screen split with shiru's neslib

[maninboots]

Hey there!
I'm a noob in need of help.

Has anyone implemented a screen split with shiru's neslib?
I've tried to do one my self but without luck (either nothing happens, or the screen flickers between the two scrolls).
Any help would be appreciated!

So basically what I need is shiru's ppu_waitnmi() routine but with a sprite 0 hit check and scroll.

Here's shirus routines for ppu_waitnmi() and scroll(x, y):

Code: Select all

_ppu_waitnmi:
	lda #1
	sta <VRAMUPDATE
	lda <FRAMECNT1
@1:
	cmp <FRAMECNT1
	beq @1
	lda <NTSCMODE
	beq @3
@2:
	lda <FRAMECNT2
	cmp #5
	beq @2
@3:
	lda #0
	sta <VRAMUPDATE
	rts


_scroll:
	sta <TEMP

	txa
	bne @1
	lda <TEMP
	cmp #240
	bcs @1
	sta <SCROLL_Y
	lda #0
	sta <TEMP
	beq @2	;bra

@1:
	sec
	lda <TEMP
	sbc #240
	sta <SCROLL_Y
	lda #2
	sta <TEMP
@2:

	jsr popax
	sta <SCROLL_X
	txa
	and #$01
	ora <TEMP
	sta <TEMP
	lda <PPU_CTRL_VAR
	and #$fc
	ora <TEMP
	sta <PPU_CTRL_VAR
	rts

and here are my messy attempts to combine whatever ppu_waitnmi() does with the sprite 0 check:
note that I was just trying random things at the end before I gave up = /

Code: Select all

;void __fastcall__ waitSprite0rel(void);

_waitSprite0rel:
	lda #1 ;no idéa what these two lines do, took it from ppu_waitnmi()
	sta <VRAMUPDATE ;but I think the sprites didn't even show up if I didn't include them = /
	lda $2002
	and #$40
	beq _waitSprite0rel
	rts
   
;void __fastcall__ waitSprite0set(void);
   
_waitSprite0set:
	lda $2002
	and #$40
	bne _waitSprite0set
;	lda $2000
;	and #$FE
;	sta $2000
	lda #0 ;same as above, these two are from ppu_waitnmi()
	sta <VRAMUPDATE
	rts
  
;void __fastcall__ waitVBLANKrel(void);
   
_waitVBLANKrel:	
	lda <FRAMECNT1
_waitVBLANKloop:
	cmp <FRAMECNT1
	beq _waitVBLANKloop
	lda #0 ;same as above, these two are from ppu_waitnmi()
	sta <VRAMUPDATE
	rts

This is how I'd like my game loop to look like

Code: Select all

updateEverything();

scroll(0, scrollY);
waitSprite0rel(); // waits until rendering starts?
waitSprite0set(); // waits for sprite 0 hit?
scroll(scrollX, scrollY); // scrolls screen directly after hit
waitVBLANKrel(); // waits for rendering to end!?

Here's a screenshot, the orange square in the hud is my sprite 0


Note that my assembly knowledge is extremely low (first time working with it last night).

Thanks in beforehand,
Mattias.

[Shiru]

Try to check the current version of the neslib. I added 'split' function today, and it has a number of other improvements added recently. Take a note that the split functionality is very limited: you have to handle PAL/NTSC difference by yourself, code execution time can't exceed frame time (split will be missed otherwise), you have to setup sprite to get sprite0 hit by yourself, you can't scroll bottom part vertically. Hopefully some of these limitations will be removed in the future.

[maninboots]

I added 'split' function today, and it has a number of other improvements added recently.

Wow, thanks!
Great work with the neslib btw, I've been using it for a year now!
I'm currently running everything in NTSC speed and allowing the slowdown on PAL, any problems with this?

[Shiru]

Yes. The problem is that the speed compensation inserts dummy frames in NTSC mode, i.e. once in six frames ppu_waitnmi waits two frames rather than one. In this extra frame split won't take effect, which will make the bottom part scroll into a wrong position for a frame.

In current version automatic speed correction is disabled by default (could enabled in the crt0.s).

[maninboots]

code execution time can't exceed frame time (split will be missed otherwise)

A couple of frames here and there flickers, so I guess my game is slow.
Anyways, might skip the split thing then =) thanks anyways!

Is there a change log somewhere? I would like to know what else is new.
Thanks,

[tepples]

If you get a flicker every once in a while, your NMI handler needs to do all screen updates and sprite 0 waiting. I don't know whether neslib supports this.

[Shiru]

Sorry, there is no change log for now, not even a version number. The code gets occasional small updates time to time, with every project is is used in, and I'm too lazy to put extra effort on documenting the changes. It may change eventually, once it get into more stable form.

You can go without the split for now, and when your game will be done more or less, contact with me, so I'd add more functionality to the split scroll code, to make it work with your project.