PC 3D Graphics Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Accelerated Graphics Port (A.G.P.)

A high-bandwidth 32-bit PC bus architecture to be introduced in 1997. It provides up to 528 MBytes/sec to a graphics controller, yielding the bandwidth necessary for texturing directly from system memory. A.G.P. is physically different from the (132 MByte/s) PCI bus, but does not replace PCI. A.G.P. uses a combination of frame buffer memory local to the graphics controller, as well as system memory, for graphics data storage.

Alpha

Additional color component in some representations of pixels, along with red, green, and blue (RGB). The alpha channel denotes transparency or opacity, often as a fractional value, used in blending and antialiasing.

Anti-aliasing

An algorithm designed to reduce the stair-stepping artifacts (sometimes called jaggies) that result from drawing graphic primitives on a raster grid. The solution usually relies on the multi-bit raster’s ability to display a number of pixel intensities. If the intensities of the neighboring pixels lie between the background and line intensities, the line becomes slightly blurred, and the jagged appearance is thereby diffused.

B

Bitmap

A flat 2D picture, or a texture map. Most 3D systems are capable of combining 2D bitmaps and 3D objects onscreen.

Back buffer

A hidden drawing buffer used in double-buffering. Graphics are drawn into the back buffer so that the rendering process cannot be seen by the user. When the drawing is complete, the front and back buffers are swapped. See double-buffering.

BLT (Bit-aLigned BLock Transfer)

The process of copying pixels or other data from one place in memory to another.

C

Camera

In 3D graphics, the viewpoint through which a scene is viewed. Flythroughs of scenes are conceptually a moving camera.

Clipping

Removing, from the processing pipeline points and surfaces which are outside the field of view (known as the "viewing frustrum").

Culling

Removing, from the processing pipeline to spare unneeded work, complete objects and surfaces which are completely hidden by other objects, or are facing away from the viewer (i.e. Backface culling)

D

Depth Cueing

Reducing an object’s color and intensity as a function of its distance from the observer. For instance, a bright, shiny red ball may look duller and darker the farther away it is from the observer.

Dithering

The process of intentionally mixing colors of adjacent pixels. Dithering is usually needed for 8-bit color, and sometimes for 16-bit. It allows a limited color set to approximate a broader range, by mixing groups of varying-color pixels in a semi-random pattern. Without dithering, color gradients like sky or sunset tend to show "banding" artifacts.

Display List

Data structure, in very compact form, describing objects and scenes to display. Usually consists of floating-point coordinates (X,Y,Z) and colors (R,G,B) for points on objects.

Double Buffering

The process of using two frame buffers for smooth animation. Graphical contents of one buffer are displayed while updates occur on the other buffer. When the updates are complete, the buffers are switched. Only complete images are displayed, and the process of drawing is not shown. The result is the appearance of smooth animation. Double buffering may be implemented by hardware which simply changes the pointer that the DAC (Digital-Analog-Converter) circuitry is using to access pixels, or by complete copies of the entire buffer via software.

F

Fogging

Also known as Haze. The alteration of the visibility or clarity of an object, depending on how far the object is from the camera. Usually implemented by adding a fixed color (fog color) to each pixel.

Frame Buffer

Display memory that temporarily stores (buffers) a full frame of picture data at one time. Frame buffers are composed of arrays of bit values that correspond to the display’s pixels. The number of bits per pixel in the frame buffer determines the complexity of images that can be displayed.

G

Gouraud shading

Also known as smooth shading. Applies a lighting calculation to each vertex of a polygon face, and linearly interpolates the results across the face to achieve a smooth lighting effect with gradual color transitions.

Graphics library

A tool set for application programmers, interfaced with an application programmer’s interface, or API. The graphics library usually includes a defined set of primitives and function calls that enable the programmer to bypass many low-level programming tasks.

J

Jaggies

Also known as Aliasing. A term for the jagged visual appearance of lines and shapes in raster pictures that results from producing graphics on a grid format. This effect can be reduced by increasing the sample rate in scan conversion.

L

Lighting

A mathematical formula for approximating the physical effect of light from various sources striking objects. Typical lighting models use light sources, an object’s position & orientation and surface type.

LFB

See Linear Frame Buffer.

Linear Frame Buffer

A buffer organized in a linear fashion, so that a single address increment can be used to step from one pixel to the pixel below it in the next scan line in the frame buffer. The entire LFB can be addressed using a single 32-bit pointer.

M

Mapping

The transformation of one coordinate system into another. In the 3-D viewing pipeline, for instance, an object is defined by the application developer in model coordinates; these are mapped to world coordinates; the world coordinates are mapped to normalized device c oordinates (NDCs); the NDCs are mapped into device coordinates; and the final picture is displayed. Also, an application for computer graphics systems.

Matrix Transform

Multiplying a 4x4 matrix times a 4x1 (X,Y,Z,1) vertex. This single operation is adequate to accomplish any rotation, translation, and projection of the vertex.

Mesh model

A graphical model with a mesh surface constructed from polygons. The polygons in a mesh are described by the graphics system as solid faces, rather than as hollow polygons, as is the case with wireframe models. Separate portions of mesh that make up the model are called polygon mesh and quadrilateral mesh.

