The proper way of disabling a sprite? (Using DisplayLibrary)

[earok]

This is probably fairly obvious but I haven't discovered the proper way to handle it.

If you draw a sprite with the DisplaySprite command, eg

DisplaySprite CopList#,Sprite#,X,Y,Sprite Channel

Then the sprite remains static until you move it or draw a different sprite on that sprite channel.

But say if you no longer want to use that sprite channel at all? How do you simply turn it off? What I've been doing is simply moving the X value outside of the screen but surely that's not the right way to do it?

[Daedalus]

To just remove it from the display, you can create a small transparent sprite and display that instead. To turn off the actual sprite display however is called "disarming" the sprite. I've never actually done it, but it seems writing 0 to the sprite control registers (SPR0CTL to SPR7CTL) disarms the sprites and disables their DMA, stopping their display and freeing that DMA slot up for other uses. Apparently this should only be done during a vertical blank however or you'll be left with vertical bars on your screen where the sprite used to be.

More info in the RKRMs here, and I'm sure plenty of people have more experience than I do with sprites - I've only ever done basic stuff with them.

Edit: SPR7CTL is the top register, not SPR8CTL...

[Lonewolf10]

Originally Posted by Daedalus

Apparently this should only be done during a vertical blank however or you'll be left with vertical bars on your screen where the sprite used to be.

That's because the SPRxDAT register is loaded with new sprite data each time a new horizontal line is reached. If you switch off a sprite whilst the SPRxDAT register still has non-zero data in it then you get the horizontal bars. Simply set SPRxDAT to 0 (where x represents the sprite number - 0 to 7) and you should avoid this problem

It should be ok to write directly to SPRxDAT as some games manually load sprite registers with data to create backgrounds - usually done using the copperlist.

[earok]

Cheers guys

[E-Penguin]

;; Disable sprite channel
;; SPRxPOS = 0, move it away
Poke.w $dff140 + (channel * 8), 0
;; SPRxCTL = 0, disable the channel
Poke.w $dff142 + (channel * 8), 0

This works. Obviously not optimised - probably a switch/case on channel would be faster than two multiplications, but it works well enough for what I'm doing.

[MickGyver]

Originally Posted by E-Penguin

;; Disable sprite channel
;; SPRxPOS = 0, move it away
Poke.w $dff140 + (channel * 8), 0
;; SPRxCTL = 0, disable the channel
Poke.w $dff142 + (channel * 8), 0

This works. Obviously not optimised - probably a switch/case on channel would be faster than two multiplications, but it works well enough for what I'm doing.

You could also do a logical left shift instead of multiplication: channel LSL 3. A shift of three bits left is the same as multiplying times eight. Bitwise operations are very usable and often faster. Have somebody tested the speed difference of multiplication/division and LSL/LSR in BB2?

https://en.wikipedia.org/wiki/Logical_shift

[E-Penguin]

Yes, good point. I don't know about BB2 but the MULU instruction on 68000 is pretty slow. https://wiki.neogeodev.org/index.php...ctions_timings

I think switch/case wrapped up in a macro is probably the fastest way, using constants rather than calculating anything.