Grand Theft Auto IV is powered by Rockstar's own RAGE game engine, along with the Euphoria run-time animation engine developed by NaturalMotion. Euphoria uses a procedural animation technology called Dynamic Motion Synthesis instead of pre-recorded animations to facilitate player motion, allowing more natural, unscripted movements. DMS animates fully interactive 3D characters "on the fly" through real-time simulations of human motor functions, giving each character a "central nervous system." NPCs exhibit different actions and reactions in every scene, so each player's experience is unique and, as a result, more realistic. Characters can cleanly dodge punches, limp away with gunshot wounds, and even get ejected through their vehicle's windshield, all in fluid motions with subtle transitions. Explosions send people flying further than ever before. There is also a new damage system that assesses cosmetic damage to vehicles and objects in the environment through more accurate measures of the force and location of impact. The game uses Image Metrics middleware for facial expressions and lip-synching. The bump maps used to generate landscape topography are much more detailed than in previous GTA universes, allowing the contours of the gamespace to have more texture and depth. Also, the relative speed of in-game time is decreased. Every two seconds of play represents one minute of in-game time, so the time it takes to complete a full day is doubled from that of the 3D universe, from 24 minutes to approximately 48 minutes. Load times during exterior-interior transitions in GTA IV have also been removed, adding significantly to the continuity of the game. Graphics GTA IV's graphics largely benefit from the high-definition capability of the seventh-generation consoles it runs on and the new game engine. New sunlight and weather effects give the environment a vividly realistic appearance as the time of day progresses. Volumetric lighting effects allow sunshine to stream into dusty interiors and fog to darken distant horizons. Modern pixel shaders reflect light in the body panels of clean cars and the glass windows of skyscrapers, and water appears staggeringly wet. Road and building textures are also more varied than in previous GTAs. Potholes, sewer plates, tar patches, and cracks in the asphalt are highly visible, and no two Burger Shot exteriors are the same. Content Many fans criticized Rockstar for the omission of many features from GTA IV that made GTA San Andreas so much fun to play. Most of the complaints were about the removal of RPG-like features and customizable elements that were present in GTA San Andreas, such as building muscle or becoming fat; the variety of clothing and tattoos to wear; the modification of cars; and many of the more amusing gameplay elements like the jetpack, parachutes, highly destructive weapons, planes, bicycles, and impractical vehicles. Other gamers commended Rockstar for adding realism, saying the believability benefits the game and enables more focus on the story. The following are some of the changes in content from previous games: -The size of the map is only about one-sixth the size of San Andreas, but the scale is no different, and the smaller worldspace is detailed to a greater depth. There is very little "wasted" space, and every inch of the city tells a story. -Player-operable airplanes have been omitted, however players can still pilot helicopters. -A new Cover System gives the player the ability to hide behind any wall, car, or sufficiently large object. -Police Bribes have been removed from gameplay. -The player's phone has become an integral part of the game; many missions and friendships rely on its use, and it enables many other gameplay features, including the use of cheats & accessing Multiplayer. -Vehicle customization like that seen in San Andreas has been omitted. Players can no longer buy upgrades and accessories for their cars in mod garages. -An in-game GPS guides the player turn-by-turn to mission destinations or selected waypoints by highlighting the shortest legal route on the mini-map and, in some cars, playing a voice recording. -There is no way to physically change the player character's body shape by eating too much or working out at a gymnasium. Similarly, the player can no longer change hairstyles at a barber shop or get tattoos at a tattoo parlor. -Vehicles are stolen more realistically; when the player takes an unoccupied vehicle, Niko must smash a window to unlock the door and then hotwire it on the inside to get it running. -Diving below the surface of water, and consequently, the underwater landscape, is no longer available. -The player can hail a taxi and get a ride to selected destinations, for a fee. -When the player mounts a motorcycle, a helmet appears on Niko's head. -The player can now toggle vehicle headlights on or off. -The player has the ability to watch television in his or her apartment. -Niko can make decisions in certain parts of the story.