function normalize(pos)
		{
			var N = planes.subarray(pos,pos+3);
			var l = vec3.length(N);
			if(l === 0) return;
			l = 1.0 / l;
			planes[pos] *= l;
			planes[pos+1] *= l;
			planes[pos+2] *= l;
			planes[pos+3] *= l;
		}
extract frustum planes given a view-projection matrix
@method extractPlanes
@param {mat4} viewprojection matrix
@return {Float32Array} returns all 6 planes in a float32array[24]