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android – GL Surface and Visibility: Gone

Posted by: admin June 15, 2020 Leave a comment

Questions:

So I have a GLSurfaceView in my app being rendered by a GLSurfaceView.Renderer and using JPCt as library.

The surface is in an invisible RelativeLayout (visibility: gone). When I change the visibility to “visible” then back to “gone”, the layout shows and hides as expected, but the GLSurfaceView don’t, it just shows and won’t hide, even though I can click on items that are now “behind” it.

It seems like some graphical buffer issue, but I didn’t find a way to get this to work… any ideas?
Thanks!

How to&Answers:

SurfaceView (and GLSurfaceView by extension) are interesting beasts in Android. Citation from Android javadoc:

The surface is Z ordered so that it is behind the window holding its
SurfaceView; the SurfaceView punches a hole in its window to allow its
surface to be displayed. The view hierarchy will take care of
correctly compositing with the Surface any siblings of the SurfaceView
that would normally appear on top of it

Android has a built-in window compositor (window has a bit different meaning here). Your status bar is a window, your activity has one window. But if your activity contains a surface view, another window is created, just to hold the surface, and android compositor draws the window with your views over the surface window. So the SurfaceView is really only a transparent area. When you hid it, the area is not drawn, does not react to touches, but the surface window is still present, android is not clever enough to hide the window.

I would recommend two solutions

  • Make your surface translucent. You can then render empty surface when you need to hide the view( Android, Transparent sub-GLSurfaceView in layout? )
  • Remove the view from view hierarchy altogether
  • Another a bit hacky way is to subclass GLSurfaceView and call onDetachedFromWindow() when visibility changes to GONE. I have not tested this and it might not work.