Risen collision mesh (._xcom)
In Risen the ordinary ._xmsh files are only used for the visual aspects of the game but not for physics. Instead, collision detection uses a less detailed version of the level mesh, which is stored in ._xcom files. This is also where the physics materials are defined that determine which footstep sound is played when a game characters moves over the level mesh.
Therefor material names are of great importance when creating own collision meshes. In Risen the following physics materials are available: none, wood, metal, water, stone, earth, ice, leather, clay, glass, flesh, snow, debris, foliage, magic, grass, springanddamper1, springanddamper2, springanddamper3, damage, sand, movement, axe
Furthermore you can append one or more of the suffixes "_i", "_c" and "_r" to the material names. The first one stands for IgnoredByTraceRay, the second for DisableCollision and the third for DisableResponse. In most cases, however, none of them is needed.
In case the collision mesh is convex, the engine can perform further optimisations. Such ._xcom files include a "_CV" in their name, although this is only a convention. The actual information of a mesh being convex is stored inside the file. As Rimy3D cannot determine efficiently whether a mesh is convex or not, the choice is left to the user through the export settings. A mesh is convex if and only if all line segments between any two vertices lie in the inside of the mesh (so cubes and spheres are convex while tori are not). In case of doubt you should specify "not convex".