, transitions, and motion. ATI and NVIDIA strongly recommend using compositing desktop/Framebuffer Objects for same functionality. Modern compositing window managers use 3D hardware acceleration. It is the digital analogue of optical film compositing. External applications called "compositing window managers" provide policy for the visual appearance. Richard Edlund's Boss Film Studios was hired for compositing and other post-production effects. The in operator is the alpha compositing equivalent of clipping. Several types of window managers exist for X11, including tiling, dynamic, stacking and compositing.