2600: Can someone help with this

[Cupcakus]

I'm trying to figure out how games write multiple sprites to the same scanline, like in Space Invaders. Here is how I was drawing multiple sprites to the same scanline:

 

I would draw the same object in two different places on the same scanline by interlacing the frames, draw one object on one frame then the other on the next frame, which causes a "flicker".

 

That works fine and dandy for me, except it still doesn't explain how games like space invaders throw several sprites on the same scan line with no flicker. I don't get it. Is there an example somewhere where I can find how this is happening.

[+johnnywc]

Now I'm no expert by any means, but I believe the way it's accomplished (in a high level explanation) is by using a combination of RESP0 (reset P0) during a scan line and NUSIZ0 (to make three copies).

 

For 6 players on one line (like Space Invaders), you could use P0 and P1 with the same graphic, both with three copies, but I think there is a way to display all 6 using just P0, NUSIZ0 and RESP0.

 

Here's a link on "The Dig" that has some code.

 

http://www.neonghost.com/the-dig/source/source.php3

 

Hope this helps!!