Texture coordinates are used to control how a texture is applied to a
polygon - i.e. what part of the texture is applied.
One texture coordinate should be assigned for each vertex.
Texture coordinates are referred to as S and T (to keep them distinct from geometric coordinates X & Y).
Texture coordinates range from 0 to 1 within the texture image. Values outside that range can be used when the texture is to be tiled.
Tiling is enabled/disabled by the WRAP parameter:
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);