iOS: Harden logic for when it's safe to use the graphics hardware

To fix QTBUG-52493 we tied the exposed state of a window to the
application being in the foreground. This has the result of a
visible flash of black between hiding the launch screen and showing
the first frame of the application, as the application is still
waiting for UIApplicationStateActive to begin rendering, which
happens after iOS hides the launch screen.

According to the iOS OpenGL ES Programming Guide, it should be safe
to render GL in UIApplicationStateInactive as well, and even in
UIApplicationStateBackground, as long as the rendering finishes
before the UIApplicationDidEnterBackgroundNotification returns.

To ensure that we catch any bugs in this area, checks have been
added that verify that no rendering happens while in the background
state.

Task-number: QTBUG-63229
Task-number: QTBUG-52493
Task-number: QTBUG-55205
Change-Id: Ib42bedbeddd7479ab0fb5e5b7de9f5805658e111
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/plugins/platforms/ios/qioscontext.h b/src/plugins/platforms/ios/qioscontext.h
index 5b7917f7b4..ce50eff1d9 100644
--- a/src/plugins/platforms/ios/qioscontext.h
+++ b/src/plugins/platforms/ios/qioscontext.h
@@ -87,6 +87,7 @@ private:
         bool isComplete;
     };
 
+    static bool verifyGraphicsHardwareAvailability();
     static void deleteBuffers(const FramebufferObject &framebufferObject);
 
     FramebufferObject &backingFramebufferObjectFor(QPlatformSurface *) const;