Managed C++/CLI

Re: Getting the Brush to apply to pictureBox instead of Form

27-Apr-09 0:58

Hi Jeff,

I have a standard reply for such a popular question, here it goes:

there are several steps to correctly draw something; it does not matter how complex the paint job is: from a single line, to a complex drawing, or a real work of art.

To make sure it all becomes visible on the screen and gets repainted automatically when moving, resizing, minimizing/maximizing/restoring or uncovering your Form, one should follow these steps:

1.
decide upon what object you want to draw; it normally is a Control (e.g. a Panel) or a Form itself. I prefer to add a Panel to a Form, then draw on the Panel.

2.
create some variables (Rectangle, struct, class, whatever) that hold the parameters of your drawing. For a rectangle that could be top and left coordinate, and width+height, or just a Rectangle. etc.

3.
create a Paint handler (either add your own paint handler to the Paint event, or
override the OnPaint method) for that Panel, and do all your drawing in there,
using the Graphics class and your variables.

4.
if and when you want to change things, modify the variables and call Panel.Invalidate() or one of its overloads (for selective invalidation).

5.
If you want to animate things, perform the move (step 4) inside the Tick handler of a Windows.Forms.Timer which ticks on the GUI thread, so you are allowed to call Invalidate() from there too.

BTW: if you need to create some objects (Fonts, Pens, Brushes, ...) either keep them
alive in class members (hence create them only once); or create them inside the Paint
handler and don't forget to call Dispose() on them.

Smile | :)

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Jeffrey Webster27-Apr-09 3:13

Re: Getting the Brush to apply to pictureBox instead of Form

27-Apr-09 3:13

Hi,
Thanks Luc. Yes, I'm aware that it is probably not a great idea to keep creating and disposing of the pens/brushes. I found in a previous application I'd written (in unmanaged C++) that it seemed to recreate the pen every time for some reason, even though I wasn't specifically telling it to do so. It kept crashing. Finally I gave up and simply created and deleted everything on each iteration. But I'll work on that again.

Mostly I'm just trying to understand the syntax/object model of managed C++ well enough to actually do some basic examples. My big goal at this point is to control where the drawing is done, which unfortunately you didn't mention in your reply.

The code examples I'm drawing from are from Msft VisualC++.Net by Templeman/Olsen (for anyone who is interested) and they are using the "Graphics" class to invoke the DrawLine method as you can see in the code. But how does this class know where to draw the line? Somehow it's assuming I want it drawn on the Form. What if I want it drawn somewhere else?

Thanks,
Jeff

Luc Pattyn27-Apr-09 3:43

Re: Getting the Brush to apply to pictureBox instead of Form

27-Apr-09 3:43

Hi Jeffrey,

I suggest you read points 1 and 3 once more.
The Paint handler must be wired to the Control you want to paint on.

Smile | :)

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Jeffrey Webster27-Apr-09 4:26

Re: Getting the Brush to apply to pictureBox instead of Form

27-Apr-09 4:26

Hi,

Unfortunately I just can't find enough documentation on this subject to proceed at this point. I'll do some more digging...

Thanks,
Jeff

Luc Pattyn27-Apr-09 4:34

Re: Getting the Brush to apply to pictureBox instead of Form

27-Apr-09 4:34

what is wrong with myControl.Paint+=myPaintHandler; except for the fact that you want C++ syntax, mine is C#?

Smile | :)

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Jeffrey Webster27-Apr-09 6:20

Re: Getting the Brush to apply to pictureBox instead of Form

27-Apr-09 6:20

Hi,
To me - and this may just reveal my ignorance - whether or not this is handled as a Paint event or simply placed within the timer sub doesn't really affect the central question which is how to get the brushes/pens to draw on the pictureBox and not the Form.

To get some idea I simply used the Designer code generator to create MouseDown and MouseUp events on the pictureBox.

This is what the code looked like:

this->pictureBox1->MouseUp += new System::Windows::Forms::MouseEventHandler(this, pictureBox1_MouseUp);
this->pictureBox1->MouseDown += new System::Windows::Forms::MouseEventHandler(this, pictureBox1_MouseDown);

then for the drawing I used this

private: System::Void pictureBox1_MouseDown(System::Object *  sender, System::Windows::Forms::MouseEventArgs *  e)
   {
	p1.X = e->X;
	p1.Y = e->Y;
   }

private: System::Void pictureBox1_MouseUp(System::Object *  sender, System::Windows::Forms::MouseEventArgs *  e)
   {
	p2.X = e->X;
	p2.Y = e->Y;
	Graphics* gr= CreateGraphics();
	Pen* pen1 = new Pen(Color::Black);
	gr->DrawLine(pen1, p1.X,p1.Y,p2.X,p2.Y);
	gr->Dispose();
   }

But this is still drawing on the Form, not the pictureBox. Puzzling.

