Merge branch '10.4' into 'master'10.4

pull in latest 10.4 from upstream

See merge request opensource-tracking/FreeFileSync!1

11 files changed, 158 insertions, 162 deletions

diff --git a/wx+/choice_enum.h b/wx+/choice_enum.h
index 97c40b68..2c424b9f 100755
--- a/wx+/choice_enum.h
+++ b/wx+/choice_enum.h
@@ -77,7 +77,9 @@ void setEnumVal(const EnumDescrList<Enum>& mapping, wxChoice& ctrl, Enum value)
         {
             selectedPos = it - mapping.descrList.begin();
 
-            if (!it->second.second.empty())
+            if (it->second.second.empty())
+                ctrl.UnsetToolTip();
+            else
                 ctrl.SetToolTip(it->second.second);
         }
     }
diff --git a/wx+/dc.h b/wx+/dc.h
index 23c70d3f..ff2f81bd 100755
--- a/wx+/dc.h
+++ b/wx+/dc.h
@@ -8,7 +8,6 @@
 #define DC_H_4987123956832143243214
 
 #include <unordered_map>
-#include <zen/optional.h>
 #include <zen/basic_math.h>
 #include <wx/dcbuffer.h> //for macro: wxALWAYS_NATIVE_DOUBLE_BUFFER
 #include <wx/dcscreen.h>
@@ -104,7 +103,7 @@ private:
     //associate "active" clipping area with each DC
     static std::unordered_map<wxDC*, wxRect>& refDcToAreaMap() { static std::unordered_map<wxDC*, wxRect> clippingAreas; return clippingAreas; }
 
-    Opt<wxRect> oldRect_;
+    std::optional<wxRect> oldRect_;
     wxDC& dc_;
 };
 
@@ -114,13 +113,13 @@ private:
 #endif
 
 #if wxALWAYS_NATIVE_DOUBLE_BUFFER
-struct BufferedPaintDC : public wxPaintDC { BufferedPaintDC(wxWindow& wnd, Opt<wxBitmap>& buffer) : wxPaintDC(&wnd) {} };
+struct BufferedPaintDC : public wxPaintDC { BufferedPaintDC(wxWindow& wnd, std::optional<wxBitmap>& buffer) : wxPaintDC(&wnd) {} };
 
 #else
 class BufferedPaintDC : public wxMemoryDC
 {
 public:
-    BufferedPaintDC(wxWindow& wnd, Opt<wxBitmap>& buffer) : buffer_(buffer), paintDc_(&wnd)
+    BufferedPaintDC(wxWindow& wnd, std::optional<wxBitmap>& buffer) : buffer_(buffer), paintDc_(&wnd)
     {
         const wxSize clientSize = wnd.GetClientSize();
         if (clientSize.GetWidth() > 0 && clientSize.GetHeight() > 0) //wxBitmap asserts this!! width may be 0; test case "Grid::CornerWin": compare both sides, then change config
@@ -134,7 +133,7 @@ public:
                 SetLayoutDirection(wxLayout_RightToLeft);
         }
         else
-            buffer = NoValue();
+            buffer = {};
     }
 
     ~BufferedPaintDC()
@@ -153,7 +152,7 @@ public:
     }
 
 private:
-    Opt<wxBitmap>& buffer_;
+    std::optional<wxBitmap>& buffer_;
     wxPaintDC paintDc_;
 };
 #endif
diff --git a/wx+/focus.h b/wx+/focus.h
index cd99d010..e2daef79 100755
--- a/wx+/focus.h
+++ b/wx+/focus.h
@@ -44,22 +44,37 @@ Preserving input focus has to be more clever than:
 */
 struct FocusPreserver
 {
+    FocusPreserver()
+    {
+        if (wxWindow* win = wxWindow::FindFocus())
+            setFocus(win);
+    }
+
     ~FocusPreserver()
     {
         //wxTopLevelWindow::IsActive() does NOT call Win32 ::GetActiveWindow()!
         //Instead it checks if ::GetFocus() is set somewhere inside the top level
         //Note: Both Win32 active and focus windows are *thread-local* values, while foreground window is global! https://blogs.msdn.microsoft.com/oldnewthing/20131016-00/?p=2913
-        if (oldFocus_)
-            if (wxTopLevelWindow* topWin = getTopLevelWindow(oldFocus_))
-                if (topWin->IsActive()) //Linux/macOS: already behaves just like ::GetForegroundWindow() on Windows!
-                    oldFocus_->SetFocus();
+
+        if (oldFocusId_ != wxID_ANY)
+            if (wxWindow* oldFocusWin = wxWindow::FindWindowById(oldFocusId_))
+                if (wxTopLevelWindow* topWin = getTopLevelWindow(oldFocusWin))
+                    if (topWin->IsActive()) //Linux/macOS: already behaves just like ::GetForegroundWindow() on Windows!
+                        oldFocusWin->SetFocus();
     }
 
