Many 3ds Max objects provide methods for hit testing (e.g. Mesh::Select(), MNMesh::Select(), PatchMesh::Select(), MNNormalSpec::HitTest(), etc.) that use a HitRegion class. A hit region is identified by its HitRegion::type member variable, and can be a point plus epsilon (POINT_RGN), rectangular region (RECT_RGN), circular region (CIRCLE_RGN), or a multi-point polygon region (FENCE_RGN).

A HitRegion class can be initialized using the MakeHitRegion global function.