Jeff

Luc Pattyn27-Apr-09 6:23

Re: Getting the Brush to apply to pictureBox instead of Form

27-Apr-09 6:23

Jeffrey Webster wrote:
Graphics* gr= CreateGraphics();

is completely wrong:
1. you are getting a Graphics associated with your Form, not your PictureBox (how is the Graphics to know you want to paint on the PictureBox??)
2. you don't need to create a Graphics at all, you get one for free in any Paint handler.

Smile | :)

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Jeffrey Webster27-Apr-09 6:34

Re: Getting the Brush to apply to pictureBox instead of Form

27-Apr-09 6:34

Okay then send me some code, an example, something I can work with. I think by now we know that simply admonishing me for not using a Paint handler is not helping me.

Thanks,
Jeff

Luc Pattyn27-Apr-09 6:52

Re: Getting the Brush to apply to pictureBox instead of Form

27-Apr-09 6:52

C# example (not tested):

private Panel panel;
private bool paintRectFlag=true;
private Rectangle rect=new Rectangle(20, 20, 300, 200);
private Pen rectPen=Pens.Black;
…
public Form1() {
    InitializeComponents();
    panel=new Panel();
    panel.Paint+=panelPaintHandler;
    Controls.Add(panel);
}
…
protected void panelPaintHandler(object sender, PaintEventArgs e) {
    Graphics g=e.Graphics;
    if (paintRectFlag) g.DrawRectangle(rectPen, rect);
}

protected void buttonClickHandler(object sender, EventArgs e) {
    paintRectFlag=!paintRectFlag;   // toggle visible flag
    panel.Invalidate();
}

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Jeffrey Webster27-Apr-09 8:01

How to Convert Strings[] to LPWSTR*???

27-Apr-09 8:01

Thanks for the code.

As I understand it, the actual drawing occurs here:

protected void panelPaintHandler(object sender, PaintEventArgs e) {
    Graphics g=e.Graphics;
    if (paintRectFlag) g.DrawRectangle(rectPen, rect);

Which draws to a panel, which I'm assuming is a sort of generalized/abstract screen object. Presumably this would be rendered according to the needs of some Form (or other) object when invoked?

So if you (were to) run this, would it draw a rectangle? Or do you need additional code to make it "work"?

Thanks,
Jeff

ANURAG VISHNOI22-Apr-09 21:14

ANURAG VISHNOI

22-Apr-09 21:14

Hello All,
I am trying to convert a list of Strings in LPWSTR* array. I am using the following way to convert it. But here the problem occurs in the returning array items. It contains all the elements same in the array. I found the problme is due to memset() which updates the memory address everytime same as earlier. Please help me out----

for(DWORD i = 0; i < itemIds->Count; i++)
{
ATL::CComBSTR itemWChar;
itemWChar = ::GetAtlBstr(itemIds[i]);
WCHAR _itemWChar[_MAX_PATH];
memset(_itemWChar, 0, sizeof(_itemWChar) / sizeof(_itemWChar[0]));
memcpy(_itemWChar, static_cast(itemWChar), itemWChar.ByteLength());
items[i] = _itemWChar;
}

ANURAG VISHNOI,
Sr. Software Engineer,

Re: How to Convert Strings[] to LPWSTR*???

Mark Salsbery23-Apr-09 6:33

Checking OS and Vista admin rights

23-Apr-09 6:33

The memset() should have no effect here (nor is it necessary).
Plus, you've calculated the number of bytes to set incorrectly...
it should be sizeof(_itemWChar), not sizeof(_itemWChar) / sizeof(_itemWChar[0])

What are "itemIds" and "items" (what are their declared types)?
This is the part that looks fishy to me:

memcpy(_itemWChar, static_cast(itemWChar), itemWChar.ByteLength());
items[i] = _itemWChar;

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

turkmeistr122-Apr-09 3:32

22-Apr-09 3:32

I'm writing a diagnostic tool in Visual C++. It's a GUI. I need to be able to have the program determine whether or not it needs to be loaded with admin privileges on Vista. The diagnostic tool works flawlessly in XP 32 bit, and it would work flawlessly on 64 bit if I could determine how to verify whether the system is 32 bit or 64 bit by redirecting the directory the batch files are automatically written to. Could anyone help me with figuring out the code used to first verify the OS and whether it's 32 or 64 bit? After that, possibly how to bypass UAC on Vista so it has the administrator rights when running batch files?

