Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/pkmn/engine

A minimal, complete, Pokémon battle simulation engine optimized for performance
https://github.com/pkmn/engine

engine game pokemon simulator

Last synced: about 20 hours ago
JSON representation

A minimal, complete, Pokémon battle simulation engine optimized for performance

Awesome Lists containing this project

README 

        


  pkmn/engine

  


  


  

    Test Status

  

  

    WIP

  

  

    License

  




> [!WARNING]  

> **This project is under heavy development** and currently the `main` branch contains numerous breaking

> changes which may not work and which are not fully documented. Please **wait for the forthcoming

> initial v0.1 release** before depending on this project (code from the

> [`old`](https://github.com/pkmn/engine/releases/tag/old) tag can also be used to experiment with a

> more stable version of the codebase).






A minimal, complete, Pokémon battle simulation engine optimized for performance and

[designed](docs/DESIGN.md) for tooling, embedded systems, and [artificial

intelligence](https://github.com/pkmn/0-ERROR) use cases. This engine aims to be a frame-accurate and

[bug-for-bug compatible](http://www.catb.org/jargon/html/B/bug-for-bug-compatible.html)

implementation of both Pokémon battles as defined by the original game code and the [Pokémon

Showdown](https://pokemonshowdown.com/)[^1] simulator which represents Pokémon battling as practically

interpreted online.



The pkmn engine is [**more than 1000× faster**](docs/TESTING.md#results) than the

[patched](docs/TESTING.md#patches) [Pokémon Showdown simulator

code](https://github.com/smogon/pokemon-showdown) when playing out supported formats in

compatibility mode and is extensively [tested](docs/TESTING.md) and [documented](docs). Note,

however, that the engine is **not a fully featured simulator** but is instead a low-level library

which can be used as a building block for more advanced use cases.



## Installation



This repository hosts both the engine code (written in [Zig](https://ziglang.org/)) and the

reference driver code (written in [TypeScript](https://www.typescriptlang.org/)).



### `libpkmn`



Binaries of the engine code can be downloaded from the

[releases](https://github.com/pkmn/engine/releases) tab on GitHub, or you can [download the source

code](https://github.com/pkmn/engine/archive/refs/heads/main.zip) directly and build it with the

latest `zig` compiler, see `zig build --help` for build options:



```sh

$ curl https://github.com/pkmn/engine/archive/refs/heads/main.zip -o engine.zip

$ unzip engine.zip

$ cd engine

$ zig build --prefix /usr/local -Doptimize=ReleaseFast

```



The Zig website has [installation instructions](https://ziglang.org/learn/getting-started/) which

walk through how to install Zig on each platform - the engine code should work on Zig v0.11.0,

though tracks Zig's master branch so this may change in the future if breaking language changes are

introduced. Note that **due to a [bug in the Zig

compiler](https://github.com/ziglang/zig/issues/17768), compiling with a version of Zig before

`0.12.0-dev.876+aaf46187a` is recommended for performance**.



`libpkmn` can be built with `-Dshowdown` to instead produce the Pokémon Showdown compatible

`libpkmn-showdown` library. Furthermore, protocol message logging can be enabled through `-Dlog`.

The `libpkmn` and `libpkmn-showdown` objects available in the binary release are both compiled with

the `-Dlog` flag by default.



### `@pkmn/engine`



The driver code can be installed from [npm](https://www.npmjs.com/package/@pkmn/engine):



```sh

$ npm install @pkmn/engine

```



The driver depends on being able to find compiled Node/WASM addons in

`node_modules/@pkmn/engine/build/lib` to be useful. When you install the package a [`postinstall`

lifecycle script](https://docs.npmjs.com/cli/v8/using-npm/scripts) runs

[`install-pkmn-engine`](src/bin/install-pkmn-engine) which checks for a compatible `zig` compiler

(see earlier regarding minimum version) and download one to `node_module/@pkmn/engine/build/bin` if

it can't find one, as well as looking for (and downloading, if necessary) the required Node headers

needed to successfully build the addons natively.



