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Ammunition | Animals | Animated Clouds & Sky | Antlions | Beams | Bushes | Cables | Color | Combat | Combine | Creatures | Doors | Dust | Elevators | Environmental Lighting | Explosions | Fire | Fog | Foliage | Glass | Grass | Headcrab | Health | Ladders | Lasers | Lighting | Moving Clouds | Music | Optimization | Outdoors | Physics | Retinal scanners | Ropes | Smoke | Sound | Special effects | Sun | Terrain | Trains | Trees | Turrets | Water | Weather | Windows | Zombie
- Physics Entity Overview—constraint entity listing
- Physics can be brush-based, like func physbox, or model-based, like prop_physics, prop_physics_respawnable, or prop_physics_multiplayer. Physics objects can be picked up either with the use key or the weapon_physcannon.
- VPhysics - Source's built-in physics engine
- Cinematic Physics - baked (precalculated) physics generated in an external physics simulator
- Optimization (level design)/Physics