prsm/packages/ngn

ngn

An ECS framework (and robust input system) for the web.

• Comprehensive sample
• Installation
• API overview
  • createWorld
    • Entities
    • Components
      • Extending components
    • Scene Management
  • Extras
    • Keyboard, mouse and gamepad input
      • Input system
      • ButtonState
      • Mouse
      • Keyboard
      • Gamepad
      • Input usage examples
        • Gamepad
        • Keyboard
        • Mouse
    • Expiring log system

Comprehensive sample

import merge from "lodash/merge";
import { createWorld, type WorldState } from "@prsm/ngn";
import {
  inputSystem,
  gamepad,
  GamepadMapping,
  SCUFVantage2,
  onGamepadConnected,
} from "@prsm/ngn/input";

// Create a mapping with unique button/key names.
const MyMapping = (): GamepadMapping => {
  return merge(SCUFVantage2(), {
    axes: {
      2: "LookHorizontal",
      3: "LookVertical",
    },
    buttons: {
      0: "Sprint", // X
      2: "Jump", // ■
      3: "Action", // ▲
    },
  });
};

// Assign this mapping to gamepads when they connect.
onGamepadConnected((e: GamepadEvent) => {
  gamepad(e.gamepad.index).useMapping(MyMapping);
});

// Create a world
const {
  state,
  query,
  createEntity,
  addSystem,
  start,
  step,
  defineMain,
} = createWorld();

// Create components
const Position = () => ({ x: 0, y: 0 });
const Velocity = () => ({ x: 0, y: 0 });
const Alive = () => ({});
const Dead = () => ({});

// Create entities
const player =
  createEntity()
    .addComponent(Position)
    .addComponent(Velocity)
    .addComponent(Alive)
    .addTag("player");

// Create a bunch of monsters
Array
  .from(Array(50))
  .forEach((i) =>
    createEntity({ name: `monster ${i}`, hp: 100 })
      .addComponent(Position)
      .addComponent(Velocity)
      .addComponent(Alive)
      .addTag("monster");

// Create queries
const movables = query({ and: [Position, Velocity] });
const livingMonsters = query({ tag: ["monster"], and: [Alive] });
const deadOrAliveMonsters = query({ tag: ["monster"], or: [Dead, Alive] });

// Create systems
const moveSystem = (_: WorldState) => {
  movables((results) => {
    results.forEach(({ entity, Position, Velocity }) => {
      Position.x += Velocity.x;
      Position.y += Velocity.y;
    });
  });
};

const monsterDeathSystem = (_: WorldState) => {
  livingMonsters((results) => {
    results.forEach(({ entity }) => {
      if (entity.hp <= 0) {
        entity.removeComponent(Alive);
      }
    })
  });

  // Just for demonstration of 'or' query results:
  deadOrAliveMonsters((results) => {
    // Since this query uses 'or', `Dead` OR `Alive` will be
    // present on the results. You will need to check for existence:
    results.forEach(({ entity, Dead, Alive }) => {
      if (Dead) { }
      if (Alive) { }
    });
  });
};

const gravitySystem = (w: WorldState) => {
  movables((results) => {
    results.
      forEach(({ Velocity }) => {
        Velocity.y += 4.9 * w.time.delta;
      })
  });
};

const playerControlSystem = (_: WorldState) => {
  if (gamepad(0).getButton("Jump").justPressed) {
    player.getComponent(Velocity).y = 1;
  }
};

// Add or remove systems at any time
addSystem(inputSystem, moveSystem, monsterDeathSystem);

// Finally, define your main entry point with `defineMain`:
defineMain(() => {
  // Once `start` is called, this will be called every frame.

  // Call `step` to call each registered system, passing the state of the world to each.
  //
  // This is intentionally handled by *you*, because there's a good chance
  // you'd prefer to dictate the order of execution here.
  step();
});

start();

Installation

npm install @prsm/ngn

API overview

createWorld

const { state, createEntity, getEntity, onEntityCreated, query, addSystem, removeSystem, start, stop, step } = createWorld();

• state

  • Stores all the entities.
  • Tracks relationships between entities and components for fast lookups.
  • Tracks query dependencies and caches results.
  • Is passed to all systems (if you use ngn's system mechanics, which is optional).
  • Contains a useful time object that looks like:
  • state.time.delta - time since last frame in ms, scaled by time.scale. Use this value for all physics and movement calculations to ensure they respect the time scale.
  • state.time.rawDelta - raw, unscaled time since last frame in ms. This is the actual time between render frames and doesn't change with time scale.
  • state.time.loopDelta - time since last call to main game loop, affected by scale.
  • state.time.scale - time scale. (default: 1).
    • Does not affect framerate at all. The scale affects both how often the main game loop is called and the delta time used for physics/movement calculations. At a scale of 1, the main loop is called every frame and delta equals rawDelta. At a scale of 0.5, the main loop is called approximately every other frame and delta is half of rawDelta.

