# What is the minimum number of points in a convex hull in most engines?

A convex hull shape in a 3D game engine defined by vertices needs at least 4 points in order to have volume, since that would make it a tetrahedron. However, some game engines may support fewer points, such as 3 points for a triangle, 2 points for a line, and 1 point is just a point.

This question is asking what the minimum sizes are between various game engines. If I am defining a standard for convex hulls and I want it to be portable between game engines, what is the minimum I should allow in the standard? If I have a convex hull that's just a line or a triangle, will that shape be usable in Unity, Unreal, Godot, Blender, Bullet, Jolt, PhysX, Havok, etc?

• All of the engines you mentioned have free versions, so you could test this yourself and report your findings. (Unity uses PhysX and Unreal uses Havok, so that saves you a couple steps) Dec 27, 2022 at 23:56
• @DMGregory Unreal Engine 5 has switched to the in-house Chaos physics engine instead of licensing the Havok or PhysX engines. Dec 29, 2022 at 3:15

The minimum common shape is a box (or plane, to which the following does not apply). A plane intersection is a simple transform, subtraction and sign check.

So the question becomes what is the minimum size for each of these objects, and that depends on there being common scales or axes across engines, a continuous collision algorithm, if used, and/or the number sub-steps allowed(user configurable in most cases).

None of which are true for all cases.

A perfect universal solution does not exist.

The grunt work is up to you.

• This question is about convex hull data structures, not planes or boxes. Convex hulls are a distinct collision primitive commonly used for mesh colliders that don't reduce neatly to planes/boxes or other standardized shapes. Dec 29, 2022 at 11:43
• When I refer to size in my post, I am referring to the complexity of the model as determined by the number of points, not the physical dimensions in meters etc. Dec 29, 2022 at 23:37
• @DMGregory, I know that. But the question involves minimization of vertices of a convex hull, that reduces to the question to simple shapes.
– user122973
Jan 3, 2023 at 4:32
• @AaronFranke, I get that. The multi-platform solution is the largest of minimizations that could be applied to the least target;. A box or plane bolh fit the requirements. The minimum number of of dimensions is 3 for all of the target platforms.
– user122973
Jan 3, 2023 at 4:42