artical-video How To Build A Game Using React Native - GeekyAnts

How To Build A Game Using React Native

React Native + Matter.js

Anurag Garg Jan 10
npx react-native init GameApp
npm install matter-js react-native-game-engine --save
import React, {PureComponent} from 'react';
import {StatusBar, StyleSheet, View} from 'react-native';
import Entities from './src/entities';
import {GameEngine} from 'react-native-game-engine';

export default class App extends PureComponent {
  constructor(props) {
    super(props);
    this.state = {
      running: true,
    };
    this.gameEngine = null;
    console.disableYellowBox = true;
  }

  render() {
    return (
      <View style={styles.container}>
        <GameEngine
          ref={ref => {
            this.gameEngine = ref;
          }}
          style={styles.gameContainer}
          entities={Entities()}
          running={this.state.running}>
          <StatusBar hidden={true} />
        </GameEngine>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#000',
  },
  gameContainer: {
    position: 'absolute',
    top: 0,
    bottom: 0,
    left: 0,
    right: 0,
  },
});
import Plane from '../components/Plane';
import Matter from 'matter-js';

Matter.Common.isElement = () => false; //-- Overriding this function because the original references HTMLElement

export default restart => {
  //-- Cleanup existing entities..
  if (restart) {
    Matter.Engine.clear(restart.physics.engine);
  }

  let engine = Matter.Engine.create({enableSleeping: false});
  let world = engine.world;
  world.gravity.y = 0.25;
  const boxSize = 50;

  return {
    physics: {engine: engine, world: world},
    Plane: Plane(
      world,
      'pink',
      {x: 220, y: 400},
      {height: boxSize, width: boxSize},
    ),
  };
};
import React from 'react';
import {Image} from 'react-native';
import {array, object, string} from 'prop-types';
import Matter from 'matter-js';

const airplane = require('../../assets/airplane.png');

const Plane = props => {
  const width = props.size[0];
  const height = props.size[1];
  const x = props.body.position.x - width / 2;
  const y = props.body.position.y - height / 2;
  return (
    <Image
      style={{
        position: 'absolute',
        left: x,
        top: y,
        width: width,
        height: height,
      }}
      resizeMode="stretch"
      source={airplane}
    />
  );
};

export default (world, color, pos, size) => {
  const initialPlane = Matter.Bodies.rectangle(
    pos.x,
    pos.y,
    size.width,
    size.height,
  );
  Matter.World.add(world, [initialPlane]);

  return {
    body: initialPlane,
    size: [size.width, size.height],
    color: color,
    renderer: <Plane />,
  };
};

Plane.propTypes = {
  size: array,
  body: object,
  color: string,
};
import Systems from './src/systems';
<GameEngine
 ref={(ref) => { this.gameEngine = ref; }}
 style={styles.gameContainer}
 running={this.state.running}
 systems={Systems}
 entities={this.entities}>
</GameEngine>
import Physics from './physics';
export default [Physics];
import Matter from 'matter-js';

const Physics = (entities, {time, dispatch}) => {
  let engine = entities.physics.engine;
  Matter.Engine.update(engine, time.delta);
  return entities;
};

export default Physics;
import Matter from 'matter-js';

const UpdatePlane = (entities, {touches, time}) => {
  const engine = entities.physics.engine;
  touches
    .filter(t => t.type === 'press')
    .forEach(t => {
      Matter.Body.setVelocity(entities.Plane.body, {
        x: entities.Plane.body.velocity.x,
        y: -3,
      });
    });
  Matter.Engine.update(engine, time.delta);
  return entities;
};

export default UpdatePlane;
import Physics from './physics';
import Plane from './plane';
export default [Physics, Plane];




import React from 'react';
import {View, Image} from 'react-native';
import {array, object, string} from 'prop-types';
import Matter from 'matter-js';

const water = require('../../assets/water.png');

const Floor = props => {
  const width = props.size[0];
  const height = props.size[1];
  const x = props.body.position.x - width / 2;
  const y = props.body.position.y - height / 2;
  return (
    <View
      style={[
        {
          position: 'absolute',
          left: x,
          top: y,
          width: width,
          height: height,
          backgroundColor: props.color || 'pink',
        },
      ]}>
      <Image
        style={{width: width, height: height}}
        source={water}
        resizeMode="stretch"
      />
    </View>
  );
};

export default (world, color, pos, size) => {
  const initialFloor = Matter.Bodies.rectangle(
    pos.x,
    pos.y,
    size.width,
    size.height,
    {isStatic: true, friction: 1},
  );
  Matter.World.add(world, [initialFloor]);

  return {
    body: initialFloor,
    size: [size.width, size.height],
    color: color,
    renderer: <Floor />,
  };
};

Floor.propTypes = {
  size: array,
  body: object,
  color: string,
};
import React from 'react';
import {View} from 'react-native';
import {array, object, string} from 'prop-types';
import Matter from 'matter-js';

const Ceiling = props => {
  const width = props.size[0];
  const height = props.size[1];
  const x = props.body.position.x - width / 2;
  const y = props.body.position.y - height / 2;
  return (
    <View
      style={[
        {
          position: 'absolute',
          left: x,
          top: y,
          width: width,
          height: height,
          backgroundColor: props.color || 'pink',
        },
      ]}
    />
  );
};

export default (world, color, pos, size) => {
  const initialCeiling = Matter.Bodies.rectangle(
    pos.x,
    pos.y,
    size.width,
    size.height,
    {isStatic: true, friction: 1},
  );
  Matter.World.add(world, [initialCeiling]);

  return {
    body: initialCeiling,
    size: [size.width, size.height],
    color: color,
    renderer: <Ceiling />,
  };
};

Ceiling.propTypes = {
  size: array,
  body: object,
  color: string,
};
import Floor from '../components/Floor';
import Ceiling from '../components/Ceiling';
Floor: Floor(world,'white',{x: width / 2, y: height - 50},{height: 100, width: width}),
Ceiling: Ceiling(world,'white',{x: width / 2, y: 0},{height: 100, width: width}),






In matter.js, by applying isStatic we can make the floor and ceiling a static body that can never change position or angle and is completely fixed. With the help of this, we can now prevent the plane from falling down or going above our game area.

