Display a customized OSD (on-screen display), like windows 10 volume OSD, when a specific hot key is pressed

Question

Hi,

I am developing Desktop/UWP application on windows 10. And I have a little development experience with WDM/WDF.
My vendor has a request to do that display a customized OSD (on-screen display), like windows 10 volume OSD, when a specific hot key is pressed.
The customized OSD will displayed for a few seconds and must be displayed on the top overlay everything.

AFAIK, it is impossible in normal application.
I already try the win7 audio osd example (https://github.com/microsoft/Windows-classic-samples/tree/master/Samples/Win7Samples/multimedia/audio/osd),
and read this article: "How do I create a topmost window that is never covered by other topmost windows?" (https://devblogs.microsoft.com/oldnewthing/?p=11253)

I also use the keyword "OSD", "on screen display" to search, but no found useful answer to me.

Our application/driver will bundle in windows 10 device.

1. Is there a way to request some privilege let application to to that?
2. Can driver do that? what kind of driver?

P.S.
Tags request but, I can not key any relative tag.
It show: The following tags do not exist, and you don't have permissions to create new ones: Windows 10, OSD, on screen display, desktop, driver

Thanks,
Emmett

Answer 1

Try configuring your application so that it runs with UIAccess=true and with a window that is WS_EX_TOPMOST.
In order to run with UIAccess it must be properly manifested, signed and loaded from a secure location (e.g., C:\Program Files..., C:\Windows\System32).

In my quick and dirty test a Windows desktop application was able to place itself in the Z-order above other windows. It always appeared above windows (even TOPMOST) of other applications that did not have UIAccess privileges. But there is no guarantee that it would always appear over TOPMOST windows created by other UIAccess enabled applications.