This is the 2nd battle theme ASM that I have developed. The other one
changed the battle theme at a specific chapter of the game. Both of these ASMs come included in the
Chrono Trigger Soundtrack Expansion project, toggleable with a 4-byte change.
What makes this possible: Chrono Trigger does something rather odd in its code. Rather than difrect-referencing the ROM for what the random battle theme is, it instead loads the theme's Index # into a RAM Byte (7E/01FA), and refreshes this value on every map load.
I have taken advantage of that and put in a hook that checks the Map Index # against a lookup table, allowing you to define a different random battle theme on a map-by-map basis. While many of the maps in the game do not have any random battles, they are included anyway to make this ASM compatible with any future romhack.
At C0/0C58 (00x0C58), the following code is in the base rom:
A9 45 LDA #$45 ;Load song $45 - Battle 1
85 FA STA 7E/01FA ;Write song to the "current battle theme" RAM byte
You will want to replace those 4 bytes with the following:
22 ?? ?? ?? JSL !freespace ;Jump to the new subroutine
Then, in the freespace area, add this code:
!freespace
DA PHX Store the old X value, to be safe
AE 00 01 LDX $7E/0100 Load the current map number to X
BF ?? ?? ?? LDA,X !battletable Look up map's battle theme in the battle table
85 FA STA $7E/01FA Save "Current battle theme"
FA PLX Retrieve the old X value
6B RTL Return
!battletable
[This table consists of $200 bytes, one corresponding to each map)
With this new code, I'm soliciting opinionson which battle theme should go where. I could take the easy approach of having a consistent battle theme for every time period. In that case, I'd do Battle 1 for Present/Past, Battle 2 for Future/Antiquity, and Burn! Bobonga! for Prehistory. I could also do this by dungeon though. Below is a list of dungeons. If a music track is written next to it, it means that the event code is specifying a specific music track. These can still be changed, but it will require event editing. If there is an "NA" it means that it is technically a "dungeon", but there are no random battles that occur there.
1000 AD - Present
Millenial Fair (Gato)
Guardia Forest
Guardia Castle Prison
Guardia Castle Basement
Heckran Cave
Sunken Desert
Northern Ruins - N/A
Forest Secret - N/A
600 AD - Past
Truce Canyon
Guardia Forest
Manoria Cathedral
Zenan Bridge
Denadoro Mountains
Cursed Woods
Magic Cave
Magus's Castle
Ozzie's Fort
Northern Ruins
Giant's Claw - Tyrano Lair
2300 AD - Future
Lab 16
Arris Dome
Lab 32
Sewer Access
Factory Ruins
Geno Dome
Death Peak
Sun Palace - N/A
65,000,000 BC - Prehistory
Mystic Mountain
Hunting Range - Burn Bobonga!
Forest Maze
Reptite Lair
Dactyl Nest
Tyrano Lair - Tyrano Lair
12,000 BC - Antiquity
Beast's Nest
Mt. Woe
Ocean Palace - Ocean Palace
Blackbird
North Cape - NA
Black Omen - Black Omen
End of Time - NA
The songs that I think work as battle themes are:
Battle 1
Battle 2
A Shot of Crisis
Bike Chase
Primitive Mountain
Burn! Bobonga!
Determination
Battle 1 Rough (Pre-release rom)
