Glossary of computer graphics

This is a glossary of terms relating computer graphics.

For more general computer hardware terms, see glossary of computer hardware terms.

0–9

7e3 format

A packed pixel format supported by some graphics processing units (GPUs) where a single 32-bit word encodes three 10-bit floating point color channels, each with seven bits of mantissa and three bits of exponent.^[1]

2D image

2D texture map

A texture map with two dimensions, typically indexed by UV coordinates.

2D vector

a two-dimensional vector, a common data type in rasterization algorithms, 2D computer graphics, graphical user interface libraries.

3D graphics pipeline

A graphics pipeline taking 3D models and producing a 2D bitmap image result.

3D scene

A collection of 3D models and lightsources in world space, into which a camera may be placed, describing a scene for 3D rendering.

3D paint tool

A 3D graphics application for digital painting of multiple texture map image channels directly onto a rotated 3D model, such as zbrush or mudbox, also sometimes able to modify vertex attributes

3D unit vector

An unit vector in 3D space.

4D vector

a common datatype in graphics code, holding homogeneous coordinates or RGBA data, or simply a 3D vector with unused W to benefit from alignment, naturally handled by machines with 4-element SIMD registers.

4×4 matrix

A matrix commonly used as a transformation of homogeneous coordinates in 3D graphics pipelines.^[2]

A

AABB

Axis aligned bounding box (sometimes called "axis oriented"), a bounding box stored in world coordinates; one of the simplest bounding volumes.

Additive blending

A compositing operation where , without the use of an alpha channel, used for various effects. Also known as linear dodge in some applications.

Alpha channel

An additional image channel (e.g. extending an RGB image) or standalone channel controlling Alpha blending.

Ambient light

An approximation to the light entering a region from a wide range of directions, used to avoid needing an exact solution to the rendering equation.

Analytic model

A mathematical model for a phenomenon to be simulated, e.g. some approximation to surface shading. Contrasts with Empirical models based purely on recorded data.

anti aliasing

methods for filtering and sampling to avoid visual artefacts associated with the uniform pixel grid in 3D rendering.

AO

Ambient occlusion, an approximation to global illumination.

Array texture

A form of texture map containing an array of 2D texture slices selectable by a 3rd 'W' texture coordinate; used to reduce state changes in 3D rendering.^[3]

AZDO

Approaching zero driver overhead, a set of techniques aimed at reducing the CPU overhead in preparing and submitting rendering commands in the OpenGL pipeline. A compromise between the traditional GL API and other high performance Low level rendering APIs.^[4]

B

Baking

Performing an expensive calculation offline, and caching the results in a Texture map or Vertex attributes. Typically used for generating lightmaps, normal maps, or low level of detail models.^[5]

Bone

Coordinate systems used to control surface deformation (via Weight maps) during Skeletal animation. Typically stored in a hierarchy, controlled by keyframes, and other procedural constraints.

Billboard

a texture map rendered with one or two of its axes parallel to the plane of the screen as a 3D sprite, typically used for vegetation

Bit depth

The number of bits per pixel,sample, or texel in a bitmap image (holding one or mode image channels, typical values being 4, 8, 16, 24, 32

Bit plane

A format for bitmap images storing 1 bit per pixel in a contiguous 2D array; Several such parallel arrays combine to produce the a higher bit depth image. Opposite of packed pixel format.

Blend operation

A render state controlling alpha blending, describing a formula for combining source and destination pixels.

Bounding box

One of the simplest type of bounding volume, consisting of axis aligned or object aligned extents.

BRDF

Bidirectional reflectance distribution functions (BRDFs), empirical models defining 4D functions for surface shading indexed by a view vector and light vector relative to a surface.^[6]

BVH

Bounding volume hierarchy

C

Camera

A virtual camera from which rendering is performed, also sometimes referred to as 'eye'.

Camera space

A space with the camera at the origin, aligned with the viewer's direction, after the application of the world transformation and view transformation.

Command buffer

A region of memory holding a set of instructions for a graphics processing unit for rendering a scene or portion of a scene. These may be generated manually in bare metal programming, or managed by low level rendering APIs, or handled internally by high level rendering APIs.

Command list

a group of rendering commands ready for submission to a graphics processing unit, see also Command buffer.

Compute API

an API for efficiently processing large amounts of data.^[7]

Compute shader

a compute kernel managed by a rendering API, with easy access to rendering resources.

