2.5D
From Wikipedia, the free encyclopedia
 |
This article has multiple issues. Please help improve the article or discuss these issues on the talk page.
|
 |
| Part of a series on: |
| Video Game Graphics |
2.5D ("two-and-a-half-dimensional"), also called pseudo-3D, is an informal term used to describe either a) graphical projections and techniques which cause a series of images or scenes to appear three-dimensional (3D) when in fact they are not, or b) gameplay in an otherwise 3D game that is restricted to a two-dimensional plane. In the former case this may be due to the image not being constructed entirely of true 3D entities (as in sprite- and tile-based video games); in the latter it may be due to a game not allowing full 3D movement. The term is used to describe games using some form of axonometric projection (either isometric, dimetric or trimetric) or oblique projection.
Contents |
[edit] Graphical techniques
When used to describe computer graphics, the term refers to rendering systems that use 2D graphics to visually simulate or fake 3D graphics. One such method is where a 2D image has an added "depth" channel (or Z-buffer) acting like a height map. Another method is when 3D scenes are built completely or partially from a composite of several flat 2D images.
[edit] Parallel projection
Parallel projection originates from paraline drawing. An parallel drawing is not a perspective projection — there is no foreshortening as the distance of an object increases — but it does represent a three-dimensional object.
In axonometric projection, an object is "considered to be in an inclined position resulting in foreshortening of all three axes", and the image is a "representation on a single plane (as a drawing surface) of a three-dimensional object placed at an angle to the plane of projection."[who?] Lines perpendicular to the plane become points, lines parallel to the plane have true length, and lines inclined to the plane are foreshortened.
There are three main divisions of axonometric projection: isometric (equal measure), dimetric (symmetrical and unsymmetrical), and trimetric (single-view or only two sides). The most common of these drawing types in engineering drawing is isometric projection. This projection is tilted so that all three axes create equal angles at intervals of 120 degrees. The result is that all three axes are equally foreshortened. In video games, a form of dimetric projection with a 2:1 pixel ratio is more common due to the problem of anti-aliasing and square pixels found on most computer monitors.
In oblique projection, typically all three axes are shown unforeshortened. All lines parallel to the axes are drawn to scale, but diagonals and curved lines are distorted. The angle of inclination has no effect.
These projections have been useful in geographic visualization (GVIS) to help understand visual-cognitive spatial representations or 3D visualization.[1]
[edit] 3/4 perspective
In portraiture and facial recognition, the terms 3/4 perspective or 3/4 view are used to describe a graphical projection which is halfway between a frontal view and a side view.[2]
In video games the term refers to a point of reference that is rotated slightly to reveal other facets of the game environment than what is visible in a top-down perspective or side view, sometimes intentionally producing a three-dimensional effect. It is a popular camera perspective in 2D video games, most commonly those released for 16-bit or earlier consoles and computers, as well as recent handheld consoles. The advantage of this perspective is that it combines the visibility and mobility of a top-down game with the character recognizability of a side-scrolling game. Both axonometric and oblique video games are often referred to as "3/4". The term is also sometimes used interchangeably with "2.5D".
Two of the most consistent examples of 3/4 perspective are the The Legend of Zelda series of games for the Game Boy, Game Boy Color, and Game Boy Advance; and the Pokémon series for Game Boy Color, Game Boy Advance, and Nintendo DS.
[edit] Billboarding
In three-dimensional scenes, the term billboarding is applied to a technique in which objects are sometimes represented by two-dimensional images applied to a single polygon which is typically kept perpendicular to the line of sight. The name refers to the fact that objects are seen as if drawn on a billboard.
[edit] Enhanced paint programs
2.5D is used as a descriptive and marketing term in some specialised 3D computer graphics software, such as Pixologic's Zbrush. The idea is that the program's canvas represents a normal 2D painting surface, but that the data structure that holds the pixel information is also able to store information regarding z-index (depth) as well as other information such as material settings, specularity, etc. With this data it is thus possible to simulate lighting, shadows, and so on.
[edit] Film animation technique
The term is also used to describe an animation effect commonly used in music videos and, more frequently, title sequences. Brought to wide attention by the motion picture The Kid Stays in the Picture based on the book by film producer Robert Evans, it involves the layering and animating of two-dimensional pictures in three dimensional space. Earlier examples of this technique include Liz Phair's music video "Down" directed by Rodney Ascher and "A Special Tree" directed by musician Giorgio Moroder and starring actor Adam Baldwin.
[edit] Image-based rendering
In 3D, polygonal virtual worlds, geometry that is sufficiently distant can be seamlessly replaced with a 2D sprite for a significant performance boost. One of the first games to use this technique was Jurassic Park: Trespasser,[3] and it was subsequently used in a number of later games.[citation needed]
[edit] Parallax scrolling
A collection of 2D sprites moving independently of each other, and/or the background, parallaxing is often used in 2D games to create a sense of depth. This type of graphical effect was first used in the 1982 arcade game Moon Patrol.[4] Mode 7, a display system effect that included rotation and scaling, allowed for a 3D effect while moving in any direction without any actual 3D models, and was used to simulate 3D graphics on systems such as the SNES.
