Use wxOverlay to show sash feedback in non-live resize mode in wxSplitterWindow

Make non-live resizing possible on all supported platforms thanks to wxOverlay.
Previously, live resizing was the only supported mode under these platforms:
wxMac, wxQt and wxGTK3 under Wayland.

Also remove no longer needed function AlwaysUsesLiveUpdate and its documentation.

include/wx/generic/splitter.h

@@ -12,6 +12,7 @@
 
 #include "wx/window.h"                      // base class declaration
 #include "wx/containr.h"                    // wxControlContainer
+#include "wx/overlay.h"
 
 class WXDLLIMPEXP_FWD_CORE wxSplitterEvent;
 
@@ -131,9 +132,6 @@ public:
     // Is the window split?
     bool IsSplit() const { return (m_windowTwo != nullptr); }
 
-    // Return true if wxSP_LIVE_UPDATE is always used.
-    bool AlwaysUsesLiveUpdate() const;
-
     // Sets the border size
     void SetBorderSize(int WXUNUSED(width)) { }
 
@@ -293,7 +291,7 @@ protected:
     int         m_minimumPaneSize;
     wxCursor    m_sashCursorWE;
     wxCursor    m_sashCursorNS;
-    wxPen      *m_sashTrackerPen;
+    wxOverlay   m_overlay;
 
     // when in live mode, set this to true to resize children in idle
     bool        m_needUpdating:1;

interface/wx/splitter.h

@@ -142,20 +142,6 @@ public:
     */
     virtual ~wxSplitterWindow();
 
-    /**
-        Returns true if splitter always behaves as if wxSP_LIVE_UPDATE were
-        specified.
-
-        This function returns true if non-live update mode is not supported and
-        live update is always used, even if wxSP_LIVE_UPDATE was not explicitly
-        specified.
-
-        @see wxClientDC::CanBeUsedForDrawing()
-
-        @since 3.3.0
-    */
-    bool AlwaysUsesLiveUpdate() const;
-
     /**
         Creation function, for two-step construction.
         See wxSplitterWindow() for details.

samples/splitter/splitter.cpp

@@ -254,7 +254,7 @@ MyFrame::MyFrame()
                       "Toggle sash invisibility");
     splitMenu->AppendSeparator();
 
-    auto itemLive = splitMenu->AppendCheckItem(SPLIT_LIVE,
+    splitMenu->AppendCheckItem(SPLIT_LIVE,
                                "&Live update\tCtrl-L",
                                "Toggle live update mode");
     splitMenu->AppendCheckItem(SPLIT_BORDER,
@@ -306,12 +306,6 @@ MyFrame::MyFrame()
     menuBar->Check(SPLIT_LIVE, true);
     m_splitter = new MySplitterWindow(this);
 
-    if ( m_splitter->AlwaysUsesLiveUpdate() )
-    {
-        // Only live update mode is supported, so this menu item can't be used.
-        itemLive->Enable(false);
-    }
-
     // If you use non-zero gravity you must initialize the splitter with its
     // correct initial size, otherwise it will change the sash position by a
     // huge amount when it's resized from its initial default size to its real

src/generic/splitter.cpp

@@ -69,19 +69,34 @@ wxBEGIN_EVENT_TABLE(wxSplitterWindow, wxWindow)
 #endif // wxMSW
 wxEND_EVENT_TABLE()
 
-bool wxSplitterWindow::AlwaysUsesLiveUpdate() const
-{
-    return !wxClientDC::CanBeUsedForDrawing(this);
-}
-
 static bool IsLive(wxSplitterWindow* wnd)
 {
     // with wxSP_LIVE_UPDATE style the splitter windows are always resized
     // following the mouse movement while it drags the sash, without it we only
     // draw the sash at the new position but only resize the windows when the
-    // dragging is finished -- but drawing the sash is done using wxClientDC,
-    // so check if we can use it and always use live resizing if we can't
-    return wnd->AlwaysUsesLiveUpdate() || wnd->HasFlag(wxSP_LIVE_UPDATE);
+    // dragging is finished
+    return wnd->HasFlag(wxSP_LIVE_UPDATE);
+}
+
+static wxBitmap wxPaneCreateStippleBitmap()
+{
+    // Notice that wxOverlay, under wxMSW, uses the wxBLACK colour i.e.(0,0,0)
+    // as the key colour for transparency. and using it for the stipple bitmap
+    // will make the sash feedback totaly invisible if the window's background
+    // colour is (192,192,192) or so. (1,1,1) is used instead.
+    unsigned char data[] = { 1,1,1,192,192,192, 192,192,192,1,1,1 };
+    wxImage img(2,2,data,true);
+    return wxBitmap(img);
+}
+
+static void DrawResizeHint(wxDC& dc, const wxRect& rect)
+{
+    wxBitmap stipple = wxPaneCreateStippleBitmap();
+    wxBrush brush(stipple);
+    dc.SetBrush(brush);
+    dc.SetPen(*wxTRANSPARENT_PEN);
+
+    dc.DrawRectangle(rect);
 }
 
