[wxDC::GetTextExtent()] Generates different values after wxMemoryDC::SelectObject()

[Vadim Zeitlin]

On Mon, 3 Sep 2007 13:13:24 +0100 Mario Figueiredo <marfig at gmail.com> wrote:

MF> Hello everyone,
MF> 
MF> This is a short code snippet that, while not related to my own code,
MF> better displays the problem and its easier to copy/paste:
MF> 
MF>     wxMemoryDC dc;
MF> 
MF>     wxString str("Mountains");
MF>     wxCoord w, h;
MF> 
MF>     wxLogDebug(wxT("Before SelectObject():"), NULL);

 You can't use wxMemoryDC before selecting a bitmap into it. All method
calls should fail.

MF> I do need to calculate GetTextExtent() before building the bitmap for
MF> the wxMemoryDC because it will be part of the calculation needed to
MF> determine that bitmap size. Later I need that value again (which I
MF> expect to be the same) to actually draw the text on the DC.

 You can select a temporary 1*1 bitmap initially, it should be enough for
the calculations to work correctly. You can also use wxClientDC of some
window -- if you use the same fonts, the results should be the same.

 Regards,
VZ

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