[edit] Virtual light source
The term also refers to the slight 3D illusion created by the virtual presence of a light source to the left (in some cases right) side, and above a computer monitor. The light source itself is always invisible but its effects are seen in the lighter colors for the top and left side, simulating reflection, and the darker colours to the right and below of such objects, simulating shadow. This technique is often used in the design of icons and entire windows in graphical user interfaces or GUIs.
[edit] Games with a limited 2D playing field
The term "2.5D" is commonly applied to 3D games that use polygonal graphics to render the world and/or characters, but whose gameplay is restricted to a 2D plane. Examples include Pandemonium, Klonoa: Door to Phantomile, Nights into Dreams..., Viewtiful Joe, Strider 2, Kirby 64: The Crystal Shards, New Super Mario Bros, Wario World, Yoshi's Story, Tomba!, The Simpsons Game (DS) and Sonic Rivals. The Crash Bandicoot series is sometimes referred to as 2.5D because although the characters and scenery are rendered in 3D, it is not as free-roaming like 'true' 3D platformers.
Some fighting games such as the Super Smash Bros. series, Marvel Vs. Capcom 2, and the Street Fighter IV also utilize 2.5D to showcase 3D backdrops and/or characters while limiting the action to a 2D plane.
The area of gameplay can be described as a two-dimensional surface twisting and bending in a three-dimensional space. Inside this surface, the character and physics behave like in a traditional 2D platformer. There are however a number of twists that aren't possible with normal 2D platformers: it is common in such games to let the two-dimensional plane cross itself or other planes on certain points, thus creating "track switches" in the course. Players can explore different areas of the 3D world that way or can be brought back to previous points seamlessy. Interactions with the "background" (non-accessible points in the 3D landscape) are also used extensively.
[edit] Examples
The 1986 video game Out Run is a good example of a classic pseudo-3D racing game. The player drives a Ferrari into depth of the game window. The palms on the left and right side of the street are the same bitmap, but have been scaled to different sizes, creating the illusion that some are closer than others. The angles of movement are left and right and into the depth (while still capable of doing so technically, this game did not allow making a U-turn or going into reverse, therefore moving out of the depth, as this did not make sense to the high-speed game play and tense time limit). Notice the view is comparable to that which a driver would have in reality when driving a car. The position and size of any billboard is generated by a (complete 3D) perspective transformation as are the vertices of the poly-line representing the center of the street. Often the center of the street is stored as a spline and sampled in a way that on straight streets every sampling point corresponds to one scan-line on the screen. Hills and curves lead to multiple points on one line and one has to be chosen. Or one line is without any point and has to be interpolated lineary from the adjacent lines. Very memory intensive billboards are used in Out Run to draw corn-fields and water waves which are wider than the screen even at the largest viewing distance and also in Test Drive to draw trees and cliffs.
Sonic the Hedgehog for the Sega Mega Drive (Sega Genesis in the US) uses parallax scrolling for aesthetic reasons. Parallax scrolling can be considered a form of pseudo-3D, as it uses 2D graphics that move corresponding to the rules of three dimensional geometry.
The Street Fighter II games used parallax scrolling on the ground of each stage, for a good pseudo-3D effect.
The same effect was used in the first real time strategy game to use pseudo-3D or 3D graphics, Stronghold (1993). The game was described as "Dungeons and Dragons meets SimCity" and displayed a pseudo-3D city with different structures built by humans, dwarves, elves etc. spread across a hilly terrain.
Examples of pseudo 3D with true 3D graphics and effects but 2D restricted gameplay are Strider 2, R-Type Delta, R-Type Final and Contra: Shattered Soldier.
Klonoa: Door to Phantomile uses pre-rendered sprites on 3-D levels. The gameplay is 2D, but the player is able to interact with objects in the background and foreground.
In Sonic Rush, Sonic and Blaze are both 3-D while running through a side-scrolling world, like the original Sonic the Hedgehog.
The Dracula X Chronicles also use this style in the first game, which is used to unlock the other games.
The PS3 game LittleBigPlanet is rendered in full 3D, but played from a side-scrolling perspective. Players and objects can exist on three planes (foreground, middleground, and background), and players can shift between them.
Street Fighter IV uses 3D graphics, but plays in 2D.
Just like Street Fighter IV, New Super Mario Bros. and Bionic Commando Rearmed both have 3D graphics and play in 2D.
The game Pandemonium uses 3D graphics, and also animates the characters in 3D movement, moving in spirals and turns. However, the controls are in 2D.
[edit] History
The first computer games that used pseudo-3D were primarily arcade games. Atari's 1976 racing game Night Driver was the first driving game to use a pseudo-3D first person perspective. Games using vector graphics had an advantage in creating pseudo 3D effects. 1978's Speed Freak recreated the perspective of Night Driver in far greater detail. The following year, a major breakthrough for pseudo-3D gaming came in the form of Atari's Battlezone, recreating a 3D perspective with unprecedented realism (though the gameplay was still planar). It was followed up that same year by Red Baron, which used scaling vector images to create a forward scrolling rail shooter.