-    wxWindow* getFocus()        const { return oldFocus_; }
-    void      setFocus(wxWindow* win) { oldFocus_ = win; }
+    wxWindowID getFocusId() const { return oldFocusId_; }
+
+    void setFocus(wxWindow* win)
+    {
+        oldFocusId_ = win->GetId();
+        assert(oldFocusId_ != wxID_ANY);
+    }
 
 private:
-    wxWindow* oldFocus_ = wxWindow::FindFocus();
+    wxWindowID oldFocusId_ = wxID_ANY;
+    //don't store wxWindow* which may be dangling during ~FocusPreserver()!
+    //test: click on delete folder pair and immediately press F5 => focus window (= FP del button) is defer-deleted during sync
 };
 }
 
diff --git a/wx+/graph.cpp b/wx+/graph.cpp
index b006cda0..38846523 100755
--- a/wx+/graph.cpp
+++ b/wx+/graph.cpp
@@ -387,8 +387,8 @@ std::vector<CurvePoint> SparseCurveData::getPoints(double minX, double maxX, con
     for (int i = posFrom; i <= posTo; ++i)
     {
         const double x = cvrtX.screenToReal(i);
-        Opt<CurvePoint> ptLe = getLessEq(x);
-        Opt<CurvePoint> ptGe = getGreaterEq(x);
+        std::optional<CurvePoint> ptLe = getLessEq(x);
+        std::optional<CurvePoint> ptGe = getGreaterEq(x);
         //both non-existent and invalid return values are mapped to out of expected range: => check on posLe/posGe NOT ptLe/ptGe in the following!
         const int posLe = ptLe ? cvrtX.realToScreenRound(ptLe->x) : i + 1;
         const int posGe = ptGe ? cvrtX.realToScreenRound(ptGe->x) : i - 1;
diff --git a/wx+/graph.h b/wx+/graph.h
index e0c2c12b..f1ae5d5a 100755
--- a/wx+/graph.h
+++ b/wx+/graph.h
@@ -14,7 +14,6 @@
 #include <wx/settings.h>
 #include <wx/bitmap.h>
 #include <zen/string_tools.h>
-#include <zen/optional.h>
 
 
 //elegant 2D graph as wxPanel specialization
@@ -63,8 +62,8 @@ struct SparseCurveData : public CurveData
 {
     SparseCurveData(bool addSteps = false) : addSteps_(addSteps) {} //addSteps: add points to get a staircase effect or connect points via a direct line
 
-    virtual Opt<CurvePoint> getLessEq   (double x) const = 0;
-    virtual Opt<CurvePoint> getGreaterEq(double x) const = 0;
+    virtual std::optional<CurvePoint> getLessEq   (double x) const = 0;
+    virtual std::optional<CurvePoint> getGreaterEq(double x) const = 0;
 
 private:
     std::vector<CurvePoint> getPoints(double minX, double maxX, const wxSize& areaSizePx) const override;
@@ -80,21 +79,21 @@ struct ArrayCurveData : public SparseCurveData
 private:
     std::pair<double, double> getRangeX() const override { const size_t sz = getSize(); return { 0.0, sz == 0 ? 0.0 : sz - 1.0}; }
 
-    Opt<CurvePoint> getLessEq(double x) const override
+    std::optional<CurvePoint> getLessEq(double x) const override
     {
         const size_t sz = getSize();
         const size_t pos = std::min<ptrdiff_t>(std::floor(x), sz - 1); //[!] expect unsigned underflow if empty!
         if (pos < sz)
             return CurvePoint(pos, getValue(pos));
-        return NoValue();
+        return {};
     }
 
-    Opt<CurvePoint> getGreaterEq(double x) const override
+    std::optional<CurvePoint> getGreaterEq(double x) const override
     {
         const size_t pos = std::max<ptrdiff_t>(std::ceil(x), 0); //[!] use std::max with signed type!
         if (pos < getSize())
             return CurvePoint(pos, getValue(pos));
-        return NoValue();
+        return {};
     }
 };
 
@@ -246,7 +245,7 @@ public:
         MainAttributes& setMinY(double newMinY) { minY = newMinY; return *this; }
         MainAttributes& setMaxY(double newMaxY) { maxY = newMaxY; return *this; }
 
-        MainAttributes& setAutoSize() { minX = maxX = minY = maxY = NoValue(); return *this; }
+        MainAttributes& setAutoSize() { minX = maxX = minY = maxY = {}; return *this; }
 
