OpenGL Programming Guide

Chapter 9Texture Mapping

Automatic Texture-Coordinate Generation

You can use texture mapping to make contours on your models or to simulate the reflections from an arbitrary environment on a shiny model. To achieve these effects, let OpenGL automatically generate the texture coordinates for you, rather than explicitly assigning them with glTexCoord*(). Actually, the mechanism for automatic texture-coordinate generation is useful for many different applications such as showing contours and environment mapping. To generate texture coordinates automatically, use the command glTexGen(). void glTexGen{ifd}{v}(GLenum coord, GLenum pname, TYPEparam);

Specifies the functions for automatically generating texture coordinates. The first parameter, coord, must be GL_S, GL_T, GL_R, or GL_Q to indicate whether texture coordinate s, t, r, or q is to be generated. The pname parameter is GL_TEXTURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE. If it's GL_TEXTURE_GEN_MODE, param is an integer (or, in the vector version of the command, points to an integer) that's either GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP. These symbolic constants determine which function is used to generate the texture coordinate. With either of the other possible values for pname, param is either a pointer to an array of values (in the vector version) or a single value specifying parameters for the texture-generation function.

Creating Contours
Environment Mapping

OpenGL Programming Guide