Sphere vs Rotation Box Custom Collision Problem (C#, Unity)

Question

I'm not really like to post questions about problems without doing the research, but I'm close to give up, so I thought I give it a shot and ask you about my problem.

I want to create a custom collision detection in Unity ( So please don't advice "use rigidbody and\or colliders" because I don't want to use them by purpose). The main idea: I want to detect Basic Sphere and Basic Box collision. I already find AABB vs Sphere theme with the following solution:

bool intersect(sphere, box) {

var x = Math.max(box.minX, Math.min(sphere.x, box.maxX));
var y = Math.max(box.minY, Math.min(sphere.y, box.maxY));
var z = Math.max(box.minZ, Math.min(sphere.z, box.maxZ));

var distance = Math.sqrt((x - sphere.x) * (x - sphere.x) + 
                         (y - sphere.y) * (y - sphere.y) + 
                         (z - sphere.z) * (z - sphere.z));

return distance < sphere.radius;
}

And this code does the job, the box bounding and the sphere center point with radius works fine, I can detect the Sphere collision on Box.

The problem is, I want to Rotating the Cube in Runtime, so that will screw up everything, the bounding will split away and the collision will gone (or collide on random places). I've read about some comments where they said, bounding not works with rotation, but I'm not sure what else can I use to solve this problem.

Can you help me with this topic please? I'll take every advice I can get (except Colliders & Rigidbodies of course).

Thank you very much.

Answer 1

You might try using the separating axis theorem . Essentially, for a polyhedron, you use the normal of each face to create an axis. Project the two shapes you are comparing onto each axis and look for an intersection. If there is no intersection along any of the axes, there is no intersection of shapes. For a sphere, you will just need to project onto the polyhedron's axes. There is a great 2D intro to this from metanet .

Edit: hey, check it out-- a Unity implementation .