Next, we'll terraform our sphere into a globe of the Earth by rendering a texture onto the surface of the sphere.
Shaders can get quite complex, implementing all kinds of specular highlights, reflections, shadows, and so on. A simpler algorithm that still makes use of a color texture and lighting is a diffuse material. This is what we'll use here. The word diffuse refers to the fact that light diffuses across the surface, as opposed to being reflective or shiny (specular lighting).
A texture is just an image file (for example, .jpg) that can be mapped (projected) onto a geometric surface. Since a sphere isn't easily flattened or unpeeled into a two-dimensional map (as centuries of cartographers can attest), the texture image will look distorted. The following is the texture we'll use for the Earth. (A copy of this file is provided with the download files for this book and similar ones can be found on the Internet at http://www.solarsystemscope.com/nexus/textures...