_initSources() {
        // finally load every sources already in our plane html element
        // load plane sources
        let loaderSize = 0;
        if(this.autoloadSources) {
            const images = this.htmlElement.getElementsByTagName("img");
            const videos = this.htmlElement.getElementsByTagName("video");
            const canvases = this.htmlElement.getElementsByTagName("canvas");

            // load images
            if(images.length) {
                this.loadImages(images);
            }

            // load videos
            if(videos.length) {
                this.loadVideos(videos);
            }

            // load canvases
            if(canvases.length) {
                this.loadCanvases(canvases);
            }

            loaderSize = images.length + videos.length + canvases.length;
        }

        this.loader._setLoaderSize(loaderSize);

        this._canDraw = true;
    }
Load our initial sources if needed and calls onReady callback
*