Mark Salsbery22-Apr-09 8:07

22-Apr-09 8:07

turkmeistr1 wrote:
verify the OS and whether it's 32 or 64 bit

How to detect programmatically whether you are running on 64-bit Windows[^]

turkmeistr1 wrote:
bypass UAC on Vista

Bypass?

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

turkmeistr122-Apr-09 8:38

22-Apr-09 8:38

Thanks for that first link, that will help tremendously. What I meant by bypass UAC on Vista is to allow the program to execute batch files as the administrator. Some commands, such as resetting tcp/ip, require the "elevated" command prompt.

Mark Salsbery22-Apr-09 12:15

22-Apr-09 12:15

Something like this?

// Run a batch file with elevated privileges

System::Diagnostics::Process ^process = gcnew System::Diagnostics::Process();
process->StartInfo->FileName = "cmd.exe";
process->StartInfo->Arguments = "/c c:\\mybatchfile.bat";
process->StartInfo->Verb = "runas";
process->Start();

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

turkmeistr122-Apr-09 12:40

22-Apr-09 12:40

I'll have to try this, would this be Vista only or would it work on XP as well? With the runas verb, would that prompt the user or have it automatically do it?

Mark Salsbery22-Apr-09 13:26

22-Apr-09 13:26

turkmeistr1 wrote:
With the runas verb, would that prompt the user

The way I showed it, yes, it will prompt.

System::Diagnostics::Process::StartInfo, as well as another System::Diagnostics::Process::Start() overload,
also have user name and password properties if you know an administrative user/password in advance.

turkmeistr1 wrote:
I'll have to try this, would this be Vista only or would it work on XP as well?

As far as I know it should work on XP...try it - you can always just test with notepad or
something... Smile | :)

System::Diagnostics::Process ^process = gcnew System::Diagnostics::Process();
process->StartInfo->FileName = "c:\\windows\\system32\\notepad.exe";
//process->StartInfo->Arguments = "/c c:\\mybatchfile.bat";
process->StartInfo->Verb = "runas";
process->Start();

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

turkmeistr123-Apr-09 7:34

23-Apr-09 7:34

Awesome, that works beautifully, final question, is there a way to verify if it's running on XP or Vista? I only want it to pull up the Run As prompt if it's Vista, otherwise it's not entirely necessary.

Mark Salsbery23-Apr-09 8:04

23-Apr-09 8:04

turkmeistr1 wrote:
is there a way to verify if it's running on XP or Vista?

I use something like this:

static public bool OsIsAtLeastVista
{
    get
    {
        bool ret = false;

        System.OperatingSystem osInfo = System.Environment.OSVersion;

        if (osInfo.Platform == System.PlatformID.Win32NT)
        {
            if (osInfo.Version.Major > 5)
            {
                ret = true;
            }
            break;
        }

        return ret;
    }
}

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

turkmeistr123-Apr-09 11:57

23-Apr-09 11:57

I get a lot of errors when using System.OperatingSystem, if I change it to System::OperatingSystem it works up unto the point of System::Environment.OSVersion, what should I use for that last dot there? The :: doesn't work for that, Platform, or Win32NT or Version.Major.

Mark Salsbery23-Apr-09 12:29

23-Apr-09 12:29

The code I posted was C#, sorry.

Use :: and -> where necessary to convert to C++/CLI.

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Mark Salsbery23-Apr-09 12:34

23-Apr-09 12:34

I ripped the code from a larger property implementation and left some
artifacts. Here's fixed, in C++/CLI:

bool ret = false;

System::OperatingSystem ^osInfo = System::Environment::OSVersion;

if (osInfo->Platform == System::PlatformID::Win32NT)
{
    if (osInfo->Version->Major > 5)
    {
        ret = true;
    }
}

return ret;

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

turkmeistr123-Apr-09 13:03