**If you have configured `npm` to `--ignore-scripts` you must either run `npx install-pkmn-engine`

directly or build the addons manually and place the artifacts in the expected paths.**



### `pkmn`



To include `pkmn`, add it as a dependency in your project's

[`build.zig.zon`](https://github.com/ziglang/zig/blob/master/doc/build.zig.zon.md) using [Zig's

Package Management

system](https://ziglang.org/download/0.11.0/release-notes.html#Package-Management):



```zig

.dependencies = .{

    .pkmn = .{

        .url = "https://github.com/pkmn/engine/archive/RELEASE.tar.gz",

    },

},

```



Replace `RELEASE` with the tag for the [release](https://github.com/pkmn/engine/releases) you wish

to use (e.g. `0.1.0` or `nightly`) or the specific hash of any commit. Next, run `zig build` and

copy the expected hash from the error message into your `build.zig.zon` alongside the `.url`:



```sh

$ zig build

error: dependency is missing hash field

            .url = "https://github.com/pkmn/engine/archive/nightly.tar.gz",

                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

note: expected .hash = "122056b93b403033cb7d9bed96a02c2eb8cc1275515976167726ada6eb4207e8ef8a",

```



Note that this hash is **not** going to be the same as the commit hash. After adding the hash to

your `build.zig.zon` you will be able to import the `pkmn` package's build helpers into your

`build.zig`:



```zig

const std = @import("std");



pub fn build(b: *std.Build) void {

    ...

    const pkmn = b.dependency("pkmn", .{ .showdown = true, .log = true });

    exe.root_module.addImport("pkmn", pkmn.module("pkmn"));

    ...

}

```



The `pkmn` package can be configured with various options such as whether or not Pokémon Showdown

compatibility mode or protocol message logging should be enabled. Alternatively, you may set options

via a `pkmn_options` [root source file

declaration](https://ziglang.org/documentation/master/#Root-Source-File). There are several

undocumented internal options that can be tweaked as well via build or root options, though these

options aren't officially supported, affect correctness, and may change meaning or behavior without

warning. Use at your own risk.



```zig

pub const pkmn_options = .{ .showdown = true, .log = true };

```



## Usage



For each Pokémon generation, the engine provides a battle structure with two functions - a function

to `update` the battle's state based on both players' choices and a function that defines which

`choices` are valid at that decision point (at the beginning of a battle both player's must "pass"

as their first choice to switch in the first member of their party). If `-Dlog` protocol logging is

enabled each update produces logs which can be decoded into a buffer (`LOGS_SIZE` constants are

provided to make it easy to allocate a buffer of the correct size). Each `update` returns a result

to indicate either that the battle has terminated or which types of choices are available for each

player.



Unlike [Pokémon Showdown's

SIM-PROTOCOL](https://github.com/smogon/pokemon-showdown/blob/master/sim/SIM-PROTOCOL.md#choice-requests)

which provides a rich request object at each decision point, the pkmn engine computes the possible

choices on demand based on the result of the previous `update` and the battle state (`CHOICES_SIZE`

is a good size to initialize the buffer passed to `choices`). **Attempting to update the battle with

a choice not present in the options returned by `choices` is undefined behavior and may corrupt

state or cause the engine to crash.**



Battles may be played out from any point but to freshly initialize a battle which is yet to start

the turn count and active Pokémon should be zeroed out (driver code should handle this for you).

Most driver code should also provide helpers to make initializing battle convenient - check the

respective documentation and examples for the bindings being used. The engine's [protocol

documentation](docs/PROTOCOL.md) goes into greater detail on the specifics of updates and the

potential logs that may result.



