escalator-web/src/scene.js

class Scene extends Screen {
    constructor(canvas, player) {
        super(canvas);
        this.player = player;
        this.currentHeight = 0;
        this.maxHeight = 0;
        this.initialize();

        this.addEventListener('touchstart', (event) => {
            this.onTouchStart(event);
        });
    }

    initialize() {
        super.initialize();
        this.player.reset();
        this.platforms = [];
        this.cameraHeight = 0;
        this.cameraSpeed = 0;
        this.currentHeight = 0;
        this.started = false;

        // Generate random initial platforms
        for (let i = 0.25; i <= 2; i += 0.33) {
            let platform = new Platform(Math.random(), i, 0.2);
            this.addPlatform(platform);
        }

    }

    start() {
        if (!this.started) {
            this.started = true;
            this.cameraSpeed = 0.005;
        }
    }

    drawBackground() {
        let pattern = this.context.createPattern(Scene.background, 'repeat');
        this.context.fillStyle = pattern;
        this.context.beginPath();
        this.context.rect(0, - this.cameraHeight * this.height(), this.width(), this.height());
        this.context.fill();
    }

    update(time = 0.002) {

        // Check if the game is lost
        if (this.player.y + this.player.size < this.cameraHeight) {
            this.initialize();
        }

        // The last platform is the highest.
        let last = this.platforms[this.platforms.length - 1];

        // If the last platform is on screen, we need to create the next platform.
        if (last.y <= this.cameraHeight + 1) {
            let diff = 0.1 + Math.random() * 0.4;
            let platform = new Platform(Math.random(), last.y + diff, 0.2);
            this.platforms.push(platform);
        }

        // Increase position of the camera
        this.cameraHeight += this.cameraSpeed * time * this.height();


        // Update high score
        this.maxHeight = Math.max(this.player.y, this.maxHeight);
        this.currentHeight = Math.max(this.player.y, this.currentHeight);

        let previous = {
            x: this.player.x,
            y: this.player.y + this.player.size / 2,
        };

        this.player.update(time);

        let next = {
            x: this.player.x,
            y: this.player.y + this.player.size / 2,
            size: this.player.size,
        };

        // Detect collision with platform
        for (let platform of this.platforms) {

            let p = {
                x: platform.x,
                y: platform.y + platform.height / 2,
                width: platform.width,
                height: platform.height,
            };

            if (previous.y >= p.y && next.y < p.y) {
                if (next.x >= p.x - p.width / 2 - next.size / 4) {
                    if (next.x <= p.x + p.width / 2 + next.size / 4) {
                        // Collision detected
                        this.player.collide(p.y - next.size/2);
                    }
                }
            }
        }

        // Collision with the ground
        if (this.player.y <= 0) {
            this.player.collide(0);
        }

        // Collisions with the border of the screen
        this.player.x = Math.max(this.player.x, this.player.size / 4);
        this.player.x = Math.min(this.player.x, 1 - this.player.size / 4);
    }

    addPlatform(object) {
        this.platforms.push(object);
    }

    render() {
        this.clear();

        this.context.translate(0, this.cameraHeight * this.height());

        this.drawBackground();

        for (let platform of this.platforms) {
            this.drawPlatform(platform);
        }

        this.drawObject(this.player);

        this.context.resetTransform();

        this.drawHud();
    }

    drawObject(object) {
        let size = object.size * this.width();

        this.context.drawImage(
            Box.texture,
            0, 64 * this.player.frameNumber, 64, 64,
            (object.x - object.size / 2) * this.width(),
            (1 - object.y - object.size / 2) * this.height(),
            size, size
        );
    }

    drawPlatform(object) {
        let width = object.width * this.width();
        let height = object.height * this.height();

        this.context.drawImage(
            Platform.texture,
            0, 0, 64, 64,
            (object.x - object.width / 2) * this.width(),
            (1 - object.y - object.height / 2) * this.height(),
            width, width,
        );
    }

    drawHud() {
        this.context.font = "20px Arial";
        this.context.fillStyle = 'rgb(255, 255, 255)';
        this.context.fillText("Current score: " + Math.floor(100 * this.currentHeight), 0, 20);
        this.context.fillText("High score: " + Math.floor(100 * this.maxHeight), 0, 50);
    }

    onTouchStart(event) {

        let e = event.changedTouches[0];
        this.start();
        if (e !== undefined) {
            this.player.jump(e.clientX / window.innerWidth, e.clientY / window.innerHeight);
        }

    }

}

Scene.background = new Image();
Scene.background.src = "img/background.png";