One Screen Turn Deserves Another
[This post is by Dan Morrill, Open Source & Compatibility Program Manager. — Tim Bray]
Android has an API for accessing a variety of sensor types, such as an accelerometer or light sensor. Two of the most commonly-used sensors are accelerometers and magnetometers (that is, compasses.) Applications and devices frequently use these as forms of user input, and to determine which way to orient the screen.
However, there’s a new wrinkle: recently, a few devices have shipped (see here and here) that run Android on screens that are naturally landscape in their orientation. That is, when held in the default position, the screens are wider than they are tall. This introduces a few fairly subtle issues that we’ve noticed causing problems in some apps. Now, part of the reason for this is that the Android SDK docs on the sensor API left a couple things unsaid, leading many developers to use them incorrectly. Even a couple of our own samples did the wrong thing. Sorry about that!
Fortunately, using these APIs correctly is pretty simple, if you keep three rules in mind:
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The sensor coordinate system used by the API for the natural orientation of the device does not change as the device moves, and is the same as the OpenGL coordinate system.
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Applications must not assume that the natural orientation is portrait. That’s not true on all devices.
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Applications that match sensor data to on-screen display must always use
android.view.Display.getRotation()to map sensor coordinates to screen coordinates
