Frustum Culling

I'm confused with the problem you're facing, all I can offer is some code I use for Frustum Culling. Hope it helps in any way.

/* Before rendering the object check if it is visible */
Object::IsVisible() {
	Frustum frustum = scene->GetCamera()->GetFrustum();
	frustum.Inside(this.position, this.radius);
}

/*
   Create: Plane planes[6]
   Iterate through all 6 planes, if the point is outside ANY plane;
   it's not visible
*/
bool Frustum::Inside(Vec3 point, float radius) {
	for (int i=0; i<6; ++i) {
		if (!planes.Inside(point, radius)) return false;
	}
	return true; // Point is inside all planes
}

/* Up to you to find out how PointToPlaneDistance function works */
bool Plane::Inside(Vec3 point, float radius) {
	float distance = Math::PointToPlaneDistance(this, point);
	return (distance >= -radius); //We are out of visible area
}

Assuming you know the point of intersection (the corner) between PB and PL (let's call it PI), you can calculate a vector V = (P - PI). If (length(V) < sphereRadius) your point is inside, otherwise, check the dot product of normalized(V) with PB and PL plane normals, if and only if both values are negative, point is outside, if the comparison fails, it's inside.

Take this with a grain of salt since I've never tested or even considered this case when doing frustum culling, but this would be my first guess to solve this issue.

Hope it helped.

IgnatusZuk, thanks, but your code has the exact same problem I am trying to solve: There are some cases, where the function return visibility, while the object is actually outside the view frustum. In most cases I expect this to be just very few objects, so anything more complicated for culling is not worth it.

TMarques, I may should have mentioned that I am culling spheres in a 3D frustum, so those corners are actually lines and not points, but my approach to get that V as the distance to the planes should be fine, except the thing you mentioned, where I have to check which side of the planes the center is on, which explains why now in my implementation too many lights are culled.

Thank you very much for that hint :)

If there are any more ideas, please post them, as I´d love to find a better way if there is one :)

I am using it to cull lights for tiled shading

this is the killer here. any unculled light will be a performance hit. if you were merely culling a mesh, it wouldn't matter, as the poly engine would eventually clip it with relatively little overhead, so it would be ok to let it "slip through" your frustum cull. i assume you have some sort of list of lights you go through and cull to see which you should activate when setting lights for the scene. have you considered a change of data structure? i've had a lot of luck recently using that approach to speed up drawing stuff. for example, instead of a list of lights, a 2d array map of lights and you simply activate all within some bounding box distance of the camera, no culling required. i've had a lot of luck copying data from my existing data structures into new ones that are in a format which can be quickly processed for drawing.

For now it is just a list, later they will probably be sorted into an octree or something similar, which should of course be an improvement but for now it is good enough to optimize the culling itself a little (for less than 1000 lights, it performs very well, using multithreading and some basic code optimizations).

My code seems to work well and looks like this now:

#define Distance(plane, op, r) { \
	float dot = (position.x * plane.normal.x + position.y * plane.normal.y + position.z * plane.normal.z);\
	distance = dot - plane.d; \
	if(distance op r) \
		continue; \
	}


const Vector3& position = light->_worldPosition;
const float range = light->_range;
float distance, dr, dl, dt, db;
Distance(plright, >, range);
dr = distance;
Distance(plleft, <, -range);
dl = distance;
Distance(plbottom, <, -range);
db = distance;
Distance(pltop, >, range);
dt = distance;

float sqrange = range*range;
if(dr > 0.0f && db < 0.0f && dr*dr+db*db > sqrange)
	continue;
if(dr > 0.0f && dt > 0.0f && dr*dr+dt*dt > sqrange)
	continue;
if(dl < 0.0f && db < 0.0f && dl*dl+db*db > sqrange)
	continue;
if(dl < 0.0f && dt > 0.0f && dl*dl+dt*dt > sqrange)
	continue;

It´s not pretty, but I have to fix some other things before cleaning up and while my planes have a function to get it´s distance to a point, at 32*24*1024*4 calls, the function call overhead was the biggest performance hit ;)