[android-developers] Re: Black screen after switching to another app

MobileVisuals <eyvind <at> astralvisuals.com> writes:

>
> My app has a SurfaceView and a GLSurfaceView. I can switch back and
> forth between these. The SurfaceView is the application GUI.
>
> I test switching to another app. I can then switch back to the
> GLSurfaceView in my app. I then try to switch back to the
> GLSurfaceView,where the application GUI is. Here is where the problem
> occurs. A black screen is shown instead of the GUI.
>
> The app still works, because the application menu is shown when the
> menu button is pressed. But nothing is drawn on the screen, it is only
> black. I have tried almost everything to fix this, I have checked that
> the thread is running and that no instance of any object (like the
> SurfaceHolder) is null. What could be the reason for this black screen?
>

I had the same problem with my app. The problem is that you lose the GL context
if your application goes to the background, and so you lose all bound textures
(if you're using texture mapping), and you also lose the viewport. You need to
reload all your textures and you need to re-set your viewport and projection
matrix, etc. You should do this on your activities onResume() method, but you
won't have a GL context there, so just set a flag in your renderer to tell it to
reload everything. Your renderer will NOT always get an onSurfaceChanged() call
after the resume, so don't rely on that to reset your viewport! Because you
can't rely on onSurfaceChanged(), you also need to use saved values to set
viewport width and height.


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