OpenGL's Command Structure

OpenGL's core API provides a number of primitives that deal with points, lines, polygon surfaces, rational polygon curves and surfaces, and bit-mapped images. These primitives can specify position coordinates, colors, surface normals, and texture coordinates. The rasterizer uses these primitives, along with OpenGL's current graphics state, to perform such graphics operations as stippling, fogging, texture-mapping, antialiasing, blending, masking, and depth testing on the resulting output pixels.

To maintain portability, OpenGL doesn't support certain basic geometric objects (e.g., a box). However, you can assemble such objects by combining multiple primitives. The OpenGL Utility Lib rary (GLU) provides commands for building such common objects as spheres, cylinders, and cones.

GLU has functions to coordinate transformations and tessellating polygons, and describe nonuniform rational B-splines (NURBS) curves and surfaces. (A NURBS curve is a 3-D surface, analogous to a Bézier curve in the 2-D PostScript language.) These NURBS surfaces can be trimmed (i.e., have holes cut in them, or irregularly shaped surfaces can be joined without cracks or overlaps), a useful property for CAD work or character animation. GLU also has utilities for scaling images and building texture-maps.

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OpenGL Contact Information

Applications developers don't need to license OpenGL. Companies that are creating and distributing OpenGL implementations and extension libraries need a license. They should contact Silicon Graphics at (415) 933-3062 for licensing information.

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Inside OpenGL's Rendering Engine

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