Add support for stretchable spaces to wxToolBar.

Stretchable spaces consume all extra toolbar space not allocated to the fixed
size items. They can in particular be used to right-align (some) toolbar tools.

Add and document the new API, change the sample to show it and implement it
for MSW, GTK and OS X/Cocoa.

Also refactor MSW background erasing/repainting code to avoid duplicated calls
to DrawThemeBackground(), call it from a new helper MSWEraseRect() function.

Note that we may want to add support for "invisible" separators, IOW
non-stretchable spaces. This could be easily done for MSW after the changes in
this commit and is supported natively by GTK+ and Cocoa so implementing this
would be trivial if there is any interest.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62850 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/tbarbase.h

@@ -101,11 +101,6 @@ public:
         m_control = control;
     }
 
-        m_toolStyle = wxTOOL_STYLE_CONTROL;
-
-        m_dropdownMenu = 0;
-    }
-
     virtual ~wxToolBarToolBase();
 
     // accessors
@@ -123,10 +118,12 @@ public:
 
     wxToolBarBase *GetToolBar() const { return m_tbar; }
 
-    // style
+    // style/kind
+    bool IsStretchable() const { return m_stretchable; }
     bool IsButton() const { return m_toolStyle == wxTOOL_STYLE_BUTTON; }
     bool IsControl() const { return m_toolStyle == wxTOOL_STYLE_CONTROL; }
     bool IsSeparator() const { return m_toolStyle == wxTOOL_STYLE_SEPARATOR; }
+    bool IsStretchableSpace() const { return IsSeparator() && IsStretchable(); }
     int GetStyle() const { return m_toolStyle; }
     wxItemKind GetKind() const
     {
@@ -135,6 +132,13 @@ public:
         return m_kind;
     }
 
+    void MakeStretchable()
+    {
+        wxASSERT_MSG( IsSeparator(), "only separators can be stretchable" );
+
+        m_stretchable = true;
+    }
+
     // state
     bool IsEnabled() const { return m_enabled; }
     bool IsToggled() const { return m_toggled; }
@@ -214,6 +218,7 @@ protected:
 
         m_clientData = NULL;
 
+        m_stretchable = false;
         m_toggled = false;
         m_enabled = true;
 
@@ -223,7 +228,7 @@ protected:
     wxToolBarBase *m_tbar;  // the toolbar to which we belong (may be NULL)
 
     // tool parameters
-    int m_toolStyle;    // see enum wxToolBarToolStyle
+    wxToolBarToolStyle m_toolStyle;
     wxWindowIDRef m_id; // the tool id, wxID_SEPARATOR for separator
     wxItemKind m_kind;  // for normal buttons may be wxITEM_NORMAL/CHECK/RADIO
 
@@ -234,6 +239,9 @@ protected:
         wxControl        *m_control;
     };
 
+    // true if this tool is stretchable: currently is only value for separators
+    bool m_stretchable;
+
     // tool state
     bool m_toggled;
     bool m_enabled;
@@ -362,6 +370,12 @@ public:
     virtual wxToolBarToolBase *AddSeparator();
     virtual wxToolBarToolBase *InsertSeparator(size_t pos);
 
+    // add a stretchable space to the toolbar: this is similar to a separator
+    // except that it's always blank and that all the extra space the toolbar
+    // has is [equally] distributed among the stretchable spaces in it
+    virtual wxToolBarToolBase *AddStretchableSpace();
+    virtual wxToolBarToolBase *InsertStretchableSpace(size_t pos);
+
     // remove the tool from the toolbar: the caller is responsible for actually
     // deleting the pointer
     virtual wxToolBarToolBase *RemoveTool(int toolid);
@@ -606,6 +620,17 @@ protected:
     virtual wxToolBarToolBase *CreateTool(wxControl *control,
                                           const wxString& label) = 0;
 
+    // this one is not virtual but just a simple helper/wrapper around
+    // CreateTool() for separators
+    wxToolBarToolBase *CreateSeparator()
+    {
+        return CreateTool(wxID_SEPARATOR,
+                          wxEmptyString,
+                          wxNullBitmap, wxNullBitmap,
+                          wxITEM_SEPARATOR, NULL,
+                          wxEmptyString, wxEmptyString);
+    }
+
     // helper functions
     // ----------------