The "Quake" engine was optimized specifically to obviate this problem. The engine could be told ahead of time to not calculate rendering for all objects in any space out of the player's view, greatly reducing the rendering load on the CPU. This effect is noticeable in the game as small tunnels with sharp 90-degree bends leading from one large space into another. This small tunnel serves to block view into the adjoining unrendered space, and a special type of transparent brush (called a "visportal") is placed within it to define the edge of where the engine should stop rendering the adjoining space. It is uncommon in the original "Quake" to be able to see across the entire length of a map, and outdoor spaces are often very tall and narrow, primarily utilizing distance above into open sky or below into lava to create a low-polygonal illusion of expanse.