Now, we should make the game more interesting by adding obstacles and increase the difficulty level.

src/components/Obstacle.js

import React from 'react';
import {View} from 'react-native';
import {array, object, string} from 'prop-types';
import Matter from 'matter-js';

const Obstacle = props => {
  const width = props.size[0];
  const height = props.size[1];
  const x = props.body.position.x - width / 2;
  const y = props.body.position.y - height / 2;
  return (
    <View
      style={[
        {
          position: 'absolute',
          left: x,
          top: y,
          width: width,
          borderRadius: 20,
          height: height,
        },
      ]}
    />
  );
};

export default (world, type, pos, size) => {
  const initialObstacle = Matter.Bodies.rectangle(
    pos.x,
    pos.y,
    size.width,
    size.height,
    {isStatic: true, friction: 1},
  );
  Matter.World.add(world, [initialObstacle]);

  return {
    body: initialObstacle,
    size: [size.width, size.height],
    type: type,
    scored: false,
    renderer: <Obstacle />,
  };
};

Obstacle.propTypes = {
  size: array,
  body: object,
  color: string,
};

src/utils/random.js☟

export const getRandom = (min, max) => {
  return Math.floor(Math.random() * (max - min + 1) + min);
};

export const topObstacleHeight = getRandom(150, 300);
export const bottomObstacleHeight = getRandom(200, 300);

We will use Math.random for producing different sizes for every obstacle.

src/utils/constants.js

const Constants = {TOP_PIPE_WIDTH: 250,BOTTOM_PIPE_WIDTH: 100,};
export default Constants;

Update src/entities/index.js

import Obstacle from '../components/Obstacle';
import {getRandom,topObstacleHeight,topObstacleHeight} from '../utils/random';
import Constants from 'src/utils/constants';
Obstacle1: Obstacle(world,'top',{x: width * 2 - Constants.TOP_PIPE_WIDTH / 2, y: getRandom(100, 400)},{height: topObstacleHeight, width: Constants.TOP_PIPE_WIDTH}),
Obstacle2: Obstacle(world,'bottom',{x: width - Constants.BOTTOM_PIPE_WIDTH / 2,y: getRandom(400, 700)},{height: bottomObstacleHeight, width: Constants.BOTTOM_PIPE_WIDTH}),

But creating obstacles is not enough, we need to move these obstacles and create never-ending obstacles. To achieve this goal we need to use matter.js.

src/systems/obstacle.js 

import Matter from 'matter-js';
import Constants from '../utils/constants';
import {getRandom} from '../utils/random';
import {width} from '../utils/styleSheet';

const UpdateObstacle = (entities, {time, dispatch}) => {
  for (let i = 1; i <= 2; i++) {
    if (
      entities['Obstacle' + i].type === 'top' &&
      entities['Obstacle' + i].body.position.x <=
        -1 * (Constants.TOP_PIPE_WIDTH / 2)
    ) {
      entities['Obstacle' + i].scored = false;
      Matter.Body.setPosition(entities['Obstacle' + i].body, {
        x: width * 2 - Constants.TOP_PIPE_WIDTH / 2,
        y: getRandom(100, 300),
      });
    } else if (
      entities['Obstacle' + i].type === 'bottom' &&
      entities['Obstacle' + i].body.position.x <=
        -1 * (Constants.BOTTOM_PIPE_WIDTH / 2)
    ) {
      entities['Obstacle' + i].scored = false;
      Matter.Body.setPosition(entities['Obstacle' + i].body, {
        x: width * 2 - Constants.BOTTOM_PIPE_WIDTH / 2,
        y: getRandom(300, 500),
      });
    } else {
      Matter.Body.translate(entities['Obstacle' + i].body, {x: -4, y: 0});
    }
  }
  return entities;
};

export default UpdateObstacle;

Update src/systems/index.js :

import Physics from './physics';
import Plane from './plane';
import Obstacle from './obstacle';
export default [Physics, Plane, Obstacle];

Matter.js has a feature called translate through which we can change the position by a given vector relative to its current position, without imparting any velocity. Due to this, we get an illusion of moving obstacles.

If the x-axis position of an obstacle body becomes negative of its width than it means it has left the screen. At that time we can set the position of that body to 2 times its original position and so on this cycle will repeat, making it a never-ending loop.

Last we want to check when a collision is made so that we can stop the game and announce the score.

Matter.Events.on help to pass a callback function whenever a particular event occurs. We can easily add a collision event with the help of this method.

Update src/systems/.js :

Matter.Events.on(engine, 'collisionStart', (event) => {
dispatch({ type: "game-over"});
});

Update App.js :

onEvent = e => 
 {
  if (e.type === 'gameOver') {
   Alert.alert('Game Over');
   this.setState({running: false,});
  } 
 };

<GameEngine
 ref={(ref) => { this.gameEngine = ref; }}
 style={styles.gameContainer}
 onEvent={this.onEvent}
 running={this.state.running}
 systems={Systems}
 entities={this.entities}>
</GameEngine>




2017 © All rights reserved. Sahu Soft India Pvt Ltd.