*The snippets below are meant to merely illustrate in broad strokes how the pkmn engine can be used

\- the [`examples`](examples) directory contains fully commented and runnable code.*



### C



[`pkmn.h`](src/include/pkmn.h) exports the C API for `libpkmn`. Symbols are all prefixed with

`pkmn_` to avoid name collisions. If `-Dlog` is enabled and logging throws an error then the error

is encoded in the `pkmn_result` and can be checked with `pkmn_error`.



```c

#include 



pkmn_battle_options options;

pkmn_gen1_battle_options_set(&options, ...);

pkmn_battle battle = ...;



pkmn_result result;

pkmn_choice c1 = 0, c2 = 0;

while (!pkmn_result_type(result = pkmn_battle_update(&battle, c1, c2, &options))) {

  c1 = choose(PKMN_PLAYER_P1, pkmn_result_p1(result));

  c2 = choose(PKMN_PLAYER_P2, pkmn_result_p2(result));

  pkmn_gen1_battle_options_set(&options, ...);

}

if (pkmn_error(result)) exit(1);

```



[(full code)](examples/c/example.c)



The C API doesn't export any helpers for creating or accessing the opaque battle objects - it's

instead intended to be used as the foundation for more ergonomic bindings in [other

languages](#other) (the lack of namespaces and bit fields having an implementation-defined layout in

C are the main contributing factors to the sparseness of what `libpkmn` chooses to expose).



### JavaScript / TypeScript



`@pkmn/engine` depends on the [`@pkmn/data`](https://www.npmjs.com/package/@pkmn/data) package which

requires a `Dex` implementation to be provided as well. The `Battle.create` function can be used to

initialize a `Battle` from the beginning, or `Battle.restore` can be used to re-instantiate a battle

which is already in progress. If logging is enabled the output can be turned into Pokémon Showdown

protocol via `Log.parse`.



```ts

import {Dex} from '@pkmn/dex';

import {Generations} from '@pkmn/data';

import {Battle, Choice} from '@pkmn/engine';



const gens = new Generations(Dex);

const battle = Battle.create(...);



const choose = (choices: Choice[]) =>

  choices[Math.floor(Math.random() * choices.length)];



let result: Result;

let c1: Choice, c2: Choice;

while (!(result = battle.update(c1, c2)).type) {

  c1 = choose(battle.choices('p1', result));

  c2 = choose(battle.choices('p2', result));

}



console.log(result);

```



[(full code)](examples/js/example.ts)



By default, the `@pkmn/engine` package compiles the engine with `-Dshowdown`, though by running

`install-pkmn-engine` directly and passing in `--options` you can override this default and build

different configurations of the extension for the driver to use. The driver can support

configurations both with and without Pokémon Showdown compatibility simultaneously if present. On

update, the post-install script attempts to rebuild whichever extensions it finds with the same

configuration parameters that were originally used meaning updating to the newest version of the

library should be seamless.



Despite relying on the native engine code, the `@pkmn/engine` code is designed to also work in

browsers which support [WebAssembly](https://webassembly.org/). Running `npm run start:web` from the

[`examples`](examples/js) directory starts a server that can be used to demonstrate the engine

running in the browser.



### Zig



The `pkmn` Zig package exposes helper methods to simplify state instantiation and any `Writer` can

be used when logging is enabled to allow for easily printing e.g. to standard out or a buffer.



```zig

const std = @import("std");

const pkmn = @import("pkmn");



var random = std.Random.DefaultPrng.init(seed).random();

var choices: [pkmn.CHOICES_SIZE]pkmn.Choice = undefined;



var battle = ...

var options = pkmn.battle.options(...);



var c1 = pkmn.Choice{};

var c2 = pkmn.Choice{};



var result = try battle.update(c1, c2, &options);

while (result.type == .None) : (result = try battle.update(c1, c2, &options)) {

    c1 = choices[random.uintLessThan(u8, battle.choices(.P1, result.p1, &choices))];

    c2 = choices[random.uintLessThan(u8, battle.choices(.P2, result.p2, &choices))];

}



std.debug.print("{}\n", .{result.type});

```



[(full code)](examples/zig/example.zig)



The Zig package also supports some APIs which are difficult to expose elsewhere such as the

`FixedRNG` which allows you to fully specify the exact RNG frames (which can be useful for ensuring

certain outcomes/effects always occur) for a battle, though doing so changes the size of the

`Battle` object.



