Hat jemand eine Idee oder ein Tip...

Besten Dank,
mit freundlichem Gruß
Marcus

Es ist sind nicht viel Zeilen, hier der Source Code

/***
	DimmerDialog - A .NET class to show a modal dialog that dims the background.

	Author	:	Nishant Sivakumar
	Email	:	voidnish@gmail.com	
	Blog	:	http://blog.voidnish.com
	Web		:	http://www.voidnish.com 	

	You may freely use this class as long as you include
	this copyright. 

	You may freely modify and use this class as long
	as you include this copyright in your modified version. 

	This code is provided "as is" without express or implied warranty. 

	Copyright © Nishant Sivakumar, 2006.
	All Rights Reserved.
***/

#pragma once

#include <windows.h>
#include <tchar.h>

using namespace System;
using namespace System::Threading;
using namespace System::Windows::Forms;
using namespace System::Drawing;
using namespace System::Drawing::Imaging;
using namespace System::Timers;

LPCTSTR g_desktopname = _T("{F375AF67-22ED-4ba2-928E-B9DB633AA79C}");

public ref class DimmerDialog
{
private:
	HDESK m_hOrigDesktop;
	HDESK m_hDimmerDesktop;
	Bitmap^ m_Image;	
	System::Timers::Timer^ m_Timer;
	Form^ m_BackgroundForm;
	Form^ m_MainForm;
	bool m_bShowForm;
	String^ m_text;
	String^ m_title;
	MessageBoxIcon m_icon;
	int m_ColorReductionStep;

	void OnTimer(Object^ source, ElapsedEventArgs^ e)
	{
		if(++m_ColorReductionStep > 4)
			m_Timer->Enabled = false;
		else
		{
			m_Timer->Enabled = false;
			((PictureBox^)m_BackgroundForm->Controls[0])->Image = DimBitmap();
			m_BackgroundForm->Controls[0]->Invalidate();
			m_BackgroundForm->Controls[0]->Update();
			m_Timer->Enabled = true;
		}
	}

	void SwitchToDimmerDesktop()
	{
		m_hOrigDesktop = GetThreadDesktop(GetCurrentThreadId());
		m_hDimmerDesktop = CreateDesktop(g_desktopname,
			NULL,NULL,0,GENERIC_ALL,NULL);
		if(m_hDimmerDesktop)
		{
			if(SetThreadDesktop(m_hDimmerDesktop))
			{
				SwitchDesktop(m_hDimmerDesktop);

				m_ColorReductionStep = 0;
				m_Timer = gcnew System::Timers::Timer;
				m_Timer->Elapsed += gcnew ElapsedEventHandler(this, &DimmerDialog::OnTimer );
				m_Timer->Interval = 100;				

				m_BackgroundForm = gcnew Form();
				m_BackgroundForm->FormBorderStyle = FormBorderStyle::None;
				m_BackgroundForm->WindowState = FormWindowState::Maximized;
				PictureBox picbox;
				picbox.Dock = DockStyle::Fill;
				picbox.Image = DimBitmap();
				m_BackgroundForm->Controls->Add(%picbox);
				m_BackgroundForm->Show();

				m_Timer->Enabled = true;
				if(m_bShowForm)
				{
					m_MainForm->StartPosition = FormStartPosition::CenterParent;
					m_MainForm->ShowDialog();
				}
				else
				{
					MessageBox::Show(m_text, m_title,
						MessageBoxButtons::OK, m_icon);
				}

				SwitchDesktop(m_hOrigDesktop);
				SetThreadDesktop(m_hOrigDesktop);
			}			
		}
		CloseDesktop(m_hDimmerDesktop);
	}

	void Show()
	{
		HDC hDC = GetDC(NULL); 
		HDC hMemDC = CreateCompatibleDC(hDC);
		SIZE size;
		size.cx = GetSystemMetrics(SM_CXSCREEN);
		size.cy = GetSystemMetrics(SM_CYSCREEN);
		HBITMAP hBitmap = CreateCompatibleBitmap(hDC, size.cx, size.cy);
		if (hBitmap)
		{
			HBITMAP hOld = (HBITMAP) SelectObject(hMemDC, hBitmap);
			BitBlt(hMemDC, 0, 0, size.cx, size.cy, hDC, 0, 0, SRCCOPY);
			SelectObject(hMemDC, hOld);
			DeleteDC(hMemDC);
			ReleaseDC(NULL, hDC);	
			m_Image = Image::FromHbitmap((IntPtr)hBitmap); 
			DeleteObject(hBitmap);
		}
		Thread^ switchthread = gcnew Thread(
			gcnew ThreadStart(this,&DimmerDialog::SwitchToDimmerDesktop));
		switchthread->Start();		
	}

