I love Pokémon. My fascination with the series began with the original games released in the US, Pokémon Red and Blue (I had the Blue version).
In the past few years, people have been disassembling Pokémon games. You can check these out for Pokémon Red and Blue, Crystal, Emerald, and others. It’s really cool to be able to compile and build a game that was such a huge part of my youth.
I thought it would be fun to play with this source code, viewing these games through a new lens. A few months ago, I discovered Graphviz, a software package for rendering graphs written in the Dot language. Dot is a very simple language, and it’s easy to filter data into its format. Graphviz includes some command line tools that can render dot files to nice human-readable output. Let’s see how we can use Graphviz to visualize Pokémon Red and Blue.
Inside of pokered, there’s a data directory with a mapHeaders subdirectory inside. mapHeaders includes metadata about every overworld map in the game. This includes the connections between maps. For example, here is the metadata for Route 10:
$ cat Route10.asm
Route10_h:
db OVERWORLD ; tileset
db ROUTE_10_HEIGHT, ROUTE_10_WIDTH ; dimensions (y, x)
dw Route10_Blocks ; blocks
dw Route10_TextPointers ; texts
dw Route10_Script ; scripts
db SOUTH | WEST ; connections
SOUTH_MAP_CONNECTION ROUTE_10, LAVENDER_TOWN, 0, 0, LavenderTown_Blocks
WEST_MAP_CONNECTION ROUTE_10, ROUTE_9, 0, 0, Route9_Blocks
dw Route10_Object ; objects
So south of Route 10 is Lavender Town, and west is Route 9. We can use this connection data and some simple uses of grep and awk to generate Dot code representing these connections. The following commands are all run from /data/mapHeaders in the pokered repository. First, we use grep to see the connections:
$ grep -R "MAP_CONNECTION" ./
.//PewterCity.asm: SOUTH_MAP_CONNECTION PEWTER_CITY, ROUTE_2, 5, 0, Route2_Blocks
.//PewterCity.asm: EAST_MAP_CONNECTION PEWTER_CITY, ROUTE_3, 4, 0, Route3_Blocks
...
Next, let’s pipe that to awk to print the endpoints of that connection:
$ grep -R "MAP_CONNECTION" ./ | awk -F" " '{ print $3 $4; }'
PEWTER_CITY,ROUTE_2,
PEWTER_CITY,ROUTE_3,
...
We can use a second awk invocation to print these as Dot edges:
$ grep -R "MAP_CONNECTION" ./ | awk -F" " '{ print $3 $4; }' | awk -F"," '{ print $1" -- "$2 }'
PEWTER_CITY -- ROUTE_2
PEWTER_CITY -- ROUTE_3
...
Undirected Dot edges are represented with the two nodes and a -- between them.
We can represent a strict (one connection between nodes) graph (non-directed, as these are bidirectional connections) by wrapping all these connections in a strict graph {}:
strict graph {
PEWTER_CITY -- ROUTE_2
PEWTER_CITY -- ROUTE_3
...
We can add two other options (overlap=false to avoid edge overlap and splines=true to use splines for edges) to get a better looking graph. Here’s my pokemon_rb_towns_and_routes.dot generated from the above steps:
strict graph {
overlap=false;
splines=true;
PEWTER_CITY -- ROUTE_2
PEWTER_CITY -- ROUTE_3
