computer-generated imagery Computer-generated imagery (CGI) is a specific-technology or application of computer graphics for creating or improving images in Digital art, art, Publishing, printed media, Training simulation, simulators, videos and video games. These images ...

and real-time

3D computer graphics 3D computer graphics, sometimes called Computer-generated imagery, CGI, 3D-CGI or three-dimensional Computer-generated imagery, computer graphics, are graphics that use a three-dimensional representation of geometric data (often Cartesian coor ...

, portal rendering is an algorithm for visibility determination. For example, consider a 3D computer game environment, which may contain many

polygons In geometry, a polygon () is a plane figure made up of line segments connected to form a closed polygonal chain. The segments of a closed polygonal chain are called its '' edges'' or ''sides''. The points where two edges meet are the polygon' ...

, only a few of which may be visible on screen at a given time. By determining which polygons are currently not visible, and not rendering those objects, significant performance improvements can be achieved. A portal system is based on using the partitioning of space to form generalizations about the visibility of objects within those spaces. Regions of map space are divided into polygonal, generally

convex Convex or convexity may refer to: Science and technology * Convex lens, in optics Mathematics * Convex set, containing the whole line segment that joins points ** Convex polygon, a polygon which encloses a convex set of points ** Convex polytop ...

, areas called ''zones'', or sometimes ''sectors''. Adjacent zones are linked to one another via shared dividing polygons termed ''portals''. Approaches that precompute visibility for zones are referred to as

potentially visible set In 3D computer graphics, Potentially Visible Sets are used to accelerate the rendering of 3D environments. They are a form of occlusion culling, whereby a candidate set of ''potentially visible'' polygons are pre-computed, then indexed at run- ...

or ''PVS'' methods. For example, in a

computer game A video game or computer game is an electronic game that involves interaction with a user interface or input device (such as a joystick, controller, keyboard, or motion sensing device) to generate visual feedback from a display device, mo ...

such as ''

Descent Descent may refer to: As a noun Genealogy and inheritance * Common descent, concept in evolutionary biology * Kinship, one of the major concepts of cultural anthropology **Pedigree chart or family tree **Ancestry **Lineal descendant **Heritage ** ...

'', the game area might be divided into several zones. These zones would then be connected to each other by small openings such as doors or windows. These openings are referred to as ''portals''. When the zone behind a portal needs to be drawn, the only parts that are visible are the parts that can be seen through the portal. Therefore, the zone can be clipped against the portal boundaries to remove overdraw. The use of portals simplifies the

game engine A game engine is a software framework primarily designed for the development of video games which generally includes relevant libraries and support programs such as a level editor. The "engine" terminology is akin to the term " software engine" u ...

's task of determining visible areas and objects from any given point of view of the level, and simplifies rendering by allowing it to use each portal as a

viewing frustum In 3D computer graphics, a viewing frustum or view frustum is the region of space in the modeled world that may appear on the screen; it is the field of view of a perspective virtual camera system. The view frustum is typically obtained by t ...

for the area it leads to. Ideally, portals are formed of confined areas (like doors or tunnels), connecting two complex areas of the scene, where each of these areas would be enclosed in such a polygonal body. Portals are best suited for indoor scenes such as mazes. Outdoor scenes do not usually have door-like objects that would clearly separate one zone from another.

Antiportals

and real-time

, antiportal rendering is a way to reduce overdraw (the rendering of detail which will not be in the final image), and in this way to optimize draw speed. Antiportals are the inverse of portals. An antiportal (or occluder) works by defining a

plane Plane most often refers to: * Aero- or airplane, a powered, fixed-wing aircraft * Plane (geometry), a flat, 2-dimensional surface * Plane (mathematics), generalizations of a geometrical plane Plane or planes may also refer to: Biology * Plane ...

volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...

which can ''never'' be seen through, normally by placing it within an

opaque Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shie ...

object. The renderer uses this to quickly calculate which objects/faces/vertices lie behind the antiportal, and so are out of line of sight, so do not need to be rendered. Many

video game A video game or computer game is an electronic game that involves interaction with a user interface or input device (such as a joystick, game controller, controller, computer keyboard, keyboard, or motion sensing device) to generate visual fe ...

s and 3D graphics programs use this technique for speed rendering. ''

Unreal Tournament 2004 ''Unreal Tournament 2004'' is a first-person arena shooter video game developed by Epic Games and Digital Extremes. Part of the ''Unreal'' franchise, it is the third game in the '' Unreal Tournament'' series and an updated rerelease of '' Unre ...

'', among many other games, uses this technique.

References

External links

Building a 3D Portal Engine
Computer graphics Unreal (video game series) {{compu-graphics-stub

Antiportals

See also

References

External links