This list contains the approved texture names for sky skins. Depending on the chosen texture names a different mapping scheme is used to render a Sky Layer. Mixing texture names from different types results in an undefined behavior. If you implement a graphic module you should stick to this list. You are not required to support all texture names mentioned here but if you support them stick to the definition below. Artist rely on the same list to produce there content. For testing new sky mapping schemes you can of course define new names and propose them for inclusion.
A Sky Box is as the name implies a textured cube with the camera at its center. This kind of sky texturing is often used since it is rather simple to produce textures for such a setup. To get a valid Sky Box up and running you have to specify 6 textures with the following names: sky.box.left, sky.box.right, sky.box.top, sky.box.bottom, sky.box.front, sky.box.back. The textures are applied to the cube side with the given relationship relative to your viewing direction ( if you look along the positive Z axis ).
Sky Spheres are a more sophisticated way of rendering a sky. In contrary to a Sky Box a Sky Sphere ( as the name implies ) maps a sky texture onto a sphere around the user. This kind of mapping avoids the stretching problems of Sky Boxes at the corners but introduces possible artifacts at the poles. Another advantage is that for a Sky Sphere you need only one texture, a so called Mercator Projection texture ( TODO: add here an image of an unwrapped mercator projection texture ). This kind of projection renders the majority of the sphere as a rectangular grid with the top and bottom of the texture stretching quickly into the poles. Producing Sky Sphere textures is more involved and tricky than Sky Box textures but usually result in better quality. To use a Sky Sphere specify one texture with the name sky.sphere. ( TODO: add the mathematical formula used to texture from such an image )