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Author Topic: Chrono Trigger Sprite Expansion  (Read 2516 times)

stewelement

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Chrono Trigger Sprite Expansion
« on: January 25, 2016, 09:57:55 pm »
Hello everyone,

I want to attempt a sprite expansion for Chrono Trigger. A very simple example would be having a second spritesheet for Crono with a red shirt on and be able to swap 'outfits' out in-game. Palette swap is not what I'm really going for, so I'd like to do more complex sprites (I know this has it's own set of difficulties), but as proof of concept I think this example works.

I know from some basic research that palettes and sprites for the main characters are uncompressed in the rom. My initial idea would be to have the second sprite sheet and palette added to the ROM while setting up some sort of pointer or other link to determine the 'active' sprite sheet between the original and the new sheets. I suspect that some ASM tricks would be needed in order to pull it off, but I am not familiar with ROM hacking to even know where to begin. I know that some manipulation has been done in existing hacks (like human Glenn) but I suspect these are just overwriting the sprite sheet. If anyone can point me to a resource to get started, please let me know. Thanks!

RedScorpion

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Re: Chrono Trigger Sprite Expansion
« Reply #1 on: January 26, 2016, 04:09:57 am »
The only way i think which could work is to use the story-RAM Adress:

During the Sprite-ASM you have to set a hook to a new adress with your new sprites / pointer



--> Load Sprite asm ->

1. common way -> Check RAM -> Load Sprite ASM -> Load rest of stuff
2. New Way -> Check RAM -> Jump to new Sprite block -> Load Sprite stuff -> Jump Back -> Load rest of stuff.

It would need a lot of a checks!

Check this:

http://www.romhacking.net/documents/444/

Thanks

red

Mauron

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Re: Chrono Trigger Sprite Expansion
« Reply #2 on: January 26, 2016, 08:47:52 pm »
I've been looking into this possibility off and on for some time now, and you're the second person who asked about it recently, so I'll try to make some progress.

I used one byte to store the flags for each character's current state, in the standard order. Some of the code had been hacked to load an alternate set, but I wasn't finished.
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stewelement

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Re: Chrono Trigger Sprite Expansion
« Reply #3 on: January 26, 2016, 10:05:27 pm »
Red,

Thanks, I will attempt to make sense of the document and start looking into Temporal Flux.

Mauron,

What is your desired end result? If you are already working on something similar, I'd rather not step on your toes, as it were, and it would probably be a pain to try and bring me up to speed. If I could lend a hand somehow though, please let me know.

Mauron

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Re: Chrono Trigger Sprite Expansion
« Reply #4 on: January 27, 2016, 02:09:49 am »
My original idea was to have a possibility to revert Frog to his human form, depending on your decision at North Cape. That was expanded to an any character toggle since it wasn't much more difficult to do that way, and the generic code would be more useful to others (Check if Frog and check mode vs determine character and check mode).

The current project will switch the character's sprite data, which controls sprite packet, sprite assembly, animations, palette, and size (PCs must be size 0 by default - hacking can allow for size 1 sprites, but that's a different project). I wanted to alter techs as well, but that was starting to get messy and was why I originally shelved the project.

What I have right now... is rather messy. I think some of my ideas were too far off from what I needed to do.
Mauron wuz here.

ThegreatBen

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Re: Chrono Trigger Sprite Expansion
« Reply #5 on: August 05, 2016, 03:17:18 pm »
How has this progressing? I'd be interested in helping.