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Lumberyard
Developer Guide (Version 1.11)

Geometry Management Functions

Geometry management functions are accessible through the geometry manager, which is a part of physical world. To obtain a pointer to the geometry manger, call the GetGeomManager() function.

CreateMesh

The CreateMesh geometry management function creates a triangular mesh object from a set of vertices and indices (3 indices per triangle) and returns the corresponding IGeometry pointer.

  • The engine uses triangle connectivity information in many places, so it is strongly recommended to have meshes closed and manifold. The function is able to recognize different vertices that represent the same point in space for connectivity calculations (there is no tolerance though, it checks only for exact duplicates). Open edges are ok only for geometries that will not be used as parts of dynamic physical entities and only if there will be little or no interaction with them.

  • For collision detection the function can create either an OBB or a memory-optimized AABB or a single box tree. Selection is made by specifying the corresponding flag. If both AABB and OBB flags are specified, the function selects the tree that fits the geometry most tightly. Since an OBB tree is tighter in most cases, priority of AABBs can be boosted to save memory (also, AABB checks are slightly faster if the trees are equally tight). The engine can either copy the vertex/index data or use it directly from the pointers provided.

  • The mesh_multycontact flags give some hints on whether multiple contacts are possible. Specifying that multiple contacts are unlikely (mesh_multycontact0) can improve performance a bit at the expense of missing multiple contacts if they do occur (note that it does not necessarily mean they will be missed, it is a hint for the algorithm to use some optimizations more aggressively). mesh_multycontact2 disables this optimization and ..1 is a recommended default setting. Convex geometries are detected and some additional optimizations are used for them, although internally there is no separate class for convex objects (this may change in the future).

  • Meshes can have per-face materials. Materials are used to look up friction, bounciness, and pierceability coefficients and can be queried by the game as a part of collision detection output.

  • The CreateMesh function is able to detect meshes that represent primitives (with the specified tolerance) and returns primitive objects instead. In order to activate this detection, the corresponding flags should be specified. Note that primitives can't store materials. They can only have one in the physical geometry structure, so this detection is not used when the material array has more than one material index in it.

CreatePrimitive

CreatePrimitive: Creates a primitive geometry explicitly. The corresponding primitive (cylinder, sphere, box, heightfield, or ray) structure should be filled and passed as a parameter, along with its ::type.

RegisterGeometry

RegisterGeometry physicalizes an IGeometry object by computing its physical properties and storing them in an auxiliary structure. Material index (surfaceidx) can be stored in it; it will be used if the geometry itself does not have any materials specified (such as if it is a primitive). AddRefGeometry and UnregisterGeometry comprise a reference "sandwich" for it. Note that the latter does not delete the object until its reference count becomes 0.

Geometries and physicalized geometries can be serialized. This saves time when computing OBB trees. That computation is not particularly slow, but serialization is faster.