Skybox (video Games) - Advanced Skyboxes

Advanced Skyboxes

As technology progressed it became clear the default skybox had severe disadvantages. It could not be animated and all objects in it appeared to be infinitely distant, even if they were close-by. Starting in the late 1990s, some game designers built small amounts of 3D geometry to appear in the skybox to create a better illusion of depth, in addition to a traditional skybox for objects very far away. This constructed skybox was placed in an unreachable location, typically outside the bounds of the playable portion of the level, to prevent players from entering the skybox.

In older versions of this technology, such as the ones presented in the game Unreal, this was limited to movements in the sky, such as the movements of clouds. Elements could be changed from level to level, such as the positions of stellar objects, or the color of the sky, giving the illusion of the gradual change from day to night. The skybox in this game would still appear to be infinitely far away, as the skybox, although containing 3D geometry, did not move the viewing point along with the player movement through the level.

Newer engines, such as the Source engine, continue on this idea, allowing the skybox to move along with the player, although at a different speed. Because depth is perceived on the compared movement of objects, making the skybox move slower than the level causes the skybox to appear far away, but not infinitely so. It is also possible, but not required, to include 3D geometry which will surround the accessible playing environment, such as unreachable buildings or mountains. They are designed and modeled at a smaller scale, typically 1/16th, then rendered by the engine to appear much larger. This results in less CPU requirements than if they were rendered full size. The effect is referred to as a "3D skybox".

In the game Half-Life 2, this effect was extensively used in showing The Citadel, a huge structure in the center of City 17. In the closing chapters of the game, the player travels through the city towards the Citadel, the skybox effect making it grow larger and larger progressively with the player movement, completely appearing to be a part of the level. As the player reaches the base of the Citadel, it is broken into two pieces. A small lower section is a part of the main map, while the upper section is in the 3D skybox. The two sections are seamlessly blended together to appear as a single structure.