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Game Development Dictionary


Graphics


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  Term Name Description

Blending

When an image is drawn so that images drawn before it can still be seen. This is done through blending the source colors with the destination colors at different percentages.

Also called Transparency.

Vector

In 3D graphics, a set of numbers representing magnitude and direction.

Bezier Surface

A curved surface created from a mesh of control points.

Blitting

A method of outputting sprites by only showing non-transparent colors, without any checking during run time. This is done by precompiling a bmp into a piece of code that contains a set of screen memory writes that only include non-trasparent colors.

VESA

Video Electronics Standards Association. An organization that sets standards for video and multimedia in PCs. They created the Super VGA (SVGA) standard and the VESA Local Bus.

Cel Shading

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

Scene Graph

A scene graph is a tree where the nodes are objects in a scene arranged in some sort of hirearchy. These nodes may be actual physical objects, or simply 'abstract' objects. For example a transformation node would apply some form of transformation to any 3D objects that are below the transformation node in the scene graph. A scene graph can be used for many things, depending on the way you order the nodes in the graph. For example you could have an octree containing object to be rendered in a scene, this would be a limited form of scene graph. You could have a scene graph that contains an octree as well as an alternative way or organising the same data, e.g. by render state. So you could use your scene graph for culling unseen objects as well as ordering objects to be rendered by render state.

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.

HDR

Real world lighting contains a high range of luminance values. HDR, or High Dynamic Range lighting, is essentially a technique that exceeds the normal computer graphics color range of 0 to 255, allowing for more realistic lighting models.

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.

Bounding Box

A box approximation of an object used for collision detection. An axis-aligned bounding box (AABB) is defined by the minimum and maximum 'x', 'y', and 'z' values. An oriented bounding box (OBB), however, generally gives a closer fit, because it is always aligned with the object.

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)

 

Z-Buffer

An array of numbers that store the proper point on an polygon and its distance from the camera. The array is usually comprised of all the pixels in a screen and only the closest points are stored and then drawn. This method eliminates the problem of overlapping objects.

Voxel

Volume pixel. These are basically another way of drawing 3D objects, instead of defining them as the polygons that make up the outside of an object, you define it as a number of points. Voxels can be the size of a pixel on the screen, or they can be large spheres, sprites or any graphical representation of a point.

Backface Removal

See Backface Culling.

Graphics

A form of data representation. Without graphics, we'd just have numeric displays. * Graphics use imagery, such as pictures, lines, points, colors and so on to represent information. It's the difference between a spreadsheet and a pie-chart. The spreadsheet is a numeric representation; the pie-chart is a graphical representation. Since computers see all things as numbers, programmers and electronics engineers have had to design ways to convert those numbers into moving images. The electronics engineers gave us the Graphics Card for this very purpose.

DirectGraphics

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

Boolean Geometry

Named after mathematician George Boole Boolean geometry refers to combining multiple objects. Common operations include "unions" which combine two shapes and "difference" operations. Difference operations can be used to cut one shape out of another. 3d Studio Max and the game Red Faction for the Playstation II are good examples of how Boolean geometry can be used in practical applications.

Corona

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

GLUT

The OpenGL Utility Toolkit. This set of libraries provides a set of helper functions to OpenGL, including methods to abstract the windowing system (for cross-platform development), rendering "standard" 3D objects, etc. For more info, visit the GLUT homepage

Interlacing

Because the electron guns that draw pictures on TV screens were initially too slow to draw the screen in one pass, the first lines at the top of the screen would be fading by the time the last lines were drawn, pictures on TVs were drawn using what is known as interlacing. First the odd lines down are drawn (line 1, 3, 5, etc.). Then the even lines are drawn (line 2, 4, 6, etc.). The image shown by one pass is known as a field, and the complete image drawn by two passes is known as a frame. Standard TV broadcasts run at 30 frames per second (fps). In an effort to boost hype for a product, sometimes ads or press releases would state that their game was "60 fields per second", instead of 30 fps. Most computer monitors are non-interlaced as well as many arcade screens.

Volume Rendering

A method of rendering that deals with the space that is used, as opposed to the faces that make up the outside of an object. Originally used for medical purposes only, it has also been adapted to do environmental effects, such as light through fog.

Bezier Patch

See Bezier Surface.

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


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