[Titlebar] Support Transparent Titlebar API.

[Sanlorng]

Description: Would you consider supporting an interface for making a transparent title bar? The Undecorated parameter cannot be easily implemented into an effect similar to ExtendContentToTitleBar in UWP applications which has system default caption button, system default corner shape, system default hit test, system default shadow and system default border. And Jetbrains/jewel seems to only be able to achieve partial effects on JBR.

Proposal:

    val state = rememberWindowState(extendToTitleBar = true)
    val contentColor = LocalContentColor.current
    LaunchEffect(state, contentColor) {
        state.titleBarBackgroundColor = Color.Transparent  
        state.captionButtonInactiveBackgroundColor = Color.Transparent
        state.captionButtonForegroundColor = contentColor.copy(0.87f)
        state.captionButtonInactiveForegroundColor = contentColor.copy(0.38f)
    }

    Window(state = state) {
        Column {
             Row(
                 modifier =  Modifier
                     .fillMaxWidth()
                     .wrapContentWidth(aligment = Aligment.End)
                     .height(WindowInsets.TitleBar.asPaddingValues().calculatePaddingTop())
            ){
                 Button(modifier = Modifier.padding(end = WindowInsets.CaptionButtons.asPaddingValues().calculatePaddingEnd(LocalRTL.current))) {
                    Text(text = "Button in titleBar")
                }
            }
        }

    }
    

Expect Behaviour : App content extend to TitleBar，and button in titleBar can padding caption buttons and interactive. Window has a system default look and feel instead of Undecorated window

[igordmn]

Thanks for proposal!

We had multiple missing features regarding customizing titlebars on different OS'es.

In the future we will revisit them, and make a consistent API that works for all OS'es (with specific API for each OS probably).

Not sure yet, but it probably won't be a part of WindowState, because its purpose to hoist states that can be changed by an user (resizing/repositioning window). It will be as an parameter of Window (one of the options is to combine some existing parameters into one rich parameter).

[mahozad]

Here is a solution for native shadows and animations for undecorated app in Windows:

• Missing animations when minimizing/maximizing/restoring undecorated window #3388 (comment)

[wwalkingg]

I think it's sufficient to not display the TitleBar, but retain the shadow and the ability to resize.

[Sanlorng]

I think it's sufficient to not display the TitleBar, but retain the shadow and the ability to resize.

I think CaptionButton is equally important for a desktop application. If developers need to draw their own CaptionButton, then the developer will have to write some wndProc-related code in order to support Windows 11 Snap.