javascript, controlling a ball's movement using mouse

Question

I was following this MDN tutorial:

https://developer.mozilla.org/es/docs/Games/Workflows/Famoso_juego_2D_usando_JavaScript_puro/Mueve_la_bola

And I was wondering how could we control the ball's movement using mouse movement event.

I have seen that mousemove works with textarea and some inputs:

https://developer.mozilla.org/en-US/docs/Web/Events/mousemove

I thought if we could put a textarea behind the canvas, we could detect the event, get the mouse's position and let the user change the ball's movement with mouse movement.

I have read:

Dynamically resize textarea width and height to contain text

So I tried:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Juego</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        canvas {
            background: #eee;
            display: block;
            margin: 0 auto;
        }
    </style>
</head>
<body>
<textarea name="ta" id="ta" cols="30" rows="10"></textarea>
<canvas id="myCanvas" width="480" height="320"></canvas>

<script>
    const textarea = document.getElementById('ta');
    const canvas = document.getElementById('myCanvas');
    const ctx = canvas.getContext('2d');

    textarea.style.height = canvas.height;
    textarea.style.width = canvas.width;

    let x = canvas.width / 2;
    let y = canvas.height - 30;

    const dx = 2;
    const dy = -2;

    let drawBall = function () {
        ctx.beginPath();
        ctx.arc(x, y, 10, 0, Math.PI * 2);
        ctx.fillStyle = "#0095DD";
        ctx.fill();
        ctx.closePath();
    };

    function draw(e) {
        console.log(e);
        ctx.clearRect(0,0,canvas.width,canvas.height);
        drawBall();

        x += dx;
        y += dy;
    }

    setInterval(draw, 10);

    canvas.addEventListener('mousemove', draw);


</script>
</body>
</html>

The expected output would be to have the textarea using canvas' width and height, and being behind it; however it is smaller and put on top left:

Thank you for your help.

score 1 · Accepted Answer · answered Apr 07 '18 at 22:28

you don't need the textarea to capture the event, and it'll be complicated because the canvas will be on top and the textarea will never know the mouse is moving on top of it, and to make the ball moving with the mouse, you have to passe the x and y of the mouse to the draw(); while it's moving function

here's a fiddle : https://jsfiddle.net/vqdyLx5u/22/

let canvas = document.getElementById('myCanvas');
let ctx = canvas.getContext('2d');

function drawBall(x, y) {
  ctx.beginPath();
  ctx.arc(x, y, 10, 0, Math.PI * 2);
  ctx.fillStyle = "#0095DD";
  ctx.fill();
  ctx.closePath();
}

function draw(x, y) {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  drawBall(x, y);
}

draw(canvas.height / 2 , canvas.width / 2); // initial draw

canvas.addEventListener('mousemove', function(e) {
  draw(e.pageX, e.pageY); // the coordinates of the mouse
});

* {
  padding: 0;
  margin: 0;
}

canvas {
  background: #eee;
  display: block;
  margin: 0 auto;
}

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

javascript, controlling a ball's movement using mouse

1 Answers1