Developer guide

Getting started

You will first need:

Standard Unix dependencies: curl, unzip, gunzip, md5sum (md5 on Mac)
Rust, at least 1.43. https://www.rust-lang.org/tools/install
On Linux, sudo apt-get install xorg-dev libxcb-shape0-dev or the equivalent for your distro

One-time setup:

Download the repository: git clone https://github.com/dabreegster/abstreet.git
Grab the minimal amount of data to get started: cargo run --bin updater.
Run the game: cd game; cargo run --release

Development tips

Compile faster by just doing cargo run. The executable will have debug stack traces and run more slowly. You can do cargo run --release to build in optimized release mode; compilation will be slower, but the executable much faster.
Some in-game features are turned off by default or don't have a normal menu to access them. The list:
- To toggle developer mode: press Control+S in game, or cargo run -- --dev
- To warp to an object by numeric ID: press Control+j
- To enter debug mode with all sorts of goodies: press Control+D
You can start the game in different modes using flags:
- cargo run -- --dev ../data/system/maps/downtown.bin starts on a particular map
- cargo run ../data/system/scenarios/downtown/weekday.bin starts with a scenario (which is tied to a certain map)
- cargo run -- --challenge=trafficsig/tut2 starts on a particular challenge. See the list of aliases by passing in a bad value here.
- cargo run ../data/player/saves/montlake/no_edits_unnamed/00h00m20.3s.bin restores an exact simulation state. Savestates are found in debug mode (Control+D) -- they're probably confusing for the normal player experience, so they're hidden for now.
- cargo run -- --tutorial=12 starts somewhere in the tutorial
- Adding --edits='name of edits' starts with edits applied to the map.
All code is automatically formatted using https://github.com/rust-lang/rustfmt; please run cargo +nightly fmt before sending a PR. (You have to install the nightly toolchain just for fmt)
More random notes here

Downloading more cities

As data formats change over time, things in the data/ directory not under version control will get out of date. At any time, you can run cargo run --bin updater from the main repository directory to update only the files that have changed.

You can also opt into downloading updates for more cities by editing data/config. Opting into everything looks like this:

runtime: seattle,huge_seattle,austin
input: seattle,huge_seattle,austin

runtime downloads new maps and scenarios in data/system/. input is used for building those maps -- see below.

Building map data

You can skip this section if you're just touching code in game, ezgui, and sim.

The first stage of the importer, --raw, will download input files from OSM, King County GIS, and so on. If the mirrors are slow or the files vanish, you could fill out data/config and use the updater described above to grab the latest input.

To run all pieces of the importer, you'll need some extra dependencies:

osmconvert: See https://wiki.openstreetmap.org/wiki/Osmconvert#Download
libgdal-dev: See https://gdal.org/ if your OS package manager doesn't have this

You can rerun specific stages of the importer:

If you're modifying the initial OSM data -> RawMap conversion in convert_osm, you need ./import.sh --raw --map.
If you're modifying map_model but not the OSM -> RawMap conversion, then you just need ./import.sh --map.
By default, all maps are regenerated. You can also specify a single map: ./import.sh --map downtown.
By default, Seattle is assumed as the city. You have to specify otherwise: ./import.sh --city=los_angeles --map downtown_la.

You can also make the importer import a new city.

Understanding stuff

The docs listed at https://github.com/dabreegster/abstreet#documentation-for-developers explain things like map importing and how the traffic simulation works.

Code organization

If you're going to dig into the code, it helps to know what all the crates are. The most interesting crates are map_model, sim, and game.

Constructing the map:

convert_osm: extract useful data from OpenStreetMap and other data sources, emit intermediate map format
gtfs: simple library to just extract coordinates of bus stops
kml: extract shapes from KML shapefiles
map_model: the final representation of the map, also conversion from the intermediate map format into the final format
map_editor: GUI for modifying geometry of maps and creating maps from scratch
importer: tool to run the entire import pipeline
updater: tool to download/upload large files used in the import pipeline

Traffic simulation:

sim: all of the agent-based simulation logic
headless: tool to run a simulation without any visualization

Graphics:

game: the GUI and main gameplay
ezgui: a GUI and 2D OpenGL rendering library, using glium + winit + glutin

Common utilities:

abstutil: a grab-bag of IO helpers, timing and logging utilities, etc
geom: types for GPS and map-space points, lines, angles, polylines, polygons, circles, durations, speeds

Example guide for implementing a new feature

A/B Street's transit modeling only includes buses as of September 2019. If you wanted to start modeling light rail, you'd have to touch many layers of the code. This is a nice, hefty starter project to understand how everything works. For now, this is just an initial list of considerations -- I haven't designed or implemented this yet.

Poking around the .osm extracts in data/input/seattle/osm/, you'll see a promising relation with route = light_rail. The relation points to individual points (nodes) as stops, and segments of the track (ways). These need to be represented in the initial version of the map, RawMap, and the final version, Map. Stations probably coincide with existing buildings, and tracks could probably be modeled as a special type of road. To remember the order of stations and group everything, there's already a notion of bus route from the gtfs crate that probably works. The convert_osm crate is the place to extract this new data from OSM. It might be worth thinking about how the light rail line gets clipped, since most maps won't include all of the stations -- should those maps just terminate trains at the stations, or should trains go to and from the map border?

Then there are some rendering questions. How should special buildings that act as light rail stations be displayed? What about the track between stations, and how to draw trains moving on the track? The track is sometimes underground, sometimes at-grade with the road (like near Colombia City -- there it even has to somehow be a part of the existing intersections!), and sometimes over the road. How to draw it without being really visually noisy with existing stuff on the ground? Should trains between stations even be drawn at all, or should hovering over stations show some kind of ETA?

For modeling the movement of the trains along the track, I'd actually recommend using the existing driving model. Tracks can be a new LaneType (that gets rendered as nice train tracks, probably), and trains can be a new VehicleType. This way, trains queueing happens for free. There's even existing logic to make buses wait at bus stops and load passengers; maybe that should be extended to load passengers from a building? How should passengers walking to the platform be modeled and rendered -- it takes a few minutes sometimes!

Finally, you'll need to figure out how to make some trips incorporate light rail. Pedestrian trips have the option to use transit or not -- if light rail is modeled properly, it hopefully fits into the existing transit pathfinding and everything, so it'll just naturally happen.

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