trianta.dev/src/pong.ts

class Box {
    x: number;
    y: number;
    width: number;
    height: number;

    constructor(_x: number, _y: number, _width: number, _height: number) {
        this.x = _x;
        this.y = _y;
        this.width = _width;
        this.height = _height;
    }

    collides(other: Box) {
        return this.x < other.x + other.width &&
                this.x + this.width > other.x &&
                this.y < other.y + other.height &&
                this.y + this.height > other.y;
    }
}

class Paddle {
    geometry: Box;
    speed: number;
    isBot: boolean;
    isLeft: boolean;
    score: number;
    dy: number;

    constructor(_geometry: Box, _isLeft: boolean) {
        this.geometry = _geometry;
        this.isLeft = _isLeft;
        this.speed = 6;
        this.isBot = true;
        this.score = 0;
        this.dy = 0;
    }

    scored() {
        this.score++;
    }

    input() {
        if (!this.isBot)
            return;
        let ballRegion = Math.floor(g_pong.ball.geometry.y / 15);
        let paddleRegion = Math.floor(this.geometry.y / 15);
        if (ballRegion < paddleRegion) this.dy = -this.speed; 
        if (ballRegion > paddleRegion) this.dy = this.speed; 
        if (ballRegion === paddleRegion) this.dy = 0; 
    }
}

class Ball {
    geometry: Box;
    speed: number;
    dx: number;
    dy: number;
    resetting: boolean;

    constructor() {
        // start in the middle of the game
        this.geometry = new Box(g_pong.width / 2, g_pong.height / 2, g_pong.grid, g_pong.grid);
        this.speed = 5;
        // ball velocity (start going to the top-right corner)
        this.dx = this.speed;
        this.dy = -this.speed;
        // keep track of when need to reset the ball position
        this.resetting = false;
    }
}

class PongCore {
    canvas: HTMLCanvasElement;
    context: CanvasRenderingContext2D;
    grid: number;
    timeout: number;
    width: number;
    height: number;
    gameover: boolean;
    ball: Ball;
    left: Paddle;
    right: Paddle;
    paddleHeight: number;
    paddleHeightMax: number;
    paddleSpeed: number;

    constructor() {
        this.canvas = document.getElementById('pong') as HTMLCanvasElement;
        this.context = this.canvas.getContext('2d') as CanvasRenderingContext2D;
        this.grid = 15; // size of grid squares
        this.paddleHeight = this.grid * 5;
        this.paddleHeightMax = this.canvas.height - this.grid - this.paddleHeight;
        this.timeout = 32; // speed in ms
        this.width = this.canvas.width;
        this.height = this.canvas.height;
        this.gameover = false;
        this.paddleSpeed = 6;
        this.ball = new Ball();
        this.left = new Paddle(new Box(this.width / 2, this.height / 2 - this.paddleHeight / 2, this.grid, this.paddleHeight), true);
        this.right = new Paddle(new Box(this.width - this.grid * 3, this.height / 2 - this.paddleHeight / 2, this.grid, this.paddleHeight), false);
    }

    start() {
        setInterval(this.loop, this.timeout);
    }

    reset() {
        this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
        let restartGame = document.getElementById("restart");
        let gameOverText = document.getElementById("gameover");
        restartGame.hidden = false;
        gameOverText.hidden = false;
        console.debug("[TRACE] Reset was triggered");
        this.gameover = false;
        this.left.score = 0;
        this.right.score = 0;
        this.draw();
    }

    // Game loop
    loop() {
        // Reset of needed
        if (this.gameover)
            this.reset();

        this.simulate();

        this.draw();
        this.updatePageText();
    }

    // Simulate game logic
    simulate() {
        this.left.input();
        this.right.input();

        // move paddles by their velocity
        this.left.geometry.y += this.left.dy;
        this.right.geometry.y += this.right.dy;

        // prevent paddles from going through walls
        if (this.left.geometry.y < this.grid) {
            this.left.geometry.y = this.grid;
        }
        else if (this.left.geometry.y > this.paddleHeightMax) {
            this.left.geometry.y = this.paddleHeightMax;
        }

        if (this.right.geometry.y < this.grid) {
            this.right.geometry.y = this.grid;
        }
        else if (this.right.geometry.y > this.paddleHeightMax) {
            this.right.geometry.y = this.paddleHeightMax;
        }

