IsSphereInFrustum

local nearD = 0 //the real distance of nearD bounces around 3e-7. Can use 0 here
local farD = 100000000000 //the real distance of farD is like 1e12. Can use a preferred distance.
//a radius of 0.63 will create a sphere that is approximately a marines waist
function IsSphereInFrustum(center,radius)
    //http://www.ijvr.org/issues/issue3-2008/7.pdf
    //http://www.lighthouse3d.com/tutorials/view-frustum-culling/radar-approach-testing-points/
    //http://www.lighthouse3d.com/tutorials/view-frustum-culling/radar-approach-implementation/
    //game programming gems 5 under the title "Improved Frustum Culling"

    local player = Client.GetLocalPlayer()

 //todo: can be moved out of function so it's not re-calculated for each point tested
    //local cameraCoords = player:GetCameraViewCoords() //more precise...more costly
    //local cameraOrigin = cameraCoords.origin
    local cameraCoords = player:GetViewAngles():GetCoords()
    local cameraOrigin = player:GetEyePos()

 //todo: these only needs to be calcuated during resolution change
    local rFactor = math.tan(player:GetRenderFov() / 2)
    local uFactor = rFactor / GetAspectRatio() //this approach came from game programming gems 5

    local v = center - cameraOrigin

    // compute and test the Z coordinate
    local P_z = Math.DotProduct(v, cameraCoords.zAxis)
    if P_z < (nearD - radius) or (farD + radius) < P_z then
        return false //behind near-plane or in front of far-plane
    end

    // compute and test the X coordinate
    local P_x = Math.DotProduct(v, cameraCoords.xAxis)
    local limit = (rFactor * P_z) + radius //half width of frustum at distance P_z from user
    if P_x < -limit or limit < P_x then
        return false //left of left-plane or right of right-plane
    end

    // compute and test the Y coordinate
    local P_y = Math.DotProduct(v, cameraCoords.yAxis)
    limit = (uFactor * P_z) + radius
    if P_y < -limit or limit < P_y then
        return false //above top-plane or below bottom-plane
    end

    return true //is visible
end