Question

This is some code that I picked up which I tried to implement. Its purpose is to create a form layer which is transparent, full screen, borderless, clickthrough, and always on top of other windows. It then lets you draw using directx over the top of it remaining otherwise transparent.

The parts that don’t work are the click-through part, and the directx render. When I run it I basically have an invisible force field in front of all other windows and have to alt-tab around to visual studio to quickly press ALT F5 and end the debug (so at least the always on top and transparency works). I have been trying to figure out why those parts don’t work, but my newbie c# skills fail me. hopefully someone can spot why and provide a modification.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Globalization;
using Microsoft.DirectX;
using Microsoft.DirectX.Direct3D;
using System.Threading;


namespace MinimapSpy
{
public partial class Form1 : Form
{

    private Margins marg;

    //this is used to specify the boundaries of the transparent area
    internal struct Margins
    {
        public int Left, Right, Top, Bottom;
    }

    [DllImport("user32.dll", SetLastError = true)]

    private static extern UInt32 GetWindowLong(IntPtr hWnd, int nIndex);

    [DllImport("user32.dll")]

    static extern int SetWindowLong(IntPtr hWnd, int nIndex, IntPtr dwNewLong);

    [DllImport("user32.dll")]

    static extern bool SetLayeredWindowAttributes(IntPtr hwnd, uint crKey, byte bAlpha, uint dwFlags);

    public const int GWL_EXSTYLE = -20;

    public const int WS_EX_LAYERED = 0x80000;

    public const int WS_EX_TRANSPARENT = 0x20;

    public const int LWA_ALPHA = 0x2;

    public const int LWA_COLORKEY = 0x1;

    [DllImport("dwmapi.dll")]
    static extern void DwmExtendFrameIntoClientArea(IntPtr hWnd, ref Margins pMargins);

    private Device device = null;



    public Form1()
    {

        //Make the window's border completely transparant
        SetWindowLong(this.Handle, GWL_EXSTYLE,
                (IntPtr)(GetWindowLong(this.Handle, GWL_EXSTYLE) ^ WS_EX_LAYERED ^ WS_EX_TRANSPARENT));

        //Set the Alpha on the Whole Window to 255 (solid)
        SetLayeredWindowAttributes(this.Handle, 0, 255, LWA_ALPHA);

        //Init DirectX
        //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;

        this.device = new Device(0, DeviceType.Hardware, this.Handle,
        CreateFlags.HardwareVertexProcessing, presentParameters);


        Thread dx = new Thread(new ThreadStart(this.dxThread));
        dx.IsBackground = true;
        dx.Start();  
        InitializeComponent();

    }

   protected override void OnPaint(PaintEventArgs e)
   {
        //Create a margin (the whole form)
      marg.Left = 0;
     marg.Top = 0;
      marg.Right = this.Width;
      marg.Bottom = this.Height;

        //Expand the Aero Glass Effect Border to the WHOLE form.
        // since we have already had the border invisible we now
        // have a completely invisible window - apart from the DirectX
        // renders NOT in black.
     DwmExtendFrameIntoClientArea(this.Handle, ref marg);  

  }
    private void Form1_Load(object sender, EventArgs e)
    {

    }
    private void dxThread()
    {
        while (true)
        {
            //Place your update logic here
            device.Clear(ClearFlags.Target, Color.FromArgb(0, 0, 0, 0), 1.0f, 0);
            device.RenderState.ZBufferEnable = false;
            device.RenderState.Lighting = false;
            device.RenderState.CullMode = Cull.None;
            device.Transform.Projection = Matrix.OrthoOffCenterLH(0, this.Width, this.Height, 0, 0, 1);
            device.BeginScene();

            //Place your rendering logic here

            device.EndScene();
            //device.Present();
        }

        this.device.Dispose();
        Application.Exit();
    }  

}

Answer 1

Here’s a refined full sample code for making a window topmost – click through – transparent (= alpha blended). The sample makes a rotating color wheel which is rendered with DirectX, or actually with XNA 4.0, because I believe Microsoft has discontinued developing the managed directx and favours XNA today.

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using Microsoft.Xna.Framework.Graphics;

namespace ClickThroughXNA
{
    public partial class Form1 : Form
    {
        // Directx graphics device
        GraphicsDevice dev = null;        
        BasicEffect effect = null;     

        // Wheel vertexes
        VertexPositionColor[] v = new VertexPositionColor[100];

        // Wheel rotation
        float rot = 0;

        public Form1()
        {
            InitializeComponent();

            StartPosition = FormStartPosition.CenterScreen;   
            Size = new System.Drawing.Size(500, 500);
            FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;  // no borders

            TopMost = true;        // make the form always on top                     
            Visible = true;        // Important! if this isn't set, then the form is not shown at all

            // Set the form click-through
            int initialStyle = GetWindowLong(this.Handle, -20);
            SetWindowLong(this.Handle, -20, initialStyle | 0x80000 | 0x20);

            // Create device presentation parameters
            PresentationParameters p = new PresentationParameters();
            p.IsFullScreen = false;
            p.DeviceWindowHandle = this.Handle;
            p.BackBufferFormat = SurfaceFormat.Vector4;
            p.PresentationInterval = PresentInterval.One;

            // Create XNA graphics device
            dev = new GraphicsDevice(GraphicsAdapter.DefaultAdapter, GraphicsProfile.Reach, p);

            // Init basic effect
            effect = new BasicEffect(dev);

            // Extend aero glass style on form init
            OnResize(null);
        }


        protected override void OnResize(EventArgs e)
        {
            int[] margins = new int[] { 0, 0, Width, Height };

            // Extend aero glass style to whole form
            DwmExtendFrameIntoClientArea(this.Handle, ref margins);  
        }


        protected override void OnPaintBackground(PaintEventArgs e)
        {
            // do nothing here to stop window normal background painting
        }


        protected override void OnPaint(PaintEventArgs e)
        {                
            // Clear device with fully transparent black
            dev.Clear(new Microsoft.Xna.Framework.Color(0, 0, 0, 0.0f));

            // Rotate wheel a bit
            rot+=0.1f;

            // Make the wheel vertexes and colors for vertexes
            for (int i = 0; i < v.Length; i++)
            {                    
                if (i % 3 == 1)
                    v[i].Position = new Microsoft.Xna.Framework.Vector3((float)Math.Sin((i + rot) * (Math.PI * 2f / (float)v.Length)), (float)Math.Cos((i + rot) * (Math.PI * 2f / (float)v.Length)), 0);
                else if (i % 3 == 2)
                    v[i].Position = new Microsoft.Xna.Framework.Vector3((float)Math.Sin((i + 2 + rot) * (Math.PI * 2f / (float)v.Length)), (float)Math.Cos((i + 2 + rot) * (Math.PI * 2f / (float)v.Length)), 0);

                v[i].Color = new Microsoft.Xna.Framework.Color(1 - (i / (float)v.Length), i / (float)v.Length, 0, i / (float)v.Length);
            }

            // Enable position colored vertex rendering
            effect.VertexColorEnabled = true;
            foreach (EffectPass pass in effect.CurrentTechnique.Passes) pass.Apply();

            // Draw the primitives (the wheel)
            dev.DrawUserPrimitives(PrimitiveType.TriangleList, v, 0, v.Length / 3, VertexPositionColor.VertexDeclaration);

            // Present the device contents into form
            dev.Present();

            // Redraw immediatily
            Invalidate();            
        }


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

        [DllImport("user32.dll")]
        static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

        [DllImport("dwmapi.dll")]
        static extern void DwmExtendFrameIntoClientArea(IntPtr hWnd, ref int[] pMargins);

    }
}