Build a HTML5 game like “Risky Road” using Phaser, Matter physcis and Simplify.js

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Did you play Risky Road game developed by Ketchapp?

Available for both iOS and Android, it’s a physics endless runner.

You must drive your car as far as you can while keeping an egg/diamond/whatever safe, by getting the right speed to pass obstacles.

In the original game, terrain is made of pre-built blocks appearing in a random sequence.

In my version, terrain is randomly generated by the infinite random terrain generator I showed you some days ago, so most of the process has already been explained. Follow horizontal endless runner game series to see how to make things work.

Look at the game:

Tap and hold to accelerate, do not make the square fall off the cart or it’s game over.

The game itself is very similar to what you have already seen in horizontal endless runner game series but here we introduced compound objects and collision detection.

Compound objects are built of some primitive objects merged into one more complex body. The cart is built of three rectangles.

Collision detection is checked between the square and the cart. If the square collides with any body which does not belong to the cart, it’s game over.

You will find everything in the commented source code:

var game;

var gameOptions = {

    // start vertical point of the terrain, 0 = very top; 1 = very bottom
    startTerrainHeight: 0.5,

    // max slope amplitude, in pixels
    amplitude: 100,

    // slope length range, in pixels
    slopeLength: [150, 350],

    // a mountain is a a group of slopes.
    mountainsAmount: 2,

    // amount of slopes for each mountain
    slopesPerMountain: 10,

    // car acceleration
    carAcceleration: 0.01,

    // maximum car velocity
    maxCarVelocity: 1
}
window.onload = function() {
    let gameConfig = {
        type: Phaser.AUTO,
        backgroundColor: 0x75d5e3,
        scale: {
            mode: Phaser.Scale.FIT,
            autoCenter: Phaser.Scale.CENTER_BOTH,
            parent: "thegame",
            width: 1334,
            height: 750
        },
        physics: {
            default: "matter",
            matter: {
                debug: true,
                debugBodyColor: 0x000000
            }
        },
        scene: playGame
    }
    game = new Phaser.Game(gameConfig);
    window.focus();
}
class playGame extends Phaser.Scene{
    constructor(){
        super("PlayGame");
    }
    create(){

        // creation of pool arrays
        this.bodyPool = [];
        this.bodyPoolId = [];

        // array to store mountains
        this.mountainGraphics = [];

        // mountain start coordinates
        this.mountainStart = new Phaser.Math.Vector2(0, 0);

        // loop through all mountains
        for(let i = 0; i < gameOptions.mountainsAmount; i++){

            // each mountain is a graphics object
            this.mountainGraphics[i] = this.add.graphics();

            // generateTerrain is the method to generate the terrain. The arguments are the graphics object and the start position
            this.mountainStart = this.generateTerrain(this.mountainGraphics[i], this.mountainStart);
        }

        // method to add the car, methods represent x and y position
        this.addCar(250, 300);

        // the car is not accelerating
        this.isAccelerating = false;

        // input management
        this.input.on("pointerdown", this.accelerate, this);
        this.input.on("pointerup", this.decelerate, this);

        // text object with terrain information
        this.terrainInfo = this.add.text(0, game.config.height - 110, "", {
            fontFamily: "Arial",
            fontSize: 64,
            color: "#00ff00"
        });

        // collision check between the diamond and the car. Any other diamond collision is not allowed
        this.matter.world.on("collisionstart", function(event, bodyA, bodyB){
            if((bodyA.label == "diamond" && bodyB.label != "car") || (bodyB.label == "diamond" && bodyA.label != "car")){
                this.scene.start("PlayGame")
            }

        }.bind(this));
    }

    // method to generate the terrain. Arguments: the graphics object and the start position
    generateTerrain(graphics, mountainStart){

        // array to store slope points
        let slopePoints = [];

        // variable to count the amount of slopes
        let slopes = 0;

        // slope start point
        let slopeStart = new Phaser.Math.Vector2(0, mountainStart.y);

        // set a random slope length
        let slopeLength = Phaser.Math.Between(gameOptions.slopeLength[0], gameOptions.slopeLength[1]);

