Many high-quality renderers support spherical environment maps. They are a lot like skyboxes, but are a single image mapped onto a sphere instead of six images mapped onto a cube. Figure 3 is what the game player sees. Figure 4 is the cubic projection, unwrapped and laid flat, and Figure 5 is the spherical projection. Notice that straight lines in the player's view or cubic map turn into curved lines in the spherical map, and vice versa.
Spherical maps can be easier to work with because they are stored as a single image.
However, interactive graphics hardware and software is designed to display flat surfaces, so cubic environment maps can be drawn quicker than spherical maps. Immersive imaging products concentrate on the problem of stitching together photographs to create a 3D environment, and they map the final image to a cylinder or partial sphere instead of a cube. Often they limit the view so you cannot look straight up or straight down, although creation of full panoramas using special camera lenses or mirrors is becoming more common. However, the restrictions on viewer movement, as well as the difficulty of incorporating fast cylindrical or spherical rendering into polygon-based game engines, limits their use in most games. Now that you have some background on skyboxes and related technologies, we'll move on to the nuts and bolts of creating them.