Technically, the loss of signal information in an image reproduced at some finite resolution. It is most often characterized by the appearance of sharp jagged edges along points, lines, or polygons due to the nature of having a limited number of fixed-sized pixels.

A fourth color value added to provide a degree of transparency to the color of an object. An alpha value of 0.0 means complete transparency; 1.0 denotes no transparency (opaque).

Light in a scene that doesn't come from any specific point source or direction. Ambient light illuminates all surfaces evenly and on all sides.

A rendering method used to smooth lines and curves and polygon edges. This technique averages the color of pixels adjacent to the line. It has the visual effect of softening the transition from the pixels on the line and those adjacent to the line, thus providing a smoother appearance.

The Architecture Review Board. The OpenGL ARB meets quarterly and consists of 3D graphics hardware vendors. The ARB maintains the OpenGL Specification document and promotes the OpenGL standard.

The ratio of the width of a window to the height of the window. Specifically, the width of the window in pixels divided by the height of the window in pixels.

A window system independent utility library. Limited but useful for quick and portable OpenGL demonstration programs. Now largely replaced by the GLUT library.

A curve whose shape is defined by control points near the curve rather than by the precise set of points that define the curve itself.

An array of bits mapped directly to screen pixels.

An area of memory used to store image information. This can be color, depth, or blending information. The red, green, blue, and alpha buffers are often collectively referred to as the color buffers.

A coordinate system based on three directional axes placed at a 90° orientation to one another. These coordinates are labeled x, y, and z.

The elimination of a portion of a single primitive or group of primitives. The points that would be rendered outside the clipping region or volume are not drawn. The clipping volume is generally specified by the projection matrix. Clipped primitives are reconstructed such that the edges of the primitive do not lay outside the clipping region.

The 2D geometric coordinates that result from the modelview and projection transformation.

A color mode in which colors in a scene are selected from a fixed number of colors available in a palette. These entries are referenced by an index into the palette. This mode is rarely used and even more rarely hardware accelerated.

A reference to the shape of a polygon. A convex polygon has no indentations, and no straight line can be drawn through the polygon that intersects it more than twice (once entering, once leaving).

The elimination of graphics primitives that would not be seen if rendered. Backface culling eliminates the front or back face of a primitive so that the face isn't drawn. Frustum culling eliminates whole objects that would fall outside the viewing frustum.

The stored color at a particular location in the color buffer. This terminology is usually used when describing blending operations to distinguish between the color already present in the color buffer and the color coming into the color buffer (source color).

A compiled list of OpenGL functions and commands. When called, a display list executes faster than a manually called list of single commands.

A method used to simulate a wider range of color depth by placing different-colored pixels together in patterns that give the illusion of shading between the two colors.

A drawing technique used by OpenGL. The image to be displayed is assembled in memory and then placed on the screen in a single update operation, rather than built primitive by primitive on the screen. Double buffering is a much faster and smoother update operation and can produce animations.

The process of taking a 2D image or shape and adding a third dimension uniformly across the surface. This process can transform 2D fonts into 3D lettering.

The coordinate system based on the position of the viewer. The viewer's position is placed along the positive z-axis, looking down the negative z-axis.

A pyramid-shaped viewing volume that creates a perspective view. (Near objects are large; far objects are small.)

The OpenGL utility library. A window system independent utility library useful for creating sample programs and simple 3D rendering programs that are independent of the operating system and windowing system. Typically used to provide portability between Windows, X-Window, Linux, and so on.

A graphics rendering mode in which commands and functions have an immediate effect on the state of the rendering engine.

A value, not a variable name. A specific string or numeric constant embedded directly in source code.

A 2D array of numbers. Matrices can be operated on mathematically and are used to perform coordinate transformations.

A technique that uses multiple levels of detail for a texture. This technique selects from among the different sizes of an image available, or possibly combines the two nearest sized matches to produce the final fragments used for texturing.

The OpenGL matrix that transforms primitives to eye coordinates from object coordinates.

A directional vector that points perpendicularly to a plane or surface. When used, normals must be specified for each vertex in a primitive.

The reduction of a normal to a unit normal. A unit normal is a vector that has a length of exactly 1.0.

An acronym for non-uniform rational b-spline. This is a method of specifying parametric curves and surfaces.

A C++ class library and toolkit for building interactive 3D applications. Open Inventor is built on OpenGL.

A drawing mode in which no perspective or foreshortening takes place. Also called parallel projection. The lengths and dimensions of all primitives are undistorted regardless of orientation or distance from the viewer.

A set of colors available for drawing operations. For 8-bit Windows color modes, the palette contains 256 color entries, and all pixels in the scene can be colored from only this set.

A curve whose shape is determined by one (for a curve) or two (for a surface) parameters. These parameters are used in separate equations that yield the individual x, y, and z values of the points along the curve.

A drawing mode in which objects farther from the viewer appear smaller than nearby objects.

Condensed from the words picture element. This is the smallest visual division available on the computer screen. Pixels are arranged in rows and columns and are individually set to the appropriate color to render any given image.

A two-dimensional array of color values that comprise a color image. Pixmaps are so called because each picture element corresponds to a pixel on the screen.

A 2D shape drawn with any number of sides (must be at least three sides).

A 2D polygonal shape defined by OpenGL. All objects and scenes are composed of various combinations of primitives.

The transformation of lines, points, and polygons from eye coordinates to clipping coordinates on the screen.

A polygon with exactly four sides.

The process of converting projected primitives and bitmaps into pixel fragments in the frame buffer.

The conversion of primitives in object coordinates to an image in the frame buffer. The rendering pipeline is the process by which OpenGL commands and statements become pixels on the screen.

A sparkling or flashing effect produced on objects when a non-mipmapped texture map is applied to a polygon that is significantly smaller than the size of the texture being applied.

The color of the incoming fragment, as opposed to the color already present in the color buffer (destination color). This terminology is usually used when describing how the source and destination colors are combined during a blending operation.

A general term used to describe any curve created by placing control points near the curve, which have a pulling effect on the curve's shape. This is similar to the reaction of a piece of flexible material when pressure is applied at various points along its length.

A binary bit pattern used to mask out pixel generation in the frame buffer. This is similar to a monochrome bitmap, but one-dimensional patterns are used for lines and two-dimensional patterns are used for polygons.

The process of breaking down a complex polygon or analytic surface into a mesh of convex polygons. This process can also be applied to separate a complex curve into a series of less complex lines.

Similar to pixel (picture element), a texel is a texture element. A texel represents a color from a texture that is applied to a pixel fragment in the frame buffer.

An image pattern of colors applied to the surface of a primitive.

The process of applying a texture image to a surface. The surface does not have to be planar (flat). Texture mapping is often used to wrap an image around a curved object or to produce patterned surfaces such as wood or marble.

The manipulation of a coordinate system. This can include rotation, translation, scaling (both uniform and nonuniform), and perspective division.

A degree of transparency of an object. In OpenGL, this is represented by an alpha value ranging from 1.0 (opaque) to 0.0 (transparent).

A single point in space. Except when used for point and line primitives, it also defines the point at which two edges of a polygon meet.

The area in 3D space that can be viewed in the window. Objects and points outside the viewing volume are clipped (cannot be seen).

The area within a window that is used to display an OpenGL image. Usually, this encompasses the entire client area. Stretched viewports can produce enlarged or shrunken output within the physical window.

The representation of a solid object by a mesh of lines rather than solid shaded polygons. Wireframe models are usually rendered faster and can be used to view both the front and back of an object at the same time.