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Author Topic: Genesis Graphics Editing  (Read 7903 times)

Category

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Genesis Graphics Editing
« on: May 25, 2013, 03:26:13 pm »
Hi all. I'm starting a little project, and looking into changing some sprites/title screens on a Genesis/Mega Drive game for part of the hack. So far my text hunting and changes seem to be working fine, but when it comes to graphics changes, having a few issues though...

Firstly, how can you get palette data from a genesis ROM? I've loaded up the game in tile layer pro, and can find some of the tiles I want to edit, but all the colours are wrong. Where do I get the palette information from?

Secondly, in the part of the title screen I want to change, some tiles are reused - and the graphic I want to replace it with won't have tiles duplicated... Where would I start looking for the layout information in the ROM?

Is there any good source for information on this, or any tips you guys have?

Cheers, Category

FAST6191

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Re: Genesis Graphics Editing
« Reply #1 on: May 25, 2013, 07:44:46 pm »
I assume you have the tech specs
http://www.romhacking.net/documents/227/

It can come from anywhere in the ROM really. In most games on most consoles it is usually found near the graphics it handles or with the other palettes. Same applies to any tile mapping as well though do note it is quite possible that there is a tile limit and simply pasting your image in might not happen so easily.

Finding it -- you can snatch it from the CRAM and feed that to your editor if you want. You can take it a step further and search the ROM for the data as found in the CRAM, dynamic palette is an option but it not common enough that I would skip searching for it.
You can trace it by setting breakpoints on the CRAM and doing basic tracing.
Corruption could work but it would be really hard as palettes are not the biggest lumps of data (same with tile maps).

You might be able to narrow some of it down a slight bit as things do tend to sit near each other.
Basically there is no simple way as it can be anywhere or even nowhere. On the flip side though this is also somewhat basic graphics hacking, being the megadrive/genesis you are unlikely to get a step by step tutorial but "set a breakpoint on the palette memory and read off the source" is the same for every console.

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Re: Genesis Graphics Editing
« Reply #2 on: May 29, 2013, 03:18:10 pm »
I wasn't expecting the title screen to be easy... Worries confirmed!

I've skimmed the technical docs (and referred to them in detail in places), so have the basics of what going down. More I suppose I was lookingto see if there are any tools that simplify the process. I've dumped CRAM to pick up palettes in places I want to, but haven't found easy ways to transpose that info in, say tpl files for tile layer pro. Are there any tools that could simplify the process? Getting RGB values and setting up palettes by hand has been a chore!

And what emulators are recommended for breakpoints/dumping? I'm running linux at the moment, and obvious choices like DebuGens, GensKMod & Exodus don't work in the slightest... May have to dual-boot/VM a windows install for the more useful tools.

FAST6191

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Re: Genesis Graphics Editing
« Reply #3 on: May 29, 2013, 06:38:41 pm »
ROM hacking is very windows centric and emulators much the same if you are after a hacking one, if I use emulators on linux it is invariably because I want to play a game rather than do any hacking. A cut down XP VM should run a genesis/megadrive emulator just fine though (it is not like you need to play in real time after all). That said you might try some of the combined emulators like mednafen which as an added bonus should be very linux compatible.

I tend not to use tile layer pro, http://home.arcor.de/minako.aino/TilEd2002/ has a 15bit RGB (and BGR) import and nice fiddling options (move one pixel/palette entry at a time for instance) and http://code.google.com/p/tiledggd/ takes care of the rest of my exotic/rare image format needs (though it lacks inbuilt editing support).