Pole Position by Namco is one of the first racing games to use the trailing camera effect that is now so familiar. In this particular example, the effect was produced by linescroll-- the practice of scrolling each line independently in order to warp an image. In this case, the warping would simulate curves and steering. To make the road appear to move towards the player, per-line color changes were used, though many console versions opted for palette animation instead.
The first home video game to use pseudo-3D, and also the first to use multiple camera angles mirrored on television sports broadcasts, was Intellivision World Series Baseball (1983) by Don Daglow and Eddie Dombrower, published by Mattel. Its television sports style of display was later adopted by 3D sports games and is now used by virtually all major team sports titles.
With the advent of computer systems that were able to handle several thousands of polygons (the most basic element of 3D computer graphics) per second and the usage of 3D specialized graphics processing unit, pseudo 3D became obsolete. But even today, there are computer systems in production, such as cellphones, which are often not powerful enough to display true 3D graphics, and therefore use pseudo-3D for that purpose. Interestingly, many games from the 1980s' pseudo-3D arcade era and 16-bit console era are ported to these systems, giving the manufactures the possibility to earn revenues from games that are now nearly twenty years old.
By 1989, 2.5D representations were surfaces drawn with depth cues and apart of graphic libraries like GINO.[5] 2.5D was also used in terrain modeling with software packages such as ISM from Dynamic Graphics, GEOPAK from Uniras and the Intergraph DTM system.[5] 2.5D surface techniques gained popularity within the geography community because of its ability to visualize the normal thickness to area ratio used in many geographic models; this ratio was very small and reflected the thinness of the object in relation to its width, which made it the object realistic in a specific plane.[5] These representations were axiomatic in that the entire subsurface domain was not used or the entire domain could not be reconstructed; therefore, it used only a surface and a surface is one aspect not the full 3D identity.[5]
The resurgence of 2.5D or visual analysis, in natural and earth science, has increased the role of computer systems in the creation of spatial information in mapping.[1] GVIS has made real the search for unknowns, real-time interaction with spatial data, and control over map display and has paid particular attention to three-dimensional representations.[1] Efforts in GVIS have attempted to expand higher dimensions and make them more visible; most efforts have focused on "tricking" vision into seeing three dimensions in a 2D plane.[1]Much like 2.5D displays where the surface of a three dimensional object is represented but locations within the solid are distorted or not accessible.[1]
[edit] Technical aspects
The reason for using pseudo-3D instead of "real" 3D computer graphics is that the system that has to simulate a three dimensional looking graphic is not powerful enough to handle the calculation intensive routines of 3D computer graphics, yet is capable of using tricks of modifying 2D graphics like bitmap. One of these tricks is to stretch a bitmap more and more, therefore making it larger with each step, as to give the effect of an object coming closer and closer towards the player.
[edit] Generalization
Even simple shading and size of an image could be considered pseudo-3D, as shading makes it look more realistic. If the light in a 2D game were 2D, it would only be visible on the outline, and because outlines are often dark, they would not be very clearly visible. However, any visible shading would indicate the usage of pseudo-3D lighting and that the image uses pseudo-3D graphics. Changing the size of an image can cause the image to appear to be moving closer or further away, which could be considered simulating a third dimension.
Dimensions are the variables of the data and can be mapped to specific locations in space; 2D data can be given 3D volume by adding a value to the x, y, or z plane. "Assigning height to 2D regions of a topographic map" associating every 2D location with a height/elevation value creates a 2.5D projection; this is not considered a "true 3D representation", however is used like 3D visual representation to "simplify visual processing of imagery and the resulting spatial cognition".
[edit] References
- ^ a b c d e MacEachren, Alan. "GVIS Facilitating Visual Thinking." In How Maps Work: Representation, Visualization, and Design, 355–458. New York: The Guilford Press, 1995.
- ^ "Reassessing the 3/4 view effect in face recognition". Cognition, Volume 83, Number 1: 31–48(18). February 2002. doi:.
- ^ Wyckoff, Richard (1999-05-14). "Postmortem: DreamWorks Interactive’s Trespasser". GamaSutra. http://www.gamasutra.com/view/feature/3339/postmortem_dreamworks_.php. Retrieved 2009-11-21.
- ^ Stahl, Ted (2006-07-26). "Chronology of the History of Video Games: Golden Age". http://www.thocp.net/software/games/golden_age.htm. Retrieved 2009-11-21.
- ^ a b c d Raper, Jonathan. “The 3-dimensional geoscientific mapping and modeling system: a conceptual design.” In Three dimensional applications in Geographic Information Systems, edited by Jonathan F. Raper, 11-19. Philadelphia: Taylor and Francis Inc., 19.
[edit] See also
[edit] External links
- Lou's Pseudo 3d Page - a study of 2.5D racing game graphics engines
- Is SimCity 4 3D? - describes usage of the term in application to SimCity 4's graphics engine.
