OpenGL Texture Mapping Commands

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1. Set up texture mapping:

void glEnable(GL_TEXTURE_2D); - enables 2D texturing

void glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

- sets texture environment parameters: GL_MODULATE specifies to blend texture with the current color of the object. Use GL_DECAL or white color for texture showing.

2. Bind texture to a texture object: achieved by

void glBindTexture(GLenum target, GLuint texture);

binds a named texture to a texturing target: specify which texture to use when multiple textures are in use.

For this to work, the texture parameter has to be bound to a specific texture object. This requires loading a texture file (bitmap, giff, jpg etc.) through some graphics file reader, e.g.

LoadTexture("earth.bmp", earthTexture);

can be followed by

glBindTexture(GL_TEXTURE_2D, earthTexture);

3. Map texture to polygons: this is achieved by

void glTexCoord2f(GLfloat s, GLfloat t) - specifies the s, t texture coordinates that map to a particular vertex of the surface polygon. Typically followed by a vertex definition (glVertex3f).

Texturing GLU quadrics: requires a

void gluQuadricTexture(GLUquadricObj *quadObject, GLboolean textureCoords)

call.

The typical calling sequence for a textured object might look like:

glEnable(GL_TEXTURE_2D);

glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

gluQuadricTexture(gluSpherePtr, true);

glBindTexture(GL_TEXTURE_2D, earthTexture);

gluSphere(gluSpherePtr, size, stacks, slices);

It is a good idea to disable texturing after such a sequence if not ALL objects are textured:

glDisable(GL_TEXTURE_2D);