Build awesome 2D games with Phaser.js and Expo
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README.md

NPM

expo-phaser

Tools for using Phaser-ce to build native 2D games in Expo 👾

Installation

yarn add expo-phaser

Usage

Import the library into your JavaScript file:

import ExpoPhaser from 'expo-phaser';

Functions

ExpoPhaser.game({ context: WebGLRenderingContext, ...extras })

Given a context from an Expo.GLView, return a Phaser.Game that draws into it.

Props

Property Type Description Default Value
context WebGLRenderingContext Required: context that the Phaser.Game will render to null
width number? Optional: height of the Phaser.Game context.drawingBufferWidth
height number? Optional: width of the Phaser.Game context.drawingBufferHeight
title string? Optional: title of the Phaser.Game "expo-phaser-game"
preventLoop boolean? Optional: Prevents the app from calling context.endFrameEXP() every frame false

Returns

Property Type Description
game Phaser.Game The Phaser-ce game used for rendering game logic

Example

const game = ExpoPhaser.game({ context });

What does it do?

Under the hood, ExpoPhaser is maintaining global instances of a few libraries.

window.PIXI = require('phaser-ce/build/custom/pixi');
window.p2 = require('phaser-ce/build/custom/p2');
window.Phaser = require('phaser-ce/build/phaser');

Other libs can be included but are not required. For instance you can import the custom Creature lib the same way. We also override the PIXI.WebGLRenderer.updateTexture to make it compatible with Expo.

Finally when a new instance of Expo.Game is created, we set the document.readyState to 'complete' and save the global instance of context

global.__context = context;
global.document.readyState = 'complete';

Then we create a standard render loop and call context.endFrameEXP() to flush the frame queue and render our context through EXGL.

const render = () => {
  requestAnimationFrame(render);
  context.endFrameEXP();
};

Example

It's important to note that you must preload all of your assets before starting the app, as the Phaser.State.preload method cannot be asynchronous. Creating a game in Expo is very simple with ExpoPhaser, we preload our assets, create a view, initialize our game, then add our assets.

We create an Expo.GLView to render our game to.

return (
  <Expo.GLView
    style={{ flex: 1 }}
    onContextCreate={context => startGame({ context })}
  />
);

Then we create our Phaser.Game instance and assign it a playable state. We can then choose to start said state.

function startGame({ context }) {
  const game = ExpoPhaser.game({ context });

  game.state.add('Playable', {
    preload: function() {
      /// This function cannot be async, preload all assets before getting here.
      game.load.image(
        'man',
        Expo.Asset.fromModule(Assets['man.json']).localUri,
      );
    },
    create: function() {},
    update: function() {},
  });

  game.state.start('Playable');
}

Preloading

In React Native all assets must be static resources, because of this we must create a reference to all the assets we may use, then download them and get their local URI. Expo has a convenient way of saving reference. We preload an Expo.Asset then if we create the same instance later we can simple call asset.localUri.

In a standard Phaser app we would load an asset like this:

game.load.image('man', './assets/man.png');

In expo we would load it like this:

const preloadedExpoAsset = Expo.Asset.fromModule(require('./assets/man.png'))
await preloadedExpoAsset.downloadAsync();

...

game.load.image('man', preloadedExpoAsset.localUri);

All together

This example shows how to load an animated texture atlas and apply arcade physics to it.

import React from 'react';
import Expo from 'expo';
import ExpoPhaser from 'expo-phaser';

const Assets = {
  'man.png': require('./assets/man.png'),
  'man.json': require('./assets/man.json'),
};

export default class App extends React.Component {
  state = { loading: true };
  async componentWillMount() {
    const downloads = [];
    for (let key of Object.keys(Assets)) {
      const asset = Expo.Asset.fromModule(Assets[key]);
      downloads.push(asset.downloadAsync());
    }
    await Promise.all(downloads);
    this.setState({ loading: false });
  }
  render() {
    if (this.state.loading) {
      return <Expo.AppLoading />;
    }

    return (
      <Expo.GLView
        style={{ flex: 1 }}
        onContextCreate={context => startGame({ context })}
      />
    );
  }
}

function startGame({ context }) {
  const game = ExpoPhaser.game({ context });

  game.state.add('Playable', {
    preload: function() {
      const atlas = Expo.Asset.fromModule(Assets['man.json']).localUri;
      const texture = Expo.Asset.fromModule(Assets['man.png']).localUri;
      game.load.atlasJSONHash('man', texture, atlas);
    },
    create: function() {
      game.stage.backgroundColor = '#4488AA';

      game.physics.startSystem(Phaser.Physics.ARCADE);

      //  Set the world (global) gravity
      game.physics.arcade.gravity.y = 100;

      const man = game.add.sprite(200, 200, 'man');
      game.physics.enable([man], Phaser.Physics.ARCADE);

      //  Here we add a new animation called 'run'
      //  We haven't specified any frames because it's using every frame in the texture atlas

      man.animations.add('run');
      man.body.collideWorldBounds = true;
      man.body.bounce.y = 0.8;
      man.body.gravity.y = 200;

      //  And this starts the animation playing by using its key ("run")
      //  15 is the frame rate (15fps)
      //  true means it will loop when it finishes
      man.animations.play('run', 15, true);
    },
    update: function() {},
  });

  game.state.start('Playable');
}

note: When working with .json asset inclusion, be sure to update the app.json file to handle .json appropriately.

"packagerOpts": {
  "assetExts": [
    "json"
  ]
},