Mip Mapping

A texture-mapping scheme, which uses multiple resolutions of each texture, pre-filtered, at typically 100%, 50%, 25%, and 12% resolution. The rasterizer either chooses the resolution (the map-level) that most closely matches the instantaneous resolution of the image being textured, or it interpolates between the two nearest mipmap levels. The resolutions are, for example, 128x128, 64x64, 32x32, and 16x16. Each is one-half the dimension of its larger neighbor. They are pre-filtered for best appearance at their particular magnification.

P

Perspective Divide

The computationally expensive division of the (X,Y) coordinates of a point by a scaling factor proportional to the Z coordinate, to give the appearance that objects near the viewer are larger, and that parallel lines (like railroad tracks) converge in the far distance.

Phosphor

A luminescent substance on the inside of the cathode-ray tube display that is illuminated by the electron gun in the pattern of graphical images as the display is scanned.

Phosphor triad

One red, one green and one blue phosphor that composes a pixel.

Pixel

Short for PIcture ELement. In a raster grid, the pixel is the smallest unit that can be addressed and given a color or intensity. The pixel is represented by some number of bits (usually 8, 16 or 24) in the frame buffer, and is illuminated by a collection of phosphor dots in the CRT that are struck by the beams of the electron gun.

Poly

Abbreviation for Polygon

Polygons

Three-sided (triangle) or 4-sided (Quadrilateral) or occasionally more-sided "simple" geometric objects. Complex objects like teapots are decomposed, or "tessellated", into many (like 700) polygons to allow regular processing of the data, and hardware acceleration of that processing.

Primitives

Smallest units in the 3D database. Usually points, lines, and polygons. Some 3D hardware and software schemes also employ curves, known as "splines":

R

Radiosity, Ray-Tracing

Complex methods of drawing 3D scenes, which result in photorealistic images, but cannot be done in real time with current hardware. Essentially, they calculate the path that light rays follow from objects to the viewer, and all the accompanying reflections.

Raster

A rectangular grid of picture elements, or pixels, on a CRT (Cathode Ray Tube) screen. The graphical data to be displayed on the raster is stored by the frame buffer. Raster operations (ROPs) can be performed on some portion or all of the raster. Such operations aid in the efficient handling of blocks of pixel data.

Rasterization

The process of creating every visible pixel's value, from the transformed display list.

Rendering

The process of translating high-level database descriptions to pixels on the screen.

RGB

A color model in which colors are specified as intensities (between 0.0 and 1.0, if floating point representation is used, or between 00 and 0xFF for integer hex) of the three CRT monitor primary colors: red, green, and blue. For RGB24 (8 bits each of red, green, and blue), a value of 0xFFFFFF hex is white. Other common RGB formats are 16-bit per pixel, in 555 or 565 bit partitions.

S

Shading(Flat, Gouraud, Phong)

The process of creating pixel colors. Gouraud is a constant increment of color from one pixel to the next, while Phong is much more complex and higher quality. Flat shading means no smooth blending of colors. In flat shading, each polygon is a single color.

Setup

Stage of a 3D rendering pipeline, where polygons are put into a data format interpretable by a rasterizer (SW or HW). Setup typically involves calculation of slopes of polygon edges, and incremental values for pixel interpolation across scanlines.

T

Tessellate

To divide an object or surface into geometric primitives (triangles, quadrilaterals, or other polygons) for simplified processing and rendering.

Texel

A colored dot in a texture map; texture element.

Texture

A (2 dimensional) bitmap pasted onto objects or polygons, to add realism

Texture filtering

Bilinear or trilinear filtering. Also known as sub-texel positioning. If a pixel is in between texels, the program colors the pixel with an average of the texels’ colors instead of assigning it the exact color of one single texel. If this is not done, the texture gets very blocky up close as multiple pixels get the exact same texel coloring, while the texture shimmers at a distance because small position changes keep producing large texel changes.

Texture mapping

The calculations required to place each point of the texture bitmap to the correct place in the 3D world, accounting for the rotation/scaling/translation/perspective of the world's objects. This mapping takes a large number of memory references and computation, often accounting for more than half the total CPU time in the 3D pipeline. May therefore be hardware accelerated in the graphics chip.

Three Dimensional Graphics

The display of objects and scenes with height, width, and depth information. The information is calculated in a coordinate system that represents three dimensions via x, y, and z axes.

V

Vertex

A point in space, described by (X,Y,Z) or (X,Y,Z,W), where "W" is a fudge factor that keeps track of perspective effects in a string of computations.

VRML

Virtual Reality Modeling Language. A database description language applied to create 3D worlds. A standard for internet-based 3D modeling, but still evolving - current Web VRML browsers implement VRML 1.0 or 2.0. Does not have as much description flexibility (yet, anyway) as Autodesk 3DS (3D Studio) format.

Z

Z-buffer

A common method of eliminating hidden surface removal (which the viewer should not see) in the rasterization process. An integer value is stored in RAM, the "z-buffer" for each point on the screen. Before each pixel is drawn, the existing z-buffer value is compared to the z (depth) of the object at that point; if the existing value is less, it is nearer, so the new pixel is discarded. However, if the new Z value is less, then it is written to replace the old value, and the corresponding pixel is updated.