Drawing on the Screen

[Anonymous]

With DirectDraw you are able to draw directly on the screen!

[albean]

Really all I'm trying to do is recreate Visual Studio's form desinger. I think adding DirectDraw would be overkill.

[Alex Korchemniy]

You got me interested! What do you mean recreate VisualStudio's form designer? I think there is a way you can just import the functionality from a the original libary. I think its located in C:\Program Files\Microsoft Visual Studio .NET\Common7\IDE\Microsoft.VSDesigner.dll. If you want to do it another way, it can get very messy very fast. Ie. if you draw directly on the screen you then have to do hooks to handle the mouse events... Good luck to you. By the way, ASP WebMatrix did an ASP think like this. They have a VisualStudio like UI, with with the ASP webforms designer surface.

[Alex Korchemniy]

To answer your question directly, this is how you can draw on the screen: System.Drawing.Graphics g = System.Drawing.Graphics.FromHwnd(System.IntPtr.Zero); -or, something like this- IntPtr handle = System.IntPtr.Zero; System.Drawing.Graphics g = System.Drawing.Graphics.FromHdc(handle); -- Basicly you need to tell it you use null as the handle. This creates a graphics object that draw on top of everything. But, it can be very messy.

[albean]

AK, I tried both suggestions. The second throws an exception and the first doesnt crash but it doesn't do anything. Can you give me a link to a web page about using the null pointer to gain access to the screen? Thanks.

[James T Johnson]

I've never tried this, so it may or may not work but here goes :-) Create a control the same size as the Form (a panel would do), now when you want to draw your grid or whatever above the Form you do several things.... form will be the Form you are trying to draw on top of parent will be the panel or whatever that the Form is sitting on top of Graphics g = parent.CreateGraphics(); PaintEventArgs e = new PaintEventArgs(e, form.Bounds); InvokePaint(form, e); // At this point the form has painted itself // to the graphics object // Do your drawing here using the Graphics object, g James "And we are all men; apart from the females." - Colin Davies

[albean]

James, Hmm, I've been trying a similar approach but I like yours better because there is only a single surface to draw on. My only question is will I need to make your panel Transparent? I ask because I’ve been trying to create a user control with the graphics drawn on it around the edges. Then I was going to make the background color transparent and place this usercontrol over the other control (lets say it is a button) already on the form. In this way the button would show threw and my usercontrol's graphics would indicate that the button has been selected; even though the user control completely covers the button. The only problem is that I can't make the usercontrol transparent!!! Will I have to make your panel transparent too. Because this just isn't working for me.

[James T Johnson]

Here you go, a quick demo showing how its done :) It doesn't paint the non-client area but I think you can send some messages to windows to get it to do that (just need to call GetHdc/ReleaseHdc when passing it to windows). InvokePaintTest.zip (8.1 Kb) James "And we are all men; apart from the females." - Colin Davies

[Li kai Liu Angus]

Hi, I read AK's article and experimented with his second solution. It did throw an exception. And I modify it as follow and now it works: IntPtr hdc = GetDC(IntPtr.Zero); // get hdc for the screen Graphics g = Graphics.FromHdc(hdc); g.DrawLine(new Pen(Color.Blue), 0,0,500,500); // draw a line for testing. g.Dispose(); // <- I don't know if I should use g.Dispose or g.ReleaseHdc here... ReleaseDC(IntPtr.Zero,hdc); GetDC & ReleaseDC are Win32 API in user32.dll Hope this could help you:)

[Alex Korchemniy]

Sorry, I forgot to tell you to use GetDC. I knew I missed something.

[albean]

Wow, thanks James :-D I tried out your sample just now and its pretty cool. I'm probably not going to use it though because I want to keep the controls on the same form BUT if the screen painting turns out to be a hassle I’ll definitely come back to your solution.