         MainAttributes& setLabelX(PosLabelX posX, int height = -1, std::shared_ptr<LabelFormatter> newLabelFmt = nullptr)
         {
@@ -272,18 +271,18 @@ public:
     private:
         friend class Graph2D;
 
-        Opt<double> minX; //x-range to visualize
-        Opt<double> maxX; //
+        std::optional<double> minX; //x-range to visualize
+        std::optional<double> maxX; //
 
-        Opt<double> minY; //y-range to visualize
-        Opt<double> maxY; //
+        std::optional<double> minY; //y-range to visualize
+        std::optional<double> maxY; //
 
         PosLabelX labelposX = LABEL_X_BOTTOM;
-        Opt<int> xLabelHeight;
+        std::optional<int> xLabelHeight;
         std::shared_ptr<LabelFormatter> labelFmtX = std::make_shared<DecimalNumberFormatter>();
 
         PosLabelY labelposY = LABEL_Y_LEFT;
-        Opt<int> yLabelWidth;
+        std::optional<int> yLabelWidth;
         std::shared_ptr<LabelFormatter> labelFmtY = std::make_shared<DecimalNumberFormatter>();
 
         std::map<PosCorner, wxString> cornerTexts;
@@ -337,7 +336,7 @@ private:
 
     MainAttributes attr_; //global attributes
 
-    Opt<wxBitmap> doubleBuffer_;
+    std::optional<wxBitmap> doubleBuffer_;
 
     using CurveList = std::vector<std::pair<std::shared_ptr<CurveData>, CurveAttributes>>;
     CurveList curves_;
diff --git a/wx+/grid.cpp b/wx+/grid.cpp
index 52ee6e6b..65311ffa 100755
--- a/wx+/grid.cpp
+++ b/wx+/grid.cpp
@@ -310,23 +310,21 @@ public:
 protected:
     void setToolTip(const std::wstring& text) //proper fix for wxWindow
     {
-        wxToolTip* tt = GetToolTip();
-
-        const wxString oldText = tt ? tt->GetTip() : wxString();
-        if (text != oldText)
+        if (text != GetToolTipText())
         {
             if (text.empty())
-                SetToolTip(nullptr); //wxGTK doesn't allow wxToolTip with empty text!
+                UnsetToolTip(); //wxGTK doesn't allow wxToolTip with empty text!
             else
             {
-                //wxWidgets bug: tooltip multiline property is defined by first tooltip text containing newlines or not (same is true for maximum width)
+                wxToolTip* tt = GetToolTip();
                 if (!tt)
-                    SetToolTip(new wxToolTip(L"a                                                                b\n\
-                                                           a                                                                b")); //ugly, but working (on Windows)
-                tt = GetToolTip(); //should be bound by now
-                assert(tt);
-                if (tt)
-                    tt->SetTip(text);
+                {
+                    //wxWidgets bug: tooltip multiline property is defined by first tooltip text containing newlines or not (same is true for maximum width)
+                    tt = new wxToolTip(L"a                                                                b\n\
+                                                           a                                                                b"); //ugly, but working (on Windows)
+                    SetToolTip(tt); //pass ownership
+                }
+                tt->SetTip(text);
             }
         }
     }
@@ -391,7 +389,7 @@ private:
     }
 
     Grid& parent_;
-    Opt<wxBitmap> doubleBuffer_;
+    std::optional<wxBitmap> doubleBuffer_;
 };
 
 //----------------------------------------------------------------------------------------------------------------
@@ -689,12 +687,12 @@ private:
         activeResizing_.reset();
         activeClickOrMove_.reset();
 
-        if (Opt<ColAction> action = refParent().clientPosToColumnAction(event.GetPosition()))
+        if (std::optional<ColAction> action = refParent().clientPosToColumnAction(event.GetPosition()))
         {
             if (action->wantResize)
             {
                 if (!event.LeftDClick()) //double-clicks never seem to arrive here; why is this checked at all???
-                    if (Opt<int> colWidth = refParent().getColWidth(action->col))
+                    if (std::optional<int> colWidth = refParent().getColWidth(action->col))
                         activeResizing_ = std::make_unique<ColumnResizing>(*this, action->col, *colWidth, event.GetPosition().x);
             }
             else //a move or single click
@@ -724,7 +722,7 @@ private:
             }
             else //notify single label click
             {
-                if (const Opt<ColumnType> colType = refParent().colToType(activeClickOrMove_->getColumnFrom()))
+                if (const std::optional<ColumnType> colType = refParent().colToType(activeClickOrMove_->getColumnFrom()))
                     sendEventNow(GridLabelClickEvent(EVENT_GRID_COL_LABEL_MOUSE_LEFT, event, *colType));
             }
             activeClickOrMove_.reset();
@@ -745,7 +743,7 @@ private:
 
