1.10. 纹理 Texturing

1.10. 纹理 Texturing

The area of texture mapping is one of the more complex areas of the OpenGL API. It has been

extended more often than most of the other areas of OpenGL primarily because this was the

area of graphics for which hardware was the least mature when OpenGL was defined in the

early 1990s. The programmability added through the OpenGL Shading Language in OpenGL 2.0

makes this area much more straightforward, but the existing OpenGL APIs are still used to

create, modify, and define the behavior of textures. This section describes the texturing

functionality as it existed for OpenGL 1.5. Some significant changes have been made to this

model by OpenGL 2.0, particularly to the concept of texture units, and are described later in

this book.

OpenGL currently supports four basic types of texture maps: onedimensional, two-dimensional,

three-dimensional, and cube maps. (Only one- and two-dimensional textures were supported in

OpenGL 1.0.) A 1D TEXTURE

is an array containing width pixel values, a 2D TEXTURE

is an array

containing width x height pixel values, and a 3D

TEXTURE is an array containing width x height x

depth pixel values. A CUBE MAP TEXTURE contains six two-dimensional textures: one for each major

axis direction (i.e., ±x, ±y, and ±z).

OpenGL has the notion of a TEXTURE UNIT. A texture unit corresponds to the underlying piece of

graphics hardware that performs the various texturing operations. With OpenGL 1.3, support

was added for multiple texture units. Each texture unit maintains the following state for

performing texturing operations: