lightweight variant (#1)

Reviewed-on: #1
Co-authored-by: Aleksandr Neychev <alexnejchev73@gmail.com>

CursorLang.Settings/Interop/WindowPlacementNative.cs

@@ -0,0 +1,53 @@
+using System.Runtime.InteropServices;
+using CursorLang.Core.Interop;
+
+namespace CursorLang.Settings.Interop;
+
+/// <summary>
+/// Win32 API for placing the settings window: its own bounds and the work area
+/// of the monitor the window is asked to be put on.
+/// </summary>
+/// <remarks>
+/// The bounds are taken from the system rather than from <c>Window.Left/Top/Width/Height</c>:
+/// the window height adapts to its content, and WPF converts those properties using the
+/// monitor DPI, while the monitor work area comes in pixels. Computing the centre in a
+/// single unit is simpler than converting back and forth.
+/// </remarks>
+internal static class WindowPlacementNative
+{
+    [DllImport("user32.dll")]
+    private static extern bool GetWindowRect(IntPtr hWnd, out PopupWindowNative.Rect lpRect);
+
+    [DllImport("user32.dll")]
+    private static extern IntPtr MonitorFromRect(ref PopupWindowNative.Rect lprc, uint dwFlags);
+
+    [DllImport("user32.dll")]
+    private static extern bool GetMonitorInfo(IntPtr hMonitor, ref MonitorInfo lpmi);
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct MonitorInfo
+    {
+        public int cbSize;
+        public PopupWindowNative.Rect rcMonitor;
+        public PopupWindowNative.Rect rcWork;
+        public uint dwFlags;
+    }
+
+    private const uint MONITOR_DEFAULTTONEAREST = 2;
+
+    /// <summary>The window bounds in screen pixels — including the frame and the title bar.</summary>
+    internal static PopupWindowNative.Rect? TryGetBounds(IntPtr hWnd) =>
+        GetWindowRect(hWnd, out PopupWindowNative.Rect bounds) ? bounds : null;
+
+    /// <summary>
+    /// The work area — without the taskbar — of the monitor that holds the
+    /// rectangle entirely, or at least most of it.
+    /// </summary>
+    internal static PopupWindowNative.Rect? TryGetWorkAreaNear(PopupWindowNative.Rect rect)
+    {
+        IntPtr monitor = MonitorFromRect(ref rect, MONITOR_DEFAULTTONEAREST);
+
+        var info = new MonitorInfo { cbSize = Marshal.SizeOf<MonitorInfo>() };
+        return GetMonitorInfo(monitor, ref info) ? info.rcWork : null;
+    }
+}

CursorLang.Settings/Interop/WindowThemeNative.cs

@@ -0,0 +1,30 @@
+using System.Runtime.InteropServices;
+
+namespace CursorLang.Settings.Interop;
+
+/// <summary>
+/// Window frame styling by the system: the title bar is drawn by Windows,
+/// and in the dark theme it has to be switched separately from the window content.
+/// </summary>
+internal static class WindowThemeNative
+{
+    [DllImport("dwmapi.dll")]
+    private static extern int DwmSetWindowAttribute(IntPtr hWnd, int attribute, ref int value, int size);
+
+    private const int DWMWA_USE_IMMERSIVE_DARK_MODE = 20;
+
+    /// <summary>
+    /// Recolours the window title bar. On Windows 10 builds before 2004 the attribute
+    /// is not supported — the title bar simply stays light.
+    /// </summary>
+    internal static void SetDarkTitleBar(IntPtr hWnd, bool isDark)
+    {
+        if (hWnd == IntPtr.Zero)
+        {
+            return;
+        }
+
+        int value = isDark ? 1 : 0;
+        DwmSetWindowAttribute(hWnd, DWMWA_USE_IMMERSIVE_DARK_MODE, ref value, sizeof(int));
+    }
+}