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September 24th, 2011, 02:36 PM
Join Date: Jul 2010
During my analysis of
, I discovered that Game Freak implemented their own script-controlled walking ASM into the Advance-generation games. There can be up to eight subroutines to run on every frame of animation, only one of which may be active at any given time. You can select a subroutine to activate using
, there is a list of ASM functions to be executed on every frame of animation. Each entry in the list is a pointer to the routine, some metadata about the list item itself, and thirty-or-so bytes for the routine to work with (so that it may maintain its state).
When on the overworld, one of the items on this list is
walking routine manager
. This routine manager will check one of the bytes in its execution-list-item (set by
) and based on that byte, it will call one of eight
Those subroutines in turn check the player's coordinates against stored values to see if the player has moved. If so, the subroutine processes player movement accordingly (check the tile they're standing on, change it if necessary, what have you).
There are eight slots for walking subroutines, and the defined subroutines (pointed to by pointers at
#0 at 0x0806E955: Nop
#1 at 0x0806EB55: Broken (R/S/E leftover: Route 113 ash-covered grass)
#2 at 0x0806E955: Nop
#3 at 0x0806E955: Nop
#4 at 0x0806E9E1: Icefall Cave ice tiles
#5 at 0x0806E955: Nop
#6 at 0x0806E955: Nop
#7 at 0x0806EC41: Broken (R/S/E leftover: Granite Cave/Sky Pillar broken floor tiles)
(The three defined subroutines basically change certain tiles out from under the player's feet. Theoretically, though, a subroutine can do anything it wants on every frame of animation that the overworld is being processed.)
What this means is that we now have an official way -- something that was
designed for this use
-- to set up our own custom-made ASM functions to run the very
the player takes a step. If we keep the broken functions in the table, we can define up to four custom ASM subroutines; if we ditch those, we can define six.
(We could also repoint and extend the subroutine pointer table, and modify the related ASM code, thereby allowing up to 255 custom subroutines to be predefined and activated with
One possible use case for all of this would be an alternate (and more script-friendly) implementation of JPAN-style walking scripts, which would work without breaking other game functions (i.e. wild encounters in tall grass).
For more information, see the description for
FireRed script command reference
Oh, something else: the R/S/E leftovers prove that this discovery applies to
Advance-generation games. The offsets will differ, and the walking subroutines will have some differences in R/S/E, but the system itself exists in all Pokemon GBA games.
PokeMart as debug input
script compilation at runtime
music: a dreadful tutorial
I'm not active and don't do this kind of stuff anymore. I'm now trying to create my own game engine.
two message boxes at once
[WIP] firered RAM map
list of all known flags/vars in firered
script command ref: 114 complete / 175 documented / 214
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