Draw directly to screen

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Guest

Is it possible to draw directly to the screen using the .net libraries? I
thought that it might be possible with GDI+ but I can't find out how to do it
anywhere. A part of me suspects I may have to look into using the Windows API.

Any ideas,

Darrell
 
You cannot draw somewhere but within your own created windows.
That means you have to create a window before you can draw something.
If you want to make appear something on the users desktop you can always
make a borderless shaped/transparent window but you cannot draw without a
window neither with .net nor with the windows API.
 
Within your own window you can draw using the Graphics object passed in the
OnPaint or Paint event arguments.

Dou you mean directly on the desktop? Yes you can by obtaining the desktop
handle and wrapping it in a GDI+ Graphics object using Graphics.FromHdc.

I generally use interop for this and import the GetDc and ReleaseDc methods.
You must remember to correctly release DC's when you do this.

It's not neat or pretty though...

[DllImport("User32.dll")]

public static extern IntPtr GetDC(IntPtr hwnd);

[DllImport("User32.dll")]

public static extern void ReleaseDC(IntPtr dc);

protected override void OnPaint(PaintEventArgs e)

{

SolidBrush b=new SolidBrush(Color.Red);


IntPtr desktopDC=GetDC(IntPtr.Zero);

Graphics g = Graphics.FromHdc(desktopDC);

g.FillEllipse(b,0,0,1024,768);

g.Dispose();

ReleaseDC(desktopDC);

}


--
Bob Powell [MVP]
Visual C#, System.Drawing

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.
 
This is great. Thanks. There's just another problem with it though. It only
draws it once. Is there any way to get it to constantly draw it? I'm
wondering if there's an event message I could capture in public override
WndProc for a screen refresh and stick it in there. I tried putting it in a
recursive while loop in it's own thread but obviously this is a bad idea and,
while it worked, it ended up just recursively drawing, jerking and generally
looking a mess.

Darrell

Bob Powell said:
Within your own window you can draw using the Graphics object passed in the
OnPaint or Paint event arguments.

Dou you mean directly on the desktop? Yes you can by obtaining the desktop
handle and wrapping it in a GDI+ Graphics object using Graphics.FromHdc.

I generally use interop for this and import the GetDc and ReleaseDc methods.
You must remember to correctly release DC's when you do this.

It's not neat or pretty though...

[DllImport("User32.dll")]

public static extern IntPtr GetDC(IntPtr hwnd);

[DllImport("User32.dll")]

public static extern void ReleaseDC(IntPtr dc);

protected override void OnPaint(PaintEventArgs e)

{

SolidBrush b=new SolidBrush(Color.Red);


IntPtr desktopDC=GetDC(IntPtr.Zero);

Graphics g = Graphics.FromHdc(desktopDC);

g.FillEllipse(b,0,0,1024,768);

g.Dispose();

ReleaseDC(desktopDC);

}


--
Bob Powell [MVP]
Visual C#, System.Drawing

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.





redneon said:
Is it possible to draw directly to the screen using the .net libraries? I
thought that it might be possible with GDI+ but I can't find out how to do
it
anywhere. A part of me suspects I may have to look into using the Windows
API.

Any ideas,

Darrell
Click to expand...
Click to expand...
 
What about this funny idea: Generate a composition between the users current
desktop wallpaper and the stuff you want to draw.
That means you have to draw into this wallpaperbitmap in memory, write it to
a new file and set it as wallpaper.
The question is how often the things you are drawing should be refreshed.
May I ask what exactly you are drawing?

redneon said:
This is great. Thanks. There's just another problem with it though. It only
draws it once. Is there any way to get it to constantly draw it? I'm
wondering if there's an event message I could capture in public override
WndProc for a screen refresh and stick it in there. I tried putting it in a
recursive while loop in it's own thread but obviously this is a bad idea and,
while it worked, it ended up just recursively drawing, jerking and generally
looking a mess.

Darrell

Bob Powell said:
Within your own window you can draw using the Graphics object passed in the
OnPaint or Paint event arguments.

Dou you mean directly on the desktop? Yes you can by obtaining the desktop
handle and wrapping it in a GDI+ Graphics object using Graphics.FromHdc.

I generally use interop for this and import the GetDc and ReleaseDc methods.
You must remember to correctly release DC's when you do this.

It's not neat or pretty though...

[DllImport("User32.dll")]

public static extern IntPtr GetDC(IntPtr hwnd);

[DllImport("User32.dll")]

public static extern void ReleaseDC(IntPtr dc);

protected override void OnPaint(PaintEventArgs e)

{

SolidBrush b=new SolidBrush(Color.Red);


IntPtr desktopDC=GetDC(IntPtr.Zero);

Graphics g = Graphics.FromHdc(desktopDC);

g.FillEllipse(b,0,0,1024,768);

g.Dispose();

ReleaseDC(desktopDC);

}


--
Bob Powell [MVP]
Visual C#, System.Drawing

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.





redneon said:
Is it possible to draw directly to the screen using the .net libraries? I
thought that it might be possible with GDI+ but I can't find out how to do
it
anywhere. A part of me suspects I may have to look into using the Windows
API.

Any ideas,

Darrell
Click to expand...
Click to expand...
Click to expand...
 
What about this funny idea: Generate a composition between the users current
desktop wallpaper and the stuff you want to draw.
Click to expand...

There are about a million problems with that. Firstly, we're not all running
Cray supercomputers so the refresh rate will kill people. Secondly, I want to
draw on top of Windows too and setting the wallpaper would draw behind them.
 
Thats why I asked you what exactly you are trying to achieve. There is
always the option to make a topmost small invible/translucent window and
draw you stuff in there.
 
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