Make ComposePanel.windowContainer public

[MatkovIvan]

Proposed Changes

• Resolve TODO from Add desktop component and window layers implementations #962
• Expose ComposePanel.windowContainer to customize behavior of additional layers (Popup/Dialog)
• Fixes inconsistency with window coordinates

Testing

Test: try to use this API with compose.layers.type=COMPONENT

@OptIn(ExperimentalComposeUiApi::class)
fun main() = SwingUtilities.invokeLater {
    System.setProperty("compose.swing.render.on.graphics", "true")
    System.setProperty("compose.layers.type", "COMPONENT")

    val window = JFrame()
    window.defaultCloseOperation = WindowConstants.EXIT_ON_CLOSE

    val contentPane = JLayeredPane()
    contentPane.layout = null

    val composePanel = ComposePanel()
    composePanel.setBounds(200, 200, 200, 200)
    composePanel.setContent {
        ComposeContent()
    }
    composePanel.windowContainer = contentPane  // Use the full window for dialogs
    contentPane.add(composePanel)
    
    window.contentPane.add(contentPane)
    window.setSize(800, 600)
    window.isVisible = true
}

@Composable
fun ComposeContent() {
    Box(Modifier.fillMaxSize().background(Color.Green)) {
        Dialog(onDismissRequest = {}) {
            Box(Modifier.size(100.dp).background(Color.Yellow))
        }
    }
}

Default windowContainer	Full-size windowContainer

[m-sasha]

Can you explain a bit why it needs to be public?

[igordmn]

Can you explain a bit why it needs to be public?

If I am not mistaken, It is needed for a case, when some small ComposePanel tries to show a popup/dialog outside of the panel. In this case, users should set layersContainer to the window.contentPane.

Worth to add an example.

Also, we need to change the description, so it can be included in the changelog and outside user can understand what the feature is about. And change the KDoc