        // determine slope end point, with an exception if this is the first slope of the fist mountain: we want it to be flat
        let slopeEnd = (mountainStart.x == 0) ? new Phaser.Math.Vector2(slopeStart.x + gameOptions.slopeLength[1] * 1.5, 0) : new Phaser.Math.Vector2(slopeStart.x + slopeLength, Math.random());

        // current horizontal point
        let pointX = 0;

        // while we have less slopes than regular slopes amount per mountain...
        while(slopes < gameOptions.slopesPerMountain){

            // slope interpolation value
            let interpolationVal = this.interpolate(slopeStart.y, slopeEnd.y, (pointX - slopeStart.x) / (slopeEnd.x - slopeStart.x));

            // if current point is at the end of the slope...
            if(pointX == slopeEnd.x){

                // increase slopes amount
                slopes ++;

                // next slope start position
                slopeStart = new Phaser.Math.Vector2(pointX, slopeEnd.y);

                // next slope end position
                slopeEnd = new Phaser.Math.Vector2(slopeEnd.x + Phaser.Math.Between(gameOptions.slopeLength[0], gameOptions.slopeLength[1]), Math.random());

                // no need to interpolate, we use slope start y value
                interpolationVal = slopeStart.y;
            }

            // current vertical point
            let pointY = game.config.height * gameOptions.startTerrainHeight + interpolationVal * gameOptions.amplitude;

            // add new point to slopePoints array
            slopePoints.push(new Phaser.Math.Vector2(pointX, pointY));

            // move on to next point
            pointX ++ ;
        }

        // simplify the slope
        let simpleSlope = simplify(slopePoints, 1, true);

        // place graphics object
        graphics.x = mountainStart.x;

        // draw the ground
        graphics.clear();
        graphics.moveTo(0, game.config.height);
        graphics.fillStyle(0x654b35);
        graphics.beginPath();
        simpleSlope.forEach(function(point){
            graphics.lineTo(point.x, point.y);
        }.bind(this))
        graphics.lineTo(pointX, game.config.height);
        graphics.lineTo(0, game.config.height);
        graphics.closePath();
        graphics.fillPath();

        // draw the grass
        graphics.lineStyle(16, 0x6b9b1e);
        graphics.beginPath();
        simpleSlope.forEach(function(point){
            graphics.lineTo(point.x, point.y);
        })
        graphics.strokePath();

        // loop through all simpleSlope points starting from the second
        for(let i = 1; i < simpleSlope.length; i++){

            // define a line between previous and current simpleSlope points
            let line = new Phaser.Geom.Line(simpleSlope[i - 1].x, simpleSlope[i - 1].y, simpleSlope[i].x, simpleSlope[i].y);

            // calculate line length, which is the distance between the two points
            let distance = Phaser.Geom.Line.Length(line);

            // calculate the center of the line
            let center = Phaser.Geom.Line.GetPoint(line, 0.5);

            // calculate line angle
            let angle = Phaser.Geom.Line.Angle(line);

            // if the pool is empty...
            if(this.bodyPool.length == 0){

                // create a new rectangle body
                this.matter.add.rectangle(center.x + mountainStart.x, center.y, distance, 10, {
                    isStatic: true,
                    angle: angle,
                    friction: 1,
                    restitution: 0
                });
            }

            // if the pool is not empty...
            else{

                // get the body from the pool
                let body = this.bodyPool.shift();
                this.bodyPoolId.shift();

                // reset, reshape and move the body to its new position
                this.matter.body.setPosition(body, {
                    x: center.x + mountainStart.x,
                    y: center.y
                });
                let length = body.area / 10;
                this.matter.body.setAngle(body, 0)
                this.matter.body.scale(body, 1 / length, 1);
                this.matter.body.scale(body, distance, 1);
                this.matter.body.setAngle(body, angle);
            }
        }

        // assign a custom "width" property to the graphics object
        graphics.width = pointX - 1

        // return the coordinates of last mountain point
        return new Phaser.Math.Vector2(graphics.x + pointX - 1, slopeStart.y);
    }