CELADON_CITY -- ROUTE_16
CELADON_CITY -- ROUTE_7
ROUTE_9 -- CERULEAN_CITY
ROUTE_9 -- ROUTE_10
ROUTE_8 -- SAFFRON_CITY
ROUTE_8 -- LAVENDER_TOWN
ROUTE_21 -- PALLET_TOWN
ROUTE_21 -- CINNABAR_ISLAND
ROUTE_20 -- CINNABAR_ISLAND
ROUTE_20 -- ROUTE_19
ROUTE_22 -- ROUTE_23
ROUTE_22 -- VIRIDIAN_CITY
PALLET_TOWN -- ROUTE_1
PALLET_TOWN -- ROUTE_21
ROUTE_23 -- INDIGO_PLATEAU
ROUTE_23 -- ROUTE_22
VERMILION_CITY -- ROUTE_6
VERMILION_CITY -- ROUTE_11
ROUTE_24 -- CERULEAN_CITY
ROUTE_24 -- ROUTE_25
ROUTE_18 -- ROUTE_17
ROUTE_18 -- FUCHSIA_CITY
ROUTE_19 -- FUCHSIA_CITY
ROUTE_19 -- ROUTE_20
ROUTE_25 -- ROUTE_24
LAVENDER_TOWN -- ROUTE_10
LAVENDER_TOWN -- ROUTE_12
LAVENDER_TOWN -- ROUTE_8
ROUTE_14 -- ROUTE_15
ROUTE_14 -- ROUTE_13
ROUTE_15 -- FUCHSIA_CITY
ROUTE_15 -- ROUTE_14
ROUTE_17 -- ROUTE_16
ROUTE_17 -- ROUTE_18
ROUTE_16 -- ROUTE_17
ROUTE_16 -- CELADON_CITY
ROUTE_12 -- LAVENDER_TOWN
ROUTE_12 -- ROUTE_13
ROUTE_12 -- ROUTE_11
ROUTE_13 -- ROUTE_12
ROUTE_13 -- ROUTE_14
ROUTE_11 -- VERMILION_CITY
ROUTE_11 -- ROUTE_12
CERULEAN_CITY -- ROUTE_24
CERULEAN_CITY -- ROUTE_5
CERULEAN_CITY -- ROUTE_4
CERULEAN_CITY -- ROUTE_9
ROUTE_10 -- LAVENDER_TOWN
ROUTE_10 -- ROUTE_9
ROUTE_5 -- CERULEAN_CITY
ROUTE_5 -- SAFFRON_CITY
FUCHSIA_CITY -- ROUTE_19
FUCHSIA_CITY -- ROUTE_18
FUCHSIA_CITY -- ROUTE_15
SAFFRON_CITY -- ROUTE_5
SAFFRON_CITY -- ROUTE_6
SAFFRON_CITY -- ROUTE_7
SAFFRON_CITY -- ROUTE_8
ROUTE_4 -- ROUTE_3
ROUTE_4 -- CERULEAN_CITY
ROUTE_6 -- SAFFRON_CITY
ROUTE_6 -- VERMILION_CITY
VIRIDIAN_CITY -- ROUTE_2
VIRIDIAN_CITY -- ROUTE_1
VIRIDIAN_CITY -- ROUTE_22
INDIGO_PLATEAU -- ROUTE_23
ROUTE_7 -- CELADON_CITY
ROUTE_7 -- SAFFRON_CITY
ROUTE_3 -- ROUTE_4
ROUTE_3 -- PEWTER_CITY
ROUTE_2 -- PEWTER_CITY
ROUTE_2 -- VIRIDIAN_CITY
CINNABAR_ISLAND -- ROUTE_21
CINNABAR_ISLAND -- ROUTE_20
ROUTE_1 -- VIRIDIAN_CITY
ROUTE_1 -- PALLET_TOWN
}
We can use a simple invocation of neato to produce a PDF file with:
neato -Tpdf pokemon_rb_towns_and_routes.dot > pokemon_rb_towns_and_routes.pdf
Check it out:
(OK, so towns and routes are cool. Can we augment this file to include buildings, tunnels, and rooms? There are warp and warp_to markers in the files in /data/mapObjects. For example, let’s look at SaffronCity.asm:
$ cat data/mapObjects/SaffronCity.asm
SaffronCity_Object:
db $f ; border block
db 8 ; warps
warp 7, 5, 0, COPYCATS_HOUSE_1F
warp 26, 3, 0, FIGHTING_DOJO
warp 34, 3, 0, SAFFRON_GYM
warp 13, 11, 0, SAFFRON_PIDGEY_HOUSE
warp 25, 11, 0, SAFFRON_MART
warp 18, 21, 0, SILPH_CO_1F
warp 9, 29, 0, SAFFRON_POKECENTER
warp 29, 29, 0, MR_PSYCHICS_HOUSE
...
; warp-to
warp_to 7, 5, SAFFRON_CITY_WIDTH ; COPYCATS_HOUSE_1F
warp_to 26, 3, SAFFRON_CITY_WIDTH ; FIGHTING_DOJO
warp_to 34, 3, SAFFRON_CITY_WIDTH ; SAFFRON_GYM
warp_to 13, 11, SAFFRON_CITY_WIDTH ; SAFFRON_PIDGEY_HOUSE
warp_to 25, 11, SAFFRON_CITY_WIDTH ; SAFFRON_MART
warp_to 18, 21, SAFFRON_CITY_WIDTH ; SILPH_CO_1F
warp_to 9, 29, SAFFRON_CITY_WIDTH ; SAFFRON_POKECENTER
warp_to 29, 29, SAFFRON_CITY_WIDTH ; MR_PSYCHICS_HOUSE
...
