Retina Hidpi display

[typometre]

Hi,
That's great. But it doesn't work at best on mobile devices or generally hidpi screens.

I have found that if I change a value in the viewport definition
var viewport = page.getViewport(domMapObject.canvas.width / page.getViewport(0.5).width);
instead of
var viewport = page.getViewport(domMapObject.canvas.width / page.getViewport(1).width);
on line 818 of app.js

make it work at retina resolution

But it works only at first. when you change page and revert back, the page is left black.

I can't find what happen when it go back to a page already drawn and why it left it all black.

How could I fix this ?
Where the viewport value is reset in some way ?

Thanks

[typometre]

As on an Ipad, I can see that if I rotate the iPad, the page appear so this seems to be a refresh view issue.
Any idea where this could be located ?