AWS Documentation » Amazon Lumberyard » User Guide » Simulating Physics Behavior with the PhysX System » Legacy Physics System » Collision Classes

Collision Classes

Use collision classes to filter collisions between two physical entities. A collision class comprises two 32-bit uints, a type, and an ignore.

You can use collision classes to implement scenarios such as "player only collisions," which are objects passable by AI actors but not passable by players. This feature allows you to configure filtering of the collision between physical entities independently of their collision types.

Setup

Physical entities can have one or more collision classes and can ignore one or more collision classes. To have a physical entity ignore a collision, use the ignore_collision attribute of the <Physics> element in the <SurfaceType> definition, as shown in the following example:

SurfaceTypes.xml

<SurfaceType name="mat_nodraw_ai_passable">
  <Physics friction="0" elasticity="0"  pierceability="15" ignore_collision="collision_class_ai"/>
</SurfaceType>

All physical entity types such as LivingEntity and ParticleEntity are supplied with default collision classes like collision_class_living and collision_class_particle. Living entity uses one additional game specific collision class: either collision_class_ai for AI actors, or collision_class_player for players.

Player.lua

Player = {
...
  physicsParams =
  {                
    collisionClass=collision_class_player,
  },
...
}

BasicAI.lua

BasicAI = {
...
  physicsParams =
  {                
    collisionClass=collision_class_ai,
  },
...
}

Code

struct SCollisionClass
{
    uint32 type;     // collision_class flags to identify the entity
    uint32 ignore;   // another entity will be ignored if *any* of these bits are set in its type
};

The type identifies which entity the collision classes belong to.

Some collision classes like the following are defined in CryPhysics:

• collision_class_terrain

• collision_class_wheeled

• collision_class_living

• collision_class_articulated

• collision_class_soft

• collision_class_roped

• collision_class_particle

Other collision classes are defined in GamePhysicsSettings.h, starting from the collision_class_game bit:

#define GAME_COLLISION_CLASSES(f) \
    f( gcc_player_capsule,     collision_class_game << 0) \
    f( gcc_player_body,        collision_class_game << 1) \
    f( gcc_pinger_capsule,     collision_class_game << 2) \
    f( gcc_pinger_body,        collision_class_game << 3) \
    f( gcc_vehicle,            collision_class_game << 4) \
    f( gcc_large_kickable,     collision_class_game << 5) \
    f( gcc_ragdoll,            collision_class_game << 6) \
    f( gcc_rigid,              collision_class_game << 7) \
    f( gcc_alien_drop_pod,     collision_class_game << 8) \
    f( gcc_vtol,               collision_class_game << 9) \

All these classes are automatically exposed to Lua. Brushes and most objects have the collision classes available in the properties through the editor.

Types

For types, you can set many or zero bits.

In the following example, of the classes LIVING, PLAYER, TEAM1, TEAM2, AI, AI_1, and AI_2, player1 belongs to the LIVING entity class, the PLAYER class, and the TEAM1 class:

SCollisionClass player1(0,0), player2(0,0), ai1(0,0), ai7(0,0), object1(0,0);
 
player1.type = LIVING|PLAYER|TEAM1;
player2.type = LIVING|PLAYER|TEAM2;
ai1.type = LIVING|AI|AI_1;
ai7.type = LIVING|AI|AI_2;
object1.type = 0;

Filtering the collision

Filtering occurs by checking the type of one entity against the ignore of another entity.

This is done both ways, and if bits overlap, then the collision is ignored. For example:

bool ignoreCollision = (A->type & B->ignore) || (A->ignore & B->type);

If you want ai7 to ignore collisions with anything that has AI_1 set, then add AI_1 to the ignore flags like this:

ai7.ignore = AI_1

If you want object1 to ignore all living physical entities, set its ignore flag like this:

object1.ignore=LIVING

Interface

• For code, see physinterface.h and GamePhysicsSettings.h.

• To access and set the collision classes on the physical entity, use *pe_collision_class struct SCollisionClass pe_params_collision_class.

• For helpers that set additional ignore maps, see GamePhysicsSettings.h.

• In Lua, see SetupCollisionFiltering and ApplyCollisionFiltering. Lua script-binding is done through SetPhysicParams(PHYSICPARAM_COLLISION_CLASS).