EVT_ERASE_BACKGROUND, wxEraseEvent::GetDC()->GetSize() and "no way to retrieve the size of generic DC" [wxMSW 2.7.0]

[Volker Bartheld]

Hi!

I use the EVT_ERASE_BACKGROUND to draw a custom background (a tiled
wxBitmap, see below [1]) for my dialog. With wxMSW2.6.3, this worked
fine, now I get the "no way to retrieve the size of generic DC"
assertion in the DEBUG build.

Is that the intended behaviour, should I rather use
EVT_PAINT/wxPaintEvent for drawing a background and will this also work
on wxLIN/wxMAC if I want transparent wxPanels ontop of a wxDialog with
custom backgound [2]? Especially wxLIN with GTK+ seemed to have problems
with those, so I needed a work-around.

Thanks for insights,

Volker


[1]
BEGIN_EVENT_TABLE(MyDialog, wxDialog)
EVT_ERASE_BACKGROUND(MyDialog::OnEraseBackground)
END_EVENT_TABLE()
void MyDialog::OnEraseBackground(wxEraseEvent& event)
{
  wxDC* pDc=event.GetDC();
  if(!m_pBackgroundBitmap->Ok()) return;
  const wxSize DcSize=pDc->GetSize();
  wxSize BmpSize(m_pBackgroundBitmap->GetWidth(), m_pBackgroundBitmap->GetHeight());
  for(wxCoord x=0x; x<DcSize.x; x+=BmpSize.x)
    for(wxCoord y=0; y<DcSize.y; y+=BmpSize.y)
      pDc->DrawBitmap(*m_pBackgroundBitmap, x, y, true);
}


[2] I was implementing EVT_ERASE_BACKGROUND in my panel featuring the
transparent background which was calling a custom DrawBackground()
function in it's parent class, passing wxEraseEvent::GetDC(). The parent
class' (has wxBG_STYLE_CUSTOM set) DrawBackground() function is more or
less drawing wxBitmap tiles into the wxDC extracted from the event.

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