lesson07.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title>Gamedev Canvas Workshop - lesson 7: collision detection</title>
    <style>* { padding: 0; margin: 0; } canvas { background: #eee; display: block; margin: 0 auto; }</style>
</head>
<body>

<canvas id="myCanvas" width="480" height="320"></canvas>

<script>
    var canvas = document.getElementById("myCanvas");
    var ctx = canvas.getContext("2d");
    var ballRadius = 10;
    var x = canvas.width/2;
    var y = canvas.height-30;
    var dx = 2;
    var dy = -2;
    var paddleHeight = 10;
    var paddleWidth = 75;
    var paddleX = (canvas.width-paddleWidth)/2;
    var rightPressed = false;
    var leftPressed = false;
    var brickRowCount = 5;
    var brickColumnCount = 3;
    var brickWidth = 75;
    var brickHeight = 20;
    var brickPadding = 10;
    var brickOffsetTop = 30;
    var brickOffsetLeft = 30;

    var bricks = [];
    for(var c=0; c<brickColumnCount; c++) {
        bricks[c] = [];
        for(var r=0; r<brickRowCount; r++) {
            bricks[c][r] = { x: 0, y: 0, status: 1 };
        }
    }

    document.addEventListener("keydown", keyDownHandler, false);
    document.addEventListener("keyup", keyUpHandler, false);

    function keyDownHandler(e) {
        if(e.code  == "ArrowRight") {
            rightPressed = true;
        }
        else if(e.code == 'ArrowLeft') {
            leftPressed = true;
        }
    }
    function keyUpHandler(e) {
        if(e.code  == "ArrowRight") {
            rightPressed = false;
        }
        else if(e.code == 'ArrowLeft') {
            leftPressed = false;
        }
    }
    function collisionDetection() {
        for(var c=0; c<brickColumnCount; c++) {
            for(var r=0; r<brickRowCount; r++) {
                var b = bricks[c][r];
                if(b.status == 1) {
                    if(x > b.x && x < b.x+brickWidth && y > b.y && y < b.y+brickHeight) {
                        dy = -dy;
                        b.status = 0;
                    }
                }
            }
        }
    }

    function drawBall() {
        ctx.beginPath();
        ctx.arc(x, y, ballRadius, 0, Math.PI*2);
        ctx.fillStyle = "#0095DD";
        ctx.fill();
        ctx.closePath();
    }
    function drawPaddle() {
        ctx.beginPath();
        ctx.rect(paddleX, canvas.height-paddleHeight, paddleWidth, paddleHeight);
        ctx.fillStyle = "#0095DD";
        ctx.fill();
        ctx.closePath();
    }
    function drawBricks() {
        for(var c=0; c<brickColumnCount; c++) {
            for(var r=0; r<brickRowCount; r++) {
                if(bricks[c][r].status == 1) {
                    var brickX = (r*(brickWidth+brickPadding))+brickOffsetLeft;
                    var brickY = (c*(brickHeight+brickPadding))+brickOffsetTop;
                    bricks[c][r].x = brickX;
                    bricks[c][r].y = brickY;
                    ctx.beginPath();
                    ctx.rect(brickX, brickY, brickWidth, brickHeight);
                    ctx.fillStyle = "#0095DD";
                    ctx.fill();
                    ctx.closePath();
                }
            }
        }
    }

    function draw() {
        ctx.clearRect(0, 0, canvas.width, canvas.height);
        drawBricks();
        drawBall();
        drawPaddle();
        collisionDetection();

        if(x + dx > canvas.width-ballRadius || x + dx < ballRadius) {
            dx = -dx;
        }
        if(y + dy < ballRadius) {
            dy = -dy;
        }
        else if(y + dy > canvas.height-ballRadius) {
            if(x > paddleX && x < paddleX + paddleWidth) {
                dy = -dy;
            }
            else {
                alert("GAME OVER");
                document.location.reload();
            }
        }

        if(rightPressed && paddleX < canvas.width-paddleWidth) {
            paddleX += 7;
        }
        else if(leftPressed && paddleX > 0) {
            paddleX -= 7;
        }

        x += dx;
        y += dy;
    }

    setInterval(draw, 10);
</script>

</body>
</html>