C# Drawing On Desktop

[elaysian]

Hi,

Got a little problem that I hope someone can help me with.

I am drawing a rectangle directly onto the desktop... and that works fine.

However I would like to restore the desktop to its original state (i.e. without rectangle) when an event occurs, for example the mouse button is released.

No matter what I do the rectangle stays put.

Anyone got any ideas????

Thanks in anticipation.

Jon

[yyy]

Maybe you should add the code which you use in order to paint and remove the rectangle. It will be easier to find out what's the problem that way.

[elaysian]

Duh! Dunno why I didn't post the code...

Here it is :

using System;

using System.Drawing;

using System.Drawing.Drawing2D;

using System.Runtime.InteropServices;

namespace DrawToScreenTestApp

{

#region UnmanagedMethods

internal class UnmanagedMethods

{

[DllImport("user32")]

internal static extern IntPtr GetDC(IntPtr hwnd);

[DllImport("User32.dll")]

internal static extern void ReleaseDC(IntPtr dc);

}

#endregion

#region DrawToScreen

public class DrawToScreen

{

public void PaintRectangleToScreen()

{

IntPtr deskDC = UnmanagedMethods.GetDC(IntPtr.Zero);

Graphics g = Graphics.FromHdc(deskDC);

g.FillRectangle(new SolidBrush(Color.FromArgb(100, Color.CadetBlue)), 0,0, 300, 300);

g.EndContainer(cont);

g.Dispose();

UnmanagedMethods.ReleaseDC(deskDC);

}

}

#endregion

}

[yyy]

That's a good question - I was also trying to do it but I have no idea what you have to do. You need to clear the screen somehow, I think.

[Menge]

send a WM_PAINT message to the desktop?

[azcodemonkey]

All you should have to do is invalidate the desktop rectangle. Import InvalidateRect from GDI, and use the ClipRectangle from the desktop's graphics object as your rectangle. If that doesn't work, I'd be surprised.

[nvme]

or maybe make a copy of the contents of the desktops device context before you modify it and restore it when you're done and want the original back

[elaysian]

Hey Guys,

Thanks for all your replies.

I have tried them all and the only one that I could get to work was weenur's suggestion.

However, it has the horrible side effect of making the whole screen flick. Not good when moving the rectangle across the screen.

So i'm gonna have to do a little more investigation :)

Thanks again

Jon

[yyy]

Is there a way to draw on desktop and be able to remove the drawing at runntime without a flicker effect? I tried weenur's suggestion but it causes the screen to flicker when the InvalidateRect is called. Any idea how to stop the flickering?

[Mordkanin]

So I was poking through MSDN....maybe this might help?

http://msdn.microsoft.com/library/default....sdn_flicker.asp

I've never tried to draw on the desktop ;)

[Ianmac45]

good luck with that msdn article.....it's in c++

[yyy]

I've tried to convert it to C# but it didn't work :rolleyes: Can somebody try to convert it to c#? Or is there another way?

[yyy]

No ideas? There must be someone who knows how to draw on screen and remove the drawing without causing the screen to flicker?

Anybody?

[AndreasV]

You are in no control of the flickering. You tell the desktop (which desktop btw: the desktop as in GetDesktopWindow() or as in the listview with all the icons ? ) to repaint, and that desktop itself is responsible for painting. If this is done flickerfree or not is up to the windows that will need repainting.

By the way, flickering occurs when you draw the same pixel twice onto the screen. This can be solved by being carefull what you are drawing or using a backbuffer. Normally, when dealing with flickering WM_ERASEBACKGROUND is not dealt with, all painting is done in WM_PAINT.

[yyy]

Thank you very much for your answer AndreasV :) So how can other programs paint over the screen without flickering? Can I draw on desktop without telling the desktop to repaint?

[Patrick_]

There is something you can do to reduce flicker greatly. Use double buffering to increase redraw speed. This renders the graphics to an in-memory bitmap, then copies the finalized bitmap to whereever you want.

Here is an MSDN article on it and here are results from Google.

Hope this helps you, good luck! :)

[yyy]

I think I've tried it with double buffering already but I'll check it again. Thanks a lot :)

[jaydacodemonkey]

It might be easier to just draw to a transparent form whose parent is the desktop. This does what programs like Samurize do when you "Pin to desktop." Here's the code for setting the window's parent to the desktop.

[DllImport("user32.dll", CharSet=CharSet.Auto)]
  public static extern IntPtr FindWindow(
  	[MarshalAs(UnmanagedType.LPTStr)] string lpClassName,
  	[MarshalAs(UnmanagedType.LPTStr)] string lpWindowName);
[DllImport("user32.dll")]
  public static extern IntPtr SetParent(
  	IntPtr hWndChild,      // handle to window
  	IntPtr hWndNewParent   // new parent window
  	);


IntPtr hwndf = this.Handle;
IntPtr hwndParent = FindWindow("ProgMan", null);
SetParent(hwndf,hwndParent);
this.TopMost = false;

And this is an excellent article for making the window transparent.

Then, you could just set this.Visible = false; to make the window disappear.

[yyy]

Thanks jaydacodemonkey - but I think that's too complicated and might take more resources. I might try it if nothing else works.