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 Post subject: Hacking sprites?
PostPosted: Mon Sep 29, 2014 12:21 pm 
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Joined: Mon Aug 21, 2006 3:07 pm
Posts: 18
Hi folks,

So FCEUX makes hacking most nametable/tilemap-related stuff simple. I can open up the nametable viewer, set write breakpoints against PPU addresses and work backwards a few steps to easily figure out how a game knows where to write, say, each entry in a list of items, or where it draws a cursor.

Unfortunately, I've hit a problem where the cursor being drawn as a sprite, not a tile in the nametable. A quick glance through FCEUX options hasn't shown anything immediately useful re: figuring out where a particular sprite is being drawn to the screen, or even which sprite the cursor is. Can someone provide a jumping-off point for this information? It'd be very helpful.

Thanks!


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 Post subject: Re: Hacking sprites?
PostPosted: Mon Sep 29, 2014 12:42 pm 
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Location: NE Indiana, USA (NTSC)
What you want is an OAM viewer. NO$SNS and VisualBoyAdvance have one; I don't know whether FCEUX, NO$NES, and Nintendulator have one. But if you don't, you can always set a breakpoint on $4014 writes to see where the game keeps its display list. For example, writing $02 means the display list is at $0200-$02FF. Then you can follow along with the description of OAM data format on the wiki.


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 Post subject: Re: Hacking sprites?
PostPosted: Mon Sep 29, 2014 1:53 pm 
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That's helpful, thanks!


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 Post subject: Re: Hacking sprites?
PostPosted: Mon Sep 29, 2014 3:23 pm 
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Nintendulator will show you the contents of OAM visually in its video debug page.

You can put a breakpoint on a write to "sprite memory" in FCEUX, but this won't be very useful. You will probably just need to find a 256 byte page of (CPU) RAM that is being used for OAM DMA and inspect writes to the RAM instead.


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