Connectivity information

Indices defining [rendering primitive]s between vertices, possibly held in index buffers. describes geometry as a graph or hypergraph.

Color channels

The set of channels in a bitmap image representing the visible color components, i.e. distinct from the alpha channel or other information.

Color resolution

CLUT

A table of RGB color values to be indexed by a lower bit depth image (typically 4-8bits), a form of vector quantisation.

Clip plane

A plane used to clip rendering primitives in a graphics pipeline. These may define the View frustum or be used for other effects.

Clip window

A rectangular region in screen space, used during clipping. A clip window may be used to enclose a region around a portal in portal rendering.

CSG

Constructive solid geometry, a method for generating complex solid models from boolean operations combining simpler modelling primitives.

D

Detail texture

texture maps repeated at high frequency combined with a main texture on a surface to prevent a blurred appearance close to the camera.

Deformation lattice

A means of controlling free-form deformation via a regular 3D grid of control points moved to arbitrary positions, with polynomial interpolation of the space between them.

Degenerate triangles

Zero area triangle primitives placed in a triangle strip between actual primitives, to allow many parts of a triangle mesh to be rendered in a single drawcall. These are trivially rejected by the triangle setup unit.^[8]

Delaunay triangulation

A method for generating an efficient triangulating between a set of vertices in a plane.

Depth buffer

a bitmap image holding depth values (either a Z buffer or a W buffer), used for visible surface determination, during rasterization of 3D scenes

Depth map

A bitmap image or texture map holding depth values. Similar to a height map or displacement map, but usually associated with a projection.

Depth value

a value in a depth map representing a distance perpendicular to the space of an image.

Displacement mapping

a method for adding detail to surfaces by subdivision and displacement of the resulting vertices form a height map.^[9]

Drawcall

A single rendering command submitted to a rendering API, referring to a single set of render states.

E

Edge vector

a vector between 2 position vertices in a polygon or polygon mesh, along an edge

Extents

The minimum and maximum values of an object or primitive along a coordinate axis or set of axes.

F

Forward rendering

A term for traditional 3D rendering pipelines which sort lightsources applicable to 3D models in world space prior to rasterization. Contrasts with Deferred shading.

Forward-plus rendering

an extension of forward rendering using compute shaders to place lightsources into screen space tiles, to accelerate the use of many lightsources, bypassing some of the disadvantages of deferred shading.^[10]

Frustum culling

A stage in a rendering pipeline, filtering out 3D models whose bounding volumes fail an intersection test with the view frustum, allowing trivial rejection.

Fixed-function pipeline

A hardware rendering pipeline without shaders, composed entirely of fixed function units. A limited number of functions may be controlled by render states.

Fixed function unit

A piece of hardware in a graphics processing unit implementing a specific function (such as triangle setup or texture sampling), without programable control by shaders.

FXAA

an approximate antialiasing method performed in a post processing step which smooths the image in screen space, guided by edge detection (contrasting with the usual supersampling approaches that require larger frame-buffers).

G

Geometry

typically used to refer to vertex & rendering primitive connectivity information (distinct from materials and textures).

G-buffer

A screen space representation of geometry and material information, generated by an intermediate rendering pass in deferred shading rendering pipelines.^[11]

Graphical shader

a shader associated with the rendering pipeline; not a compute shader.

Global illumination

Grid cell index

Integer coordinates in a multidimensional array.

H

HDR

High dynamic range imaging, an image format using floating-point values. Allows additional realism with post processing.

Heightmap

a 2D array or texture map holding height values; typically used for defining landscapes, or for displacement mapping

I

Image channel

A single component (referred to as a channel) of a bitmap image; one of multiple components per pixel, e.g. for RGB or YUV color space, or additional channels for alpha blending

Image format

A specific way of representing a bitmap image in memory, also refers to image file formats.

Image generation

synonymous with rendering; taking a 3D scene (or other form of encoded data) and producing a bitmap image result.

Image generator

A hardware accelerator for image generation, almost synonymous with a graphics processing unit, but historically used to refer to devices aimed at realtime rendering for simulation (e.g. Evans & Sutherland ESIG line).

Immediate mode rendering

the submission of rendering commands and rendering primitive data without the extensive use of managed resources; rendering primitive vertex attribute data may be embedded directly into a command list, rather than referenced indirectly from resources.