     void onMouseLeftDouble(wxMouseEvent& event) override
     {
-        if (Opt<ColAction> action = refParent().clientPosToColumnAction(event.GetPosition()))
+        if (std::optional<ColAction> action = refParent().clientPosToColumnAction(event.GetPosition()))
             if (action->wantResize)
             {
                 //auto-size visible range on double-click
@@ -790,7 +788,7 @@ private:
         }
         else
         {
-            if (const Opt<ColAction> action = refParent().clientPosToColumnAction(event.GetPosition()))
+            if (const std::optional<ColAction> action = refParent().clientPosToColumnAction(event.GetPosition()))
             {
                 highlightCol_ = action->col;
 
@@ -801,7 +799,7 @@ private:
             }
             else
             {
-                highlightCol_ = NoValue();
+                highlightCol_ = {};
                 SetCursor(*wxSTANDARD_CURSOR);
             }
         }
@@ -823,7 +821,7 @@ private:
 
     void onLeaveWindow(wxMouseEvent& event) override
     {
-        highlightCol_ = NoValue(); //wxEVT_LEAVE_WINDOW does not respect mouse capture! -> however highlight_ is drawn unconditionally during move/resize!
+        highlightCol_ = {}; //wxEVT_LEAVE_WINDOW does not respect mouse capture! -> however highlight_ is drawn unconditionally during move/resize!
 
         Refresh();
         event.Skip();
@@ -831,9 +829,9 @@ private:
 
     void onMouseRightDown(wxMouseEvent& event) override
     {
-        if (const Opt<ColAction> action = refParent().clientPosToColumnAction(event.GetPosition()))
+        if (const std::optional<ColAction> action = refParent().clientPosToColumnAction(event.GetPosition()))
         {
-            if (const Opt<ColumnType> colType = refParent().colToType(action->col))
+            if (const std::optional<ColumnType> colType = refParent().colToType(action->col))
                 sendEventNow(GridLabelClickEvent(EVENT_GRID_COL_LABEL_MOUSE_RIGHT, event, *colType)); //notify right click
             else assert(false);
         }
@@ -847,7 +845,7 @@ private:
 
     std::unique_ptr<ColumnResizing> activeResizing_;
     std::unique_ptr<ColumnMove>     activeClickOrMove_;
-    Opt<size_t>                     highlightCol_; //column during mouse-over
+    std::optional<size_t>                     highlightCol_; //column during mouse-over
 };
 
 //----------------------------------------------------------------------------------------------------------------
@@ -1080,8 +1078,8 @@ private:
 
             activeSelection_.reset();
         }
-            highlight_.row = -1;
-            Refresh();
+        highlight_.row = -1;
+        Refresh();
         //event.Skip(); -> we DID handle it!
     }
 
@@ -1146,8 +1144,8 @@ private:
         size_t getStartRow     () const { return rowStart_;       }
         size_t getCurrentRow   () const { return rowCurrent_;     }
         bool   isPositiveSelect() const { return positiveSelect_; } //are we selecting or unselecting?
-        bool   gridWasCleared  () const { return gridWasCleared_; } 
-        
+        bool   gridWasCleared  () const { return gridWasCleared_; }
+
         const GridClickEvent& getFirstClick() const { return firstClick_; }
 
         void evalMousePos()
@@ -1823,7 +1821,7 @@ wxWindow& Grid::getMainWin    () { return *mainWin_;     }
 const wxWindow& Grid::getMainWin() const { return *mainWin_; }
 
 
-Opt<Grid::ColAction> Grid::clientPosToColumnAction(const wxPoint& pos) const
+std::optional<Grid::ColAction> Grid::clientPosToColumnAction(const wxPoint& pos) const
 {
     const int absPosX = CalcUnscrolledPosition(pos).x;
     if (absPosX >= 0)
@@ -1851,7 +1849,7 @@ Opt<Grid::ColAction> Grid::clientPosToColumnAction(const wxPoint& pos) const
             }
         }
     }
-    return NoValue();
+    return {};
 }
 
 
diff --git a/wx+/grid.h b/wx+/grid.h
index b9a04842..732a4fcb 100755
--- a/wx+/grid.h
+++ b/wx+/grid.h
@@ -12,7 +12,6 @@
 #include <vector>
 #include <wx/scrolwin.h>
 #include <zen/basic_math.h>
-#include <zen/optional.h>
 
