Editing Parallax scrolling (section)

== Methods ==
{{Original research|section|date=March 2015}}

There are four main methods of [[parallax]] scrolling used in titles for [[arcade system board]], [[video game console]] and [[personal computer]] systems.{{citation needed|date=March 2015}}

=== Layer method ===
{{multiple image
| align     = right
| direction = vertical
| header    = Demonstration of the layer method
| width     = 500

| image1    = The Whispered World parallax scrolling sample 1.jpg
| alt1      = 
| caption1  = A side view of the layers used for parallax scrolling in ''[[The Whispered World]]''

| image2    = TWW parallax scrolling sample 2.jpg
| alt2      = 
| caption2  = The same image as above, viewed from the front
}}

Some display systems support multiple background layers that can be scrolled independently in horizontal and vertical directions and [[Compositing|composited]] on one another, simulating a [[multiplane camera]]. On such a display system, a game can produce parallax by simply changing each layer's position by a different amount in the same direction. Layers that move more quickly are perceived to be closer to the virtual camera. Layers can be placed in front of the ''playfield''—the layer containing the objects with which the player interacts—for various reasons such as to provide increased dimension, obscure some of the action of the game, or distract the player.

=== Sprite method ===
Programmers may also make pseudo-layers of [[sprite (computer graphics)|sprites]]—individually controllable moving objects drawn by hardware on top of or behind the layers—if they are available on the display system. For instance ''[[Star Force]]'', an overhead-view vertically scrolling shooter for [[Nintendo Entertainment System|NES]], used this for its starfield, and ''[[Final Fight (video game)|Final Fight]]'' for the Super NES used this technique for the layer immediately in front of the main playfield.

The [[Amiga]] computer has sprites which can have any height and can be set horizontal with the copper co-processor, which makes them ideal for this purpose.

[[Risky Woods]] on the [[Amiga]] uses sprites multiplexed with the copper to create an entire fullscreen parallax background layer<ref>{{cite web|url=http://www.codetapper.com/amiga/sprite-tricks/risky-woods/|title=Risky Woods|website=codetapper.com|access-date=2015-04-23|archive-url=https://web.archive.org/web/20150219002353/http://www.codetapper.com/amiga/sprite-tricks/risky-woods/|archive-date=2015-02-19|url-status=live}}</ref> as an alternative to the system's dual playfield mode.

=== Repeating pattern/animation method ===
Scrolling displays built up of individual tiles can be made to 'float' over a repeating background layer by animating the individual tiles' bitmaps in order to portray the parallax effect. [[Color cycling]] can be used to animate tiles quickly on the whole screen. This software effect gives the illusion of another (hardware) layer. Many games used this technique for a scrolling star-field, but sometimes a more intricate or multi-directional effect is achieved, such as in the game ''Parallax'' by [[Sensible Software]].

=== Raster method ===
<!-- linked from redirect [[Raster effect]] -->
In [[raster graphics]], the lines of pixels in an image are typically composited and refreshed in top-to-bottom order with a slight delay (called the [[horizontal blanking interval]]) between drawing one line and drawing the next line.
Games designed for older graphical chipsets—such as those of the [[History of video game consoles (third generation)|third]] and [[History of video game consoles (fourth generation)|fourth]] generations of video game consoles, those of dedicated [[Handheld TV game|TV game]]s, or those of similar handheld systems—take advantage of the raster characteristics to create the illusion of more layers.

Some display systems have only one layer. These include most of the classic 8-bit systems (such as the [[Commodore 64]], [[Nintendo Entertainment System]], [[Master System]], [[TurboGrafx-16|PC Engine/TurboGrafx-16]] and original [[Game Boy]]). The more sophisticated games on such systems generally divide the layer into horizontal strips, each with a different position and rate of scrolling. Typically, strips higher on the screen will represent things farther away from the virtual camera or one strip will be held stationary to display status information. The program will then wait for horizontal blank and change the layer's scroll position just before the display system begins to draw each scanline. This is called a "raster effect" and is also useful for changing the system [[Palette (computing)|palette]] to provide a gradient background.

