GDI: Creating a pen VS taking it as a stock object.

This is a discussion on GDI: Creating a pen VS taking it as a stock object. within the Windows Programming forums, part of the Platform Specific Boards category; Hi there. I am studying some Visual C++ MFC programming just to understand some GUI programming in Windows. Mind you ...

  1. #1
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    GDI: Creating a pen VS taking it as a stock object.

    Hi there. I am studying some Visual C++ MFC programming just to understand some GUI programming in Windows.

    Mind you that my environment is Visual Studio 6, and I'm following the book "Learn Visual C++ Programming in 21 Days".

    (I am following too a book on C++ and one on Direct-X, the first just to make the transition from Java, and the latter because I am interested in Direct X).

    Anyway, my problem (was) this:

    In one of the examples wanted to trace a white line instead of a black one. First I came across (nice MSDN documentation) the DeviceContext.GetStockObject() function, and I tried to pass it to DeviceContext.SelectObject()...

    I tried to do this:

    Code:
    dc.SelectObject((CPen *)(dc.SelectStockObject(WHITE_PEN))
    This did not work, even if it looked as a legal function: the value returned was different than null (signal that the White Pen was loaded) and I think no exception was thrown since the program continued to go on without problems (mind you, I come from a Java background).

    After some research I was convinced to create a white pen by myself and to use it:

    Code:
    CPen zPen(PS_SOLID, 1, RGB(255, 255, 255));
    dc.SelectObject(&zPen);
    This works.
    Why?
    Is the GetStockObject an obsolete function? Does it work in Windows 2000? Did I make a mess out of pointers? (I used some C a long long long time ago... that is 2 years ago, always hated all the pointer stuff )

    Thankyou at least for reading!

  2. #2
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    >>dc.SelectObject((CPen *)(dc.SelectStockObject(WHITE_PEN))

    I think you are trying to select the pen twice

    try either;

    dc.SelectObject((CPen *)(dc.GetStockObject(WHITE_PEN))

    or

    dc.SelectStockObject(WHITE_PEN);



    By the way, if you change the GDI objects in a DC you MUST return the original before you delete the DC.

    If you create a GDI object then you must remove it from the DC then delete it (or release it if you used a Get function)

    Stock objects do not have to be deleted but must be removed from the dc.
    "Man alone suffers so excruciatingly in the world that he was compelled to invent laughter."
    Friedrich Nietzsche

    "I spent a lot of my money on booze, birds and fast cars......the rest I squandered."
    George Best

    "If you are going through hell....keep going."
    Winston Churchill

  3. #3
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    So you mean something like...

    Code:
    CPen tempPen = dc.GetCurrentPen();
    dc.RemoveObject(tempPen);
    dc.SelectStockObject(WHITE_PEN);
    ?

    Edit:

    Ok, RemoveObject doesn't exist (I wrote it without checking the manuals before).
    What do I have to use in this case to remove the stuff? Haven't found anything, neither watching the CClientDC, nor the CDC member functions.

    SelectStockObject instead works fine ^^;

    Thankyou.
    Last edited by limacat; 03-31-2003 at 01:52 AM.

  4. #4
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    the return from SelectObject() is the GDI resource already contained in the DC. Catch it for later use.


    hdc=GetDC(NULL);
    hOldPen=(HPEN*)SelectObject(hdc,hNewPen);

    //draw

    SelectObject(hdc,hOldPen);
    DeleteObject(hNewpen);
    ReleaseDC(NULL,hdc);//if you created the dc then you must use deleteDC
    "Man alone suffers so excruciatingly in the world that he was compelled to invent laughter."
    Friedrich Nietzsche

    "I spent a lot of my money on booze, birds and fast cars......the rest I squandered."
    George Best

    "If you are going through hell....keep going."
    Winston Churchill

  5. #5
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    Thank you very much novacain. I owe you a beer (If you like beers that is ).

  6. #6
    It's full of stars adrianxw's Avatar
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    >>> If you like beers that is

    He's Australian...
    Wave upon wave of demented avengers march cheerfully out of obscurity unto the dream.

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