 
 //a user-friendly, extensible and high-performance grid control
@@ -52,13 +51,13 @@ struct GridSelectEvent : public wxCommandEvent
 {
     GridSelectEvent(size_t rowFirst, size_t rowLast, bool positive, const GridClickEvent* mouseClick) :
         wxCommandEvent(EVENT_GRID_SELECT_RANGE), rowFirst_(rowFirst), rowLast_(rowLast), positive_(positive),
-        mouseClick_(mouseClick ? *mouseClick : Opt<GridClickEvent>()) { assert(rowFirst <= rowLast); }
+        mouseClick_(mouseClick ? *mouseClick : std::optional<GridClickEvent>()) { assert(rowFirst <= rowLast); }
     GridSelectEvent* Clone() const override { return new GridSelectEvent(*this); }
 
     const size_t rowFirst_; //selected range: [rowFirst_, rowLast_)
     const size_t rowLast_;
     const bool   positive_; //"false" when clearing selection!
-    const Opt<GridClickEvent> mouseClick_; //filled unless selection was performed via keyboard shortcuts
+    const std::optional<GridClickEvent> mouseClick_; //filled unless selection was performed via keyboard shortcuts
 };
 
 struct GridLabelClickEvent : public wxMouseEvent
@@ -299,12 +298,12 @@ private:
     int                      getColWidthsSum(int mainWinWidth) const;
     std::vector<int> getColStretchedWidths(int clientWidth) const; //final width = (normalized) (stretchedWidth + offset)
 
-    Opt<int> getColWidth(size_t col) const
+    std::optional<int> getColWidth(size_t col) const
     {
         const auto& widths = getColWidths();
         if (col < widths.size())
             return widths[col].width;
-        return NoValue();
+        return {};
     }
 
     void setColumnWidth(int width, size_t col, GridEventPolicy columnResizeEventPolicy, bool notifyAsync = false);
@@ -321,7 +320,7 @@ private:
         bool wantResize = false; //"!wantResize" means "move" or "single click"
         size_t col = 0;
     };
-    Opt<ColAction> clientPosToColumnAction(const wxPoint& pos) const;
+    std::optional<ColAction> clientPosToColumnAction(const wxPoint& pos) const;
     void moveColumn(size_t colFrom, size_t colTo);
     ptrdiff_t clientPosToMoveTargetColumn(const wxPoint& pos) const; //return < 0 on error
 
@@ -363,18 +362,10 @@ private:
 template <class ColAttrReal>
 std::vector<ColAttrReal> makeConsistent(const std::vector<ColAttrReal>& attribs, const std::vector<ColAttrReal>& defaults)
 {
-    using ColTypeReal = decltype(ColAttrReal().type);
-    std::vector<ColAttrReal> output;
-
-    std::set<ColTypeReal> usedTypes; //remove duplicates
-    auto appendUnique = [&](const std::vector<ColAttrReal>& attr)
-    {
-        std::copy_if(attr.begin(), attr.end(), std::back_inserter(output),
-        [&](const ColAttrReal& a) { return usedTypes.insert(a.type).second; });
-    };
-    appendUnique(attribs);
-    appendUnique(defaults); //make sure each type is existing!
-
+    std::vector<ColAttrReal> output = attribs;
+    //make sure each type is existing!
+    output.insert(output.end(), defaults.begin(), defaults.end());
+    removeDuplicates(output, [](const ColAttrReal& lhs, const ColAttrReal& rhs) { return lhs.type < rhs.type; });
     return output;
 }
 
diff --git a/wx+/image_resources.cpp b/wx+/image_resources.cpp
index bbeeff8b..d0449fe5 100755
--- a/wx+/image_resources.cpp
+++ b/wx+/image_resources.cpp
@@ -106,7 +106,7 @@ class DpiParallelScaler
 public:
     DpiParallelScaler(int hqScale) : hqScale_(hqScale) { assert(hqScale > 1); }
 
-    ~DpiParallelScaler() { threadGroup_ = zen::NoValue(); } //DpiParallelScaler must out-live threadGroup!!!
+    ~DpiParallelScaler() { threadGroup_ = {}; } //DpiParallelScaler must out-live threadGroup!!!
 
