Textures can be used to simulate a surface that has a component that is purely reflective (a mirror-like surface such as chrome). In order to do so, we need a texture that is representative of the environment surrounding the reflective object. This texture could then be mapped onto the surface of the object in a way that represents how it would look when reflected off the surface. This general technique is known as environment mapping.

In general, environment mapping involves creating a texture that is representative of the environment and mapping it onto the surface of an object. It is typically used to simulate the effects of reflection or refraction.

A cube map is one of the more common varieties of textures used in environment mapping. A cube map is a set of six separate images that represent the environment projected onto each of the six faces of a cube. The six images represent a view of the environment from the point of view of a viewer located at the center of the cube. An example of a cube map is shown in the following image. The images are laid out as if the cube was unfolded and laid flat. The four images across the middle would make up the sides of the cube, and the top and bottom images correspond to the top and bottom of the cube:

OpenGL provides built-in support for cube map textures (using the GL_TEXTURE_CUBE_MAP target). The texture is accessed using a three-dimensional texture coordinate (s, t, r). The texture coordinate is interpreted as a direction vector from the center of the cube. The line defined by the vector and the center of the cube is extended to intersect one of the faces of the cube. The image that corresponds to that face is then accessed at the location of the intersection.

In this example, we'll demonstrate using a cube map to simulate a reflective surface. We'll also use the cube map to draw the environment around the reflective object (sometimes called a skybox).