Fix blur gets lost when display list for target view is not available

[Rosemoe]

Bug Description

When using RenderNode for blur, the blurred content can get lost if the RenderNode of target view has no valid display list. This typically happens when the display list is recycled by the framework.

Here is a sample case of the bug:
When using BlurView as my Dialog background view, after switching the app background and foreground, the blurred background is lost and becomes white.

WhiteBgAfterTaskSwitching_Compressed.mp4

Test Device: Redmi K50 (Android 14)
Library Version: Latest master Branch

Fix Description

This PR fixes the issue by fallback to software path when display list is unavailable.

Limitations

There can be slight difference between hardware and software blurred content, as the images shown below. The first is hardware path while the second is fallback software path.

Alternative Fix

Another possible fix is calling postInvalidate() on both blurView and targetView when the display list is unavailable. In this case, we can get valid display list next time the view draws and continue with hardware path. On my test device, I didn't get visual latency (not seeing white background).
However, this violates the library principle to not invalidate the target view.

[Dimezis]

Thank for the contribution.
Can you also please share a branch with the dialog example?
I'm tempted to try the postInvalidate fix since I don't want the BlurView to get stuck in the software path in this scenario

[Rosemoe]

Can you also please share a branch with the dialog example?

Sure, here is the dialog sample with postInvalidate fix: https://github.com/Rosemoe/BlurView/tree/repro/dialog-bg

[Dimezis]

@Rosemoe I think you forgot to commit the dialog's XML layout

[Rosemoe]

@Rosemoe I think you forgot to commit the dialog's XML layout

Sorry, I uploaded the file now.