     void add(const wxString& name, const wxImage& img)
     {
@@ -141,7 +141,7 @@ private:
     Protected<std::vector<std::pair<std::wstring, ImageHolder>>> result_;
 
     using TaskType = FunctionReturnTypeT<decltype(&getScalerTask)>;
-    Opt<ThreadGroup<TaskType>> threadGroup_{ ThreadGroup<TaskType>(std::max<int>(std::thread::hardware_concurrency(), 1), "xBRZ Scaler") };
+    std::optional<ThreadGroup<TaskType>> threadGroup_{ ThreadGroup<TaskType>(std::max<int>(std::thread::hardware_concurrency(), 1), "xBRZ Scaler") };
     //hardware_concurrency() == 0 if "not computable or well defined"
 };
 
diff --git a/wx+/image_tools.cpp b/wx+/image_tools.cpp
index 0cb0e328..4748a590 100755
--- a/wx+/image_tools.cpp
+++ b/wx+/image_tools.cpp
@@ -14,38 +14,45 @@ using namespace zen;
 
 namespace
 {
-void writeToImage(const wxImage& source, wxImage& target, const wxPoint& pos)
+void writeToImage(wxImage& output, const wxImage& top, const wxPoint& pos)
 {
-    const int srcWidth  = source.GetWidth ();
-    const int srcHeight = source.GetHeight();
-    const int trgWidth  = target.GetWidth ();
+    const int topWidth  = top.GetWidth ();
+    const int topHeight = top.GetHeight();
+    const int outWidth  = output.GetWidth();
 
-    if (srcWidth > 0 && srcHeight > 0)
-    {
-        assert(0 <= pos.x && pos.x + srcWidth  <= trgWidth          ); //draw area must be a
-        assert(0 <= pos.y && pos.y + srcHeight <= target.GetHeight()); //subset of target image!
-        assert(target.HasAlpha());
+    assert(0 <= pos.x && pos.x + topWidth  <= outWidth          ); //draw area must be a
+    assert(0 <= pos.y && pos.y + topHeight <= output.GetHeight()); //subset of output image!
+    assert(top.HasAlpha() && output.HasAlpha());
 
-        {
-            const unsigned char* sourcePtr = source.GetData();
-            unsigned char*       targetPtr = target.GetData() + 3 * (pos.x + pos.y * trgWidth);
+    //https://en.wikipedia.org/wiki/Alpha_compositing
+    const unsigned char* topRgb   = top.GetData();
+    const unsigned char* topAlpha = top.GetAlpha();
 
-            for (int row = 0; row < srcHeight; ++row)
-                ::memcpy(targetPtr + 3 * row * trgWidth, sourcePtr + 3 * row * srcWidth, 3 * srcWidth);
-        }
+    for (int y = 0; y < topHeight; ++y)
+    {
+        unsigned char* outRgb   = output.GetData () + 3 * (pos.x + (pos.y + y) * outWidth);
+        unsigned char* outAlpha = output.GetAlpha() +      pos.x + (pos.y + y) * outWidth;
 
-        //handle alpha channel
+        for (int x = 0; x < topWidth; ++x)
         {
-            unsigned char* targetPtr = target.GetAlpha() + pos.x + pos.y * trgWidth;
-            if (source.HasAlpha())
+            const int w1 = *topAlpha; //alpha-composition interpreted as weighted average
+            const int w2 = *outAlpha * (255 - w1) / 255;
+            const int wSum = w1 + w2;
+
+            auto calcColor = [w1, w2, wSum](unsigned char colTop, unsigned char colBot)
             {
-                const unsigned char* sourcePtr = source.GetAlpha();
-                for (int row = 0; row < srcHeight; ++row)
-                    ::memcpy(targetPtr + row * trgWidth, sourcePtr + row * srcWidth, srcWidth);
-            }
-            else
-                for (int row = 0; row < srcHeight; ++row)
-                    ::memset(targetPtr + row * trgWidth, wxIMAGE_ALPHA_OPAQUE, srcWidth);
+                return static_cast<unsigned char>(wSum == 0 ? 0 : (colTop * w1 + colBot * w2) / wSum);
+            };
+            outRgb[0] = calcColor(topRgb[0], outRgb[0]);
+            outRgb[1] = calcColor(topRgb[1], outRgb[1]);
+            outRgb[2] = calcColor(topRgb[2], outRgb[2]);
+
+            *outAlpha = static_cast<unsigned char>(wSum);
+
+            topRgb += 3;
+            outRgb += 3;
+            ++topAlpha;
+            ++outAlpha;
         }
     }
 }
@@ -64,16 +71,12 @@ wxImage zen::stackImages(const wxImage& img1, const wxImage& img2, ImageStackLay
 
     int width  = std::max(img1Width,  img2Width);
     int height = std::max(img1Height, img2Height);
-    switch (dir)
-    {
-        case ImageStackLayout::HORIZONTAL:
-            width  = img1Width + gap + img2Width;
-            break;
 
