CODEWITHSUNDEEP
javascripthtmlcanvasmove
HoneyPoop
HoneyPoop

Reputation: 513

How do I move an element on a canvas around with an animation?

I have been looking for a while on how to move a certain square around on a canvas with JavaScript, and haven't found much. I have done one where it removes itself and replaces itself every frame, but I want it to be smoother and animated. This is my code:

<canvas id="myCanvas" width="200" height="100" style="border:1px solid grey;"></canvas><br />
<button onclick="#">Move Up</button>
<script>
canvas = document.getElementById("myCanvas");
  ctx = canvas.getContext("2d");
  ctx.fillStyle = "#FF0000";
  ctx.fillRect(20, 60, 20, 20);
</script>

So far the button does nothing, is there a function I could add that would move the square around? (in this case up)

Upvotes: 1

Views: 78

Answers (1)

Treast
Treast

Reputation: 1105

To make smooth animations, check about the requestAnimationFrame function (https://developer.mozilla.org/fr/docs/Web/API/Window/requestAnimationFrame).

Here an example with your code:

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

var squareY = 60;
var isButtonPressed = false;

ctx.fillStyle = '#FF0000';
ctx.fillRect(20, squareY, 20, 20);

function moveUp() {
  window.requestAnimationFrame(moveUp);

  if (isButtonPressed) {
    squareY -= 10 / 16;
  }

  squareY = Math.max(squareY, 5);

  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.fillStyle = '#FF0000';
  ctx.fillRect(20, squareY, 20, 20);
}

function onMouseUp() {
  isButtonPressed = false;
}

function onMouseDown() {
  isButtonPressed = true;
}
canvas = document.getElementById('myCanvas');
ctx = canvas.getContext('2d');

var squareY = 60;
var isButtonPressed = false;

ctx.fillStyle = '#FF0000';
ctx.fillRect(20, squareY, 20, 20);

function moveUp() {
  window.requestAnimationFrame(moveUp);

  if (isButtonPressed) {
    squareY -= 10 / 16;
  }

  squareY = Math.max(squareY, 5);

  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.fillStyle = '#FF0000';
  ctx.fillRect(20, squareY, 20, 20);
}

function onMouseUp() {
  isButtonPressed = false;
}

function onMouseDown() {
  isButtonPressed = true;
}

window.addEventListener('keydown', function (e) {
  if (e.key == 'ArrowUp') {
    // if the arrow key is pressed
    squareY -= 10 / 16;
  }
});

moveUp();
<canvas id="myCanvas" width="200" height="100" style="border:1px solid grey;"></canvas><br />
<button onmousedown="onMouseDown()" onmouseup="onMouseUp()">Move Up</button>
<script>
</script>

Upvotes: 1

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