Glossary





This glossary describes terms and acronyms found in this manual.

24 bit color
See true color.
API
Application programmer's interface. The style and usage conventions that determine the "look and feel" of a graphics user interface.
ASIC
Application Specific Integrated Circuit.
BLOP
Blending operations. See also raster operations.
b
Blue value. See also, g and r.
Blt
Block image transfer.
bs
The blue value of the starting point of a triangle. See also, gs and rs.
CLUT
Color lookup table. See color map.
color lookup table (CLUT)
See color map.
color map
The color options in a graphics system, arranged by index number. Typically, the system has a default color map. The index of colors in the color map can be reallocated, however, depending on the application. There is one color map in the hardware (often called a color lookup table) but many color maps can be allocated in software and indexed as appropriate for separate applications. See also indexed color.
count12
The height of a triangle in scan lines, from P2 to P1 (see Figure G-1). See also, count13.

    Figure G-1 Triangle Processing

count13
The height of a triangle in scan lines, from P3 to P1 (see Figure G-1). See also, count12.
DAC
See digital-to-analog converter.
dbDu
Delta of Blue value (db) divided by delta u (Du). Used in vector and triangle calculations to define the blue value for the second point. See also, dgDu and drDu.
dbDv
Delta of Blue value (db) divided by delta v (Dv). Used in triangle calculations to define the blue value for the third point. See also, dgDv and drDv.
DDA
See Digital Differential Analyzer.
denorm
Underflow number.
depth buffer
See Z-buffer.
dgDu
Delta of Green value (dg) divided by delta u (Du). Used in vector and triangle calculations to define the green value for the second point. See also, dbDu and drDu.
dgDv
Delta of Green value (dg) divided by delta v (Dv). Used in triangle calculations to define the green value for the third point. See also, dbDv and drDv.
digital-to-analog converter (DAC)
An electronic device used to convert discrete digital numbers to continuous analog signals.
Digital Differential Analyzer (DDA)
The algorithm used for drawing lines in Leo.
display list
A description of the desired image via a list of primitives and attributes. Display lists provide an intermediate picture storage for quick image redraw. In GKS, the display list is a 2D, segmented data storage method and cannot be edited. In PHIGS, the display list structure is a 3D, hierarchical data list that can be edited.
double buffering
The process of using two frame buffers for smooth animation. Graphical contents of one frame 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.
drDu
Delta of Red value (dr) divided by delta u (Du). Used in vector and triangle calculations to define the red value for the second point. See also, dbDu and dgDu.
drDv
Delta of Red value (dr) divided by delta v (Dv). Used in triangle calculations to define the red value for the third point. See also, dbDv and dgDv.
dvDu
Delta v (dv) divided by u (Du). Used in vector calculations to locate the second point of the vector in uv space (the first point is defined by us. See also, dzDu.
dxeDv
Delta xe (dxe) divided by delta v (Dv). Used in triangle calculations to locate the ending point in x space. See also dxsDv.
dxe2Dv
Delta xe2 (dxe2) divided by delta v (DV). Used in triangle calculations to locate the third point is x space. See also dxeDv.
dxsDv
Delta xs (dxs) divided by delta v (Dv). Used in triangle calculations to locate the next point in x space.
dzDu
Delta z (dz) divided by delta u (Du). Used in vector calculations to locate the second point of the vector in z space (the first point is defined by zs.
edge detection
An image processing technique in which edge pixels are identified by examining their neighboring pixels.
face list
The list of faces and their vertices that make up the surface shape of a mesh model.
g
Green value. See also, b and r.
gamma correction
The intensity of the luminescent phosphor on the raster display when struck by the electron beam is non-linear. Gamma correction is an adjustment to the color map to make up for this inherent non-linearity, and results in a truer mix of colors when objects are displayed.
gs
The green value of the starting point of a triangle. See also, bs and rs.
gs
The green value of the starting point of a triangle. See also, bs and rs.
hidden line removal
In 3D wireframe graphics, an algorithm that eliminates the lines from a drawing that would be hidden if the object were opaque. This method reduces the potential of ambiguity in an object's appearance.
hidden surface removal
An algorithm that ensures that objects surfaces which are closer to the viewer in 3D space are drawn so that they occlude any objects or portions of objects that should be hidden behind them. See also Z-buffer.
HSR
Hidden surface removal.
indexed color