-        case ImageStackLayout::VERTICAL:
-            height = img1Height + gap + img2Height;
-            break;
-    }
+    if (dir == ImageStackLayout::HORIZONTAL)
+        width = img1Width + gap + img2Width;
+    else
+        height = img1Height + gap + img2Height;
+
     wxImage output(width, height);
     output.SetAlpha();
     ::memset(output.GetAlpha(), wxIMAGE_ALPHA_TRANSPARENT, width * height);
@@ -96,13 +99,13 @@ wxImage zen::stackImages(const wxImage& img1, const wxImage& img2, ImageStackLay
     switch (dir)
     {
         case ImageStackLayout::HORIZONTAL:
-            writeToImage(img1, output, wxPoint(0,               calcPos(img1Height, height)));
-            writeToImage(img2, output, wxPoint(img1Width + gap, calcPos(img2Height, height)));
+            writeToImage(output, img1, wxPoint(0,               calcPos(img1Height, height)));
+            writeToImage(output, img2, wxPoint(img1Width + gap, calcPos(img2Height, height)));
             break;
 
         case ImageStackLayout::VERTICAL:
-            writeToImage(img1, output, wxPoint(calcPos(img1Width, width), 0));
-            writeToImage(img2, output, wxPoint(calcPos(img2Width, width), img1Height + gap));
+            writeToImage(output, img1, wxPoint(calcPos(img1Width, width), 0));
+            writeToImage(output, img2, wxPoint(calcPos(img2Width, width), img1Height + gap));
             break;
     }
     return output;
@@ -111,26 +114,6 @@ wxImage zen::stackImages(const wxImage& img1, const wxImage& img2, ImageStackLay
 
 namespace
 {
-void calcAlphaForBlackWhiteImage(wxImage& image) //assume black text on white background
-{
-    assert(image.HasAlpha());
-    if (unsigned char* alphaPtr = image.GetAlpha())
-    {
-        const int pixelCount = image.GetWidth() * image.GetHeight();
-        const unsigned char* dataPtr = image.GetData();
-        for (int i = 0; i < pixelCount; ++ i)
-        {
-            const unsigned char r = *dataPtr++;
-            const unsigned char g = *dataPtr++;
-            const unsigned char b = *dataPtr++;
-
-            //black(0,0,0) becomes fully opaque(255), while white(255,255,255) becomes transparent(0)
-            alphaPtr[i] = static_cast<unsigned char>((255 - r + 255 - g + 255 - b) / 3); //mixed mode arithmetics!
-        }
-    }
-}
-
-
 std::vector<std::pair<wxString, wxSize>> getTextExtentInfo(const wxString& text, const wxFont& font)
 {
     wxMemoryDC dc; //the context used for bitmaps
@@ -201,32 +184,39 @@ wxImage zen::createImageFromText(const wxString& text, const wxFont& font, const
     wxImage output(newBitmap.ConvertToImage());
     output.SetAlpha();
 
-    calcAlphaForBlackWhiteImage(output);
-
-    //apply actual text color
-    unsigned char* dataPtr = output.GetData();
+    unsigned char* rgb   = output.GetData();
+    unsigned char* alpha = output.GetAlpha();
     const int pixelCount = output.GetWidth() * output.GetHeight();
-    for (int i = 0; i < pixelCount; ++ i)
+
+    for (int i = 0; i < pixelCount; ++i)
     {
-        *dataPtr++ = col.Red();
-        *dataPtr++ = col.Green();
-        *dataPtr++ = col.Blue();
+        //black(0,0,0) becomes wxIMAGE_ALPHA_OPAQUE(255), while white(255,255,255) becomes wxIMAGE_ALPHA_TRANSPARENT(0)
+        *alpha++ = static_cast<unsigned char>((255 - rgb[0] + 255 - rgb[1] + 255 - rgb[2]) / 3); //mixed mode arithmetics!
+
+        rgb[0] = col.Red  (); //
+        rgb[1] = col.Green(); //apply actual text color
+        rgb[2] = col.Blue (); //
+
+        rgb += 3;
     }
     return output;
 }
 
 
-wxBitmap zen::layOver(const wxBitmap& background, const wxBitmap& foreground,  int alignment)
+wxBitmap zen::layOver(const wxBitmap& back, const wxBitmap& front,  int alignment)
 {
-    if (!foreground.IsOk()) return background;
+    if (!front.IsOk()) return back;
+
+    const int width  = std::max(back.GetWidth(),  front.GetWidth());
+    const int height = std::max(back.GetHeight(), front.GetHeight());
 
