Double Sprites

November 28, 2024

So, I wanted to have up to two other things on the screen at once; one on the top floor of the screen, and one on the bottom.

I figured, hey, I’m never displaying these on the same line, so what’s the harm?

Well, because they’ll have their own X position, it turns out that I need to do my H positioning again.¹

I anticipated this, which is half of why I put a wide floor between the two halves, so I could re-calculate the positions in between the top and bottom. Because I can’t update and render my Player sprite during this, I’ve put the Playfield in front of the characters, so that it doesn’t look weird when he disappears.

I don’t get to render the ladders all the way up now — the big gap between the rungs is where the H-positioning is happening — though I’m not super fussed about that. I’ll just call it an “artistic choice”.

But, uh oh:

Flashing the HMOVE seems to take a chunk of clock cycles which makes the Horizontal Blanking bleed into the screen. I spent several hours trying to find a solution, till I decided that the solution was that the floor would go black for a bit.

That looks better, and my kernel is stable again. I’ll come back and play around with the graphics a bit later, to make the rest of the screen look consistent. But for now, I’m happy.

I’m sure there are better ways to do this — I know there are strategies to handle multisprites; Bezerk doesn’t seem to have massive black bars between every robot; but this works well enough.

I’m becomming painfully aware of my RAM budget, and this chewed up a bit. I’ve still got plenty, but I may have to refactor some of this later and shuffle things around.