OpenGL Programming Guide

Chapter 9Texture Mapping

Specifying the Texture

The command glTexImage2D() defines a two-dimensional texture. It takes several arguments, which are described briefly here and in more detail in the subsections that follow. The related command for one-dimensional textures, glTexImage1D(), is described in "One-Dimensional Textures." void glTexImage2D(GLenum target, GLint level, GLint components, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const GLvoid *pixels);

Defines a two-dimensional texture. The target parameter is intended for future use by OpenGL; for this release, it must be set to the constant GL_TEXTURE_2D. You use the level parameter if you're supplying multiple resolutions of the texture map; with only one resolution, level should be 0. (See "Multiple Levels of Detail" for more information about using multiple resolutions.)

The next parameter, components, is an integer from 1 to 4 indicating which of the R, G, B, and A components are selected for use in modulating or blending. A value of 1 selects the R component, 2 selects the R and A components, 3 selects R, G, and B, and 4 selects R, B, G, and A. See "Modulating and Blending" for a discussion of how these selected components are used.

The width and height parameters give the dimensions of the texture image; border indicates the width of the border, which is usually zero. (See "Using a Texture's Borders." ) Both width and height must have the form 2m+2b, where m is an integer (which can have a different value for width than for height) and b is the value of border. The maximum size of a texture map depends on the implementation of OpenGL, but it must be at least 64 × 64 (or 66 × 66 with borders). If width or height is set to zero, texture mapping is effectively disabled.

The format and type parameters describe the format and data type of the texture image data. They have the same meaning as they do for glDrawPixels(), which is described in "Storing, Transforming, and Mapping Pixels." In fact, texture data is in the same format as the data used by glDrawPixels(), so the settings of such modes as GL_ALIGNMENT apply. (In the checkered-squares example, the call

glPixelStorei(GL_ALIGNMENT, 1); 

is made because the data in the example isn't padded at the end of each texel row.) The format parameter can be GL_COLOR_INDEX, GL_RGB, GL_RGBA, GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_LUMINANCE, or GL_LUMINANCE_ALPHA - that is, the same formats available for glDrawPixels() with the exceptions of GL_STENCIL_INDEX and GL_DEPTH_COMPONENT. Similarly, the type parameter can be GL_BYTE, GL_UNSIGNED_BYTE, GL_SHORT, GL_UNSIGNED_SHORT, GL_INT, GL_UNSIGNED_INT, GL_FLOAT, or GL_BITMAP.

Finally, pixels contains the texture-image data. This data describes the texture image itself as well as its border.

The next sections give more detail about using the border and level parameters. The level parameter, which specifies textures of different resolutions, naturally raises the topic of filtering textures as they're applied; filtering is the subject of "Controlling Filtering." Finally, one-dimensional textures are discussed in "One-Dimensional Textures."

Using a Texture's Borders
Multiple Levels of Detail
Controlling Filtering
One-Dimensional Textures

OpenGL Programming Guide