Different result on laptop and stationary computer - c++

Question

The code below calculates the size of a the rect holding the text to a checkbox. Code works fine when i'm using a stationary computer with monitors with different screen resolution. But when I run the exact same code on a laptop with an external monitor connected the box is too small. Laptop screen res is 1680x1050 and the monitor is 1920x1080.
pclRect has the same values no matter which computer I run it on.
Anybody's got an idea how to solve this?
Results:
void CForm::SetSize(CWnd *pCWnd, CRect *pclRect)
{
CDC *pclDC = m_pclPanel->GetDC();
CFont* font = pCWnd->GetFont();
LOGFONT logFont;
font->GetLogFont(&logFont);
CString str;
pCWnd->GetWindowText(str);//Get controller text
CClientDC dc(pCWnd);
dc.SelectObject(font);
int iWidth;
int iHeight;
long lFontSize = -MulDiv(logFont.lfHeight, GetDeviceCaps(pclDC->m_hDC, LOGPIXELSY), 72);
iWidth = dc.GetTextExtent(str).cx; //Get controller text length
iWidth += GetExtraWidth(); //This adds 18 to the width since it's the width of the checkbox itself
iHeight = abs(lFontSize) + GetExtraHeight();
pclRect->bottom = pclRect->top + iHeight;
pclRect->right = pclRect->left + iWidth;
pCWnd->MoveWindow(pclRect);
}

Answer 1

If target window is Vista or higher, use BCM_GETIDEALSIZE to find the minimum size. But check box cannot have multi-line flag (BS_MULTILINE). For example
m_checkBox.SetWindowText(L"long text xxx xxx xxx xxx xxx xxx");
SIZE sz;
if (Button_GetIdealSize(m_checkBox.m_hWnd, &sz) && sz.cx > 0 && sz.cy > 0)
{
m_checkBox.SetWindowPos(0, 0, 0, sz.cx, sz.cy, SWP_NOZORDER|SWP_NOMOVE);
}
else
{
//use another method ...
}
Otherwise, modify your code and instead of supplying 18 pixels for checkbox width, use
GetSystemMetrics to find the check box width (this results in 15 pixels in default DPI, so you have to add few more pixels for text padding).
Use GetThemePartSize if theme is active. For example:
CClientDC dc(this);
SIZE sz;
HTHEME ht = OpenThemeData(m_hWnd, L"Button");
if (ht)
{
GetThemePartSize(ht, dc, BP_CHECKBOX, CBS_CHECKEDNORMAL, NULL, TS_TRUE, &sz);
CloseThemeData(ht);
//sz.cx is 13 pixels in default DPI
}
else
{
sz.cx = GetSystemMetrics(SM_CXMENUCHECK);
//sz.cx is 15 pixels in default DPI
}
Screen resolution is not relevant here. The posted images suggest that both displays have the same DPI settings. Note that if DPI settings changes, and your application is DPI aware then sz.cx will be different.