[screen-orientation] screen orientation angle


The Screen Orientation API defines an angle relationship between
portrait-primary and landscape-primary. The reason for that is that
developers would know which orientation is at 90 degrees from the
current orientation, which one is at 180 degrees, etc. However, by
forcing the two primary orientations to have a relationship, we prevent
UA to do clever things like having landscape-primary being related to
how the user uses his phone (eg. usually depending on which hand is
used, the most common landscape is not going to be different).

In addition, some use cases might need to know the angle between the
current orientation and the native device orientation. For example, a
compass using DeviceOrientation would need to know this angle to be able
to draw the correct information on the screen [1].

This is also a UC that Mozilla has with Firefox OS where some apps want
to lock the orientation to the native device orientation (ie. angle=0)

So, the Screen Orientation API should allow locking to a specific
orientation angle. For that, we could allow an integer to be passed to
the lockOrientation() function, a modulo operation would be applied on
the number to have it in the [0; 360[ range. If the UA is not able to
lock to the specified angle, the method should fail (return false for
the moment, the promise should fail in the future).

The orientation angle should also be read. It would be possible to
simply use window.orientation. I am not a big fan of that solution [3]
but this is implemented by most Mobile UAs already so it might as well
be the best thing to do. An alternative would be to have something like
screen.orientationAngle or screen.orientation.angle (and


[1] http://oldworld.fr/google/compass.html
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=908058
[3] the value can be negative, which is a footgun and the having this
value living in window and the rest in window.screen is odd


Received on Tuesday, 26 November 2013 16:38:35 UTC