Finding the AABB surface normal from an intersection point on AABB

Spa8nky · 2009-10-30T07:46:43

Hello folks, If I know the point of intersection on an AABB, is there a easy way of obtaining the surface normal using that point? The following is the ray/AABB intersection test I am using: private bool IntersectAABB(CD_AxisAlignedBoundingBox aABB, ref Contact contact) { float t_Min = 0.0f; float t_Max = float.MaxValue; // Maximum distance ray can travel (makes it a segment, otherwise it would be infinite) float ood = 0.0f; float t1 = 0.0f; float t2 = 0.0f; // For all 3 slabs if (Math.Abs(Direction.X) < float.Epsilon) { // Ray is parallel to slab. No hit if origin (p in book) not within slab if (Origin.X < aABB.MinPoint.X || Origin.X > aABB.MaxPoint.X) { return false; } } else { // Compute intersection t value of ray with near and far plane of slab ood = 1.0f / Direction.X; t1 = (aABB.MinPoint.X - Origin.X) * ood; t2 = (aABB.MaxPoint.X - Origin.X) * ood; // Make (t1) be intersection with near plane, (t2) with far plane if (t1 > t2) { Swap(ref t1, ref t2); } // Compute the intersection of slab intersection intervals t_Min = Math.Max(t_Min, t1); t_Max = Math.Min(t_Max, t2); // Exit with no collision as soon as slab intersection becomes empty if (t_Min > t_Max) { return false; } } if (Math.Abs(Direction.Y) < float.Epsilon) { // Ray is parallel to slab. No hit if origin (p in book) not within slab if (Origin.Y < aABB.MinPoint.Y || Origin.Y > aABB.MaxPoint.Y) { return false; } } else { // Compute intersection t value of ray with near and far plane of slab ood = 1.0f / Direction.Y; t1 = (aABB.MinPoint.Y - Origin.Y) * ood; t2 = (aABB.MaxPoint.Y - Origin.Y) * ood; // Make (t1) be intersection with near plane, (t2) with far plane if (t1 > t2) { Swap(ref t1, ref t2); } // Compute the intersection of slab intersection intervals t_Min = Math.Max(t_Min, t1); t_Max = Math.Min(t_Max, t2); // Exit with no collision as soon as slab intersection becomes empty if (t_Min > t_Max) { return false; } } if (Math.Abs(Direction.Z) < float.Epsilon) { // Ray is parallel to slab. No hit if origin (p in book) not within slab if (Origin.Z < aABB.MinPoint.Z || Origin.Z > aABB.MaxPoint.Z) { return false; } } else { // Compute intersection t value of ray with near and far plane of slab ood = 1.0f / Direction.Z; t1 = (aABB.MinPoint.Z - Origin.Z) * ood; t2 = (aABB.MaxPoint.Z - Origin.Z) * ood; // Make (t1) be intersection with near plane, (t2) with far plane if (t1 > t2) { Swap(ref t1, ref t2); } // Compute the intersection of slab intersection intervals t_Min = Math.Max(t_Min, t1); t_Max = Math.Min(t_Max, t2); // Exit with no collision as soon as slab intersection becomes empty if (t_Min > t_Max) { return false; } } // Ray intersects all 3 slabs // Only update contact parameters if this is the closest intersected so far if (contact.KeepClosest(t_Min)) { contact.location = Origin + t_Min * Direction; //contact.normal // Only allow this test to return true if the primitive tested is the closest to the ray origin return true; } return false; } Thanks.

Math and Physics Programming

Started by Spa8nky October 29, 2009 09:01 AM

10 comments, last by Spa8nky 14 years, 5 months ago

Zakwayda

2,389

October 30, 2009 06:46 AM

Quote:How would I create a Vector3 class that allows for this as I can only figure out a method that would allow me to create a *.Normal.Elements[n] or Triangle.A.Elements[n].

Is it operator overloading that you're looking for? (In this case, it would be the [] operator that you'd want to overload.)

Spa8nky

230

Author

October 30, 2009 07:46 AM

I think so.

Essential I would like to be able to do this:

Vector3 Normal = new Vector3(x,y,z);

Normal[0] would then = x
Normal[1] = y
Normal[2] = z

Is that possible with a Vector3 class? Sorry to sound a little noobish but I have used operators such as *, + and % but I have never come across a [] operator before.

Thanks.

Finding the AABB surface normal from an intersection point on AABB

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Finding the AABB surface normal from an intersection point on AABB

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