Impostor

A dynamically rendered Billboard texture map used to stand in for geometry in the distance. A form of level of detail optimization.^[12]

Incremental error algorithm

A set of rasterization algorithms which use simple integer arithmetic to update an error term that determines if another quantity is incremented, avoiding the need for expensive division or multiplication operations; e.g. bresenham's line algorithm, or rasterizing heightmap landscapes.^[13]

Index buffer

A rendering resource used to define rendering primitive connectivity information between vertices.

Intersection test

determining if two pieces of geometry intersect, commonly required in simulation, rendering pipelines, and 3D modelling applications.

K

K-DOP

A type of Bounding volume used for fast intersection tests; a discrete oriented polytope (DOP). These generalise bounding boxes with extents additional discrete planes (e.g. diagonals formed by each pair of coordinate axes, etc)

L

Low level rendering API

A library providing a minimal abstraction layer over a graphics processing unit's raw command lists, such as Vulkan, LibGCM, or Metal (API). The user typically has more control over(and responsibility for) resource management, command buffers, synchronisation issues.

Lumels

A term for Texels in the texture map representing a Lightmap.

Light vector

In shading calculations, a 3D unit vector representing the direction of incident light onto a model's surface.

Light field

a data structure approximating the 4D flux of light rays through a space (or in the general case, 5D); it may be captured using multiple cameras (e.g. light stage), or rendered from a 3D model by ray tracing.

Line primitive

A rendering primitive or modelling primitive representing a line segment, used for wireframes.

M

Marching cubes

A method for triangulating implicit surfaces.

Modelling primitive

Basic elements from which 3D models and 3D scenes are composed. Also known as a Geometric primitive.

Model transformation matrix

a transformation matrix producing world coordinates from a 3D model's local coordinates.

Microtexture

An alternative term sometimes used for Detail textures.

Multiply blend

A blending operation used for lightmaps,.

N

Near clipping

The clipping of 3D rendering primitives against the near clip plane. Necessary to correctly display rendering primitives that partially pass behind the camera

O

Occlusion query

A command passed to a Graphics processing unit requesting the testing of bounding volume geometry against the depth buffer to determine if any contents in the potentially visible set; used for hardware accelerated occlusion culling.

OOBB

An Object oriented bounding box (sometimes called object aligned); a bounding box stored in some object's local coordinate system

Outcode

A small integer holding a bit for the result of every plane test (or clip window edge test) failed in clipping. Primitives may be trivially rejected if the bitwise AND of all its vertices outcodes is non zero

P

Packed pixel format

an image format where the image channels are interleaved contiguously in memory, possibly containing multiple channels within single machine words, equivalent to an array of structures for bitmap data. Contrasts with planar image formats.

Parameter gradient

The derivative of a vertex attribute with respect to screen space coordinates during rasterization, used for interpolation across a rendering primitive surface.

Physically based rendering

rendering algorithms based on physics simulation of light, including conservation of energy, empirical models of surfaces.^[14]

Planar image format

an image format where the image channels (or even bits) for a single pixel is separated into several parallel arrays, equivalent to a structure of arrays for bitmap data.

Point cloud

a surface defined by a collection of vertices without connectivity information.^[15]

Point sprite

A rendering primitive in 3D graphics pipelines, allowing one vertex plus radius to define a billboard; corner vertices are automatically generated. Typically used for particle systems

Polygon mesh

A 3D model consisting of vertices connected by polygon primitives.

Polygon primitive

A rendering or modelling primitive defining a flat surface connecting 3 or more vertices.

Portal

A means of occlusion culling, defining a visible window between adjacent bounding volumes, used in portal rendering.

Post processing

Effects applied to a bitmap image in screen space after 3D rendering pipeline, for example tone mapping, some approximations to motion blur,and blooms.^[16]

Predicated rendering

A feature facilitating occlusion culling within a graphics pipeline, performed by a command list asynchronously form the CPU, where a group of rendering commands are flagged to be conditional on the result of an earlier occlusion query.

Premultiplied alpha

A variation of a bitmap image or alpha blending calculation in which the RGB color values are assumed to be already multiplied by an alpha channel, to reduce computations during Alpha blending; uses the blend operation: ; capable of mixing alpha blending with additive blending effects

Primitive

A basic unit of geometry for rendering or modelling

Q

Quaternion

a means of representing rotations in a 4D vector, useful for skeletal animation, with advantages for interpolation compared to euler angles (i.e. not suffering from gimbal lock).^[17]

R

Ray tracing

tracing paths of light rays through a 3D scene, may be used for 3D rendering (more commonly for offline rendering), or other tests

Recursive subdivision

The process of subdividing an object (either geometric object, or a data structure) recursively until some criteria is met.

