Over a million developers have joined DZone.
{{announcement.body}}
{{announcement.title}}

Zoom-on-rotate fix for WebKit mobile browsers

DZone's Guide to

Zoom-on-rotate fix for WebKit mobile browsers

· Web Dev Zone
Free Resource

Try RAD Studio for FREE!  It’s the fastest way to develop cross-platform Native Apps with flexible Cloud services and broad IoT connectivity. Start Your Trial Today!

 

This blog post is a part of Mobilizing websites with responsive design and HTML5 tutorial. For all posts please see the Introduction post.

After adding meta viewport tag for your mobile site its width is properly formatted for mobile browsers. However, there exists a common glitch you should be aware of.

On iOS devices, and on some Android devices, the mobile browser re-zooms the web page when the device orientation changes. The browser applies heuristics and try to determine a new zoom level after the rotation, but sometimes the result is not desirable. When you rotate from the portrait mode to the landscape mode, the page zooms in too much.

In our case, the project client specifically requested to disable this little feature if possible, as it was irritating the test users on iPad devices.

This can be worked around by resetting the viewport with Javascript after the orientation changes.

An example code going into HTML <head> section:


  <!--

    Don't break scale on iPad rotate.

    By default iPad re-zooms the page when the device orientation changes.
    The heuristics here do not work always; our page got zoomed in
    though it should be max zoomed out.

    This snippet fixes the situation so that you can still zoom in, but when
    the device is rotated the scale is restored.

   -->
<script type="text/javascript">
(function(doc) {

    var addEvent = 'addEventListener',
        type = 'gesturestart',
        qsa = 'querySelectorAll',
        scales = [1, 1],
        meta = qsa in doc ? doc[qsa]('meta[name=viewport]') : [];

    function fix() {
        meta.content = 'width=device-width,minimum-scale=' + scales[0] + ',maximum-scale=' + scales[1];
        doc.removeEventListener(type, fix, true);
    }

    if ((meta = meta[meta.length - 1]) && addEvent in doc) {
        fix();
        scales = [.25, 1.6];
        doc[addEvent](type, fix, true);
    }

}(document));
</script>

Please edit the scales part of the code for the desired min and max scaling level.

Note: Dynamic viewport manipulation is badly supported on older Android devices and contains many pitfalls.

1. More info

Get Your Apps to Customers 5X Faster with RAD Studio. Brought to you in partnership with Embarcadero.

Topics:

Published at DZone with permission of Mikko Ohtamaa, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

THE DZONE NEWSLETTER

Dev Resources & Solutions Straight to Your Inbox

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.

X

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}