Two-line kernel and sprite motion weirdness

[Luigi301]

I'm trying to convert my program's one-line kernel into a two-line kernel. It works perfectly with the one-line kernel, but I can't get it to work with a two-line kernel. The problem is, something's broken somewhere and I can't figure out what.

 

In theory, each time a sprite is drawn on the line, its position (SpriteYPosition) is shifted down one line so it can be drawn on the next line. At the beginning of the next frame, it's shifted back up the number of scanlines it was shifted down.

 

In this converted kernel, it goes up with no joystick movement no matter what I set the sprite's height to in the repositioning code. Worse, no matter if I press up or down, it speeds up going up. This is probably related to my hacky collision detection code.

 

Can someone help me get my sprites to stop moving on their own?

[Luigi301]

Well, there was an attachment. I don't know where it went.

getout-game.txt