	Bitmap^ DimBitmap()
	{
		if(m_ColorReductionStep == 0)
			return m_Image;
		Bitmap^ imagecopy = (Bitmap^)m_Image->Clone();
		BitmapData^ bmData = imagecopy->LockBits(
			System::Drawing::Rectangle(0, 0, imagecopy->Width, imagecopy->Height), 
			ImageLockMode::ReadWrite, PixelFormat::Format24bppRgb); 
		BYTE* p = (BYTE*)bmData->Scan0.ToPointer();
		int nOffset = bmData->Stride - imagecopy->Width * 3; 
		BYTE red, green, blue;
		for(int y=0; y < imagecopy->Height; y++)
		{
			for(int x=0; x < imagecopy->Width; x++)
			{
				blue = p[0];
				green = p[1];
				red = p[2];

				switch(m_ColorReductionStep)
				{
				case 1:
					p[0]  = (BYTE)(.001 * red + .286 * green + .713 * blue);
					p[1]  = (BYTE)(.001 * red + .986 * green + .013 * blue);
					p[2]  = (BYTE)(.899 * red + .087 * green + .013 * blue);
					break;
				case 2:
					p[0]  = (BYTE)(.099 * red + .387 * green + .514 * blue);
					p[1]  = (BYTE)(.099 * red + .887 * green + .014 * blue);
					p[2]  = (BYTE)(.699 * red + .287 * green + .013 * blue);
					break;
				case 3:
					p[0]  = (BYTE)(.199 * red + .487 * green + .314 * blue);
					p[1]  = (BYTE)(.199 * red + .787 * green + .014 * blue);
					p[2]  = (BYTE)(.499 * red + .487 * green + .014 * blue);
					break;
				case 4:
					p[0] = p[1] = p[2] = (BYTE)(.299 * red + .587 * green + .114 * blue);
					break;
				}				
				p += 3;
			}
			p += nOffset;
		}
		imagecopy->UnlockBits(bmData);
		return imagecopy;
	}
public:
	DimmerDialog()
	{
		m_hOrigDesktop = nullptr;
		m_hDimmerDesktop = nullptr;
	}

	void ShowForm(Form^ form)
	{
		m_bShowForm = true;
		m_MainForm = form;
		Show();
	}

	void ShowMessageBox(String^ text, String^ title, MessageBoxIcon icon)
	{
		m_bShowForm = false;
		m_MainForm = nullptr;
		m_text = text;
		m_title = title;
		m_icon = icon;
		Show();
	}
};

Leider steig ich da nicht ganz durch, ich brauch das ganze in einem reinen VC6 Projekt mit einem Dialog Basierenden Programm.
Hab schon mal etwas mit dem "SetThreadDesktop", "SwitchDesktop" experimientiert, bekomm ab immer den Fehler "170 The requested resource is in use.". Hier mein Testcode, jemand eine Idee wie ich weiter komme, soweit ich das verstehe kann man damit eine zusätzlichen Desktop anlegen und den Desktop Thread darauf setzen, somit ist der vorherige Desktop "disabled"...

_AFX_THREAD_STATE *pState = AfxGetThreadState();

    bool blUnhookOk = UnhookWindowsHookEx(pState->m_hHookOldMsgFilter);
    pState->m_hHookOldMsgFilter = NULL;

    LPTSTR g_desktopname = _T("{F375AF67-22ED-4ba2-928E-B9sdfasdfasdfasdf3AA79C}");
	HDESK m_hOrigDesktop;
	HDESK m_hDimmerDesktop;
	m_hOrigDesktop = GetThreadDesktop(GetCurrentThreadId());
	m_hDimmerDesktop = CreateDesktop(g_desktopname,
		NULL,NULL,0,GENERIC_ALL,NULL);
	if(m_hDimmerDesktop)
	{
		if(SetThreadDesktop(m_hDimmerDesktop))
		{
			SwitchDesktop(m_hDimmerDesktop);
            AfxMessageBox(_T("Anderer Desktop"));

			SwitchDesktop(m_hOrigDesktop);
			SetThreadDesktop(m_hOrigDesktop);
        }
        else {
            DWORD dwError = GetLastError();
            CString sOut;
            sOut.Format(_T("%d"),dwError);
            AfxMessageBox(sOut);
        }
    }

Besten Dank,
gruss
Marcus

MSDN schrieb:

The SetThreadDesktop function will fail if the calling thread has any windows or hooks on its current desktop (unless the hDesktop parameter is a handle to the current desktop).

_AFX_THREAD_STATE *pState = AfxGetThreadState();

    bool blUnhookOk = UnhookWindowsHookEx(pState->m_hHookOldMsgFilter);
    pState->m_hHookOldMsgFilter = NULL;

Aber scheint keine Verbesserung zu bringen.

gruss
Marcus