        // move ball by its velocity
        this.ball.geometry.x += this.ball.dx;
        this.ball.geometry.y += this.ball.dy;

        // prevent ball from going through walls by changing its velocity
        if (this.ball.geometry.y < this.grid) {
            this.ball.geometry.y = this.grid;
            this.ball.dy *= -1;
        }
        else if (this.ball.geometry.y + this.grid > this.canvas.height - this.grid) {
            this.ball.geometry.y = this.canvas.height - this.grid * 2;
            this.ball.dy *= -1;
        }

        // reset ball if it goes past paddle (but only if we haven't already done so)
        if ( (this.ball.geometry.x < 0 || this.ball.geometry.x > this.canvas.width) && !this.ball.resetting) {
            this.ball.resetting = true;

            if (this.ball.geometry.x < 0) {
                this.right.scored();
            }
            if (this.ball.geometry.x > this.canvas.width) {
                this.left.scored();
            }

            // give some time for the player to recover before launching the ball again
            setTimeout(() => {
                this.ball.resetting = false;
                this.ball.geometry.x = this.canvas.width / 2;
                this.ball.geometry.y = this.canvas.height / 2;
            }, 400);
        }

        // check to see if ball collides with paddle. if they do change x velocity
        if (this.left.geometry.collides(this.ball.geometry)) {
            this.ball.dx *= -1;
            this.left.dy = 0;

            // move ball next to the paddle otherwise the collision will happen again
            // in the next frame
            this.ball.geometry.x = this.left.geometry.x + this.left.geometry.width;
        }
        else if (this.right.geometry.collides(this.ball.geometry)) {
            this.ball.dx *= -1;
            this.right.dy = 0;

            // move ball next to the paddle otherwise the collision will happen again
            // in the next frame
            this.ball.geometry.x = this.right.geometry.x - this.ball.geometry.width;
        }

    }

    // Draw game to canvas
    draw() {
        // Clear the screen
        this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);

        // draw score
        this.context.font = "30px Arial";
        this.context.fillText(this.left.score.toString(), 200, 50);
        this.context.fillText(this.right.score.toString(), 560, 50);

        // draw paddles
        this.context.fillStyle = 'white';
        this.fillRect(this.left.geometry);
        this.fillRect(this.right.geometry);

        // draw ball
        this.fillRect(this.ball.geometry);

        // draw walls
        this.context.fillStyle = "#f4dbd6";
        this.fillRect(new Box(0, 0, this.canvas.width, this.grid));
        this.fillRect(new Box(0, this.canvas.height - this.grid, this.canvas.width, this.canvas.height));

        // draw dotted line down the middle
        for (let i = this.grid; i < this.canvas.height - this.grid; i += this.grid * 2) {
            this.fillRect(new Box(this.canvas.width / 2 - this.grid / 2, i, this.grid, this.grid));
        }
    }
    
    fillRect(_box: Box) {
        this.context.fillRect(_box.x, _box.y, _box.width, _box.height);
    }

    // Update text on page to match game
    updatePageText() {
        document.getElementById("leftPaddle").innerHTML = this.left.geometry.y.toString();
        document.getElementById("rightPaddle").innerHTML = this.right.geometry.y.toString();
    }
}

// listen to keyboard events to move the paddles
document.addEventListener('keydown', function(e) {
    // up arrow key
    if (e.which === 38) {
        g_pong.right.dy = -g_pong.paddleSpeed;
    }
    // down arrow key
    else if (e.which === 40) {
        g_pong.right.dy = g_pong.paddleSpeed;
    }

    // w key
    if (e.which === 87) {
        g_pong.left.dy = -g_pong.paddleSpeed;
    }
    // a key
    else if (e.which === 83) {
        g_pong.left.dy = g_pong.paddleSpeed;
    }
});

// listen to keyboard events to stop the paddle if key is released
document.addEventListener('keyup', function(e) {
    if (e.which === 38 || e.which === 40) {
        g_pong.right.dy = 0;
    }
    if (e.which === 83 || e.which === 87) {
        g_pong.left.dy = 0;
    }
});

const g_pong: PongCore = new PongCore();
g_pong.start();