The basics behind “jumping on enemies” feature, explained with Phaser and ARCADE physics

One of the most interesting features introduce in platform games is the ability to jump on enemies and maybe squashing them to death. I am not sure which game was the first to introduce this feature, I would say some chapter in the Mario Bros series, although I am pretty sure in the very first game you couldn’t squash enemies. Anyway, we are going to see how we can develop this feature in our HTML5 games using Phaser and ARCADE physics. Let’s have a look at the result:
Our hero is the green character, while the red one is the enemy. Both characters run and change direction once they hit the wall, and you can make green character jump by clicking/tapping on the canvas. If red character hits green character, the game restarts. Try to jump over the red character and you will bounce over it. This is made by checking the side of the collision between red and green character. We can say the green character is jumping over the red character when the red character collides on its TOP side while the green character collides on its BOTTOM side. Have a look at the completely commented source code:
var game;
var gameOptions = {

    // width of the game, in pixels
    gameWidth: 640,

    // height of the game, in pixels
    gameHeight: 192,

    // background color
    bgColor: 0x444444,

    // player gravity
    playerGravity: 1900,

    // player horizontal speed
    playerSpeed: 200,

    // player force
    playerJump: 400,

    // enemy horizontal speed
    enemySpeed: 150
}
window.onload = function() {
    game = new Phaser.Game(gameOptions.gameWidth, gameOptions.gameHeight);
    game.state.add("PreloadGame", preloadGame);
    game.state.add("PlayGame", playGame);
    game.state.start("PreloadGame");
}
var preloadGame = function(game){}
preloadGame.prototype = {
    preload: function(){
        game.stage.backgroundColor = gameOptions.bgColor;
        game.scale.scaleMode = Phaser.ScaleManager.SHOW_ALL;
        game.scale.pageAlignHorizontally = true;
        game.scale.pageAlignVertically = true;
        game.stage.disableVisibilityChange = true;

        // loading level tilemap
        game.load.tilemap("level", 'level.json', null, Phaser.Tilemap.TILED_JSON);

        // loading game assets
        game.load.image("tile", "tile.png");
        game.load.image("hero", "hero.png");
        game.load.image("enemy", "enemy.png");
    },
    create: function(){
        game.state.start("PlayGame");
    }
}
var playGame = function(game){}
playGame.prototype = {
    create: function(){

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

        // creatin of "level" tilemap
        this.map = game.add.tilemap("level");

        // adding tiles (actually one tile) to tilemap
        this.map.addTilesetImage("tileset01", "tile");

        // tile 1 (the black tile) has the collision enabled
        this.map.setCollision(1);

        // which layer should we render? That's right, "layer01"
        this.layer = this.map.createLayer("layer01");

        // adding the hero sprite
        this.hero = game.add.sprite(game.width / 2, 152, "hero");

        // setting hero anchor point
        this.hero.anchor.set(0.5);

        // enabling ARCADE physics for the enemy
        game.physics.enable(this.hero, Phaser.Physics.ARCADE);

        // setting hero gravity
        this.hero.body.gravity.y = gameOptions.playerGravity;

        // setting hero horizontal speed
        this.hero.body.velocity.x = gameOptions.playerSpeed;

        // adding the enemy sprite
        this.enemy = game.add.sprite(game.width / 4, 152, "enemy");

        // setting enemy anchor point
        this.enemy.anchor.set(0.5);

        // enabling ARCADE physics for the enemy
        game.physics.enable(this.enemy, Phaser.Physics.ARCADE);

        // setting enemy horizontal speed
        this.enemy.body.velocity.x = gameOptions.enemySpeed;

        // the hero can jump
        this.canJump = true;

        // waiting for player input
        game.input.onDown.add(this.handleJump, this);
    },
    handleJump: function(){

        // the hero can jump when:
        // canJump is true AND the hero is on the ground (blocked.down)
        if((this.canJump && this.hero.body.blocked.down)){

            // applying jump force
            this.hero.body.velocity.y = -gameOptions.playerJump;

            // hero can't jump anymore
            this.canJump = false;
        }
    },
    update: function(){

        // handling collision between the hero and the tiles
        game.physics.arcade.collide(this.hero, this.layer, function(hero, layer){

            // hero on the ground
            if(hero.body.blocked.down){

                // hero can jump
                this.canJump = true;
            }

            // hero on the ground and touching a wall on the right
            if(this.hero.body.blocked.right && this.hero.body.blocked.down){

                // horizontal flipping hero sprite
                this.hero.scale.x = -1;
            }

            // same concept applies to the left
            if(this.hero.body.blocked.left && this.hero.body.blocked.down){
                this.hero.scale.x = 1;
            }

            // adjusting hero speed according to the direction it's moving
            this.hero.body.velocity.x = gameOptions.playerSpeed * this.hero.scale.x;
        }, null, this);

        // handling collision between the enemy and the tiles
        game.physics.arcade.collide(this.enemy, this.layer, function(hero, layer){

            // enemy touching a wall on the right
            if(this.enemy.body.blocked.right){

                // horizontal flipping enemy sprite
                this.enemy.scale.x = -1;
            }

            // same concept applies to the left
            if(this.enemy.body.blocked.left){
                this.enemy.scale.x = 1;
            }

            // adjusting enemy speed according to the direction it's moving
            this.enemy.body.velocity.x = gameOptions.enemySpeed * this.enemy.scale.x;
        }, null, this);

        // handling collision between enemy and hero
        game.physics.arcade.collide(this.hero, this.enemy, function(hero, enemy){

            // hero is stomping the enemy if:
            // hero is touching DOWN
            // enemy is touching UP
            if(enemy.body.touching.up && hero.body.touching.down){

                // in this case just jump again
                this.hero.body.velocity.y =  -gameOptions.playerJump;
            }
            else{

                // any other way to collide on an enemy will restart the game
                game.state.start("PlayGame");
            }
        }, null, this);
    }
}
We can create a lot of various platformer games using this feature together with wall jump, next time I’ll merge them into one single prototype, meanwhile download the source code.

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