Birdview.js wraps all
body HTML content inside a custom DOM structure: everything is put inside an inner div
birdview_child, itself wrapped inside an outer div
<body> <div id="birdview_parent"> <div id="birdview_child"> HTML content... </div> </div> </body>
The birdview effect is performed using CSS scale transforms on the
birdview_child div. To ensure a continuous transition between the current scrolling position and the birdview, the Y origin of the scale transform must be at the vertical midpoint of the viewport.
The vertical midpoint of the viewport is then projected into the document, and a CSS scale transform is applied to the
... read the whole story at achrafkassioui.com.