Skeetendo

’Cause all games were better on the GBC

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#1 2018-06-06 00:22:23

spider
New member
Registered: 2018-06-06
Post 1/1

Editing Text of any GBC ROM

Hey guys. I'm looking to edit the text in a GBC game called Harry Potter and the Chamber of Secrets. The game has a lot in it and it really deserves more research.

TCRF has ripped unused text from the game, so it must be possible to rip and edit text from the game, right? The thing is, I don't know the first thing about how to do so. I've tried looking in a hex editor and seeing if the binary interprets certain bytes as letters, but no luck. Can anybody help me on how to do this?

Thanks

Last edited by spider (2018-06-06 00:24:08)

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#2 2018-06-08 18:33:04

Miksy91
Member
Registered: 2010-10-16
Post 2,331/2,339

Re: Editing Text of any GBC ROM

At least for pokemon G/S/C, the game happens to store the graphics of chacters in video ram area starting at $8800 so that mark "A" is stored in $8800, "B" in $8810, "C" in $8820 etc. "A" letter is also described in text with byte 80, "B" with 81, "C" with 82 etc.

In other words, the following condition holds for all displayable characters:

"VRAM address" = 0x8000 + 0x10 * "char (byte code)"

and thus

"char (byte code)" = ("VRAM address" - "0x8000") / 0x10

It's not necessary, but it would make sense that this Harry Potter game would also have some general way of different byte codes referring to different address in VRAM where font is located. In other words, if you check the contents of video ram with VBA when some general text is displayed in the game, you should see where the font graphics are located and what they look like (is B stored 0x10 bytes ahead of A like in GSC or are they further from each other and so on).

In case the font graphics happen to be stored in a rational way in vram, there could also be a rational "transformation" for different byte codes in "text data" telling the text processing code to load graphics data from different addresses in vram.

Also if you're having hard time understanding what I wrote above, download pokemon gold, silver or crystal and see how it works in practice.

Last edited by Miksy91 (2018-06-08 18:35:19)

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