Add wxRescaleCoord() helper and use it

No real changes, just make the code a bit shorter and more clear by
using a dedicated function rather than wxMulDivInt32() directly.

include/wx/gdicmn.h

@@ -1104,5 +1104,23 @@ extern wxRect WXDLLIMPEXP_CORE wxGetClientDisplayRect();
 // set global cursor
 extern void WXDLLIMPEXP_CORE wxSetCursor(const wxCursor& cursor);
 
+// Scale the given value by the ratio between 2 other values, with rounding.
+// Do not scale the value if it's -1, just return it unchanged in this case.
+extern int WXDLLIMPEXP_CORE wxRescaleCoord(int n, int newScale, int oldScale);
+
+inline wxPoint
+wxRescaleCoord(wxPoint pt, wxSize newScale, wxSize oldScale)
+{
+    return wxPoint(wxRescaleCoord(pt.x, newScale.x, oldScale.x),
+                   wxRescaleCoord(pt.y, newScale.y, oldScale.y));
+}
+
+inline wxSize
+wxRescaleCoord(wxSize sz, wxSize newScale, wxSize oldScale)
+{
+    return wxSize(wxRescaleCoord(sz.x, newScale.x, oldScale.x),
+                  wxRescaleCoord(sz.y, newScale.y, oldScale.y));
+}
+
 #endif
     // _WX_GDICMNH__

interface/wx/gdicmn.h

@@ -1345,3 +1345,20 @@ void wxDisplaySizeMM(int* width, int* height);
 wxSize wxGetDisplaySizeMM();
 //@}
 
+/**
+    Scale the given value by the ratio between 2 other values, with rounding.
+
+    Do not scale the value if it's -1, just return it unchanged in this case.
+
+    This simply calls wxMulDivInt32() with the provided arguments, but provides
+    a more clear name for this operation.
+
+    @since 3.1.6
+ */
+int wxRescaleCoord(int n, int newScale, int oldScale);
+
+/// @overload
+wxPoint wxRescaleCoord(wxPoint pt, wxSize newScale, wxSize oldScale);
+
+/// @overload
+wxSize wxRescaleCoord(wxSize sz, wxSize newScale, wxSize oldScale);

src/common/gdicmn.cpp

@@ -16,6 +16,7 @@
 
 #include "wx/display.h"
 #include "wx/gdiobj.h"
+#include "wx/math.h"
 
 #ifndef WX_PRECOMP
     #include "wx/log.h"
@@ -32,6 +33,10 @@
     #include "wx/math.h"
 #endif
 
+#ifdef __WINDOWS__
+    // Required in order to use wxMulDivInt32().
+    #include "wx/msw/wrapwin.h"
+#endif
 
 wxIMPLEMENT_ABSTRACT_CLASS(wxGDIObject, wxObject);
 
@@ -921,3 +926,8 @@ wxResourceCache::~wxResourceCache ()
         node = node->GetNext ();
     }
 }
+
+int wxRescaleCoord(int n, int newScale, int oldScale)
+{
+    return n == -1 ? -1 : wxMulDivInt32(n, newScale, oldScale);
+}

src/common/wincmn.cpp

@@ -2907,10 +2907,7 @@ wxWindowBase::FromDIP(const wxSize& sz, const wxWindowBase* w)
 
     const int baseline = wxDisplay::GetStdPPIValue();
 
-    // Take care to not scale -1 because it has a special meaning of
+    return wxRescaleCoord(sz, dpi, wxSize(baseline, baseline));
-    // "unspecified" which should be preserved.
-    return wxSize(sz.x == -1 ? -1 : wxMulDivInt32(sz.x, dpi.x, baseline),
-                  sz.y == -1 ? -1 : wxMulDivInt32(sz.y, dpi.y, baseline));
 }
 
 /* static */
@@ -2921,10 +2918,7 @@ wxWindowBase::ToDIP(const wxSize& sz, const wxWindowBase* w)
 
     const int baseline = wxDisplay::GetStdPPIValue();
 
-    // Take care to not scale -1 because it has a special meaning of
+    return wxRescaleCoord(sz, wxSize(baseline, baseline), dpi);
-    // "unspecified" which should be preserved.
-    return wxSize(sz.x == -1 ? -1 : wxMulDivInt32(sz.x, baseline, dpi.x),
-                  sz.y == -1 ? -1 : wxMulDivInt32(sz.y, baseline, dpi.y));
 }
 
 #endif // !wxHAVE_DPI_INDEPENDENT_PIXELS
@@ -2963,28 +2957,14 @@ wxPoint wxWindowBase::ConvertPixelsToDialog(const wxPoint& pt) const
 {
     const wxSize base = GetDlgUnitBase();
 
-    // NB: wxMulDivInt32() is used, because it correctly rounds the result
+    return wxRescaleCoord(pt, wxSize(4, 8), base);
-
-    wxPoint pt2 = wxDefaultPosition;
-    if (pt.x != wxDefaultCoord)
-        pt2.x = wxMulDivInt32(pt.x, 4, base.x);
-    if (pt.y != wxDefaultCoord)
-        pt2.y = wxMulDivInt32(pt.y, 8, base.y);
-
-    return pt2;
 }
 
 wxPoint wxWindowBase::ConvertDialogToPixels(const wxPoint& pt) const
 {
     const wxSize base = GetDlgUnitBase();
 
-    wxPoint pt2 = wxDefaultPosition;
+    return wxRescaleCoord(pt, base, wxSize(4, 8));
-    if (pt.x != wxDefaultCoord)
-        pt2.x = wxMulDivInt32(pt.x, base.x, 4);
-    if (pt.y != wxDefaultCoord)
-        pt2.y = wxMulDivInt32(pt.y, base.y, 8);
-
-    return pt2;
 }
 
 // ----------------------------------------------------------------------------

src/msw/button.cpp

@@ -185,11 +185,8 @@ wxSize wxButtonBase::GetDefaultSize(wxWindow* win)
         // character width metadata stored in the font; see
         // http://support.microsoft.com/default.aspx/kb/145994 for detailed
         // discussion.
-        //
-        // NB: wxMulDivInt32() is used, because it correctly rounds the result
 
-        s_sizeBtn.SetAtNewDPI(wxSize(wxMulDivInt32(50, base.x, 4),
+        s_sizeBtn.SetAtNewDPI(wxRescaleCoord(wxSize(50, 14), base, wxSize(4, 8)));
-                                     wxMulDivInt32(14, base.y, 8)));
     }
 
     return s_sizeBtn.Get();