### Other



Developers who wish to use the engine in other languages should find writing bindings against

[`libpkmn`](#libpkmn) relatively straightforward based on the existing documentation, though to

simplify the process even further [`src/data`](src/data) contains JSON dumps of all of the Pokémon

data, structure sizes and offsets, and protocol information used by the reference driver code. The

following is a list of known `libpkmn` bindings written by developers outside of the [pkmn

organization](https://github.com/pkmn) that may be helpful (though note that these projects may not

necessarily be up-to-date/complete/correct - inclusion in this list doesn't imply endorsement):



| Language   | License   | URL                                  |

| ---------- | --------- | ------------------------------------ |

| **C++**    | `BSL-1.0` | https://github.com/pasyg/wrapsire    |

| **Python** | `MIT`     | https://github.com/AnnikaCodes/PyKMN |



#### `pkmn-debug`



The [`@pkmn/engine`](#pkmnengine) package ships with a `pkmn-debug` tool which exists to decode the

binary data structures and protocols used by the engine and to output a [standalone

webpage](https://pkmn.cc/debug.html) that can be used for debugging. To use this tool in a folder

that has the `@pkmn/engine` package installed locally you can use `npx pkmn-debug`, though you may

also wish to install the package globally to be able to use this tool anywhere without

[`npx`](https://docs.npmjs.com/cli/v7/commands/npx):



```sh

$ npm install --global @pkmn/engine

```



By default, `pkmn-debug` expects to read [binary debug protocol](docs/PROTOCOL.md#debugging) from

[standard input](https://en.wikipedia.org/wiki/Standard_streams) and output HTML to standard output:



```sh

$  | pkmn-debug > index.html

```



Alternatively, if a single filename argument is passed to the `pkmn-debug` it reads from that

instead:



```sh

$ pkmn-debug  > index.html

```



## Status



The engine is currently expected to be developed over multiple stages:



| Stage   | Deliverables                                    |

| ------- | ----------------------------------------------- |

| **0**   | documentation, integration, benchmark, protocol |

| **1**   | RBY & GSC                                       |

| **2**   | ADV & DPP                                       |

| ***3*** | *modern generations*                            |



Currently, most of the foundational work from stage 0 is done:

  

- [benchmark and integration testing](src/test) infrastructure

- [documentation](docs) about design, research, methodology, etc

- definition and implementation of the [protocol](docs/PROTOCOL.md) that's used by the engine



**Stage 1 is currently in progress** and involves the implementation of the actual Generation I & II

battle engines, followed by Generation III & IV in stage 2. The implementation of further Pokémon

generations is in scope for the project but shouldn't be considered part of the immediate roadmap

(i.e. exploring the options for broadening support for old generation APIs is given higher priority

than implementing more modern generations). Furthermore, implementation of modern generations is

soft-blocked on the [availability of high quality

decompilations](https://github.com/orgs/pret/repositories) of the original games in question.



Certain features will always be deemed **out of scope**:



- team/set validation or custom rule ("format") enforcement

- first-class support for "mods" to core Pokémon data and mechanics

- [battle variants](https://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_battle#Battle_variants)

  other than single (full) or double battles

- code for exposing the engine to users (input validation, game socket server, etc)



## License



The pkmn engine is distributed under the terms of the [MIT License](LICENSE).



[^1]: In the case of Pokémon Showdown, only bugs which stem from a misimplementation of specific

  effects are reproduced in the engine, bugs which are the result of a misunderstanding of the

  fundamental mechanics of Pokémon or which simply arise due to specific Pokémon Showdown

  implementation details that aren't replicable without making the same (incorrect) architectural

  choices aren't. Furthermore, the "Pokémon Showdown" code referenced by this project includes

  several [patches](docs/TESTING.md#patches) to improve accuracy and smooth over some of the more

  egregious implementation issues. In practical terms, the vast majority of games played out in the

  pkmn engine's compatibility mode and on this patched Pokémon Showdown simulator are the same,

  it's only in a well defined and documented set of circumstances where the two implementations

  diverge.