what is a raster interrupt and how do i code one?

2

jpospTynker 2025-07-18 21:51 (Edited)

read title. also, how do i stop sprites and cells from wrapping around from the top when they get too far off the screen.

was8bit 2025-07-18 21:57 (Edited)

Go here...

https://lowresnx.inutilis.com/topic.php?id=3737

And pay attention how sprite coordinates differ from cell image coordinates...

.... then simply read a sprites coordinates as it move, and restrain how far it goes

was8bit 2025-07-18 21:58

Raster interupt is something totally different...

wryhode 2025-07-18 21:59 (Edited)

Raster interrupts are SO neat and useful! To use them here is also very simple:

  1. Define a SUB that takes a single argument (RASTER). E.g. SUB RASTERFX(RASTER). The RASTER argument will be the line number of the screen that is about to be drawn. (0 - 127)
  2. Write whatever code you want to run for each line as it gets drawn to the screen. One drawback is that they have to be very small (<54 cycles iirc). For example, you can make the background wavy with: SCROLL 0, SIN(RASTER / 40) * 8, 0
  3. For the raster sub to be executed, you need to 'register' it with: ON RASTER CALL {name of your SUB}
  4. Profit!!

wryhode 2025-07-18 22:04 (Edited)

Sprites overflow because their position is stored as a byte, which wraps to 0 when over 255. You can prevent this in code by checking if the coordinate the sprite is getting drawn to is within the screen coordinates.

yeah, or listen to was8bit!

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