Also pseudo-color. The Leo indexed color graphics systems is equipped with eight memory bits per pixel. A limited set of colors, selected from a much larger color palette, are indexed in a color lookup table or color map, and the application accesses them by their index numbers.
interpolation
A method of determining intermediate values between those provided, such as shades of pink along a line (or across a polygon) between vertex colors of white and red.
LC
Lighting Coordinates.
LUT
Look-up table. See also color map.
NAN
Not a Number. An overflow number.
NPC
Normalized Projection Coordinates.
NSI
Non-stereo interlaced monitor. See also NSNI and SNI.
NSNI
Non-stereo, non-interlaced monitor. See also NSI and SNI.
normal
Adjective: perpendicular or orthogonal. At right angles to another line segment, object, or plane. Noun: a surface normal. The vector that is perpendicular to a surface at a specific point.
orthogonal
Perpendicular, or normal.
overlay planes
Bit planes in the frame buffer can be assigned as overlay planes to enable images to be superimposed over one another. Images in the overlay planes can be superimposed over the frame buffer image without causing damage to the image in the frame buffer. The application is therefore not required to redraw the picture in the frame buffer when it is overlaid by other windows. This is especially beneficial when the data in the rest of the frame buffer are extremely complex.
picking
Picking, also known as pick aperture clipping, defines a three-dimensional pick aperture volume. Objects that draw any pixels inside this volume are picked as they pass the subsequent Z buffer test.
primitive
Fundamental shapes and objects in computer graphics, used primarily in construction of more complex objects. Graphics primitives include point, line segment, polyline, circle, ellipse, triangle, square, and rectangle.
pseudo color
See indexed color.
PWID
P (image) window ID.
QWID
Q (overlay) window ID.
r
Red value. See also, b and g.
RAMDAC
A digital-to-analog converter (DAC) that contains on-chip random-access memory (RAM) for use in gamma correction. See also digital-to-analog converter.
raster
A two-dimensional array of pixels, usually organized into x and y addressing.
raster operation
Logical Boolean operations.
RMW
Read-modify write.
ROP
Raster operation.
rs
The red value of the starting point of a triangle. See also, bs and gs.
screen door transparency
Screen door transparency allows the user to create the effect of viewing inside a volume without the obstruction of its surface. An m by n pattern table is indexed by pixel location (x mod m, y mod m). If the table has a one, the transparent surface is completely visible and its color is written into the frame buffer. If the table has a zero, the transparent surface is completely invisible and nothing is written into the frame buffer, allowing whatever is behind to show through.
SF
Single-precision floating point.
SNI
Stereo, non-interlaced monitor. See also NSI and NSNI.
SOE
Serial output enable.
true color
Also known as RGB color or 24-bit color. True color graphics systems are usually equipped with at least 24 bits per pixel. In the 24-bit system, for instance, three primary colors in the color graphics system - red, green, and blue - are allotted eight bits each. There are 28, or 256 intensities each for red, green, and blue. This translates to a total palette range of 16.7 million colors (256 \xb4 256 \xb4 256). Because the human eye cannot detect the subtlety available in a palette of 16.7 million colors, this range makes it possible to compute what appears to be gradual shading.
twenty-four bit color
See true color.
ue
Ending address for point u.
us
The starting address for point u. See also, vs and zs.
vertex
The location at which vectors and polygon faces or edges intersect. The vertices of an object are used in transformation algorithms to describe the objects location and its location in relation to other objects.
vs
The starting address for point v. See also, us and zs.
WID
See window ID plane.
WID LUT
Window ID lookup table. See also window ID plane.
window ID plane
Memory space associated with each pixel of a display dedicated to identifying which window is associated with that pixel. Used to clip new graphics imagery to the appropriate window.
xe2
The address of the third point, in x, of a triangle. See also, xs and xe.
xs
The starting address, in x, for triangle calculations. See also, ys and zs.
ys
The starting address in y, for triangle calculations.
Z-buffer
The depth buffer in 3D graphics. The Z-buffer memory locations, like those in the frame buffer, correspond to the pixels on the screen. The Z-buffer, however, contains information relating only to the z-axis (or depth axis). The Z-buffer is used in hidden surface removal algorithms, so that for each pixel written, the depth of that pixel is stored in the Z-buffer. When subsequent objects attempt to draw to that pixel, that object's z value is compared with the number in the Z-buffer, and the write is omitted if the object is farther away from the eye.
zs
starting address for point z. See also, us and vs.