Improve calculating wxButton best size under wxMSW

We can use BCM_GETIDEALSIZE message to get the size of the button that
best fits its text and image (if present).
It gives better results for text wxButton with wxBU_EXACTFIT style.

include/wx/msw/anybutton.h

@@ -59,6 +59,7 @@ protected:
     // Should only be called if we do have a button, i.e. if m_imageData is
     // non-NULL.
     void AdjustForBitmapSize(wxSize& size) const;
+    void AdjustForBitmapMargins(wxSize& size) const;
 
     class wxButtonImageData *m_imageData;
 

src/msw/anybutton.cpp

@@ -75,6 +75,11 @@ using namespace wxMSWImpl;
     #endif
 #endif // wxUSE_UXTHEME
 
+// BCM_GETIDEALSIZE is defined since XP
+#ifndef BCM_GETIDEALSIZE
+    #define BCM_GETIDEALSIZE    0x1601
+#endif // BCM_GETIDEALSIZE
+
 #ifndef ODS_NOACCEL
     #define ODS_NOACCEL         0x0100
 #endif
@@ -516,6 +521,16 @@ void wxAnyButton::AdjustForBitmapSize(wxSize &size) const
             size.x = sizeBmp.x;
     }
 
+    // and also for the margins we always add internally (unless we have no
+    // border at all in which case the button has exactly the same size as
+    // bitmap and so no margins should be used)
+    AdjustForBitmapMargins(size);
+}
+
+void wxAnyButton::AdjustForBitmapMargins(wxSize& size) const
+{
+    wxCHECK_RET(m_imageData, wxT("shouldn't be called if no image"));
+
     // and also for the margins we always add internally (unless we have no
     // border at all in which case the button has exactly the same size as
     // bitmap and so no margins should be used)
@@ -565,6 +580,18 @@ wxSize wxAnyButton::DoGetBestSize() const
 
     wxSize size;
 
+    // BCM_GETIDEALSIZE works properly only it there is a text label in the button.
+    if ( !IsOwnerDrawn() && ShowsLabel() )
+    {
+        SIZE idealSize = { 0, 0 };
+        ::SendMessage(GetHwnd(), BCM_GETIDEALSIZE, 0, (LPARAM)&idealSize);
+        size.Set(idealSize.cx, idealSize.cy);
+
+        if ( m_imageData )
+            AdjustForBitmapMargins(size);
+    }
+    else
+    {
         // Account for the text part if we have it.
         if ( ShowsLabel() )
         {
@@ -591,6 +618,7 @@ wxSize wxAnyButton::DoGetBestSize() const
 
         if ( m_imageData )
             AdjustForBitmapSize(size);
+    }
 
     return wxMSWButton::IncreaseToStdSizeAndCache(self, size);
 }