How to apply blur to an activity under an open dialog?

Question

Android

Recently I set out to make a blur under the dialog box. But on the Internet, something could not google anything intelligible. Image blur only + now unsupported instructions
WindowManager.LayoutParams.FLAG_BLUR_BEHIND
Does anyone have any more or less straightforward ways than to "take a picture" of our activity in a bitmap and then put it in the foreground and blur, raise the dialog?