How to draw directly on the Windows desktop, C#?

Question

This question has been asked for other languages, and even for those other languages, I have found their answers lacking in how to exactly do it, cleanly (no messed up screen repaints, etc..).

Is it possible to draw onto the Windows Desktop from C#? I am looking for an example if possible.

• Franci Penov: There is no officially supported clean way to draw on the desktop window from any language. In practice, most of the methods that achieve the closest to clean drawing on the desktop involve injecting your own dll into the Explorer process and subclassing the window procedure for the desktop window. I would not recommend doing this in C#, though. Also, there's no guarantee that such methods would continue to work on any future versions of Windows, or with any future Service packs or hotfixes for existing versions of Windows.

Answer 1

Try the following:

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Runtime.InteropServices;
class Program {
 [DllImport("User32.dll")]
 static extern IntPtr GetDC(IntPtr hwnd);
 [DllImport("User32.dll")]
 static extern int ReleaseDC(IntPtr hwnd, IntPtr dc);
 static void Main(string[] args) {
 IntPtr desktop = GetDC(IntPtr.Zero);
 using (Graphics g = Graphics.FromHdc(desktop)) {
 g.FillRectangle(Brushes.Red, 0, 0, 100, 100);
 }
 ReleaseDC(IntPtr.Zero, desktop);
 }
}

• esac: FYI for those who say you can't, this did work for me, although moving any window over it repaints it immediately :(
• Alex: I've just tried this in a WPF, C# 4.0 application and I get "PInvokeStackImbalance was detected" as soon as I moved the mouse after launching it. Just an FYI for others who pass by.
• gonzobrains: I got the same unbalanced stack error. What's the fix? Change your project back to 3.5 client profile? :)
• gonzobrains: it looks like changing my project to .NET 3.5 made this unbalance issue go away.
• Frank Hagenson: The stack imbalance is caused by the fact the ReleaseDC method is defined incorrectly. It should be: static extern int ReleaseDC(IntPtr hwnd, IntPtr dc)

Answer 2

You can try:

Graphics.FromHwnd(IntPtr.Zero)

• chrismead: Paolo Tedesco's answer used to work for me, but stopped and I couldn't figure out why. Leppie's answer got it working again for me.

Answer 3

You can see a real-world code example within https://uiautomationverify.codeplex.com/SourceControl/latest#UIAVerify/Tools/visualuiverify/utils/screenrectangle.cs

This draws a rectangle that will appear on the screen until the user chooses to remove it at an arbitrary position (wont be repainted over). It uses a windows form thats hidden/ appears as a popup.

This is the code behind the UIAVerify.exe tool in the current Windows SDK.

If you want to use the above, copy the following files into your project:

• utils\screenboundingrectangle.cs
• utils\screenrectangle.cs
• win32\*

Might need to update namespaces accordingly + add references to System.Drawing + System.Windows.Forms

Then you can draw a rectangle with the following code:

namespace Something
{
 public class Highlighter
 {
 ScreenBoundingRectangle _rectangle = new ScreenBoundingRectangle();
 public void DrawRectangle(Rectangle rect)
 {
 _rectangle.Color = System.Drawing.Color.Red;
 _rectangle.Opacity = 0.8;
 _rectangle.Location = rect;
 this._rectangle.Visible = true;
 }
 }
}

and

var rect = Rectangle.FromLTRB(100, 100, 100, 100);
var hi = new Highlighter();
hi.DrawRectangle(rect);

• frank koch: Code can now be found here github.com/TestStack/UIAVerify/blob/master/VisualUiaVerify/…