  Important: Time scaling separates rendering framerate from simulation speed. The game will always render at the device's refresh rate (e.g., 60fps), but the simulation speed (how fast objects move, animations play, etc.) is controlled by the time scale. Always use delta in your movement and physics calculations to ensure they respect the time scale:

  // This will move at half speed when time.scale is 0.5
  position.x += velocity.x * state.time.delta;
  

  • state.time.elapsed - time since start was called in ms.
  • state.time.fps - frames per second.

  Note: The "last frame" and "last call to main game loop" are different concepts. The engine always runs at the device's refresh rate (e.g. 60fps), so rawDelta and delta update every frame. However, the main game loop (where your game logic runs) may be called less frequently based on the time scale. For example, at scale 0.5, the main game loop runs every other frame, resulting in a loopDelta that's approximately twice the delta.

This table may help provide clarity to the behavior of time.scale:

scale	fps	rawDelta	delta	loopDelta	Description
1	60	16.67	16.67	16.67	Normal speed - main loop called exactly once per frame
0.5	60	16.67	8.33	33.34	Half speed - main loop called every ~2 frames
2.0	60	16.67	33.34	8.33	Double speed - main loop called ~twice per frame

The engine always renders at the device's refresh rate (fps), but the frequency of main loop calls and the simulation time (delta) are affected by the time scale.

Entities

• World > createEntity

  const { id, addTag, removeTag, getTag, addComponent, hasComponent, getComponent, removeComponent, destroy } = createEntity({ optional: "default values" });
  

  Forcefully setting the entity ID

  You can forcefully set the entity ID by providing it as one of the properties of the object passed to createEntity. This is a feature that's probably not very useful in the context of this library alone, but this is a critical feature that @prsm/ngn-net relies on. An authoritative game server must be able to assign IDs to entities.

  // IDs are not numbers, but this example serves to
  // illustrate a behavior.
  
  // This entity will have id 1 (not really, but go with it).
  const firstEntity = createEntity();
  // Now this entity has id 1, and `firstEntity` has id 2.
  const secondEntity = createEntity({ id: 1 });
  // This entity has id 3.
  const thirdEntity = createEntity();
  

  • Entity > addTag

    Adds a tag to the entity. Tags are only useful for querying entities. An entity can only have one tag.

    entity.addTag("coin");
    

  • Entity > removeTag

    Removes the tag from the entity.

    entity.removeTag();
    

  • Entity > getTag

    Returns the tag of the entity.

    const tag = entity.getTag();
    

  • Entity > destroy

    Destroys the entity. Removes it from the world.

    entity.destroy();
    

• World > getEntity

  Returns the entity with the given ID.

  const entity = getEntity("ngnluxhlpj30271be3f727d31");
  

Components

• Entity > addComponent

  Adds a component to the entity. Components are functions that return an object. An entity can only have one of each type of a component. Components are just stored as an array of objects on the entity.

  const Position = () => ({ x: 50, y: 50 });
  const Velocity = () => ({ x: 0, y: 0 });
  entity.addComponent(Position).addComponent(Velocity);
  
  // entity:
  // {
  //   ...,
  //   components: [
  //     { x: 50, y: 50 }, <-- Position
  //     { x: 0, y: 0 },   <-- Velocity
  //   ],
  // }
  

  If the object returned by the component function includes an onAttach function, it is called at this time.

  const MeshComponent = () => ({
    entityId: null,
    mesh: null,
    onAttach(entity: Entity) {
      this.entityId = entity.id;
    },
  });
  

  You can override default values:

  entity.addComponent(Position, { y: 10 });
  
  // entity:
  // {
  //   ...,
  //   components: [
  //     { x: 50, y: 10 }, <-- Position
  //   ],
  // }
  

• Entity > hasComponent

  Returns true if the entity has the component.

  const hasPosition = entity.hasComponent(Position);
  

• Entity > getComponent

  Returns the component of the entity.

  const position = entity.getComponent<typeof Position>(Position);
  

• Entity > removeComponent

  Removes the component from the entity. Provide either the component function or the string name of the component (.name property).

  entity.removeComponent(Position);
  // is the same as:
  entity.removeComponent("Position");
  

  If the object returned by the component function includes an onDetach function, it is called at this time.

  const MeshComponent = () => ({
    mesh: null,
    onDetach(entity: Entity) {
      if (mesh) {
        dispose(mesh);
      }
    },
  });
  

Extending components

Occasionally you will want to override the component defaults when instantiating a component.

