javascript - How to detect when an image has finished rendering in the browser (i.e. painted)?

Question

On a web app I need to work with a lot of high-res images, which are dynamically added to the DOM tree. They are pre-loaded, then added to the page.

It's one thing to detect when such an image has finished loading, for this I use the load event, but how can I detect when it has finished being rendered within the browser, using Javascript? When working with high resolution images, the actual painting process can take a lot of time and it's very important to know when it ends.

Answer 1

I used requestAnimationFrame to do the trick. After image loaded it will be rendered during the next animation frame. So if you wait two animation frames your image will be rendered.

function rendered() {
    //Render complete
    alert("image rendered");
}

function startRender() {
    //Rendering start
    requestAnimationFrame(rendered);
}

function loaded()  {
    requestAnimationFrame(startRender);
}

See http://jsfiddle.net/4fg3K/1/