Function TestFrustumOBB

engine/dlib/src/dlib/intersection.cpp:112–158

Returns 'false' if the bounding box is off the frustum. Returning 'true' does not guarantee that the object intersects the frustum or is inside it.

// Returns 'false' if the bounding box is off the frustum. Returning 'true' does not guarantee that the object intersects the frustum or is inside it.
bool TestFrustumOBB(const Frustum& frustum, const dmVMath::Matrix4& world, dmVMath::Vector3& aabb_min, dmVMath::Vector3& aabb_max)
{
    // calculate coordinates of all 8 corners of the bounding cube.
    // To find them we'll take all points P(Xi,Yj,Zk) i=aabb_min.x|aabb_max.x, j=aabb_min.y|aabb_max.y, k=aabb_min.z|aabb_max.z
    dmVMath::Point3 point0 = dmVMath::Point3(aabb_min.getX(), aabb_min.getY(), aabb_min.getZ());
    dmVMath::Point3 point1 = dmVMath::Point3(aabb_min.getX(), aabb_min.getY(), aabb_max.getZ());
    dmVMath::Point3 point2 = dmVMath::Point3(aabb_min.getX(), aabb_max.getY(), aabb_min.getZ());
    dmVMath::Point3 point3 = dmVMath::Point3(aabb_min.getX(), aabb_max.getY(), aabb_max.getZ());
    dmVMath::Point3 point4 = dmVMath::Point3(aabb_max.getX(), aabb_min.getY(), aabb_min.getZ());
    dmVMath::Point3 point5 = dmVMath::Point3(aabb_max.getX(), aabb_min.getY(), aabb_max.getZ());
    dmVMath::Point3 point6 = dmVMath::Point3(aabb_max.getX(), aabb_max.getY(), aabb_min.getZ());
    dmVMath::Point3 point7 = dmVMath::Point3(aabb_max.getX(), aabb_max.getY(), aabb_max.getZ());

    dmVMath::Vector4 corner_points[8]; // corner points in world coords

    corner_points[0] = world * point0;
    corner_points[1] = world * point1;
    corner_points[2] = world * point2;
    corner_points[3] = world * point3;
    corner_points[4] = world * point4;
    corner_points[5] = world * point5;
    corner_points[6] = world * point6;
    corner_points[7] = world * point7;

    // for any of the six frustum planes if the all corner points lie in the negative halfspace, do cull the object
    int num_planes = frustum.m_NumPlanes;
    for (int plane_i = 0; plane_i < num_planes; ++plane_i)
    {
        // get plane normal/equation
        bool positive_found = false;
        for (int corner_i = 0; corner_i < 8; ++corner_i)
        {
            float distance = DistanceToPlane(frustum.m_Planes[plane_i], corner_points[corner_i]);
            if (distance >= 0)
            {
                positive_found = true;
                break; // no need to check for the rest of the points
            }
        }
        if (!positive_found) // if all corners are in the negative halfspace for the plane, we're done
        {
            return false; // no intersection, do cull
        }

    }
    return true; // inside the frustum but false positives may also happen. They are ok when used for frustum culling where the object will be hidden later in the rendering pipeline.
}

} // dmIntersection