PreSolveContact Struct

Contact information passed to the pre-solve filter registered with SetPreSolveFilter(Func<PreSolveContact,bool>). Return false to cancel the contact for the current step without generating collision response forces.

public readonly struct PreSolveContact

Remarks

The pre-solve callback is invoked by the Box2D solver on the simulation thread every step for every active contact pair. Keep the callback allocation-free.

Primary use-case: one-way platforms. Check Normal and cancel the contact when the body is approaching from the wrong side:

world.SetPreSolveFilter(c =>
{
    bool platformIsA = c.BodyA.Entity?.Name == "Platform";
    var normal = platformIsA ? c.Normal : -c.Normal;
    return normal.Y <= 0f; // only collide from above (Y-down)
});

Properties
BodyA	Body A in the contact pair.
BodyB	Body B in the contact pair.
Normal	The contact normal pointing from BodyA toward BodyB.
SubShapeA	The sub-shape on BodyA involved in the contact, or null when the primary shape is the contact shape.
SubShapeB	The sub-shape on BodyB involved in the contact, or null when the primary shape is the contact shape.