Spritemultiplexing example V2.1 by Lasse Öörni (loorni@gmail.com) Available at http://cadaver.github.io
Additions by Ricki Sickenger (ricki.sickenger@gmail.com)
Quite easy (?) to understand example how to make a spritemultiplexer, using 32 sprites. The routine is capable of more but the screen starts to become very crowded, as they move randomly...
Uses a "new" more optimal sortmethod that doesn't take as much time as bubblesort. This method is based on the idea of an orderlist that is not recreated from scratch each frame; but instead modified every frame to create correct top-bottom order of sprites.
Why sorted top-bottom order of sprites is necessary for multiplexing:
because raster interrupts are used to "rewrite" the sprite registers
in the middle of the screen and raster interrupts follow the
top->bottom movement of the TV/monitor electron gun as it draws each
frame.
Light grey color in the bottom of the screen measures the time taken by sprite sorting.
What is missing from this tutorial for sake of simplicity:
- Elimination of "extra" (more than 8) sprites on a row
Additions by Ricki:
- Added support for multicolor sprites
- Added X-position msb table checks
- Converted to ACME format
To use multicolor sprites:
- Set the byte at the correct index in the 'sprmc'-table to a non-zero value. The 'sprmc' index follows the 'sprf' table index.
To set the sprite msb x position:
- Set the byte at the correct index in the 'sprx_msb'-table to a non-zero value.
This source code is in ACME format.