Re: draw image as per system DPI setting

"David Ching" <>
Thu, 13 Aug 2009 08:12:49 -0700
"heavenlysmile" <> wrote in message

I have an issues related to loading and drawing the bitmap.
I have an mfc application mfc with transparent ctrlbutton. I have bitmap
file with 96 dpi resolution, but if i chage the system setting to 120 dpi
image does not appear proper on the dialog box. I used stretchblt to
the issue , but at the same time, image loading on control button (to make
transparent i used bitblt) does not show properly.

Is there any function in VC to get the current screen resolution and draw
the bitmap accordingly ?

It's been a few years, but here's some code that I copied from an old

// Call from a CWnd derived class
CClientDC dc(this);
int nLogicalPixelsX = dc.GetDeviceCaps(LOGPIXELSX); // will be 96 for
small fonts (default)
int nLogicalPixelsY = dc.GetDeviceCaps(LOGPIXELSY); // will be 72 for
small fonts (default)?

This might work to scale the bitmap size to the current dpi returned by
these functions. But I also wanted to keep my dialog the same width and
height no matter the dpi, so I resize it to the original size and reduce
font size for larger dpi so my text fit on my dialog. I tried the above
calculations to determine the font size, but it did not work in Japanese on
WinME (and Korean also was hard). I ended up not using the above and

    if ( HIWORD(GetDialogBaseUnits()) != 16 )
        lf.lfHeight = MulDiv(lf.lfHeight, 16, HIWORD(GetDialogBaseUnits()));
        // Round up
        if (lf.lfHeight < 0)

You may not be concerned about keeping your dialog the same size in larger
dpi, if so ignore the above.

-- David

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