Sprites Multiplexing

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Sprites Multiplexing is a technic often used on other machines with Hardware Sprite Capability.

It was often used on the C64.

On the Amstrad Plus range, it couldn't be used as well. But some possibilities exist.

It allows to "Multiplex" the same Sprite at different rasters lines.

Limitations of Sprites Multiplexing on Amstrad Plus

The technic impose some limitations due to the somewhat unachieved design of the Amstrad Plus and the complex specificity of the ASIC :

  • The same Sprite is simply copied/duplicated as it is.
  • No multiplexed sprites can be at the same Line.

Multiplexing on the PLUS is much more difficult than on the C64. The reason is that the location for the graphics are fixed on the PLUS. e.g. Sprite 0 always looks at &4000 in the ASIC sprite RAM. This can't be changed.

On the PLUS however you can freely change the X,Y position so it is possible to perform some multiplexing of the sprites.

Another way to multiplex sprites is to use screen rupture, because the sprite X,Y coordinate is based on the CRTC's Raster and Line Counter.

Possible uses

This can then be used for games like Shoot'emups... as the sprites don't always need to be well animated (just moved) and as enemies waves are often pre-determined (R-Type is the typical example).

So it fit well for Vertical Waves of enemies.

Also for vertical or even diagonal special effects.

Examples of Sprites Multiplexing on an Amstrad Plus

This Technic wasn't really exploited on the amstrad Plus, mainly because the Amstrad Plus wasn't really exploited.

  • Black Sabbath by BDC-Iron (first harwired sprites multiplexing demo as claimed by its author)
  • Delirium Tremens preview by BDC-Iron (32 Harware sprites per line with actually only 8 sprites slots used)

In games, Prehistorik 2 by Titus Software uses sprite multiplexing for the (second) big cloud/rocks that appear in the front. Did you notice that there are always 2 identical big clouds/rocks on screen at once..? Each one is drawn using all 16 hardware sprites.


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