My OpenGL app animates only every now and then, so I decided to use
RENDERMODE_WHEN_DIRTY to save some battery life. However, I found that
when I go to Home Screen and return to my app, I often get a black
screen, and I see this in logcat:
E/SurfaceComposerClient( 6055): using an invalid surface id=1,
identity=735 should be 738
This seems to be caused by this code in GLSurfaceView (1.6 here, but
2.0 has same problem):
synchronized (this) {
........
if (mPaused) {
mEglHelper.finish();
needStart = true;
}
while (needToWait()) {
wait();
}
.......
}
if (needStart) {
mEglHelper.start();
......
If I use RENDERMODE_WHEN_DIRTY, I will be stuck inside the wait()
call. When my app is paused/resumed, GLSurfaceView.{onPause,onResume}
will be called, by the change in mPaused will be lost. So when wait()
finally finishes, the mEglHelper.finish() and mEglHelper.start() lines
are not executed, and I end up drawing into the wrong surface.
The work around is simple but a bit ugly:
public MyView(....) {
super(....);
setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
}
public void onResume() {
super.onResume();
setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
requestRender();
}
public void onPause() {
setRenderMode(GLSurfaceView.RENDERMODE_CONTINUOUSLY);
android.os.SystemClock.sleep(60);
super.onPause();
}
The trick is to temporarily get the GLSurfaceView to run in
RENDERMODE_CONTINUOUSLY. I found the sleep(60) to be necessary to
avoid race conditions that somehow left me hanging inside the wait()
---- but I am not sure if this is 100% scientific.
Anyway, cheers, and save a few battery bars!
P.S., I found this to be somewhat disconcerting ... as the longevity
of this bug shows not too many people are trying to use OpenGL to make
their UI faster -- and battery efficient. This probably means that
iPhone apps will continue to look-and-feel better than Android for
quite some time :-(
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