Some platforms (such as the Commodore 64, [[Amiga]], Master System,<ref>{{Cite web |url=https://www.smspower.org/uploads/Development/richard.txt |title=Archived copy |access-date=2018-09-04 |archive-url=https://web.archive.org/web/20171109095042/http://www.smspower.org/uploads/Development/richard.txt |archive-date=2017-11-09 |url-status=live }}</ref> PC Engine/TurboGrafx-16,<ref>{{cite web |url=http://cgfm2.emuviews.com/txt/pcetech.txt |title=Archived copy |access-date=2014-03-18 |url-status=dead |archive-url=https://web.archive.org/web/20140318183739/http://cgfm2.emuviews.com/txt/pcetech.txt |archive-date=2014-03-18 }}</ref> [[Mega Drive|Sega Mega Drive/Genesis]], [[Super Nintendo Entertainment System|Super NES]], [[Game Boy]], [[Game Boy Advance]] and [[Nintendo DS]]) provide a [[horizontal blank interrupt]] for automatically setting the registers independently of the rest of the program. Others, such as the NES, require the use of cycle-timed code, which is specially written to take exactly as long to execute as the video chip takes to draw one scanline, or [[Interrupt request|timers]] [[Memory management controller|inside game cartridges]] that generate [[Raster interrupt|interrupts]] after a given number of scanlines have been drawn. Many NES games use this technique to draw their status bars, and ''[[Teenage Mutant Ninja Turtles (arcade game)#Home versions|Teenage Mutant Ninja Turtles II: The Arcade Game]]'' and ''[[Vice: Project Doom]]'' for NES use it to scroll background layers at different rates.

More advanced raster techniques can produce interesting effects. A system can achieve a very effective depth of field if layers with rasters are combined; ''[[Sonic the Hedgehog (1991 video game)|Sonic the Hedgehog]]'', ''[[Sonic the Hedgehog 2 (16-bit)|Sonic The Hedgehog 2]]'', ''[[ActRaiser]]'', ''[[Lionheart (video game)|Lionheart]]'', ''[[Kid Chaos (video game)|Kid Chaos]]'' and ''[[Street Fighter II]]'' used this effect well. If each scanline has its own layer, the ''[[Pole Position (video game)|Pole Position]]'' effect is produced, which creates a pseudo-3D road (or a pseudo-3D ball court as in ''[[NBA Jam (1993 video game)|NBA Jam]]'') on a 2D system.

If the display system supports rotation and scaling in addition to scrolling—an effect popularly known as [[Mode 7]]—changing the rotation and scaling factors can draw a projection of a plane (as in ''[[F-Zero (video game)|F-Zero]]'' and ''[[Super Mario Kart]]'') or can warp the playfield to create an extra challenge factor.

Another advanced technique is row/column scrolling, where rows/columns of [[Tile engine|tiles]] on a screen can be scrolled individually.<ref>{{cite web|url=http://mamedev.org/devwiki/index.php?title=Using_MAME%27s_tilemap_system|title=Using MAME's tilemap system - DevWiki|date=2 January 2014|archive-url=https://web.archive.org/web/20140102211938/http://mamedev.org/devwiki/index.php?title=Using_MAME%27s_tilemap_system|archive-date=2014-01-02}}</ref> This technique is implemented in the [[Graphics processing unit|graphics chips]] of various [[List of Sega arcade system boards|Sega arcade system boards]] since the [[Sega Space Harrier]] and [[Sega System 16|System 16]],<ref>{{cite web |url=http://cgfm2.emuviews.com/txt/s16tech.txt |title=Archived copy |access-date=2016-08-08 |url-status=dead |archive-url=https://web.archive.org/web/20160304034742/http://cgfm2.emuviews.com/txt/s16tech.txt |archive-date=2016-03-04 }}</ref> the Sega Mega Drive/Genesis console,<ref>{{cite web|url=http://www.gamepilgrimage.com/content/sega-genesis-vs-super-nintendo|title=Sega Genesis vs Super Nintendo|date=2009-08-11|website=gamepilgrimage.com|access-date=2014-09-26|archive-url=https://web.archive.org/web/20150924020645/http://www.gamepilgrimage.com/content/sega-genesis-vs-super-nintendo|archive-date=2015-09-24|url-status=live}}</ref> and the [[CP System|Capcom CP System]],<ref>{{cite web|url=https://github.com/mamedev/mame/tree/master/src/mame/video/cps1.c|archive-url=https://hookagency.com/new-forgotten-world-clone-cp-system-code/|archive-date=25 May 2015|first=Paul|last=Leaman|title=New Forgotten World Clone – CP System Code|website=[[GitHub]] }}</ref> [[Irem M-92]]<ref>{{cite web|url=http://www.system16.com/hardware.php?id=747|title=System 16 - Irem M92 Hardware (Irem)|website=www.system16.com|access-date=2014-09-26|archive-url=https://web.archive.org/web/20141224152637/http://www.system16.com/hardware.php?id=747|archive-date=2014-12-24|url-status=live}}</ref> and [[Taito F3 System]]<ref>{{cite web|url=http://www.system16.com/hardware.php?id=665|title=System 16 - Taito F3 System Hardware (Taito)|website=www.system16.com|access-date=2014-09-26|archive-url=https://web.archive.org/web/20140421134650/http://www.system16.com/hardware.php?id=665|archive-date=2014-04-21|url-status=live}}</ref> [[arcade game]] boards.