You can do something like addComponent(Position, { y: CURRENT_Y }), but for something more generic you can extend the component:

import { extend } from "@prsm/ngn";

const Health = () => ({ max: 100 });
const WarriorHealth = extend(Health)({ max: 200 });
const MageHealth = extend(Health)({ max: 75 });

// Internally, `WarriorHealth` and `MageHealth` are still
// identified as a `Health` components.
// This means that queries that match against `Health` will be updated
// to include anything that has `WarriorHealth` or `MageHealth`.

warriorEntity.addComponent(WarriorHealth));

const mortals = query({ and: [Health] });

mortals((results) => {
  // results includes warriorEntity
});

• World > query

  Queries the world for entities with the given tags and components.

  query returns a function that accepts a callback. The callback is immediately called with an array of results. Each result is an object that contains an entity key, and a key for each component that is found on the entity.

  query accepts an object with the following properties:

  {
    and: [], // matched Entities will have all of these components
    or: [], // matched Entities will have any of these components
    not: [], // matched Entities will have none of these components
    tags: [], // matched Entities will have any of these tags
  }
  

  createEntity().addComponent(Position).addComponent(Velocity);
  createEntity().addComponent(Position).addComponent(Velocity).addComponent(Dead);
  
  const movables = query({ and: [Position, Velocity], not: [Dead] });
  
  movables((results) => {
    results.forEach(({ Position, Velocity }) => {
      Position.x += Velocity.x;
      Position.y += Velocity.y;
    });
  });
  

  For optimum performance, query results are cached while entity state is clean. When an entity is created, destroyed, or has a component added or removed, the cache is invalidated.

• World > addSystem

  Adds a system to the world. Systems are either:

  • A function that receives the WorldState as its only argument.
  • An object with an update function that receives the WorldState as its only argument.
  • An instance of a class that has an update function that receives the WorldState as its only argument.

  None of these need to return anything, and the WorldState they receive is mutable.

  Systems are called in the order they were added.

  const MovementSystem = (state: WorldState) => {};
  addSystem(MovementSystem);
  
  const MovementSystem = { update: (state: WorldState) => {} };
  addSystem(MovementSystem);
  
  class MovementSystem {
    update(state: WorldState) {}
  }
  addSystem(new MovementSystem());
  

• World > removeSystem

  Removes a system from the world. Preserves the order of the remaining systems.

  removeSystem(movableSystem);
  

  World > defineMain

  Defines the main program loop. The callback will be called every frame once start is called.

  defineMain(() => {
    // ..
  });
  

• World > start

  Starts the main program loop. Does not do anything other than call the callback provided to defineMain.

  You can use your own loop instead of this one if you prefer, but the builtin loop does things like calculate fps and frame delta for you. These values are stored in state.time. If you create your own loop, it would be a good idea to calculate these values yourself and populate state.time with them.

  start();
  

• World > stop

  Stops the main program loop (which was defined by passing it to defineMain).

  // if gameover, or something
  stop();
  

Scene Management

NGN doesn't enforce any specific scene management pattern, giving you the freedom to implement what works best for your game. The simplest approach is to use separate worlds as scenes:

// Create different worlds for different scenes
const menuScene = createWorld();
const gameScene = createWorld();
const pauseScene = createWorld();

// Configure each scene
menuScene.defineMain(() => { /* menu logic */ });
gameScene.defineMain(() => { /* game logic */ });

// Track current scene
let currentScene = menuScene;

// Switch scenes
function switchToScene(newScene) {
  currentScene.stop();
  currentScene = newScene;
  currentScene.start();
}

// Start with menu
menuScene.start();

// Later, switch to game
switchToScene(gameScene);

• World > step

  Calls all systems once. Passes the WorldState to each system. You should do this in your main program loop, e.g.:

  const main = () => {
    step();
  };
  
  defineMain(main);
  
  start();
  
  // later on:
  stop();
  

Extras

Some completely optional extras are provided.

Keyboard, mouse and gamepad input

Input system

This input system recognizes keyboard, mouse and gamepad input and has a simple API.

There is a provided input system that is responsible for deriving the state of devices from their inputs. Import it, and make sure it's called before any systems that depend on the latest input state.

import { inputSystem } from "@prsm/ngn/input";

world.addSystem(inputSystem);

ButtonState

For keyboard and mouse devices, the state of a button is represented as a ButtonState object:

export interface ButtonState {
  // This is true for one frame only.
  justPressed: boolean;
  // This is true for as long as the button is being pressed.
  pressed: boolean;
  // This is true for one frame only.
  justReleased: boolean;
}

Gamepad button state is represented as a GamepadButtonState object:

export interface GamepadButtonState extends ButtonState {
  // This is true for as long as the button is being touched (e.g. the touchpad on a PS5 controller)
  touched: boolean;
  // This is the value of the button, between 0 and 1. For triggers, this is the amount the trigger is pressed.
  value: number;
}

Mouse

import { mouse } from "@prsm/ngn/input";

• useMapping

  mouse.useMapping(m: MouseMapping): void
  

  Defines a human-readable mapping to mouse buttons and axes.

