Adjust the font size when DPI of window changes

src/common/wincmn.cpp

@@ -1726,6 +1726,8 @@ wxFont wxWindowBase::GetFont() const
         if ( !font.IsOk() )
             font = GetClassDefaultAttributes().font;
 
+        font.WXAdjustToPPI(GetDPI());
+
         return font;
     }
     else
@@ -1744,6 +1746,9 @@ bool wxWindowBase::SetFont(const wxFont& font)
     m_hasFont = font.IsOk();
     m_inheritFont = m_hasFont;
 
+    if ( m_hasFont )
+        m_font.WXAdjustToPPI(GetDPI());
+
     InvalidateBestSize();
 
     return true;

src/msw/font.cpp

@@ -512,7 +512,8 @@ wxFontEncoding wxNativeFontInfo::GetEncoding() const
 void wxNativeFontInfo::SetFractionalPointSize(float pointSizeNew)
 {
     // We don't have the correct DPI to use here, so use that of the
-    // primary screen.
+    // primary screen and rely on WXAdjustToPPI() changing it later if
+    // necessary.
     const int ppi = ::GetDeviceCaps(ScreenHDC(), LOGPIXELSY);
     lf.lfHeight = GetLogFontHeightAtPPI(pointSizeNew, ppi);
 
@@ -899,6 +900,19 @@ void wxFont::SetPixelSize(const wxSize& pixelSize)
     M_FONTDATA->SetPixelSize(pixelSize);
 }
 
+void wxFont::WXAdjustToPPI(const wxSize& ppi)
+{
+    // We only use vertical component here as we only adjust LOGFONT::lfHeight.
+    const int heightNew = M_FONTDATA->GetLogFontHeightAtPPI(ppi.y);
+
+    if ( heightNew != M_FONTDATA->GetLogFontHeight() )
+    {
+        AllocExclusive();
+
+        M_FONTDATA->SetLogFontHeight(heightNew);
+    }
+}
+
 void wxFont::SetFamily(wxFontFamily family)
 {
     AllocExclusive();

src/msw/window.cpp

@@ -4837,6 +4837,17 @@ wxSize wxWindowMSW::GetDPI() const
     return dpi;
 }
 
+void wxWindowMSW::MSWUpdateFontOnDPIChange(const wxSize& newDPI)
+{
+    if ( m_font.IsOk() )
+    {
+        m_font.WXAdjustToPPI(newDPI);
+
+        // WXAdjustToPPI() changes the HFONT, so reassociate it with the window.
+        wxSetWindowFont(GetHwnd(), m_font);
+    }
+}
+
 // Helper function to update the given coordinate by the scaling factor if it
 // is set, i.e. different from wxDefaultCoord.
 static void ScaleCoordIfSet(int& coord, float scaleFactor)
@@ -4861,6 +4872,9 @@ wxWindowMSW::MSWUpdateOnDPIChange(const wxSize& oldDPI, const wxSize& newDPI)
 
     InvalidateBestSize();
 
+    // update font if necessary
+    MSWUpdateFontOnDPIChange(newDPI);
+
     // update children
     wxWindowList::compatibility_iterator current = GetChildren().GetFirst();
     while ( current )