Partitioners

During the render process it is important for the engine to be able to quickly gather the StageNodes that are visible for rendering. The best method for quickly calculating this visible geometry may vary depending on the type of scene which is being rendered. For example, a 3D terrain may be better suited to some kind of Quadree based culling while an enclosed level may be rendered more efficiently using some kind of BSP-type culling.

Simulant uses a simple pluggable system for defining partitioners that provide two methods to the renderinga system:

• geometry_visible_from(CameraID)
• lights_visible_from(CameraID)

The partitioner keeps track of all StageNodes (aside from the Stage itself) and then returns the visible geometry or lights when required. The partitioner is selected when a Stage is constructed (via new_stage()).

One thing to note is that if a Geom is visible, the renderable returned will be the result of an additional Octree culling step. This allows for entire chunks of static geometry to be culled out by the partitioner, and then if they are visible, to only return the polygons visible rather than the whole chunk.

Geom Octree Culling

When you load a mesh, there are two ways of rendering it. You can either attach it to an Actor; allowing you to move and rotate it. Or, you can generate a Geom from it. Geoms are static once they have been created and they internally use an Octree or Quadtree to provide an additional culling step once the partitioner has deemed it visible.

When creating a Geom, as well as specifying its rotation and position, you can also specify the GeomCullerOptions. GeomCullerOptions is a struct which has properties for the type of culler (e.g. GEOM_CULLER_TYPE_OCTREE or GEOM_CULLER_TYPE_QUADTREE) and the properties of the selected culler.

NOTE: Once you have created a Geom from a MeshPtr, DO NOT manipulate the Mesh's vertex_data. Doing so will cause visual corruption or a crash! You might be able to get away with manipulating diffuse colours, texture coordinates or normals, but changing the positions or number of vertices will cause errors.