nesdev.com

Dumb question. Can you do a rough X/Y scroll split with 2 writes to $2006.

(If I remember correctly, affecting all but the fine Y bits)

I've never tried it.

_________________
nesdoug.com -- blog/tutorial on programming for the NES

Reference:
https://wiki.nesdev.com/w/index.php?title=PPU_scrolling#Summary

It doesn't set any of the fine X bits, and it sets the top bit of fine Y to 0.

Ok, I see. So if your fine X is wrong, 2 writes to $2006 might not be enough for...say...a HUD at the bottom of the screen?

What about...
LDA #0
STA $2005
STA $2005
LDA #something
STA $2006
LDA #something
STA $2006

(ie, during rendering, perhaps after a sprite zero hit)

_________________
nesdoug.com -- blog/tutorial on programming for the NES

That makes the math easier, but makes the raster timing much worse. The first write to $2005 will immediately cause glitches for the remainder of the drawn scanline.

In contrast, the 6-5-5-6 method requires more calculation, but only the last two writes need to be during horizontal blanking.

Of course you can. Most games do it that way. My game does it that way too. Fine X scroll stays the same.


This is the "standard" way to do it. All games does it that way. The 6-5-5-6 method was only decovered by the reverse-engineering retroscene in the 2000s.