The Data Behind Battle Backgrounds
Now that DrFuji has taught you how to edit Battle Backgrounds, I am going to take you into the data aspect. For right now, this lesson will just be for FireRed. If you do want it for another game and you are actually going to use it, I will attempt to do my best to help you.
To start off with, apply the patch at the bottom of this post to your rom. What it does is move the battle BG table to 0xF10000 where we can work with and expand it, and it also hacks the BG loading routine with branches placed 0xF00000 (I will completely explain this later).
To be honest, the table is quite simple. To start off, it has 20 backgrounds already in it designated by Game Freak. They are as follows:
9. Multi/Indoor- White & Grey & some Yellow in the Palette (Normal Trainer Battle)
10. Multi/Indoor- Green & a little Yellow (Rival Trainer Battle)
11. Multi/Indoor- White & Grey ()
12. Multi/Indoor- White & Grey & some Tan in the Palette ("Gym" Trainer Battles (that option in A-Map))
13. Multi/Indoor- White & Grey & some Tan in the Palette (2) ("Gym" Gym Leader battle (yes the Leaders have different BG))
14. Multi2/Indoor2- White & Grey
15. Multi2/Indoor2- White & Grey & some Purple in the Palette
16. Multi2/Indoor2- Blue & some Tan in the Palette
17. Multi2/Indoor2- Yellow & Tan
18. Multi2/Indoor2- Purple & some Tan in the Palette
19. Multi2/Indoor2- Turquoise & some Tan in the Palette
20. Multi2/Indoor2- White & Grey & some Purple in the Palette
For each background, there are 5 pointers in order with this format:
VV VV VV 08 WW WW WW 08 XX XX XX 08 YY YY YY 08 ZZ ZZ ZZ 08
VV = Image Offset
WW = TileMap Offset
XX = Entry Image
(Ex. The Grass that moves in front of the screen at the beginning of a grass battle.)
YY = Entry Image Tilemap
ZZ = Palette
Here is the documentation of each background and their pointers in the original table:
So, expanding this is really quite simple. Just follow the setup of the table and add on to the end. Don't delete any of them if you are not going to replace them.
This may sound obvious, but you never know what people will do:p.
So, I expanded it... Now what?
This is probably what you are thinking after completing the above. This is where the hack of the loading routine that comes in. What it does is allows you to very easily change the battle background to whatever you wish.
If you remember, all of the backgrounds are in order. If the first grass is 0, then numbering from there will give you the number of background, which means that background slots from 0 to 19 are already filled. So, let's say we add 4 more backgrounds to the end of the table: Fire, Snow, Storm, and Metal, respectively.
The games coding does not directly allow access to these backgrounds, which is what the hacked routine does. Basically, it branches to a section of ASM that checks var 0x40F7. If this var is set to 0, it will automatically return to the regular routine and continue as normal. However, if it is set to any other number, the routine will operate from there and load the battle background of that number instead.
So, if you set var 0x40F7 to 20, then the Fire background will be loaded. If you set it to 22, then the Storm bg will be loaded, and so on. This will stay until you change it to something else. In order to return to the normal background for that map, then you simply set the var to 0.
Please note that this routine overrides every type of battle. This means you can change trainer battles, sea battles, grass battles, cave battles, etc, all by setting that one var. Also, the routine loads a half-word, not a byte, which means that you can have up to 0xFFFF backgrounds in the table, which is a little over 65,000. Granted, there isn't enough space in the rom to have unique backgrounds in each slot, but don't worry about over expanding the table. You won't have a problem there.:)
Well, that about wraps this up. Originally I had planned to give you the ASM routines and explain how to use them, but that got overly complicated with the branches, so I made it really simple with the patch.
Also, I did my best to make this compatible with both JPAN's engine and Jambo51's 649 patch. I haven't tested it on either, but I asked Jambo if there would be any complications or things I should avoid and the only thing he gave me was which var to use since he had used a few. For JPAN's, I avoided using any RAM that he used (which didn't matter in the end because Jambo had me switch to a var) and I don't think he had any routines and such that would affect this.
In order to make this even better for people, on case you have already used the free space at 0xF00000, I have included the source code here:
You can do as you wish with this code.
EDIT: Courtesy of Zeturic, here's the source code designed to work with armrips
If there are complications, please let me know!
Driver - Driver was an old-time German hacker whom originally accomplished this for his own hack. Instead of using a var, he freed up some RAM and used that. About two months ago, I received a rom and some notes of his from Narutoactor via Tajaros. It took me a while to make heads or tails of them, but once I did, I set out to port it over to English FireRed and this was the result! So, most of the credit goes to him!
Jambo51 - A HUGE help in making this. He taught me how to access vars and answered a lot of questions. I know he hates people bugging him with questions, so I really appreciate him not ignoring me!
Darthatron - For being a really good friend and giving me a lot of help. When I was stuck and didn't have access to the var_access routine due to being on the go, but I still wanted to write up the ASM for it, he Pastied it me and I got a lot done. As usual, he also answered a lot of questions and was really helpful.
Mat - While I didn't end up using it because I switched to a var, Mat spent over an hour helping me try to find some free save-able RAM for this project. I really appreciated the time he gave me as we explored the save blocks and got almost nowhere, but he stuck with me until he had to go, so I have to give him a huge thanks!
Tajaros (Not Shadowraze, this was before the switch:p) - For starting this whole project by sending me all of Drivers stuff and asking for my help in deciphering it. He also decoded a lot of the table and documented the first 9 backgrounds before I even started working, which was a huge help.
Narutoactor - For sharing all of Driver's research, and attempting to help me contact Driver which, unfortunately, never happened:(.
Lastly, DrFuji - For digging into the archives and redoing his old private bg editing tutorial and completely rewriting it to go along with this research to make this ultimate guide to hacking battle backgrounds.
Well, that is all for now! On to the next project.... !