Save last wxSplitterWindow position before it was unsplit

Use this position when the window is split again and also save and
restore it from persistent storage in wxPersistentSplitter.

Closes #24329.

include/wx/generic/splitter.h

@@ -226,6 +226,15 @@ public:
     // all any more.
     wxDEPRECATED_INLINE( void SetSashSize(int WXUNUSED(width)), return; )
 
+    // Get the sash position that was last used before Unsplit() was called.
+    // Horizontal and vertical components correspond to the split in the
+    // corresponding direction, and are 0 if the splitter hadn't been split in
+    // this direction at all.
+    wxPoint GetLastSplitPosition() const;
+
+    // Set the default initial sash position to use when the splitter is split.
+    void SetLastSplitPosition(const wxPoint& pos);
+
 protected:
     // event handlers
 #if defined(__WXMSW__) || defined(__WXMAC__)
@@ -289,6 +298,7 @@ protected:
     wxPoint     m_ptStart;      // mouse position when dragging started
     int         m_sashStart;    // sash position when dragging started
     int         m_minimumPaneSize;
+    wxPoint     m_lastSplitPosition;
     wxCursor    m_sashCursorWE;
     wxCursor    m_sashCursorNS;
     wxOverlay   m_overlay;

include/wx/persist/splitter.h

@@ -23,6 +23,9 @@
 // Special position value of -1 means the splitter is not split at all.
 #define wxPERSIST_SPLITTER_POSITION wxASCII_STR("Position")
 
+#define wxPERSIST_SPLITTER_DEFAULT_HORIZONTAL wxASCII_STR("LastHorz")
+#define wxPERSIST_SPLITTER_DEFAULT_VERTICAL wxASCII_STR("LastVert")
+
 // ----------------------------------------------------------------------------
 // wxPersistentSplitter: supports saving/restoring splitter position
 // ----------------------------------------------------------------------------
@@ -41,6 +44,14 @@ public:
 
         int pos = splitter->IsSplit() ? splitter->GetSashPosition() : -1;
         SaveValue(wxPERSIST_SPLITTER_POSITION, pos);
+
+        // Save the previously used position too if we have them.
+        const wxPoint lastSplitPos = splitter->GetLastSplitPosition();
+        if ( lastSplitPos.x || lastSplitPos.y )
+        {
+            SaveValue(wxPERSIST_SPLITTER_DEFAULT_HORIZONTAL, lastSplitPos.y);
+            SaveValue(wxPERSIST_SPLITTER_DEFAULT_VERTICAL, lastSplitPos.x);
+        }
     }
 
     virtual bool Restore() override
@@ -54,6 +65,14 @@ public:
         else
             Get()->SetSashPosition(pos);
 
+        // Note that it's possible that default position was not stored, in
+        // which case lastSplitPos will just remain as (0, 0) and that's ok.
+        wxPoint lastSplitPos;
+        RestoreValue(wxPERSIST_SPLITTER_DEFAULT_HORIZONTAL, &lastSplitPos.x);
+        RestoreValue(wxPERSIST_SPLITTER_DEFAULT_VERTICAL, &lastSplitPos.y);
+
+        Get()->SetLastSplitPosition(lastSplitPos);
+
         return true;
     }
 

interface/wx/splitter.h

@@ -477,6 +477,36 @@ public:
         before showing the top-level window.
     */
     void UpdateSize();
+
+    /**
+        Get the last sash position before the splitter was unsplit.
+
+        The last sash position gets updated each time the window is unsplit. It
+        is kept internally to allow restoring the sash in its previous position
+        when if it is split again.
+
+        @return Point whose x/y component corresponds to the position of the
+            vertical/horizontal sash before the last unsplit or 0 if the
+            splitter was never split in the corresponding direction.
+
+        @since 3.3.0
+    */
+    const wxPoint& GetLastSplitPosition() const;
+
+    /**
+        Sets the last sash position.
+
+        This does not affect the actual sash position while the window is split
+        but determines the initial position of the sash when the window gets
+        split in the future.
+
+        @param pos
+            Point containing the default positions for wxSPLIT_VERTICAL and
+            wxSPLIT_HORIZONTAL modes respectively in its x and y components.
+
+        @since 3.3.0
+    */
+    void SetLastSplitPosition(const wxPoint& pos);
 };
 
 

src/generic/splitter.cpp

@@ -840,6 +840,18 @@ int wxSplitterWindow::ConvertSashPosition(int sashPosition) const
     }
     else // sashPosition == 0
     {
+        // Use last split position if we have it.
+        if ( m_splitMode == wxSPLIT_VERTICAL )
+        {
+            if ( m_lastSplitPosition.x )
+                return m_lastSplitPosition.x;
+        }
+        else if ( m_splitMode == wxSPLIT_HORIZONTAL )
+        {
+            if ( m_lastSplitPosition.y )
+                return m_lastSplitPosition.y;
+        }
+
         // default, put it in the centre
         return GetWindowSize() / 2;
     }
@@ -871,6 +883,15 @@ bool wxSplitterWindow::Unsplit(wxWindow *toRemove)
         return false;
     }
 
+    if (m_splitMode == wxSPLIT_VERTICAL)
+    {
+        m_lastSplitPosition.x = m_sashPosition;
+    }
+    else if (m_splitMode == wxSPLIT_HORIZONTAL)
+    {
+        m_lastSplitPosition.y = m_sashPosition;
+    }
+
     OnUnsplit(win);
     DoSetSashPosition(0);
     SizeWindows();
@@ -1086,6 +1107,17 @@ void wxSplitterWindow::OnUnsplit(wxWindow *winRemoved)
     winRemoved->Show(false);
 }
 
+wxPoint wxSplitterWindow::GetLastSplitPosition() const
+{
+    return m_lastSplitPosition;
+}
+
+void wxSplitterWindow::SetLastSplitPosition(const wxPoint& pos)
+{
+    m_lastSplitPosition = pos;
+}
+
+
 #if defined( __WXMSW__ ) || defined( __WXMAC__)
 
 // this is currently called (and needed) under MSW only...