A Skybox is a catch-all term used to describe ways of representing a sky or background that 'wraps around' a computer game-world the name coming from the traditional method of using of a big literal cube to enclose the level, with a seamless texture applied across all 6 faces. Other game engines may use a large dome or sphere instead, but the name "Skybox" stuck.
Traditionally, a skybox is represented by a static image that represents the entire background of a level including the sun, clouds, distant mountains, buildings, etc. More modern games will typically break up these elements either as separate 2D image planes or low poly objects, allowing the developers to apply animation to the textures to give the appearance of moving clouds or distant traffic, as well as allowing the player to come closer to the background elements as they progress though the level. A notable example of this is the Citadel in Half-Life 2, which appears increasingly larger as the player progresses further towards it.
Some game engines, such as the Source Engine, treat the skybox as a distinct element of the level, where the level designer creates a miniature enclosed area somewhere out of bounds on the map, which is then projected onto the playable space in some way (such as the lighthouses in Team Fortress 2's "Sunshine" map, or the Powerplant towers in CS:GO's "Nuke" map). This type of skybox design utilises what are known as "skybox models"; variants of the "to scale" models the game world otherwise uses that are really small. Other game engines, such as Unreal Engine 3 and 4, make no distinction the skybox merely describes the background elements placed outside the levels intended playable area, and although the engine comes with a built in "sky sphere", this is simply just a large mesh that can be optionally placed in within the level.
The Skybox equivalent in CG films and VFX is typically called a Backplate, and is usually either a large dome or 2D image projected behind the CG elements, which can either be part of a live action shot, a matte painting, or a mixture of both. Typically however the CG elements and the background will be rendered separately and later composited together in post-production.
Note: This trope is so ubiquitous among 3D videogames, that it'd be pointless listing most of them here, as the great majority of them use skyboxes. When adding a game, there needs to be a notable reason for it to be on this list, otherwise it simply doesn't need to be added.
- Used in Sonic Adventure 2. The levels look like they occur in the real world, but there are glitches that allow the user to jump out of a level. Doing so reveals that the levels are hallways built in one large skybox.
- In Spyro the Dragon, flying outside the bounds of the flight levels reveal that you are inside a skybox.
- One of the maps in Team Fortress 2, a train-yard called "Well", uses the skybox to conceal the interiors of the teams' bases, which are Bigger on the Inside. The top half of the buildings' façades are 3D miniatures projected onto the skybox. Generally this is not feasible in the game's engine, since the technique requires that there not be a direct line of sight to any part of the area being hidden.
- In Mabinogi: Fantasy Life, the skybox moves as time flows; since time is sped up in the game compared to real life, you can actually watch the clouds/moon/sun move across the sky.
- A toggelable option in Runescape. Used most notably in the Clan Citadels.
- Roblox has tons and tons.
- Modern Game Engines come with built-in skyboxes; an example is Unreal Engine from Epic Games. It's most likely the first thing you see when you load up the development environment.
- Some especially enterprising Kerbal Space Program modder came up with a utility for replacing the default skybox, among other features.
- In the final scene of Half-Life: Opposing Force, the skybox was cleverly used to present a teleportation event without breaking the flow with a loading screen. Since the player has a very limited view of "outside" through the open door of an Osprey, giving each side of the skybox a different texture was sufficient to create the illusion of seeing Earth one moment and Xen the next. An unseen side of the skybox contains a hidden message◊ which alludes to this "hack".
- Second Life features a traditional skybox as part of the game world, but its inherently customizable nature allows for a great deal of variation: skyboxes can be concealed within structures, attached to specific parts of a sim, or even equipped to avatars. Among the Second Life community, the term Skybox refers to a structure placed far enough above the ground to be outside of rendering distance, commonly used to create the illusion a structure is Bigger on the Inside. While these are often fully enclosed structures, some of these Skyboxes have traditional skyboxes placed around them to create the illusion of being at ground level. By combining these effects, you create some truly otherworldy examples ofBizarchitecture.
- SCP Foundation has SCP-1165, titled "Minus Level", a physical Minus World. There's a recreation of the Eiffel Tower in the distance, but it turns out to be part of the world's equivalent of a skybox; if one tries to reach it, they'll just notice the tower remaining at the same distance from them no matter how far they go. One survey team sent to investigate it had to call off their journey because lethal things would happen to them if they went beyond 100 km of their starting point within the strange world.
- Unreal (1998) contains the Ur-Example of the miniature encosed out-of-bounds area and sometimes employed it to multiple levels i.e. skybox in skybox.