    // method to build the car
    addCar(posX, posY){

        // car is made by three rectangle bodies which will be merged into a compound object
        let floor = Phaser.Physics.Matter.Matter.Bodies.rectangle(posX, posY, 100, 10, {
            label: "car"
        });
        let rightBarrier = Phaser.Physics.Matter.Matter.Bodies.rectangle(posX + 45, posY - 15, 10, 20, {
            label: "car"
        });
        let leftBarrier = Phaser.Physics.Matter.Matter.Bodies.rectangle(posX - 45, posY - 15, 10, 20, {
            label: "car"
        });

        // this is how we create the compund object
        this.body = Phaser.Physics.Matter.Matter.Body.create({

            // array of single bodies
            parts: [floor, leftBarrier, rightBarrier],
            friction: 1,
            restitution: 0
        });

        // add the body to the world
        this.matter.world.add(this.body);

        // the diamond. It cannot fall off the car
        this.diamond = this.matter.add.rectangle(posX, posY - 40, 30, 30, {
            friction: 1,
            restitution: 0,
            label: "diamond"
        });

        // add front wheel. A circle
        this.frontWheel = this.matter.add.circle(posX + 35, posY + 25, 30, {
            friction: 1,
            restitution: 0
        });

        // add rear wheel
        this.rearWheel = this.matter.add.circle(posX - 35, posY + 25, 30, {
            friction: 1,
            restitution: 0
        });

        // these two constraints will bind front wheel to the body
        this.matter.add.constraint(this.body, this.frontWheel, 40, 0, {
            pointA: {
                x: 30,
                y: 10
            }
        });
        this.matter.add.constraint(this.body, this.frontWheel, 40, 0, {
            pointA: {
                x: 45,
                y: 10
            }
        });

        // same thing for rear wheel
        this.matter.add.constraint(this.body, this.rearWheel, 40, 0, {
            pointA: {
                x: -30,
                y: 10
            }
        });
        this.matter.add.constraint(this.body, this.rearWheel, 40, 0, {
            pointA: {
                x: -45,
                y: 10
            }
        });
    }

    // method to accelerate
    accelerate(){
        this.isAccelerating = true;
    }

    // method to decelerate
    decelerate(){
        this.isAccelerating = false;
    }

    update(){

        // make the game follow the car
        this.cameras.main.scrollX = this.body.position.x - game.config.width / 8

        // adjust velocity according to acceleration
        if(this.isAccelerating){
            let velocity = this.frontWheel.angularSpeed + gameOptions.carAcceleration;
            velocity = Phaser.Math.Clamp(velocity, 0, gameOptions.maxCarVelocity);

            // set angular velocity to wheels
            this.matter.body.setAngularVelocity(this.frontWheel, velocity);
            this.matter.body.setAngularVelocity(this.rearWheel, velocity);
        }

        // loop through all mountains
        this.mountainGraphics.forEach(function(item){

            // if the mountain leaves the screen to the left...
            if(this.cameras.main.scrollX > item.x + item.width + 100){

                // reuse the mountain
                this.mountainStart = this.generateTerrain(item, this.mountainStart)
            }
        }.bind(this));

        // get all bodies
        let bodies = this.matter.world.localWorld.bodies;

        // loop through all bodies
        bodies.forEach(function(body){

            // if the body is out of camera view to the left side and is not yet in the pool..
            if(this.cameras.main.scrollX > body.position.x + game.config.width && this.bodyPoolId.indexOf(body.id) == -1){

                // ...add the body to the pool
                this.bodyPool.push(body);
                this.bodyPoolId.push(body.id);
            }
        }.bind(this))

        // update terrain info text
        this.terrainInfo.x = this.cameras.main.scrollX + 50;
        this.terrainInfo.setText("distance: " + Math.floor(this.cameras.main.scrollX / 100))
    }

    // method to apply a cosine interpolation between two points
    interpolate(vFrom, vTo, delta){
        let interpolation = (1 - Math.cos(delta * Math.PI)) * 0.5;
        return vFrom * (1 - interpolation) + vTo * interpolation;
    }
}

The game has also room for customization by changing values in gameOptions global object.

How far will you go? Download the source code and build your own Risky Road clone.

