magnifierWpf.cs

using System.Windows.Threading;
using System.Windows;
using System.Windows.Interop;

namespace MagnifierWpf;

public class MagWindow : Window
{
    private float magnification;
    private int _sourceWidth = 400;
    private int _sourceHeight = 50;
    private static double StableScreenWidth = NativeMethods.GetSystemMetrics(NativeMethods.SM_CXSCREEN);
    private static double StableScreenHeight = NativeMethods.GetSystemMetrics(NativeMethods.SM_CYSCREEN);

    public MagWindow()
    {
        // DPI に関わる
        var dpi = 2;
        var screenWidth = StableScreenWidth / dpi;
        var screenHeight = StableScreenHeight / dpi;

        magnification = screenWidth / _sourceWidth;
        Console.WriteLine($"Scale x{magnification}");

        Left = 0;
        Width = screenWidth;
        Height = _sourceHeight * magnification;
        Top = screenHeight - Height;

        AllowsTransparency = true;
        WindowStyle = WindowStyle.None;
        Background = System.Windows.Media.Brushes.Transparent;

        Loaded += MagWindowOnLoaded;
        Closed += MagWindowOnClosed;
    }


    private RECT _magWindowRect = new RECT();
    private nint _handle;
    private DispatcherTimer _timer = new();
    private nint _hwndMag;

    private void MagWindowOnLoaded(object? sender, RoutedEventArgs e)
    {
        // 順番　initialize -> Setuo -> Start timer
        var initialized = NativeMethods.MagInitialize();
        if (initialized)
        {
            // Just like a fill parameter
            var hInst = NativeMethods.GetModuleHandle(null);
            _handle = new WindowInteropHelper(this).Handle;

            // Create a magnifier control that fills the client area.
            NativeMethods.GetClientRect(_handle, ref _magWindowRect); // _magWindowRect get the window height width

            _hwndMag = NativeMethods.CreateWindow(
                (int)ExtendedWindowStyles.WS_EX_CLIENTEDGE, 
                NativeMethods.WC_MAGNIFIER,
                "MagnifierWindow", 
                (int)WindowStyles.WS_CHILD | (int)MagnifierStyle.MS_SHOWMAGNIFIEDCURSOR | (int)WindowStyles.WS_VISIBLE,
                _magWindowRect.left, _magWindowRect.top, _magWindowRect.right, _magWindowRect.bottom, 
                _handle, // this parameter bind to wpf window
                IntPtr.Zero, hInst, IntPtr.Zero);

            if (_hwndMag == IntPtr.Zero)
            {
                throw new ArgumentNullException();
            }
            // var isSmoothingActive = NativeMethods.MagSetLensUseBitmapSmoothing(_hwndMag, true);

            // Set the magnification factor.
            Transformation matrix = new Transformation(magnification);
            NativeMethods.MagSetWindowTransform(_hwndMag, ref matrix);

            _timer.Tick += UpdateMaginifier;
            _timer.Interval = TimeSpan.FromMilliseconds(NativeMethods.USER_TIMER_MINIMUM);
            _timer.Start();
        }
    }


        private void UpdateMaginifier(object? sender, EventArgs e)
        {
            // NativeMethods.GetSystemMetrics(NativeMethods.SM_CXSCREEN)
            RECT sourceRect = new RECT();
            sourceRect.left = 0;
            sourceRect.top = 0;
            sourceRect.right = sourceRect.left + _sourceWidth;
            sourceRect.bottom = sourceRect.top + _sourceHeight;

            // Set the source rectangle for the magnifier control.
            NativeMethods.MagSetWindowSource(_hwndMag, sourceRect);

            // Reclaim topmost status, to prevent unmagnified menus from remaining in view. 
            NativeMethods.SetWindowPos(
                _handle, 
                NativeMethods.HWND_TOPMOST, 0, 0, 0, 0,
                (int)SetWindowPosFlags.SWP_NOACTIVATE | (int)SetWindowPosFlags.SWP_NOMOVE | (int)SetWindowPosFlags.SWP_NOSIZE);

            // Force redraw.
            NativeMethods.InvalidateRect(_hwndMag, IntPtr.Zero, true);
        }

    private void MagWindowOnClosed(object? sender, EventArgs e)
    {
        _timer.Stop();
        NativeMethods.MagUninitialize();
    }
}