(MFC)Comfused in OnEraseBkgnd & OnPaint

[Hamed Musavi]

1.I created some ownerdrawn controls and put them on a dialog. 2.I want to use a custom gradient as the background of the dialog. 3.I override OnEraseBkgnd:

BOOL CDlgButtons::OnEraseBkgnd(CDC* pDC)
{
// I draw a gradient here, using gdi+ and pDC
return TRUE;
}

4.I leave OnPaint without any changes. Problem: None of the buttons on the form draw correctly. I don't have any other control. Ownerdraw buttons are completely hidden. None ownerdraw, turn to white rectangles, no text, nothing. if I draw my gradient without using pDC in OnEraseBkgnd, and instead use a new dc: CPaintDC dc(this); it's ok. I am completely confused. Can any one please describe this strange behavior?

// "Life is very short and is very fragile also." Yanni
while (I'm_alive)
{
cout<<"I love programming.";
}

[Mark Salsbery]

Something wrong is happening elsewhere. I use this code in the main dialog of the app I use for quickly testing code I post here on CP:

BOOL CMFCTesterDlg::OnEraseBkgnd(CDC* pDC)
{
    CRect rect;
    GetClientRect(&rect);
    COLORREF c1 = RGB(64, 0, 64);
    COLORREF c2 = RGB(0, 128, 128);
    for(int i = 0; i < rect.Height(); i++)
    {
        int r, g, b;
        r = GetRValue(c1) + (GetRValue(c2) - GetRValue(c1)) * i / rect.Height();
        g = GetGValue(c1) + (GetGValue(c2) - GetGValue(c1)) * i / rect.Height();
        b = GetBValue(c1) + (GetBValue(c2) - GetBValue(c1)) * i / rect.Height();
        pDC->FillSolidRect(0, i, rect.Width(), 1, RGB(r, g, b));
    }
    return TRUE;
}

There's a potpourri of controls on the dialog and they all draw correctly. What happens if you comment-out the ON_WM_ERASEBKNGD() entry in the message map? Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[karle]

I would use the device Context given as parameter. May this pDC has cliping areas defined. CPaintDC is not useful here because it calls BeginPaint / EndPaint. Beginpaint emit's an WM_ERASEBACKGROUND. see MSDN documentation of BeginPaint. You should also consider setting WS_CLIPCHILDREN style for dialog window.

[Hamed Musavi]

Sorry for late response.:sigh: I was out for a (long) while. Thank you for your help. I have more time to find the problem, today. I think the problem is with clipping. Thank you again for your help. :)

// "Life is very short and is very fragile also." Yanni
while (I'm_alive)
{
    cout<<"I love programming.";
}

[Hamed Musavi]

Sorry for late response.:sigh: I was out for a (long) while.

karle wrote:

CPaintDC is not useful here because it calls BeginPaint / EndPaint. Beginpaint emit's an WM_ERASEBACKGROUND.

However I'm not sure how it works exactly, but it was also strange to me that why it does not cause an infinite loop. It's more like every time OnPaint or OnEraseBkgnd is called, it's in a new thread! I forgot clipping totally. Thank you for your kind helpful answer. :)

// "Life is very short and is very fragile also." Yanni
while (I'm_alive)
{
    cout<<"I love programming.";
}