RGB888

an RGB color value] encoded as 8 bits per channel

RGBA

An RGB color value together with an alpha channel, typically held in bitmap images or intermediates in shading calculations.

RGBA888

an RGBA color value encoded as 8 bits per channel

RGB image

A bitmap image holding RGB color values in 3 image channels

RGB color value

a 3D vector describing a color using the RGB color model; may use fixed point or floating-point representations.

Rendering API

A software library for submitting rendering commands, and managing render states and rendering resources;examples include OpenGL, Direct3D, Vulkan. Provides an abstraction layer for a graphics processing unit.

Render mapping

The baking of a rendering of a 3D model surface into a texture map to capture surface properties. Also known as 'render surface map'.^[18][19]

Render pass

A stage in a rendering pipeline generating some (possibly incomplete) representation of the scene.

Render states

Information controlling a graphics pipeline, composed of modes and parameters, including resource identifiers, and shader bindings.

Render target

A graphics resource into which rendering primitives are rasterized by a graphics pipeline. Render targets may be frame buffers or texture maps.

Render to texture

The process of rasterizing into a texture map (or texture buffer) for further use as a resource in subsequent render passes. Used for environment mapping, impostor rendering, shadow mapping and post processing filters. Requires the ability to use a texture map as a render target

Rendering command

An instruction for rasterizing geometry in a 3D graphics pipeline, typically held in a command buffer, or submitted programatically through a rendering API

Rendering primitive

geometry that can be drawn by a rasterizer or Graphics processing unit, connecting vertices,e.g. points, lines, triangles, quadrilaterals

Rendering resources

Data managed by a graphics API, typically held in device memory, including vertex buffers, index buffers, texture maps and framebuffers

Repeating texture

A texture map applied with wrap-round UV coordinates extending between the 0-1 range (representing one unit of the image), exhibiting periodicity. Contrasts with clamped, mirrored modes or unique mappings.

Resource

Data (often held in a buffer managed by a rendering API) read by a graphics pipeline, e.g. texture maps, vertex buffers, shaders, index buffers, or other pieces of 3D model data.

Rounding radius

a value used in smoothing the corners of a geometric figure such as a 2D polygon or 3D polygon mesh^[20]

S

Screen space

The coordinate space of the resulting 2D image during 3D rendering. The result of 3D projection on geometry in camera space.

Screen space directional occlusion

An enhancement of Screen space ambient occlusion (SSAO) taking direction into account to sample the ambient light, to better approximate global illumination.^[21]

Shader

a subroutine written in a shading language describing: vertex transformations, skinning and possibly vertex lighting (in vertex shaders); shading calculations (in pixel shaders); control over tessellation(tessellation shaders); or general purpose computation.

Shading calculation

surface lighting and texturing blending operations, e.g. including specularity, bump mapping etc.

Shadow map

A texture buffer holding depth values rendered in a separate render pass from the perspective of a lightsource, used in Shadow mapping; it is typically rendered onto other geometry in the main rendering pass.^[22]

Shadow buffer

A synonym for shadow map.

Signed triangle area

Found using half the Z component of cross product of a pair of screen-space triangle edge vectors, useful for backface culling and computing parameter gradients in triangle rasterization.

Sliverous triangle

Sliver triangle

A triangle with one or two extremely acute angles, hence a long/thin shape, which has undesirable properties during some interpolation or rasterization processes.^[23]

State changes

the passing of changes in render states in a graphics pipeline, incurring a performance overhead. This overhead is typically minimised by scene sorting.

Spatial hashing

A form of hashing to accelerate spatial testing e.g. for AI, collision detection, typically using a grid cell index as a key.

Specular exponent

Controls the glossiness in the phong shading model.

Spline

A curve defined by polynomial interpolation through control points.

Surface normal vector

In shading calculations, the normal to a 3D model surface, typically compared with the light and view vectors to compute the resulting visible colour. Also used for displacement mapping.

Swizzled texture

A texture map stored out of the natural pixel order; see Swizzling (computer graphics). For example, it may be stored in morton order, giving improved cache coherency for 2D memory access patterns.^[24]

T

Terrain rendering

Rendering of landscapes, typically using heightmaps or voxels.

