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Game Development Dictionary


Graphics


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  Term Name Description

Cel Shading

A technique which causes rendered objects to look as though they are hand-drawn, cartoon images.

CG

nVidia's (relatively) simple shader language. It's currently one of the most commonly used shader languages, and it supports OpenGL and Direct3D even on non-nVidia cards. Toolkit and information can be found at www.developer.nvidia.com

Channel

Commonly used to describe a color component that makes up an image. A 24-bit image can have red, green, and blue channels. 32-bit images have room for a fourth channel, commonly known as an alpha channel.

Clear Reduction

An optimization of Z-buffering that buffers 1/Z values rather than Z values. Traditionally, Z-buffers are cleared each frame, but clear reduction makes it so they must only be cleared far less frequently.

Clipping Pane

The Clipping Pane is a barrier to determine the loading and display points of 3d models and textures. The farther away the clipping pane from the main object, the further you can "see", but comes at a heavy performance cost.

Clipping Plane

The Clipping Plane is a barrier to determine the loading and display points of 3d models and textures. The farther away the clipping pane from the main object, the further you can "see", but comes at a heavy performance cost.

CLUT

Color Look Up Table. An index of colors, for instance to hold 256 different colors in a single byte and look up a color using 3 bytes.

Color bleeding

The idea of colors blending or "bleeding" into their surroundings, creating a smooth and realistic effect.

Color Cycling

Normally used with Indexed Color, this is a method of changing the index information for an image so that the colors change in a way that makes it appear to animate or cycle colors.

Color Depth

Refers to the amount of memory used to represent a single pixel, and is most commonly measured in bits. Common values are 8-bit, 16-bit, 24-bit, and 32-bit. More bits means a wider range of colors.

Color Key

A value indicating the color to be used for transparent or translucent effects. For example, when using a hardware blitter, all the pixels of a rectangular area are blitted, except the value that was set as the color key; this creates nonrectangular sprites on a surface.

Complete Binary Tree

A binary tree in which all leaf nodes are at level n or n-1, and all leaves at level n are towards the left.

Coordinate system

(see also: Matrix) An orthogonal grid in which elements are placed. For displays, each point in the coord system is a pixel. Note: On a computer monitor, x-coords increase from left to right, but y-coords indrease from top to bottom (contrary to traditional math).

Corona

The artifacts that appear around a bright light source. Often in circular or star like shapes.

Cross-Product

Cross Product (Vector Product)

The cross product is a little more tricky. The cross product between two vectors yields a third vector which is perpendicular to the first two.

For vectors A, B, and a resultant C :

A X B = C

Or in component form :

( A.x , A.y , A.z ) X ( B.x , B.y , B.z ) = ( A.y * B.z - A.z * B.y , A.z * B.x - A.x * B.z , A.x * B.y - A.y * B.x)

 

This is commonly utilized to compute something known as a surface normal. As by the cross product formula, a normal is simply a vector that is perpendicular to some plane. In graphics, this plane is usually a polygon of some type.

 

Please note that A X B <> B X A . Ordering is very important in cross products. What actually happens is that B X A will yield a vector which points in the opposite direction of A X B.

 

Cube Mapping

An alternative to sphere mapping used in environment mapping, cube mapping gets a 'screenshot' looking in 6 different directions and arranges them in a rolled out cube. When applied, the object appears to reflect the environment around it. A 'cheap' alternative to raytracing reflections, cube mapping is fast enough for realtime.

Cut Vertex

A vertex whose deletion along with incident edges breaks up the remaining graph into two or more disconnected pieces.

Depth Cueing

A scene effect to make objects that are farther away from the camera are rendered with a lighter color so that they are given the illusion of distance

DirectGraphics

Introduced in DirectX 8; DirectGraphics combines both Direct3D and DirectDraw. (DirectDraw was removed after DirectX 7)

Dirty Rectangles

A method of updating only the changed parts of the screen. The screen is divided up into rectangles and only rectangles that have changes are makred "dirty" and then are redrawn to clean them up. Increases drawing speed as less is drawn.

Dithering

The process of creating an illusion of more colors than are really available in the current color depth by creatively arranging individual pixel patterns.

Dot-Product

Dot Product (Scalar Product)

The dot product shouldn't cause you any trouble. It is simply a way to multiply vectors. Keep in mind that we would normally describe these vectors in unit vector notation.

Here is a typical representation of a dot product for vectors A and B:

A · B

Or we can describe the same equation in terms of vector components:

A · B = A.x * B.x + A.y * B.y + A.z * B.z

Using a Dot Product, we can obtain the angle between two vectors A and B as follows:

Cos q = (A · B) / (|A| · |B|)

q = arcCos ((A · B) / (|A| · |B|))

Okay, lets break down what just occurred above. What we are saying is that the cosine of theta is equal to the dot product of A and B divided by the product of A and B's magnitudes. The magnitude of a vector V is denoted by : |V|

 

One can calculate the magnitude of a vector simply by taking the square root of each term

in the vector squared. Ie.

|A| = sqrt (A.x * A.x + A.y * A.y + A.z * A.z)

 

Double Buffering

A video buffer consists of a memory allocation for the information that is drawn to the screen. The first buffer is what is actually drawn to the screen, a second and third buffer are used to create a workspace to draw to that doesn't require synchronization to the vertical retrace of the monitor.

Double buffering gives the program a buffer to draw on that is not dependent on the retrace. The second buffer can be held in video memory and then "flipped" to change places with the primary buffer, which then is used as the second buffer until the next flip.

Drop Out

A drop out occures when a few polygons vanish because there are too many polygons being displayed on screen for the computer to handle.

Environment Mapping

An effect where an object reflects its surroundings, much like chrome.


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