How to set focus / activation to Unity Player window...

Unity Engine
1

Hi all,

Early in the launch of my game (in player, not editor) I need to spawn Blender to act as a backend to my game…

Unfortunately I was not able to find a way to start Blender hidden or minimized and when I spawn that process while the player loads my game, windows activates Blender and my user needs to Alt-Tab back to Unity Player to play…

Is there a way to re-activate the Unity player window? (Say by obtaining the window handle of it and calling a user32 command?)

Many thanks!

2

Hi guys figured this out…

First remember Unity’s HWND early in your game init when you know it has the focus:

_hWnd_Unity = (IntPtr)GetActiveWindow(); //###NOTE: Obtain the HWND of our Unity editor / player window. We will need this to re-activate our window. (Starting blender causes it to activate and would require user to alt-tab back to game!!)

Later on when you need to regain focus call:

SetForegroundWindow(_hWnd_Unity); // Set our editor / player back into focus (away from just-spawned Blender)

With these user32 function defined:
[DllImport(“user32.dll”)] static extern uint GetActiveWindow();
[DllImport(“user32.dll”)] static extern bool SetForegroundWindow(IntPtr hWnd);

4 Likes
3

This is excellent. I was trying hard to find a good solution. But, your solution worked perfectly well
Just to optimize it a bit more, (For a kiosk mode application) we should focus a window only when it goes out of focus.
Cameron’s answer describes it very well here

4

Yes this solution is great, the system32 way of doing it. Since it’s low level you just want to be cautious about it if you’re deploying to certain platforms.

5

This solution isn’t great, it’s flaky.

If you launch the game and just focus another window while the splash screen is running or while it’s still starting up - you will get the hwnd of a different window. Might be good enough for some personal tool or a game jam game where 10 people run it, but this is not a robust solution anyone should ship with.

Unity needs to expose the hwnd, or better yet: fix whatever is causing Process.GetCurrentProcess().MainWindowHandle to be 0 perpetually.

6

Alright, I managed to scrape together a working solution.

[DllImport("user32.dll")]
static extern bool EnumThreadWindows(int dwThreadId, EnumThreadDelegate lpfn, IntPtr lParam);

[DllImport("Kernel32.dll")]
static extern int GetCurrentThreadId();

static IntPtr GetWindowHandle()
{
    IntPtr returnHwnd = IntPtr.Zero;
    var threadId = GetCurrentThreadId();
    EnumThreadWindows(threadId,
        (hWnd, lParam) => {
            if(returnHwnd == IntPtr.Zero) returnHwnd = hWnd;
            return true;
        }, IntPtr.Zero);
    return returnHwnd;
}

I can then use both of these functions I want to use:

[DllImport("user32.dll", EntryPoint = "SetWindowPos")]
public static extern IntPtr SetWindowPos(IntPtr hWnd, int hWndInsertAfter, int x, int Y, int cx, int cy, int wFlags);
[DllImport("user32.dll", EntryPoint = "SetWindowText")]
public static extern bool SetWindowText(System.IntPtr hwnd, System.String lpString);

For any questions on what parameters to pass to those functions, see microsoft’s documentation on them.

Edit: User Bunny83 has a good note on using lambdas with yhese callbacks here: How do you reliably the hwnd (window handle) of the game's own window? - Unity Engine - Unity Discussions

Basically: Lambdas in native callbacks will break with il2cpp

7

The issue is tracked and can be voted on here: