Parallax scrolling: Difference between revisions

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Revision as of 07:22, 5 September 2021

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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|Sega 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 scan|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]], Sega 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)#PortsHome 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.