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Game Development Dictionary


Graphics


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  Term Name Description

Albedo Texture

An albedo is a physical measure of a material's reflectivity, generally across the visible spectrum of light. An albedo texture simulates a surface albedo as opposed to explicitly defining a colour for it.

Palette

A table of colors indexed by a buffer as a color source.

Palette Swap

A method of swapping colors in the color table (palette) to change the appearance of images using that color table.

Parallax Occlusion Mapping

Employs per-pixel ray-tracing for dynamic lighting of surfaces in real-time on the GPU. The method uses a high precision algorithm for approximating view-dependent surface extrusion for a given height field to simulate motion parallax and perspective-correct depth. Additionally, the method allows generation of soft shadows in real-time for surface occlusions. Alternatively, POM can be coupled with well-known bump mapping algorithms such as normal mapping if physical accuracy can be sacrificed for greater computational efficiency.

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.

Asset

A generic term for graphics, sounds, maps, levels, models, and any other resources. Generally assets are compiled into large files. The file formats may be designed for fast loading by matching in-memory formats, or tight compressions for handheld games, or designed to otherwise help in-game use. It is often useful to have an asset tool chain. The original models may be high-density models with R8G8B8A8 images. You may have a model striper and image compresser that reduces the model for LOD, and compresses the texture to a DXT compressed image. These assets may then go through further transformations, and end up in the large resource file.

Wu-antialiasing

Antialiasing algorithm that extends the Bresenham-line by drawing additional (background-)blended pixels above and below each original pixel. What is considered "above" and "below" is decided by the direction of the plotting. Some implementations also blend the original pixels.

Color bleeding

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

Alpha buffer

A linked list of depth-sorted colors, typically representing each pixel in a z-buffer. The colors may either be added to the list in a pre-sorted order or the list may be able to sort them by itself. After all colors are added the list is used to create on resulting color by blending the containing colors from the back and forward using their alpha channel.

Perlin Noise

A function, inveted by Ken Perlin, who invented it to generate textures for the movie Tron (1982). One of the first films to use computer graphics extensively, Tron has a distinctive visual style. He won a special Academy Award for Perlin noise in 1997. Perlin noise is widely used in computer graphics for effects like fire, smoke and clouds. It is also frequently used to generate textures when memory is extremely limited, such as in demos.

antialias

Antialiasing refers to the process of adding additional pixels around the border of an object in order to blend it into it's background more smoothly, and to reduce the appearance of jagged edges. Typically, the colour used is the average of the surrounding background pixels and that of the object being antialiased, or an approximation of the average. This technique was invented by MIT's Media Lab.

HSR

Hidden Surface Removal The CPU removes hidden surfaces before sending meshes to the videocard. Because the CPU can remove entire meshes at a time, this can save a lot of time when checking individual triangles.

Sub-Surface Scattering

A rendering technique used on objects to determine how much light is allowed through the object. This is a very demanding technique since it calculates the amount of the material is it going through and the denisty of the material. This is most commonly used on skin, plant material, and cloth materials.

SSS

Refers to sub-surface scattering

Quads

Common term used in modeling when refering to a model made up of four point polygonal faces.

Indot

Indot refers to non-quad and non-tri polygons. For instance a pentegon without triangulation or quads. (This is only appreant during modeling in a 3d application that supports this feature.)

Maya

A premium modelling program produced by Alias, it is used by several companies in the games industry as their primary modelling tool. A free version is available at alias.com

Prerendered

This type of 3D scene is rendered and then stored, usually as a bitmap, and are often used as backgrounds and 2D sprites in games, like Nintendo’s Donkey Kong country. Unlike scenes that are rendered in real-time, prerendered images cannot have their viewing angle changed during runtime.

Photorealistic

Image which approaches photographic quality. With a large enough color palette (around 16,000 colors) it is possible to display these types of images on a TV or computer screen.

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.

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.

Photon Tracing

The most realistic, but also the slowest, 3D rendering technique where you spawn photons from all light sources and use realistic photon physics (including reflection, refraction, diffraction, dispersion, etc...) to find out which ones reach the camera. This technique may also be used to pre-render photon maps to add a more realistic touch to games.

Normal Mapping

Normal Mapping is a lighting technique used to light a low-polygon model like a high-polygon model by means of a bitmap image. Each RGB value of each individual texel within the normal map is used to represent the x,y,z components of the mesh normal at each texel. Rather than using interpolated vertex normals to calculate the lighting data, the normals from from the normal map are used.

Alpha Testing

A method for creating transparency by checking the alpha value of a given pixel.

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.


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