Zoom in on a web page using WebBrowser .NET control

There appears to be a solution at IE Zoom that involves overriding AttachInterfaces and DetachInterfaces in the WebBrowser to get a IWebBrowser2 interface, and then calling ExecWB with OLECMDID_OPTICAL_ZOOM.

I’ve tried his sample code and it appears to work; the (abridged) relevant class looks like this:

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace ZoomBrowser
{
    public partial class MyBrowser : WebBrowser
    {
        #region enums
        public enum OLECMDID
        {
            // ...
            OLECMDID_OPTICAL_ZOOM = 63,
            OLECMDID_OPTICAL_GETZOOMRANGE = 64,
            // ...
        }

        public enum OLECMDEXECOPT
        {
            // ...
            OLECMDEXECOPT_DONTPROMPTUSER,
            // ...
        }

        public enum OLECMDF
        {
            // ...
            OLECMDF_SUPPORTED = 1
        }
        #endregion

        #region IWebBrowser2
        [ComImport, /*SuppressUnmanagedCodeSecurity,*/
         TypeLibType(TypeLibTypeFlags.FOleAutomation | 
                     TypeLibTypeFlags.FDual |       
                     TypeLibTypeFlags.FHidden), 
         Guid("D30C1661-CDAF-11d0-8A3E-00C04FC9E26E")]
        public interface IWebBrowser2
        {
            [DispId(100)]  void GoBack();
            [DispId(0x65)] void GoForward();
            [DispId(0x66)] void GoHome();
            [DispId(0x67)] void GoSearch();
            [DispId(0x68)] void Navigate([In] string Url, 
                                         [In] ref object flags, 
                                         [In] ref object targetFrameName, 
                                         [In] ref object postData, 
                                         [In] ref object headers);
            [DispId(-550)] void Refresh();
            [DispId(0x69)] void Refresh2([In] ref object level);
            [DispId(0x6a)] void Stop();
            [DispId(200)]  object Application 
                           { [return: 
                              MarshalAs(UnmanagedType.IDispatch)] get; }
            [DispId(0xc9)] object Parent 
                           { [return: 
                              MarshalAs(UnmanagedType.IDispatch)] get; }
            [DispId(0xca)] object Container 
                           { [return: 
                              MarshalAs(UnmanagedType.IDispatch)] get; }
            [DispId(0xcb)] object Document 
                           { [return: 
                              MarshalAs(UnmanagedType.IDispatch)] get; }
            [DispId(0xcc)] bool TopLevelContainer { get; }
            [DispId(0xcd)] string Type { get; }
            [DispId(0xce)] int Left { get; set; }
            [DispId(0xcf)] int Top { get; set; }
            [DispId(0xd0)] int Width { get; set; }
            [DispId(0xd1)] int Height { get; set; }
            [DispId(210)]  string LocationName { get; }
            [DispId(0xd3)] string LocationURL { get; }
            [DispId(0xd4)] bool Busy { get; }
            [DispId(300)]  void Quit();
            [DispId(0x12d)] void ClientToWindow(out int pcx, out int pcy);
            [DispId(0x12e)] void PutProperty([In] string property, 
                                             [In] object vtValue);
            [DispId(0x12f)] object GetProperty([In] string property);
            [DispId(0)] string Name { get; }
            [DispId(-515)] int HWND { get; }
            [DispId(400)] string FullName { get; }
            [DispId(0x191)] string Path { get; }
            [DispId(0x192)] bool Visible { get; set; }
            [DispId(0x193)] bool StatusBar { get; set; }
            [DispId(0x194)] string StatusText { get; set; }
            [DispId(0x195)] int ToolBar { get; set; }
            [DispId(0x196)] bool MenuBar { get; set; }
            [DispId(0x197)] bool FullScreen { get; set; }
            [DispId(500)] void Navigate2([In] ref object URL, 
                                         [In] ref object flags, 
                                         [In] ref object targetFrameName, 
                                         [In] ref object postData, 
                                         [In] ref object headers);
            [DispId(0x1f5)] OLECMDF QueryStatusWB([In] OLECMDID cmdID);
            [DispId(0x1f6)] void ExecWB([In] OLECMDID cmdID, 
                                        [In] OLECMDEXECOPT cmdexecopt, 
                                        ref object pvaIn, IntPtr pvaOut);
            [DispId(0x1f7)] void ShowBrowserBar([In] ref object pvaClsid, 
                                                [In] ref object pvarShow, 
                                                [In] ref object pvarSize);
            [DispId(-525)] WebBrowserReadyState ReadyState { get; }
            [DispId(550)] bool Offline { get; set; }
            [DispId(0x227)] bool Silent { get; set; }
            [DispId(0x228)] bool RegisterAsBrowser { get; set; }
            [DispId(0x229)] bool RegisterAsDropTarget { get; set; }
            [DispId(0x22a)] bool TheaterMode { get; set; }
            [DispId(0x22b)] bool AddressBar { get; set; }
            [DispId(0x22c)] bool Resizable { get; set; }
        }
        #endregion

        private IWebBrowser2 axIWebBrowser2;

        public MyBrowser()
        {           
        }

        protected override void AttachInterfaces(
            object nativeActiveXObject)
        {
            base.AttachInterfaces(nativeActiveXObject);
            this.axIWebBrowser2 = (IWebBrowser2)nativeActiveXObject;
        }

        protected override void DetachInterfaces()
        {
            base.DetachInterfaces();
            this.axIWebBrowser2 = null;
        }

        public void Zoom(int factor)
        {
            object pvaIn = factor;
            try
            {
                this.axIWebBrowser2.ExecWB(OLECMDID.OLECMDID_OPTICAL_ZOOM,
                   OLECMDEXECOPT.OLECMDEXECOPT_DONTPROMPTUSER, 
                   ref pvaIn, IntPtr.Zero);
            }
            catch (Exception)
            {
                throw;
            }
        }
    }
}