MPR

What is MPR?

Minkowski Portal Refinement is comparable to GJK, as it also relies on support functions and also is designed for convex objects. Unlike GJK however, MPR does not provide the shortest distance between separated objects. However in return MPR can be used to extract collision information from an intersection, namely a hit point, the penetration depth and the minimum translation vector: A normal that when scaled by the penetration depth can be used to depenetrate two intersecting objects.

In Bolt specifically, MPR performs both an intersection test and the collision information extraction.

MPR is great for objects that don’t have flat faces with multiple contact points, it can handle the remaining shape pairs that SAT doesn’t cover just fine.

Usage

As MPR does not provide the shortest distance, only intersection tests can be done with MPR.

bolt.mpr.intersects(
    cframe_a: CFrame,
    shape_a: Shape,
    cframe_b: CFrame,
    shape_b: Shape,
    in_tolerance: number
): (boolean, Vector3, number?, Vector3?, Vector3?)

This function will give you a boolean to indicate whether or not an intersection has happened, the minimum translation vector, penetration depth, the intersection point on shape A and lastly the intersection point on shape B in that order.

The minimum translation vector will always be returned, and it can be used to quickly check if the two objects are still separated to dramatically speed up intersection tests in cases where objects generally don’t move a lot inbetween calls.

MPR will not give you a contact manifold, you will have to implement clipping yourself if you need one.

The function to use for this check is

bolt.mpr.is_separated(
    cframe_a: CFrame,
    shape_a: Shape,
    cframe_b: CFrame,
    shape_b: Shape,
    cached_normal: Vector3 --previously returned MTV
): boolean