Re: Drawing on the Screen - C# Discussion Boards

14-Aug-02 5:53

I'm trying to draw directly on the screen. Whatever is drawn needs to be "above" the controls on the form. And, of course, I need to erase whatever is drawn to restore the way things looked before I did my drawing.

I looked at the "Reversible" drawing functions on the ControlPaint object but these don't give me the control over the color that I need. (I really only need Black, White, and a dotted grid of Gray.)

What should I be looking at now to get GDI+ to work with me on this?

-----
I'm essentially trying allow users to select controls. If one control overlaps another I still want the selection cues to appear atop the covering control.

Anonymous14-Aug-02 6:04

Anonymous

14-Aug-02 6:04

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

albean14-Aug-02 6:13

14-Aug-02 6:13

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

Alex Korchemniy14-Aug-02 6:28

Alex Korchemniy

14-Aug-02 6:28

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 Korchemniy14-Aug-02 6:42

Alex Korchemniy

14-Aug-02 6:42

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.

albean14-Aug-02 7:13

14-Aug-02 7:13

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.

Li-kai Liu (Angus)15-Aug-02 3:12

Li-kai Liu (Angus)

15-Aug-02 3:12

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 Smile | :)

Alex Korchemniy15-Aug-02 9:05

Alex Korchemniy

15-Aug-02 9:05

Sorry, I forgot to tell you to use GetDC.

I knew I missed something.

James T. Johnson14-Aug-02 7:51

14-Aug-02 7:51

I've never tried this, so it may or may not work but here goes Smile | :)

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

<br />
Graphics g = parent.CreateGraphics();<br />
PaintEventArgs e = new PaintEventArgs(e, form.Bounds);<br />
<br />
InvokePaint(form, e); <br />
// At this point the form has painted itself <br />
// to the graphics object<br />
<br />
// Do your drawing here using the Graphics object, g<br />

James
"And we are all men; apart from the females." - Colin Davies

albean14-Aug-02 8:32

14-Aug-02 8:32

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. Johnson14-Aug-02 8:58

14-Aug-02 8:58

Here you go, a quick demo showing how its done Smile | :)

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

albean15-Aug-02 16:40

15-Aug-02 16:40

Wow, thanks James Big Grin | :-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.

Looking for attribute

leppie14-Aug-02 4:54

14-Aug-02 4:54

Hi all,

I was wondering if there is an attribute that can be applied to a class/struct that tells the compiler not to compile it?

Thanx Smile | :)

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

James T. Johnson14-Aug-02 5:00

14-Aug-02 5:00

Am I missing something? Could you explain your situation a bit more?

James
"And we are all men; apart from the females." - Colin Davies

leppie14-Aug-02 6:04

14-Aug-02 6:04

I mean it must have some functionality e.g. lets call it an IncompleteAttribute (maybe NotImplementedAttribute) that one would be able to apply to a class/struct (what about maethods and properties) , so when one compile the project that those classes/structs doesnot get compiled.

This would be neat especcially working on a library of classes when certian classes might not be working as it should or the structure has just been put in place. Hey, even class status for example, like WorkingButWithErrors, etc.

I hope you understand a better. Smile | :)

PS: If there is not such an Attribute, would it be difficult to do?

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

James T. Johnson14-Aug-02 6:16

14-Aug-02 6:16

There aren't any attributes to stop code from getting compiled, because attributes don't play a part until code execution (except for attributes that the compiler looks for, but this is after the code has been compiled but before the assembly is created).

So you are left with commenting out or #if/#endif

James
"And we are all men; apart from the females." - Colin Davies

Nnamdi Onyeyiri14-Aug-02 7:22

Nnamdi Onyeyiri

14-Aug-02 7:22

leppie wrote:
This would be neat especcially working on a library of classes

hey - good luck with that, i hope to see the finished thing Big Grin | :-D

Suspicious | :suss: Email: theeclypse@hotmail.com URL: http://www.onyeyiri.co.uk
"All programmers are playwrights and all computers are lousy actors."

David Stone14-Aug-02 5:58

David Stone

14-Aug-02 5:58

I hear this works fine:

/*<br />
class MyClass<br />
{<br />
     //Insert methods here<br />
}<br />
*/

David Stone

It seemed similar to someone saying, "Would you like to meet my knife collection?"
Ryan Johnston on Elaine's sig

albean14-Aug-02 6:03

14-Aug-02 6:03

Hey leppie,

Did you try the following compiler directive?

#if(false)
.... Your Class
#endif

(But David's solution is easier to type);)

This will keep the compiler from even seeing your class. (But is this what you want to do?) Perhaps what you want is a forward reference? What is your situation?

leppie14-Aug-02 6:09

14-Aug-02 6:09

Ahhh, mite just be what im looking for Smile | :)

Re David solution: I prefer the colors Smile | :)

although it works just as well Smile | :)

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

Andy Smith14-Aug-02 6:30

Andy Smith

14-Aug-02 6:30

if you are using vstudio, and you are being a good boy and putting each class in its own file... then you can change the "Build Action" property of the file to "None".

leppie14-Aug-02 6:53