CameraFrustum.lua

local Frustum = {}

local function planeFromPoints(p0, p1, p2)
	local normal = (p1 - p0):Cross(p2 - p1).Unit

	return {
		normal = normal,
		d = -normal:Dot(p0),
	}
end

function Frustum.sphereInFrustum(frustum, origin, radius)
	for _, plane in frustum do
		local distance = origin:Dot(plane.normal) + plane.d + radius

		if distance <= 0 then
			return false
		end
	end

	return true
end

function Frustum.fromCamera(camera, farPlaneZ)
	local aspectRatio = camera.ViewportSize.X / camera.ViewportSize.Y
	local halfFov = math.rad(camera.FieldOfView / 2)

	local halfFarPlaneHeight = 2 * math.tan(halfFov) * farPlaneZ / 2
	local halfFarPlaneWidth = halfFarPlaneHeight * aspectRatio

	local halfNearPlaneHeight = 2 * math.tan(halfFov) * -camera.NearPlaneZ / 2
	local halfNearPlaneWidth = halfNearPlaneHeight * aspectRatio

	local farTopLeft = camera.CFrame * Vector3.new(-halfFarPlaneWidth, halfFarPlaneHeight, -farPlaneZ)
	local farTopRight = camera.CFrame * Vector3.new(halfFarPlaneWidth, halfFarPlaneHeight, -farPlaneZ)
	local farBottomRight = camera.CFrame * Vector3.new(halfFarPlaneWidth, -halfFarPlaneHeight, -farPlaneZ)

	local nearTopLeft = camera.CFrame * Vector3.new(-halfNearPlaneWidth, halfNearPlaneHeight, camera.NearPlaneZ)
	local nearTopRight = camera.CFrame * Vector3.new(halfNearPlaneWidth, halfNearPlaneHeight, camera.NearPlaneZ)
	local nearBottomLeft = camera.CFrame * Vector3.new(-halfNearPlaneWidth, -halfNearPlaneHeight, camera.NearPlaneZ)
	local nearBottomRight = camera.CFrame * Vector3.new(halfNearPlaneWidth, -halfNearPlaneHeight, camera.NearPlaneZ)

	local frustum = {}

	frustum.near = planeFromPoints(nearTopRight, nearBottomRight, nearTopLeft)
	frustum.far = planeFromPoints(farTopRight, farTopLeft, farBottomRight)
	frustum.top = planeFromPoints(nearTopRight, nearTopLeft, farTopRight)
	frustum.bottom = planeFromPoints(nearBottomRight, farBottomRight, nearBottomLeft)
	frustum.left = planeFromPoints(nearTopLeft, nearBottomLeft, farTopLeft)
	frustum.right = planeFromPoints(nearTopRight, farTopRight, nearBottomRight)

	return frustum
end

return Frustum