freeCodeCamp/guide/english/canvas/animation-in-canvas/index.md

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Animation

Animation in Canvas

To animate things in canvas, use window.requestAnimationFrame to set up a draw loop.

function draw() {
  /* code goes here */
  window.requestAnimationFrame(draw);
}
window.requestAnimationFrame(draw);

The below code will cause the draw function to be run every frame.

canvas has no special functions that allow for animating. You just have to be used to writing in animation loops. The usual design paradigm for animation loops is to update the state, then draw the state. For instance, to draw a square moving across the screen:

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

var x=0;
var y=50;
function draw() {
  // reset canvas
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  //update state
  x+=1;

  // render state
  ctx.beginPath();
  ctx.rect(x, y, 50, 50);
  ctx.fill();

  window.requestAnimationFrame(draw);
}
window.requestAnimationFrame(draw);

To see this concept in action, see the 'Particle Sim' page.

More Information:

• MDN Canvas API