Parallax scrolling: Difference between revisions

Revision as of 17:16, 4 September 2004

Revision as of 12:29, 20 October 2004

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This is called a "[[raster effect]]" and is also useful for changing the system [[palette]] to provide a gradient background.

Some platforms ([[Super Nintendo Entertainment System|Super NES]], [[Sega Genesis]], [[Game Boy Advance]], [[Game Boy]]) provide horizontal-blank interrupts for automatically setting the registers; others, such as the NES require the use of cycle-timed code.

Many NES games such as the classic ''[[Super Mario Bros.]]'' use this technique to draw their status bars, and ''[[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. You can achieve breathtaking depth of field if you combine layers with rasters; ''[[Sonic the Hedgehog 2]]'', ''[[ActRaiser]]'', and ''[[Street Fighter II]]'' used this effect well. If you make each scanline its own sub-layer, you get the ''[[Pole Position]]'' effect, which creates a pseudo-3D road (or in ''[[NBA Jam]]''<nowiki>'</nowiki>s case, a pseudo-3D ball court) on a 2D system.

If your display system supports rotation and scaling in addition to scrolling, changing the rotation and scaling factors can draw a projection of a plane (''[[F-Zero]]'', ''[[Super Mario Kart]]'') or can warp the image to create an extra challenge factor (''[[Tetanus On Drugs]]'').

=== The sprite way ===

If you have a lot of [[sprite (computer graphics)|sprite]]s (individually controllable moving objects drawn by hardware on top of or behind the layers) available on your display system, you may want to make a pseudo-layer out of sprites.

''[[Star Force]]'', an overhead-view vertically-scrolling shooter for NES, used this for its starfield, and ''[[Final Fight]]'' for Super NES used this technique for the layer immediately in front of the main playfield.

But watch out for sprite flicker; you'll want to heed these tips for [http://everything2.com/index.pl?node=preventing%20sprite%20flicker%20on%20old%20consoles preventing sprite flicker on old consoles].