Question

I want to draw DirectX content so that it appears to be floating over top of the desktop and any other applications that are running. I also need to be able to make the directx content semi-transparent, so other things show through. Is there a way of doing this?

I am using Managed DX with C#.

Answer 1

I found a solution which works on Vista, starting from the link provided by OregonGhost. This is the basic process, in C# syntax. This code is in a class inheriting from Form. It doesn’t seem to work if in a UserControl:

//this will allow you to import the necessary functions from the .dll using System.Runtime.InteropServices;  //this imports the function used to extend the transparent window border. [DllImport('dwmapi.dll')] static extern void DwmExtendFrameIntoClientArea(IntPtr hWnd, ref Margins pMargins);  //this is used to specify the boundaries of the transparent area internal struct Margins {     public int Left, Right, Top, Bottom; } private Margins marg;  //Do this every time the form is resized. It causes the window to be made transparent. marg.Left = 0; marg.Top = 0; marg.Right = this.Width; marg.Bottom = this.Height; DwmExtendFrameIntoClientArea(this.Handle, ref marg);  //This initializes the DirectX device. It needs to be done once. //The alpha channel in the backbuffer is critical. PresentParameters presentParameters = new PresentParameters(); presentParameters.Windowed = true; presentParameters.SwapEffect = SwapEffect.Discard; presentParameters.BackBufferFormat = Format.A8R8G8B8;  Device device = new Device(0, DeviceType.Hardware, this.Handle, CreateFlags.HardwareVertexProcessing, presentParameters);  //the OnPaint functions maked the background transparent by drawing black on it. //For whatever reason this results in transparency. protected override void OnPaint(PaintEventArgs e) {     Graphics g = e.Graphics;      // black brush for Alpha transparency     SolidBrush blackBrush = new SolidBrush(Color.Black);     g.FillRectangle(blackBrush, 0, 0, Width, Height);     blackBrush.Dispose();      //call your DirectX rendering function here }  //this is the dx rendering function. The Argb clearing function is important, //as it makes the directx background transparent. protected void dxrendering() {     device.Clear(ClearFlags.Target, Color.FromArgb(0, 0, 0, 0), 1.0f, 0);      device.BeginScene();     //draw stuff here.     device.EndScene();     device.Present(); } 

Lastly, a Form with default setting will have a glassy looking partially transparent background. Set the FormBorderStyle to ‘none’ and it will be 100% transparent with only your content floating above everything.