Texture cache

A specialised read-only cache in a graphics processing unit for buffering texture map reads, accelerating texture sampling operations.

Texture sampling

The process of texture lookup with texture filtering. Performed by a texture sampling unit in a graphics processing unit

Texture sampling unit

A fixed function unit performing texture sampling; also known as a texture mapping unit.

Texture buffer

A region of memory (or resource) used as both a render target and a texture map.

Texture map

A bitmap image/rendering resource used in texture mapping, applied to 3D models and indexed by UV mapping for 3D rendering.

Texture space

The coordinate space of a texture map, usually corresponding to UV coordinates in a 3D model. Used for some rendering algorithms such as texture space diffusion

Transform feedback

A feature of a rendering pipeline where transformed vertices may be written back to a buffer for later use (e.g. for re-use in additional render passes or subsequent rendering commands), e.g. caching the result of skeletal animation for use in shadow rendering.^[25]

Triangulation

the process of turning arbitrary geometric models into triangle primitives, suitable for algorithms requiring triangle meshes

Triangle primitive

The most common rendering primitive defining triangle meshes, rendered by graphics processing units

Triangle setup

the process of ordering triangle primitive vertices, calculating signed triangle area and parameter gradients between vertex attributes as a prerequisite for rasterization.^[26]

Triangle setup unit

A fixed function unit in a GPU performing triangle setup (and may perform backface culling), prior to actual rasterization.^[27]

Tristrip

A common rendering primitive defining a sequence of adjacent triangle primitives, where each triangle re-uses 2 vertices from the previous one.

Trivial accept

The process of accepting an entire rendering primitive, 3D model, or bounding volume contents without further tests for clipping or occlusion culling. The opposite of trivial rejection.

Trivial rejection

Rejecting a rendering primitive or 3D model based on a cheap calculation performed early in a graphics pipeline, (e.g. using outcodes in clipping). The opposite of trivial accept.

U

UV unwrapping

The process of flattening a 3D model's surface into a flat 2D plane in a contiguous, spatially coherent manner for texture mapping.

Unified memory

A memory architecture where the CPU and GPU share the same address space, and often the same physical memory. More common in SoCs and video game consoles. Supported on some discrete GPUs with the use of an MMU.

UV coordinates

Coordinates in texture space, assigned as vertex attributes and/or calculated in vertex shaders, used for texture lookup, defining the mapping from texture space to a 3D model surface or any rendering primitive.

V

Vector maths library

A library defining mathematical operations on vector spaces used in 3D graphics, concentrating on 3D and 4D vectors, and 4x4 matrices, often with optimised SIMD implementations.^[28]

Vertex buffer

A rendering resource managed by a rendering API holding vertex data. May be connected by primitive indices to assemble rendering primitives such as triangle strips. Also known as a Vertex buffer object in OpenGL.

Vertex cache

A specialised read-only cache in a graphics processing unit for buffering indexed vertex buffer reads.

Volume texture

A type of texture map with 3 dimensions.

Voxels

An extension of pixels into 3 dimensions.

View transformation

A matrix transforming world space coordinates into camera space.

View vector

In shading calculations, a 3D unit vector between the camera and the point of interest on a surface.

View frustum

a truncated pyramid enclosing the subset of 3D space that projects onto a 'viewport' (a rectangular region in screen space, usually the entire screen)

W

W buffering

A depth buffer storing inverse depth values, which has some advantages for interpolation and precision scaling.

Weight map

A set of Vertex attributes controlling deformation of a 3D model during skeletal animation.Per-vertex weights are assigned to control the influence of multiple bones (achieved by interpolating the transformations from each).^[29]

Window

A rectangular region of a screen or bitmap image.

Wireframe

may refer to Wireframe models or wireframe rendering.

Wireframe rendering

a rendering of a 3D model displaying only edge connectivity; used in 3D modelling applications for greater interactive speed, and clarity for mesh editing.

World space

The global coordinate system in a 3D scene, reached by applying a model transformation matrix from the objects' local coordinates

Z

Z buffer

a 2D array holding depth values in screen space; a component of a framebuffer; used for hidden surface determination.

Z test culling

a form of occlusion culling by testing bounding volumes against a Z buffer; may be performed by a graphics processing unit using occlusion querys.

Z order

A morton order space filling curve, useful for increasing cache coherency of spatial traversals.

References

• http://ftp.factor.lg.ua/books/Computer_Graphics_Principles_and_Practice.pdf