DIRECTX OVERLAY - CHANGE WALLPAPER ON DESKTOP WITH DIRECTX

//overlay trick: desktop color:0x80010
//OverlayEffects avec color: ck.ColorSpaceLowValue = ck.ColorSpaceHighValue = 0x100008;


// OverlayDirectX
//Première étape enlevé le wallpaper et mettre a black pour Overlay:
        private void SwitchWallpaperMode(bool onOff)
        {

            int[] elements = { 1 };
            if (onOff)
            {
                int[] backgorund = { ColorTranslator.ToWin32(SystemColors.Desktop) }; //save the current desktop color
                color_bkg = backgorund;
                int[] colors = { 0x80010 };
                SetSysColors(elements.Length, elements, colors); // put black to the desktop color
                SystemParametersInfo(20, 0, "", 0); //remove wallaper
                ToggleScreenSaverActive(onOff); //switch off the screensaver
            }
            else
            {
                SetSysColors(elements.Length, elements, color_bkg); //restore old desktop color
                SystemParametersInfo(20, 0, null, 0); //restore wallpaper
                ToggleScreenSaverActive(onOff); //switch on the screensaver
            }

        }
//Deuxième étape DirectXInitDDraw (initialise les directdraw surface:
        private void DirectXInitDDraw()
        {
            _displayDevice = new Microsoft.DirectX.DirectDraw.Device(); //create the device
            _displayDevice.SetCooperativeLevel(null, CooperativeLevelFlags.Normal);
            SurfaceDescription description = new SurfaceDescription();
            description.SurfaceCaps.PrimarySurface = true;
            _front = new Surface(description, _displayDevice); //set the front to the primary surface
            description.Clear();
            description.SurfaceCaps.Overlay = true;  //prepare the description of overlay surface
            description.SurfaceCaps.Flip = true;
            description.SurfaceCaps.Complex = true;
            //description.SurfaceCaps.VideoMemory = true;
            description.Width = _screenWidth;
            description.Height = _screenHeight;
            description.BackBufferCount = 1;

            PixelFormat pxFrmt;
            pxFrmt.FourCC = 0x32595559; //Yuv2
            pxFrmt.FourCcIsValid = true;

            description.PixelFormatStructure = pxFrmt;
            overlay = new Surface(description, _displayDevice);
            SurfaceCaps caps = new SurfaceCaps();
            caps.BackBuffer = true;

            _back = overlay.GetAttachedSurface(caps); //caps surface
 
            ColorKey ck = new ColorKey();
            ck.ColorSpaceLowValue = ck.ColorSpaceHighValue = 0x100008; //color overlay effect to draw on desktop color 0x80010 (see SwitchWallpaperMode)

            overFX.DestinationColorKey = ck;
            overFX.ArithmeticStretchY = true;


        }

//troisieme étape
//blit un bitmap to backbuffer
//exemple:
//Blit((Bitmap)m_RenderTarget, _back);
//overlay.Flip(null, FlipFlags.Wait);
//voir code pour le blit c'est du GDI+
//Attention à la première image updaté l'overlay ex:
//overlay.UpdateOverlay(_back, OverlayFlags.Show | OverlayFlags.Effects | OverlayFlags.KeyDestinationOverride, overFX); //update overlay for the first time
                    
//Class Transition
//voir class pour code du birghtness et setcolormatrix pour l'opacity.