-    assert(foreground.HasAlpha() == background.HasAlpha()); //we don't support mixed-mode brittleness!
+    assert(front.HasAlpha() == back.HasAlpha()); //we don't support mixed-mode brittleness!
     const int offsetX = [&]
     {
         if (alignment & wxALIGN_RIGHT)
-            return background.GetWidth() - foreground.GetWidth();
+            return back.GetWidth() - front.GetWidth();
         if (alignment & wxALIGN_CENTER_HORIZONTAL)
-            return (background.GetWidth() - foreground.GetWidth()) / 2;
+            return (back.GetWidth() - front.GetWidth()) / 2;
 
         static_assert(wxALIGN_LEFT == 0);
         return 0;
@@ -235,19 +225,22 @@ wxBitmap zen::layOver(const wxBitmap& background, const wxBitmap& foreground,  i
     const int offsetY = [&]
     {
         if (alignment & wxALIGN_BOTTOM)
-            return background.GetHeight() - foreground.GetHeight();
+            return back.GetHeight() - front.GetHeight();
         if (alignment & wxALIGN_CENTER_VERTICAL)
-            return (background.GetHeight() - foreground.GetHeight()) / 2;
+            return (back.GetHeight() - front.GetHeight()) / 2;
 
         static_assert(wxALIGN_TOP == 0);
         return 0;
     }();
 
-    wxBitmap output(background.ConvertToImage()); //attention: wxBitmap/wxImage use ref-counting without copy on write!
-    {
-        wxMemoryDC dc(output);
-        dc.DrawBitmap(foreground, offsetX, offsetY);
-    }
+    //can't use wxMemoryDC and wxDC::DrawBitmap(): no alpha channel support on wxGTK!
+    wxImage output(width, height);
+    output.SetAlpha();
+    ::memset(output.GetAlpha(), wxIMAGE_ALPHA_TRANSPARENT, width * height);
+
+    const wxPoint posBack(std::max(-offsetX, 0), std::max(-offsetY, 0));
+    writeToImage(output, back .ConvertToImage(), posBack);
+    writeToImage(output, front.ConvertToImage(), posBack + wxPoint(offsetX, offsetY));
     return output;
 }
 
diff --git a/wx+/image_tools.h b/wx+/image_tools.h
index ca82a031..06d7f0ba 100755
--- a/wx+/image_tools.h
+++ b/wx+/image_tools.h
@@ -34,7 +34,7 @@ wxImage stackImages(const wxImage& img1, const wxImage& img2, ImageStackLayout d
 
 wxImage createImageFromText(const wxString& text, const wxFont& font, const wxColor& col, ImageStackAlignment textAlign = ImageStackAlignment::LEFT); //CENTER/LEFT/RIGHT
 
-wxBitmap layOver(const wxBitmap& background, const wxBitmap& foreground, int alignment = wxALIGN_CENTER);
+wxBitmap layOver(const wxBitmap& back, const wxBitmap& front, int alignment = wxALIGN_CENTER);
 
 wxImage greyScale(const wxImage& img); //greyscale + brightness adaption
 wxBitmap greyScale(const wxBitmap& bmp); //
diff --git a/wx+/rtl.h b/wx+/rtl.h
index e479c5a8..26380f9d 100755
--- a/wx+/rtl.h
+++ b/wx+/rtl.h
@@ -7,7 +7,6 @@
 #ifndef RTL_H_0183487180058718273432148
 #define RTL_H_0183487180058718273432148
 
-#include <zen/optional.h>
 #include <wx/dcmemory.h>
 #include <wx/image.h>
 #include <wx/app.h>
@@ -16,7 +15,7 @@
 namespace zen
 {
 //functions supporting right-to-left GUI layout
-void drawBitmapRtlMirror  (wxDC& dc, const wxBitmap& image, const wxRect& rect, int alignment, Opt<wxBitmap>& buffer);
+void drawBitmapRtlMirror  (wxDC& dc, const wxBitmap& image, const wxRect& rect, int alignment, std::optional<wxBitmap>& buffer);
 void drawBitmapRtlNoMirror(wxDC& dc, const wxBitmap& image, const wxRect& rect, int alignment);
 //wxDC::DrawIcon DOES mirror by default -> implement RTL support when needed
 
@@ -56,7 +55,7 @@ void drawBitmapAligned(wxDC& dc, const wxBitmap& image, const wxRect& rect, int
 
 
 inline
-void drawBitmapRtlMirror(wxDC& dc, const wxBitmap& image, const wxRect& rect, int alignment, Opt<wxBitmap>& buffer)
+void drawBitmapRtlMirror(wxDC& dc, const wxBitmap& image, const wxRect& rect, int alignment, std::optional<wxBitmap>& buffer)
 {
     if (dc.GetLayoutDirection() == wxLayout_RightToLeft)
     {