Frustum culling when Bounding Box is really big

Question

When bounding box's all 8 vertex is out side the frustum, it won't be rendered. But if sth happened like shown above. That object should be in the display list. Any idea?

Answer 1

Because you are calculating the intersection as if the box is bunch of points, instead of a bunch of lines. This is how I do it in pseudo-code:

inter = Inside
for ( plane : frustum ) {
    verts[2] = findOpposingPointsMostPerpendicularToPlane( box, plane )
    near = plane.signedDistance( verts[0] ) > 0.0
    far = plane.signedDistance( verts[1] ) > 0.0

    if ( !near && !far )
        inter = Outside
        break
    else ( near ^ far )
        inter = Intersecting
}

If your box is an AABB, you create a static array of vertex indices for findOpposingPointsMostPerpendicularToPlane() and then map to them using the sign of the plane normal components.

Answer 2

Compute the bounding sphere from your bbox and check the center distance from each one of the 6 frustum planes. If one of them is less than the sphere radius include your object in the display list.