mpv.net/src/Native/Native.cs

using System;
using System.Drawing;
using System.Runtime.InteropServices;

public class Native
{
    static Version Windows_10_1607 = new Version(10, 0, 14393); // Windows 10 1607

    [DllImport("kernel32.dll")]
    public static extern bool AttachConsole(int dwProcessId);

    [DllImport("kernel32.dll")]
    public static extern bool FreeConsole();

    [DllImport("kernel32.dll")]
    public static extern IntPtr LoadLibrary(string path);

    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    public static extern IntPtr FindWindowEx(
        IntPtr parentHandle, IntPtr childAfter, string lclassName, string windowTitle);

    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    public static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    public static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, ref COPYDATASTRUCT lParam);

    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    public static extern IntPtr PostMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    public static extern int RegisterWindowMessage(string id);

    [DllImport("user32.dll")]
    public static extern bool AllowSetForegroundWindow(int dwProcessId);

    [DllImport("user32.dll")]
    public static extern void ReleaseCapture();

    [DllImport("user32.dll")]
    public static extern int GetDpiForWindow(IntPtr hwnd);

    [DllImport("user32.dll")]
    public static extern bool AdjustWindowRect(ref RECT lpRect, uint dwStyle, bool bMenu);

    [DllImport("user32.dll")]
    public static extern bool AdjustWindowRectExForDpi(
        ref RECT lpRect, uint dwStyle, bool bMenu, uint dwExStyle, uint dpi);

    [DllImport("user32.dll")]
    public static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int x, int y, int cx, int cy, uint uFlags);

    [DllImport("user32.dll", EntryPoint = "GetWindowLong")]
    static extern IntPtr GetWindowLong32(IntPtr hWnd, int nIndex);

    [DllImport("user32.dll", EntryPoint = "GetWindowLongPtr")]
    static extern IntPtr GetWindowLong64(IntPtr hWnd, int nIndex);

    public static IntPtr GetWindowLong(IntPtr hWnd, int nIndex)
    {
        if (IntPtr.Size == 8)
            return GetWindowLong64(hWnd, nIndex);
        else
            return GetWindowLong32(hWnd, nIndex);
    }

    [DllImport("gdi32.dll")]
    public static extern int GetDeviceCaps(IntPtr hdc, int nIndex);

    [StructLayout(LayoutKind.Sequential)]
    public struct RECT
    {
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;

        public RECT(Rectangle r)
        {
            Left = r.Left;
            Top = r.Top;
            Right = r.Right;
            Bottom = r.Bottom;
        }

        public RECT(int left, int top, int right, int bottom)
        {
            Left = left;
            Top = top;
            Right = right;
            Bottom = bottom;
        }

        public Rectangle ToRectangle() => Rectangle.FromLTRB(Left, Top, Right, Bottom);
        public Size Size => new Size(Right - Left, Bottom - Top);
        public int Width => Right - Left;
        public int Height => Bottom - Top;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct COPYDATASTRUCT
    {
        public IntPtr dwData;
        public int cbData;
        [MarshalAs(UnmanagedType.LPTStr)]
        public string lpData;
    }

    public static int GetResizeBorder(int v)
    {
        switch (v)
        {
            case 1 /* WMSZ_LEFT        */ : return 3;
            case 3 /* WMSZ_TOP         */ : return 2;
            case 2 /* WMSZ_RIGHT       */ : return 3;
            case 6 /* WMSZ_BOTTOM      */ : return 2;
            case 4 /* WMSZ_TOPLEFT     */ : return 1;
            case 5 /* WMSZ_TOPRIGHT    */ : return 1;
            case 7 /* WMSZ_BOTTOMLEFT  */ : return 3;
            case 8 /* WMSZ_BOTTOMRIGHT */ : return 3;
            default: return -1;
        }
    }

    public static void SubtractWindowBorders(IntPtr hwnd, ref RECT rc, int dpi)
    {
        RECT r = new RECT(0, 0, 0, 0);
        AddWindowBorders(hwnd, ref r, dpi);
        rc.Left -= r.Left;
        rc.Top -= r.Top;
        rc.Right -= r.Right;
        rc.Bottom -= r.Bottom;
    }

    public static void AddWindowBorders(IntPtr hwnd, ref RECT rc, int dpi)
    {
        uint windowStyle   = (uint)GetWindowLong(hwnd, -16); // GWL_STYLE
        uint windowStyleEx = (uint)GetWindowLong(hwnd, -20); // GWL_EXSTYLE

        if (Environment.OSVersion.Version >= Windows_10_1607)
            AdjustWindowRectExForDpi(ref rc, windowStyle, false, windowStyleEx, (uint)dpi);
        else
            AdjustWindowRect(ref rc, windowStyle, false);
    }

    public static int GetDPI(IntPtr hwnd)
    {
        if (Environment.OSVersion.Version >= Windows_10_1607)
            return GetDpiForWindow(hwnd);
        else
            using (Graphics gx = Graphics.FromHwnd(hwnd))
                return GetDeviceCaps(gx.GetHdc(), 88 /*LOGPIXELSX*/);
    }
}