Sprite 0 Bug

[St_grld]

So, I just got done rewriting my code, so that it could fix a few problems with the code (mainly adding stuff to the NMI), until I got to a section where it uses a sprite 0 split, instead of splitting the screen like it did before so it could show a dialogue box and the background, it's now pushing down the background, so it can display the box. It's a little hard to explain, so here's a drawing of it:

Background:
\\\\\\\\\\\\\\\\\\\\\\\\\\\
\ _________________\
\ _________________\
\ _________________\
\ _________________\
\ _________________\
\ _________________\
\ _________________\
\\\\\\\\\\\\\\\\\\\\\\\\\\\

Before with the box:
---------------------------
|__________________|
|__________________|
---------------------------
\ _________________\
\ _________________\
\ _________________\
\ _________________\
\\\\\\\\\\\\\\\\\\\\\\\\\\\

Now with the box:

---------------------------
|__________________|
|__________________|
---------------------------
\\\\\\\\\\\\\\\\\\\\\\\\\\\
\ _________________\
\ _________________\
\ _________________\
\ _________________\

I hope you guys understand what I mean

[pubby]

It looks like you're setting the Y-scroll to 0 at the sprite 0 hit. That's not what you want. Set the scroll to the background position you want to see.

[St_grld]

That only seems to move the box around, which is not what I meant (unless I'm doing it wrong).

[Quietust]

It would help to explain exactly what your code is doing - from your description, I can only assume that you're doing a pair of writes to $2006 to point the VRAM address at the beginning of a nametable and then trying to set X/Y scroll using $2005, something which will not work because vertical scroll only updates once per frame (unless you use special tricks, like those described on the PPU scrolling wiki page).

[tokumaru]

It would really help if you could show us what the code around the sprite 0 hit detection looks like.

[St_grld]

Thanks! It works now!
I've removed the $2006 writes and that was the problem!

Here's how it was

Code: Select all

NMI
	lda #$00
	sta $2006
	sta $2006	
	sta $2005
	sta $2005	

;other NMI stuff        

sprite0
	lda #$40
.waitnospr0
	bit $2002
	bvs .waitnospr0
.waitspr0
	bit $2002
	bvc .waitspr0	
	ldx #$00
.waitscan
	inx
	cpx #$78
	bne .waitscan
	ldx #$00
	lda #$00
	sta $2006
	sta $2006	
	lda scrollh
	sta $2005
	lda scrollv
	sta $2005	
	rts