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215 GAME PROTOTYPES EXPLAINED WITH SOURCE CODE
// 1+2=3
// 100 rounds
// 10000000
// 2 Cars
// 2048
// A Blocky Christmas
// A Jumping Block
// A Life of Logic
// Angry Birds
// Angry Birds Space
// Artillery
// Astro-PANIC!
// Avoider
// Back to Square One
// Ball Game
// Ball vs Ball
// Ball: Revamped
// Balloon Invasion
// BallPusher
// Ballz
// Bar Balance
// Bejeweled
// Biggification
// Block it
// Blockage
// Bloons
// Boids
// Bombuzal
// Boom Dots
// Bouncing Ball
// Bouncing Ball 2
// Bouncy Light
// BoxHead
// Breakout
// Bricks
// Bubble Chaos
// Bubbles 2
// Card Game
// Castle Ramble
// Chronotron
// Circle Chain
// Circle Path
// Circle Race
// Circular endless runner
// Cirplosion
// CLOCKS - The Game
// Color Hit
// Color Jump
// ColorFill
// Columns
// Concentration
// Crossy Road
// Crush the Castle
// Cube Jump
// CubesOut
// Dash N Blast
// Dashy Panda
// Deflection
// Diamond Digger Saga
// Don't touch the spikes
// Dots
// Down The Mountain
// Drag and Match
// Draw Game
// Drop Wizard
// DROP'd
// Dudeski
// Dungeon Raid
// Educational Game
// Elasticity
// Endless Runner
// Erase Box
// Eskiv
// Farm Heroes Saga
// Filler
// Flappy Bird
// Fling
// Flipping Legend
// Floaty Light
// Fuse Ballz
// GearTaker
// Gem Sweeper
// Globe
// Goat Rider
// Gold Miner
// Grindstone
// GuessNext
// Helicopter
// Hero Emblems
// Hero Slide
// Hexagonal Tiles
// HookPod
// Hop Hop Hop Underwater
// Horizontal Endless Runner
// Hundreds
// Hungry Hero
// Hurry it's Christmas
// InkTd
// Iromeku
// Jet Set Willy
// Jigsaw Game
// Knife Hit
// Knightfall
// Legends of Runeterra
// Lep's World
// Line Rider
// Lumines
// Magick
// MagOrMin
// Mass Attack
// Math Game
// Maze
// Meeblings
// Memdot
// Metro Siberia Underground
// Mike Dangers
// Mikey Hooks
// Nano War
// Nodes
// o:anquan
// One Button Game
// One Tap RPG
// Ononmin
// Pacco
// Perfect Square!
// Perfectionism
// Phyballs
// Pixel Purge
// PixelField
// Planet Revenge
// Plants Vs Zombies
// Platform
// Platform game
// Plus+Plus
// Pocket Snap
// Poker
// Pool
// Pop the Lock
// Pop to Save
// Poux
// Pudi
// Pumpkin Story
// Puppet Bird
// Pyramids of Ra
// qomp
// Quick Switch
// Racing
// Radical
// Rebuild Chile
// Renju
// Rise Above
// Risky Road
// Roguelike
// Roly Poly
// Run Around
// Rush Hour
// SameGame
// SamePhysics
// Save the Totem
// Security
// Serious Scramblers
// Shrink it
// Sling
// Slingy
// Snowflakes
// Sokoban
// Space Checkers
// Space is Key
// Spellfall
// Spinny Gun
// Splitter
// Spring Ninja
// Sproing
// Stabilize!
// Stack
// Stairs
// Stick Hero
// String Avoider
// Stringy
// Sudoku
// Super Mario Bros
// Surfingers
// Survival Horror
// Talesworth Adventure
// Tetris
// The Impossible Line
// The Moops - Combos of Joy
// The Next Arrow
// Threes
// Tic Tac Toe
// Timberman
// Tiny Wings
// Tipsy Tower
// Toony
// Totem Destroyer
// Tower Defense
// Trick Shot
// Tunnelball
// Turn
// Turnellio
// TwinSpin
// vvvvvv
// Warp Shift
// Way of an Idea
// Whack a Creep
// Wheel of Fortune
// Where's my Water
// Wish Upon a Star
// Word Game
// Wordle
// Worms
// Yanga
// Yeah Bunny
// Zhed
// zNumbers