Custom Control Loses Device Context

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  • Dennis
    #1

    Custom Control Loses Device Context

    I'm using VS 2003 my project uses COM interop and the Tao Framework.

    I have a custom control derived from UserControl. It implements many
    functions similar to the Tao's SimpleOpenGLCon trol, for example I also have a
    MakeCurrent() method. Inside of the overriden method for CreateParams() I
    also set the CS_OWNDC bit so that my control has a private DC. During
    instantiation of my control I make a call to User32.dll to GetDC(IntPtr
    handle) passing this.Handle as the argument and hold that as a member
    variable, m_hDC, of my class. Then using Tao I then get the Rendering
    Context with a m_hRC = Wgl.wglCreateCo ntext(m_hDC);

    My application is to take data from a COM object's Connection Point.
    Basically it looks like this ReceivedData(SA FEARRAY(BYTE)* buffer). Using VS
    to create the event handler for me I get in C#

    private void myObj_ReceivedD ata(ref Array buffer)


    My custom control has a method called SetData(byte[] data) so inside of my
    event handler the code looks like this

    private void myObj_ReceivedD ata(ref Array buffer)
    {
    myGlCtrl.SetDat a((byte[])buffer);
    }


    Now here is my problem. When the event handler is triggered my control
    throws out errors. When I step into SetData() I fall into a position where
    I'm watching the m_hDC and it all of the sudden doesn't match the
    User32.GetDC(th is.Handle) function call. When this happens I can't
    successfully MakeCurrent. When I make calls to Marshal.GetLast Win32Error()
    I've had it return #6, "The handle is invalid." and also #170, "The requested
    resource is in use." I'm not sure which handle the error is referring to but
    I do know that my control's Handle is constant and did not change.

    Shouldn't the device context remain the same value since it is a private DC?

    I also know that my control does draw. Because as a test I was at first
    using a timer on my application that randomly filled a byte[] at every 500ms.
    Inside the timer1_Tick(... ) event handler I made the
    myGlCtrl.SetDat a(m_data) call and it drew fine. But when I switched my
    application to the COM object as the data source things went bad.

    Is there another step I need to perform when getting data from the COM object?

    Any help will be greatly appreciated.
    Thanks in advance,

    Dennis
    Tags: None
    • Dennis
      #2
      RE: Custom Control Loses Device Context

      It appears that my COM object's connection Point is coming in on a seperate
      thread other than my UI thread.

      Since this is using OpenGL that is invalid for my rendering context. There
      can be only one ACTIVE rendering context per thread.

      I believe I've found the solution. I had to use modify my code slightly so
      that my SetData routine did no GL commands and only manipulated the data.
      Then I used Invoke to get the other thread to start my Rendering on the UI
      thread.

      I hope this may help someone else in the future. I now I've spent to much
      time with it.


      Dennis

      "Dennis" wrote:
      [color=blue]
      > I'm using VS 2003 my project uses COM interop and the Tao Framework.
      >
      > I have a custom control derived from UserControl. It implements many
      > functions similar to the Tao's SimpleOpenGLCon trol, for example I also have a
      > MakeCurrent() method. Inside of the overriden method for CreateParams() I
      > also set the CS_OWNDC bit so that my control has a private DC. During
      > instantiation of my control I make a call to User32.dll to GetDC(IntPtr
      > handle) passing this.Handle as the argument and hold that as a member
      > variable, m_hDC, of my class. Then using Tao I then get the Rendering
      > Context with a m_hRC = Wgl.wglCreateCo ntext(m_hDC);
      >
      > My application is to take data from a COM object's Connection Point.
      > Basically it looks like this ReceivedData(SA FEARRAY(BYTE)* buffer). Using VS
      > to create the event handler for me I get in C#
      >
      > private void myObj_ReceivedD ata(ref Array buffer)
      >
      >
      > My custom control has a method called SetData(byte[] data) so inside of my
      > event handler the code looks like this
      >
      > private void myObj_ReceivedD ata(ref Array buffer)
      > {
      > myGlCtrl.SetDat a((byte[])buffer);
      > }
      >
      >
      > Now here is my problem. When the event handler is triggered my control
      > throws out errors. When I step into SetData() I fall into a position where
      > I'm watching the m_hDC and it all of the sudden doesn't match the
      > User32.GetDC(th is.Handle) function call. When this happens I can't
      > successfully MakeCurrent. When I make calls to Marshal.GetLast Win32Error()
      > I've had it return #6, "The handle is invalid." and also #170, "The requested
      > resource is in use." I'm not sure which handle the error is referring to but
      > I do know that my control's Handle is constant and did not change.
      >
      > Shouldn't the device context remain the same value since it is a private DC?
      >
      > I also know that my control does draw. Because as a test I was at first
      > using a timer on my application that randomly filled a byte[] at every 500ms.
      > Inside the timer1_Tick(... ) event handler I made the
      > myGlCtrl.SetDat a(m_data) call and it drew fine. But when I switched my
      > application to the COM object as the data source things went bad.
      >
      > Is there another step I need to perform when getting data from the COM object?
      >
      > Any help will be greatly appreciated.
      > Thanks in advance,
      >
      > Dennis[/color]

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