Windows and the title bar

ShellWindow

ShellWindow is the base Window. It pre-wires the extended client area so the window paints into the title bar region, the thick macOS title bar via MacOSTitleBar, frontmost activation on first open, and the keyboard path: a tunnelled KeyDown handler that gives the subclass first crack through OnPreviewKeyDownAsync, then the injected KeyboardDispatcher, then OnUnhandledKeyDown. It also implements ICommandSurface by delegating to that dispatcher, so toolbars and the palette fire commands by name with nothing to wire. All of the macOS plumbing no-ops elsewhere.

ShellDialog is the same window for modal children shown through ShowDialog. It keeps the chrome but fixes the activation cascade a modal child needs on macOS: it does not re-activate the app on open, which would re-key the parent and leave the dialog with dimmed traffic lights, and it makes itself key one dispatcher tick after opening, once AppKit has it in the window list.

AlloyTitleBar

The integrated title bar for extended-client-area windows. It never draws caption buttons. Native chrome owns them, and the control measures around them:

• Content fills the bar, padded by Padding, whose platform default clears the macOS traffic lights. Set Padding="0" for content that centers itself.
• RightContent is pinned right and inset past the OS caption buttons. It uses WindowDecorationMargin when the platform reports it, else the exact DWM caption-button bounds on Windows, DPI-aware and three-or-four-button-aware, else a worst-case reservation.
• Empty bar space drags the window through BeginMoveDrag, and a double-tap toggles Normal and Maximized, honouring the window's CanMaximize. A press on any focusable child, a button, a menu item, a text box, is left alone. CanDrag and CanToggleWindowStateOnDoubleTapped switch each off.

<tb:AlloyTitleBar MinHeight="44" Padding="0" Background="{DynamicResource Surface.Window}">
  <TextBlock Text="My App" Classes="secondary" HorizontalAlignment="Center" VerticalAlignment="Center"/>
  <tb:AlloyTitleBar.RightContent>
    <StackPanel Orientation="Horizontal" Spacing="4">
      <Button Classes="bare"><icons:GlyphIcon Glyph="moon" Size="15"/></Button>
    </StackPanel>
  </tb:AlloyTitleBar.RightContent>
</tb:AlloyTitleBar>

TitleBarHeaderReserve keeps a header zone hosted in the bar clear of both ends: the right margin reserves the actions cluster, and the left margin tracks a live leading width, typically the sidebar's reserved column, updated every dock-animation frame.

ShellChrome.axaml, included once from avares://Avalloy.Core/Themes/ShellChrome.axaml, supplies the shell class that collapses the caption-button and sizing boilerplate and the ShellTitleBarContentInset resource that keeps the traffic-light measurement in Avalloy.

Geometry

WindowGeometry.BindGeometry restores size, position and maximized state onto a window and writes them back as they change. The model is an IWindowGeometry on a preferences object, or IMaximizableWindowGeometry to remember the maximized flag. Position is nullable: null means let the OS place the window, which is the first launch and after a reset. Keep geometry in the per-machine state file rather than roaming preferences; it is display-bound.

WindowPlacement centres a top-level window over another without parenting it. On macOS an owned window never becomes key, so its traffic lights stay grey; these helpers give the opens-over-the-window-I-am-in placement while keeping it an independent top-level.