AppWindow (WAS) titlebar customization & WinUI 3 titlebar customization

[AzAgarampur]

So it seems there are two ways to customize a titlebar for a desktop app, (correct me if I'm wrong)

1. Use WinUI 3's Window.ExtendsContentIntoTitleBar. This will: recalculate the client area of the window and remove the top frame (titlebar) by handling WM_NCCALCSIZE, extends the default DWM frame into the background, set the window frame's theme (according to the user's theme settings), and then draws the WinUI 3 caption buttons on top.
2. Use AppWindow's AppWindowTitleBar.ExtendsContentIntoTitleBar. This will: set window attributes so that the caption buttons are not drawn, and then draw the appropriate caption buttons/titlebar using a separate pair of DirectComposition & Direct3D devices.

Approach number 2 seems to be the best one. Not only does it look better, but it is more complete. In fact, it is almost doing the same thing that ApplicationFrameHost.exe does to show UWP application's windows (CoreWindow). WinUI 3's "titlebar" looks completely out of place, with tiny caption buttons that jitter and jump all over the place when resizing, and they also show the DWM frame beneath them, making it appear as if there are two titlebars. Another reason number 2 is better is because it can allow titlebar customization from any ui framework, as the titlebar isn't linked to any XAML UI elements, and this method of customization does not require Windows 11. You can see Windows 10's ApplicationFrame window have the same drawing behavior. I don't know why it is currently supported on Windows 11 only.

My suggestion is that WinUI 3 should "forward" its titlebar customization calls to Microsoft.UI.Windowing.AppWindow. Since WinUI will maintain complete control of the Window/Graphics of the app, it can also forward other behavior to Microsoft.UI.Windowing.AppWindow instead of re-implementing it.

There are a few other things I was thinking would be cool if WinUI 3 and Windows can do:

• Maybe AppWindow can have some private/internal functions that WinUI 3 can call so that a XAML UI element/Visual can act as the title. This is just like what UWP currently does. This routine could also be made public and accept an IDCompositionVisual* so that classic Win32 apps that use a DirectComposition based UI framework (that isn't WinUI 3, XAML, etc) can use AppWindow to allow a Visual to act as the titlebar. In this case, AppWindow may use DCompositionAttachMouseDragToHwnd to make it act like the titlebar.
• AppWindow and Windows (the DWM, ApplicationFrame, etc) itself should stop using DrawThemeTextEx/TextOut/DrawText to draw text for the titlebars of custom AppWindow titlebars, ApplicationFrameWindow tilebars, and standard Win32 HWNDs. Using these GDI based function doesn't allow certain things, like color emojis as caption text, text styling, etc. Since the DWM controls basically every window, it could use Direct2D's DrawText to draw the window caption. UWP and AppWindow should also do the same.
• CompactOverlay mode with AppWindow should be more like the UWP CompactOverlay, rather than simply making a window always on-top and making it have only a close button.

Once again, if some of these features could be used from WinUI 3 only by "propagating" its actual functionality as calls into AppWindow, that would make it a lot better than having to use 2 separate things.

Overall I'm very happy with AppWindow and how it'll help developers have easy customization via the system, just like how UWP apps have it. However, I think these few suggestions will make it even better.

[kmgallahan]

https://portal.productboard.com/winappsdk/1-windows-app-sdk/c/48-integrate-appwindow-with-winui-3

[AzAgarampur]

For AppWindow integration with WinUI 3, I was thinking: a possible way to integrate them is to have an internal AppWindow object used by WinUI 3 internally. So, we can just grab the titlebar using WinUI 3 (maybe like m_MainWindow.TitleBar) and then apply customizations via that way. In the end, you'd have a UWP style interface to change titlebar colors.