 bool wxSplitterWindow::Create(wxWindow *parent, wxWindowID id,
@@ -134,7 +149,6 @@ void wxSplitterWindow::Init()
     m_minimumPaneSize = 0;
     m_sashCursorWE = wxCursor(wxCURSOR_SIZEWE);
     m_sashCursorNS = wxCursor(wxCURSOR_SIZENS);
-    m_sashTrackerPen = new wxPen(*wxBLACK, 2, wxPENSTYLE_SOLID);
 
     m_needUpdating = false;
     m_isHot = false;
@@ -142,7 +156,6 @@ void wxSplitterWindow::Init()
 
 wxSplitterWindow::~wxSplitterWindow()
 {
-    delete m_sashTrackerPen;
 }
 
 // ----------------------------------------------------------------------------
@@ -280,10 +293,10 @@ void wxSplitterWindow::OnMouseEvent(wxMouseEvent& event)
             return;
         }
 
-        // Erase old tracker
+        // Hide sash tracker
         if ( !isLive )
         {
-            DrawSashTracker(m_oldX, m_oldY);
+            m_overlay.Reset();
         }
 
         // the position of the click doesn't exactly correspond to
@@ -361,9 +374,6 @@ void wxSplitterWindow::OnMouseEvent(wxMouseEvent& event)
 
             m_sashPositionCurrent = posSashNew;
 
-            // Erase old tracker
-            DrawSashTracker(m_oldX, m_oldY);
-
             m_oldX = (m_splitMode == wxSPLIT_VERTICAL ? m_sashPositionCurrent : x);
             m_oldY = (m_splitMode != wxSPLIT_VERTICAL ? m_sashPositionCurrent : y);
 
@@ -380,7 +390,6 @@ void wxSplitterWindow::OnMouseEvent(wxMouseEvent& event)
                 m_oldY = 0;
 #endif // __WXMSW__
 
-            // Draw new one
             DrawSashTracker(m_oldX, m_oldY);
         }
         else
@@ -414,10 +423,10 @@ void wxSplitterWindow::OnMouseCaptureLost(wxMouseCaptureLostEvent& WXUNUSED(even
 
     SetCursor(* wxSTANDARD_CURSOR);
 
-    // Erase old tracker
+    // Erase sash tracker
     if ( !IsLive(this) )
     {
-        DrawSashTracker(m_oldX, m_oldY);
+        m_overlay.Reset();
     }
 }
 
@@ -612,43 +621,30 @@ void wxSplitterWindow::DrawSashTracker(int x, int y)
     int x1, y1;
     int x2, y2;
 
+    const int sashTrackerWidth = GetDefaultSashSize();
+
     if ( m_splitMode == wxSPLIT_VERTICAL )
     {
-        x1 = x2 = wxClip(x, 0, w) + m_sashTrackerPen->GetWidth()/2;
-        y1 = 2;
-        y2 = h-2;
+        x1 = wxClip(x, 0, w);
+        x2 = sashTrackerWidth;
+        y1 = 0;
+        y2 = h;
     }
     else
     {
-        y1 = y2 = wxClip(y, 0, h) + m_sashTrackerPen->GetWidth()/2;
-        x1 = 2;
-        x2 = w-2;
+        y1 = wxClip(y, 0, h);
+        y2 = sashTrackerWidth;
+        x1 = 0;
+        x2 = w;
     }
 
-#if defined(__WXGTK3__)
     wxClientDC dc(this);
+    wxDCOverlay overlaydc( m_overlay, &dc );
+    overlaydc.Clear();
 
-    // In the ports with wxGraphicsContext-based wxDC, such as wxGTK3 or wxOSX,
-    // wxINVERT only works for inverting the background when using white
-    // foreground (note that this code is not used anyhow for __WXMAC__ due to
-    // always using live-resizing there, see IsLive()).
-    dc.SetPen(*wxWHITE_PEN);
-#else
-    // We need to use wxScreenDC and not wxClientDC at least for wxMSW where
-    // drawing in this window itself would be hidden by its children windows,
-    // that cover it almost entirely.
-    wxScreenDC dc;
-    ClientToScreen(&x1, &y1);
-    ClientToScreen(&x2, &y2);
+    const wxRect rect{x1, y1, x2, y2};
 
-    dc.SetPen(*m_sashTrackerPen);
-#endif
-
-    dc.SetLogicalFunction(wxINVERT);
-
-    dc.SetBrush(*wxTRANSPARENT_BRUSH);
-
-    dc.DrawLine(x1, y1, x2, y2);
+    DrawResizeHint(dc, rect);
 }
 
 int wxSplitterWindow::GetWindowSize() const