  By default, the StandardMouse mapping is used and you probably don't need to call this.

• getButton

  mouse.getButton(): ButtonState
  

  Returns the state of a mouse button, e.g.:

  const { pressed, justPressed, justReleased } = mouse.getButton("Mouse1");
  

• getAxis

  mouse.getAxis(axis: string): number
  

  Returns the value of a mouse axis. With the StandardMouse mapping, the axes are: Horizontal, Vertical, and Wheel.

• getPosition

  mouse.getPosition(): { x: number, y: number }
  

  Returns the position of the mouse relative to the window.

• getAcceleration

  mouse.getAcceleration(): number
  

  Returns the acceleration of the mouse.

Keyboard

import { keyboard } from "@prsm/ngn/input";

• useMapping

  keyboard.useMapping(m: KeyboardMapping): void
  

  Defines a human-readable mapping to keyboard keys.

  By default, the StandardKeyboard mapping is used and you probably don't need to call this, unless you want to rename some keys:

  import { StandardKeyboard } from "@prsm/ngn";
  
  const MyKeyboardMapping = (): KeyboardMapping => {
    return {
      ...StandardKeyboard(),
      [KeyboardKey.Space]: "Jump",
      [KeyboardKey.KeyC]: "FireLazerz",
    };
  };
  
  keyboard.useMapping(MyKeyboardMapping);
  keyboard.getKey("FireLazerz");
  

• getKey

  keyboard.getKey(b: string): ButtonState
  

  Returns the state of a keyboard key. The key should be the human readable name value defined in the mapping used.

Gamepad

import { gamepad } from "@prsm/ngn/input";

• useMapping

  gamepad(index: number).useMapping(m: GamepadMapping): void
  

  Defines a human-readable mapping to gamepad buttons and axes.

  The default mapping is assigned by inspecting the Gamepad.id property.

  You can see all of the built-in mappings here, which includes mappings for PlayStation5, Xbox, and SCUF Vantage 2 controllers.

  PRs that add additional mappings are welcome!

• getButton

  gamepad(index: number).getButton(button: string): GamepadButtonState
  

  Returns the state of a gamepad button.

• getAxis

  gamepad(index: number).getAxis(axis: string): number
  

  Returns the value of a gamepad axis.

  if (gamepad(0).getAxis("Look") < 0) {
    /* Left */
  }
  

• device

  gamepad(index: number).device: Gamepad
  

  Returns the Gamepad object from the navigator at the provided index.

• rumble

  gamepad(index: number).rumble(options: RumbleOptions): void
  

  Rumble the device.

  gamepad(1).rumble({
    startDelay: 0,
    duration: 500,
    strongMagnitude: 1.0,
    weakMagnitude: 1.0,
  });
  

Input usage examples

Gamepad

import { keyboard, mouse, gamepad } from "@prsm/ngn/input";

if (gamepad(0).getAxis("Look") < 0) {
  /* Left */
}
if (gamepad(0).getAxis("Look") > 0) {
  /* Right */
}

gamepad(1).rumble({
  startDelay: 0,
  duration: 500,
  strongMagnitude: 1.0,
  weakMagnitude: 1.0,
});

Keyboard

import { keyboard } from "@prsm/ngn/input";

if (keyboard.getKey("Space").justPressed) {
  /* Jump! */
}

Mouse

import { mouse } from "@prsm/ngn/input";

if (mouse.getAxis("Wheel")) {
  /* Scrolling */
}
if (mouse.getAcceleration() > 5) {
  /* Woah, slow down */
}

Expiring log system

• logSystem

  This log system takes advantage of state.time.delta to expire log entries over time. By default, this is 10 seconds, but this is configurable.

  The whole point of this system is to draw debug messages to a canvas, but have them disappear after a while.

  import { createLogSystem, type WorldState } from "@prsm/ngn";
  
  const logSystem = createLogSystem({ maxLifetime: 5_000 });
  
  const logDrawSystem = (state: WorldState) => {
    logSystem.expiringLogs.forEach(({ message }, index) => {
      drawTextToCanvas(message, { x: 0, y: index * 20 });
    });
  
    logSystem.update(state);
  };
  
  addSystem(logDrawSystem);
  
  logSystem.log("some useful debug message");