Add support for Windows 11 "Snap Layout" to the custom title bar (WindowChrome)

[d2phap]

As Windows 11 introduce Snap Layout when we hover on Restore/Maximize caption button, I want to have this feature on my custom title bar using WindowChrome.

The current SystemCommands class does not have it:

public static class SystemCommands
{
  public static void CloseWindow(Window window);
  public static void MaximizeWindow(Window window);
  public static void MinimizeWindow(Window window);
  public static void RestoreWindow(Window window);
  public static void ShowSystemMenu(Window window, Point screenLocation);
}

Custom Title bar

Default Title bar

[lindexi]

Ref #4749

[batzen]

Does anyone know if there is an API to trigger the new snap layout "menu"?

[miloush]

It is not a system command.

If you have a custom maximize button, it is your job to tell that to the OS by responding HTMAXBUTTON to WM_NCIHITTEST. That will give you the snap options on hover.

I think there is an opportunity for API improvement to simplify this task through an attached WindowChrome property

[mdtauk]

It is not a system command.

If you have a custom maximize button, it is your job to tell that to the OS by responding HTMAXBUTTON to WM_NCIHITTEST. That will give you the snap options on hover.

I think there is an opportunity for API improvement to simplify this task through an attached WindowChrome property

This would be helpful for Windows Terminal, as well as other WinUI 3 apps.

[batzen]

@miloush While returning HT.MAXBUTTON works and shows the menu it causes various unwanted side effects.

• MouseOver does not work anymore (highlight)
• Clicking a button which returned some window button HT causes the system button to be rendered for a short time

[miloush]

@batzen I guess you can still handle the mouse over, however yeah I will give you that the system-rendered button on click is sad; feels like a bug in the shell.

[Splitwirez]

@miloush The events aren't even raised when the caption button HT values are returned. The WPF stuff just acts like the cursor isn't even over the window.

[billhenn]

We also have been digging into this issue of trying to show the Snap Layout Menu in a WPF app that uses our custom WindowChrome, where we render all custom title bar buttons. We've run into the same issues when returning HTMAXBUTTON from WM_NCHITTEST as described above, where WPF no longer receives any pointer input (due to HTCLIENT not being returned), and clicking our custom button renders a classic Win32 maximize button.

We really need some other API than responding to WM_NCHITTEST to get this working for those of us who have powerful custom window chromes and need the WPF elements in those chromes to remain responsive.

[batzen]

FYI: The WindowChromeBehavior from ControlzEx will provide a solution for this problem during Hacktoberfest.