Physics tags characterize the dynamic physics and propulsion of vehicles. They are essentially a collection of spherical mass points. Since vehicles can have both model_
- Physics are used in collisions between vehicles and is responsible for Halo 1's charactistic "bouncy" vehicles.
- Physics are used in collisions with the BSP. Because the mass points are somewhat "fuzzy" and are not continuous geometry, vehicles can become stuck in thin BSP.
- Physics are used in collisions with device_
machine and scenery.
- Collision geometry is used in collisions with bipeds, items, and projectiles.
- Note that vehicles cannot collide with device_
Physics tags are created by compiling a JMS with specially-named markers parented to nodes. The markers become mass points.
Mass points (also known as physics spheres) are spherical volumes with mass and density. They can have various types of friction and may provide powered impulse for flight and driving.
Even though mass points are parented to nodes, they do not move with base, overlay, or aiming animations unlike model_
|center of mass|
A coefficient which modifies the amount of friction applied to the vehicle when colliding with "ground" surfaces, which may just mean any BSP surface which is not a water plane. It is unknown if this also modifies friction on scenery collisions. A typical value from the Warthog is 0.23.
|ground damp fraction|
|ground normal k1|
Used to determine how steep of a surface the vehicle can climb before its powered mass points no longer have an effect. A typical value is ~0.7, while a value near 1.0 allows vertical climbing assuming sufficient friction.
|ground normal k0|
This is also used to determine how steep of a surface the vehicle can climb and seems to be some sort of lower range bound for fading out powered mass points. A typical value is ~0.5, with -1.0 allowing vertical wall climbing.
|inertial matrix and inverse|
|powered mass points|
Thanks to the following individuals for their research or contributions to this topic:
- Conscars (Mass point node testing)
- Kavawuvi (Invader tag definitions)
- MosesOfEgypt (Tag structure research)