Is there a way to detect when another app enters fullscreen?

Question

I have an always on top application that I want to hide when another app enters fullscreen. Is there a way to detect this?

Answer 1

Hello Adam,

Another technique might be to consume events generated by the Microsoft-Windows-Win32k provider in real-time, using a keyword filter such as UIUnresponsiveness or AutoRotation to reduce the number of irrelevant events reported. There are "Start" and "Stop" events for "ForegroundWindowFullScreen":

Update:

Another option is to receive WM_SHELLHOOKMESSAGE messages (either by calling RegisterShellHookWindow or by hooking WH_SHELL messages); the HSHELL_ values for entering/leaving full screen appear to be 53/54 (undocumented values).

Gary

Answer 2

Hello,

Welcome to Microsoft Q&A!

You could try to use SetWinEventHook function.

In SetWinEventHook()’s callback, you could handle the EVENT_OBJECT_LOCATIONCHANGE event and check if the window is in maximized state by calling the GetWindowPlacement() function and comparing the showCmd property with the SW_SHOWMAXIMIZED constant.

You could refer to the thread: https://stackoverflow.com/a/34549801

Thank you.

Jeanine

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Answer 3

If you read Raymond Chen's article at How do I switch a window between normal and fullscreen? you can see that the procedure to switch a windows to Fullscreen does not maximize the window. Following images use Spy++ to demonstrate this - Maximized Window -

Note that the taskbar is visible at the bottom of the screen and the window's caption bar is visible. Also, take a look at the various reported window rectangles. And now the same window switched to Fullscreen using as described in the article -

Note that the taskbar is not visible and the windows caption bar is not present. So it seems to me that you can use WinEvents to check if upon receiving EVENT_OBJECT_LOCATIONCHANGE the window's rectangle is identical to the dimensions of the monitor that is associated with the window. For the window discussed in the article you should also be able to check the window style to see that WS_OVERLAPPEDWINDOW is not present.

Answer 4

I want to hide when another app enters fullscreen

If an other application in fullscreen comes in focus, then it overlapp everything incl. your app; so what do you want to hide, no-one sees it anyway?

Answer 5

An old method is with DirectDraw (like the test I posted in this thread, mainly for DirectX app in Fullscreen : https://learn.microsoft.com/en-in/answers/questions/557345/determining-whether-game-mode-is-active) (not tested on Windows 11...)