(These _WIDTH suffixes seem to indicate the coordinates are inside of the width of the map. We’ll clean them up later.)
So, if we parse out the warp_to statements, we should be able to get a more complete view of the game’s locations and how they connect. Let’s start with a simple grep to find all the warp_to statements (run from /data/mapObjects):
grep -R "warp_to " ./
.//RocketHideoutB4F.asm: warp_to 19, 10, ROCKET_HIDEOUT_B4F_WIDTH ; ROCKET_HIDEOUT_B3F
.//RocketHideoutB4F.asm: warp_to 24, 15, ROCKET_HIDEOUT_B4F_WIDTH ; ROCKET_HIDEOUT_ELEVATOR
.//RocketHideoutB4F.asm: warp_to 25, 15, ROCKET_HIDEOUT_B4F_WIDTH ; ROCKET_HIDEOUT_ELEVATOR
...
Next, pipe to awk to find the endpoints of the warp:
$ grep -R "warp_to " ./ | awk -F"," '{ print $3; }'
ROCKET_HIDEOUT_B4F_WIDTH ; ROCKET_HIDEOUT_B3F
ROCKET_HIDEOUT_B4F_WIDTH ; ROCKET_HIDEOUT_ELEVATOR
ROCKET_HIDEOUT_B4F_WIDTH ; ROCKET_HIDEOUT_ELEVATOR
CELADON_MART_3F_WIDTH ; CELADON_MART_4F
CELADON_MART_3F_WIDTH ; CELADON_MART_2F
CELADON_MART_3F_WIDTH ; CELADON_MART_ELEVATOR
BRUNOS_ROOM_WIDTH ; LORELEIS_ROOM
BRUNOS_ROOM_WIDTH ; LORELEIS_ROOM
BRUNOS_ROOM_WIDTH ; AGATHAS_ROOM
BRUNOS_ROOM_WIDTH ; AGATHAS_ROOM
BIKE_SHOP_WIDTH
...
This is close, but includes some warps that appear to point to themselves (like BIKE_SHOP_WIDTH above). No problem - we can only print lines with ; in them using grep:
$ grep -R "warp_to " ./ | awk -F"," '{ print $3; }' | grep ";"
ROCKET_HIDEOUT_B4F_WIDTH ; ROCKET_HIDEOUT_B3F
ROCKET_HIDEOUT_B4F_WIDTH ; ROCKET_HIDEOUT_ELEVATOR
ROCKET_HIDEOUT_B4F_WIDTH ; ROCKET_HIDEOUT_ELEVATOR
CELADON_MART_3F_WIDTH ; CELADON_MART_4F
CELADON_MART_3F_WIDTH ; CELADON_MART_2F
CELADON_MART_3F_WIDTH ; CELADON_MART_ELEVATOR
...
OK, almost done. Next, let’s strip out the _WIDTH text and put in edge connections:
$ grep -R "warp_to " ./ | awk -F"," '{ print $3; }' | grep ";" | sed -e "s/_WIDTH//" | sed -e "s/;/--/"
ROCKET_HIDEOUT_B4F -- ROCKET_HIDEOUT_B3F
ROCKET_HIDEOUT_B4F -- ROCKET_HIDEOUT_ELEVATOR
ROCKET_HIDEOUT_B4F -- ROCKET_HIDEOUT_ELEVATOR
CELADON_MART_3F -- CELADON_MART_4F
CELADON_MART_3F -- CELADON_MART_2F
CELADON_MART_3F -- CELADON_MART_ELEVATOR
...
(note the leading space here - not a big deal for the Graphviz tools)
Now, we’ll put this all into a pokemon_rb_all.dot file (along with the connections from pokemon_rb_towns_and_routes.dot) to make a graph of all of the locations in Pokémon Red and Blue. For this invocation, I also used neato:
neato -Tpdf pokemon_rb_all.dot > pokemon_rb_all.pdf
This graph is so cool! Check it out:
(PDF file here, dot file here)
There are so many sections of this graph with interesting details, like Victory Road leading into the Indigo Plateau and Elite Four:
Or the maze-like Silph Company building:
I think it’s really cool how easy it is to use simple tools to see these games from a new angle. I hope to look at other aspects of these games sometime in the future.