What are the different types of Environmental Mapping provided by DirectX?

Environment mapping is a technique that simulates highly reflective surfaces without using ray tracing. In practice, environment mapping applies a special texture map that contains an image of the scene surrounding an object to the object itself. The result approximates the appearance of a reflective surface, close enough to fool the eye, without incurring any of the complex computations involved in ray tracing. There are many types of environment mapping in use throughout the graphics industry. DirectX supports the two most common forms - Cubic environment mapping and spherical environment mapping.

Cubic environment maps (sometimes referred to as cube maps) are textures that contain image data representing the scene surrounding an object, as if the object were in the center of a cube. Each face of the cubic environment map covers a 90-degree field of view in the horizontal and vertical vision. There are six faces per cube map. The faces of a cube map don't need to contain extremely detailed renderings of the surrounding scene. In most cases, environment maps are applied to curved surfaces. Given the amount of curvature used by most applications, the resulting reflective distortion makes extreme detail in the environment map wasteful in terms of memory and rendering overhead.

Unlike cubic environment maps, sphere maps don't directly represent an object's surroundings. A sphere map is a 2-D representation of the full 360-degree view of the scene surrounding of an object, as if taken through a fish-eye lens.

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