# AABB In Frustum

Testing if an AABB is within a frustum is a bit of a brute force method. We first have to get every vertex of the AABB, this part is simple enough. We alrady did this when we split the BVH tree. We just need the 8 points.

Once we have the 8 points it's a nested loop.

For every plane of the frustum, we check all 8 corners of the AABB. If there is any plane where all 8 corners of the AABB are outside of the plane (Have a negative half-space test), then the AABB and frustum do not intersect!

By default, if everything passes we assume an intersection to be true

## The Algorithm

foreach Plane plane in frustum {
int inCount = 8;
foreach Point corner in corners{
if HalfSpaceTest(corner, plane) < 0.0f {
inCount -= 1;
}
}
if inCount <= 0
return false;
}
return true; // by default


Add the following function to the Collisions class:

public static bool Intersects(Plane[] frustum, AABB aabb) {
// TODO
}

public static bool Intersects(AABB aabb, Plane[] frustum) {
return Intersects(frustum, aabb);
}


And provide an implementation for it!

### Unit Test

Add the following unit test to the bottom of the Initialize function in CameraSample

if (!Collisions.Intersects(new AABB(), camera.Frustum)) {
System.Console.WriteLine("Error with aabb in frustum! 0");
}
if (Collisions.Intersects(new AABB(new Point(-650, -650, -650), new Point(-600, -600, -600)), camera.Frustum)) {
System.Console.WriteLine("Error with aabb in frustum! 1");
}
if (!Collisions.Intersects(new AABB(new Point(2, 30, 4), new Point(25, 35, 45)), camera.Frustum)) {
System.Console.WriteLine("Error with aabb in frustum! 2");
}