The asynchronous widget redraw is now handled by an Event::Draw, which calls FApplication::onDraw()

Author: gansm

ChangeLog

@@ -1,3 +1,7 @@
+2026-10-06  Markus Gans  <guru.mail@muenster.de>
+	* The asynchronous widget redraw is now handled by an Event::Draw, 
+	  which calls FApplication::onDraw()
+
 2026-09-23  Markus Gans  <guru.mail@muenster.de>
 	* Widget redraw() now runs asynchronously in the main event loop to 
 	  prevent blocking event processing

doc/event-processing.md

@@ -82,6 +82,7 @@ enum class Event : uInt8
   WindowLowered,     // Lower window
   Accelerator,       // Keyboard accelerator
   Resize,            // Terminal resize
+  Draw,              // Widget redraw
   Show,              // Widget is shown
   Hide,              // Widget is hidden
   Close,             // Widget close

examples/choice.cpp

@@ -3,7 +3,7 @@
 *                                                                      *
 * This file is part of the FINAL CUT widget toolkit                    *
 *                                                                      *
-* Copyright 2017-2022 Markus Gans                                      *
+* Copyright 2017-2026 Markus Gans                                      *
 *                                                                      *
 * FINAL CUT is free software; you can redistribute it and/or modify    *
 * it under the terms of the GNU Lesser General Public License as       *
@@ -132,8 +132,8 @@ auto main (int argc, char* argv[]) -> int
     preset(os);
 
     // Scroll to the focused child element
-    finalcut::FFocusEvent cfi (finalcut::Event::ChildFocusIn);
-    app.queueEvent(&checkButtonGroup, &cfi);
+    auto cfi = std::make_unique<finalcut::FFocusEvent>(finalcut::Event::ChildFocusIn);
+    app.queueEvent(&checkButtonGroup, std::move(cfi));
 
     // Create a OK button
     finalcut::FButton ok("&OK", &dgl);

final/fapplication.cpp

@@ -251,14 +251,14 @@ auto FApplication::sendEvent (FObject* receiver, FEvent* event ) -> bool
 }
 
 //----------------------------------------------------------------------
-void FApplication::queueEvent (FObject* receiver, FEvent* event)
+void FApplication::queueEvent (FObject* receiver, std::unique_ptr<FEvent>&& event)
 {
-  if ( ! (bool(receiver) && bool(event)) )
+  if ( ! (bool(receiver) && bool(event.get())) )
     return;
 
   // queue this event
   setQueued(*event);
-  event_queue.emplace_back (receiver, event);
+  event_queue.emplace_back (receiver, std::move(event));
 }
 
 //----------------------------------------------------------------------
@@ -268,7 +268,7 @@ void FApplication::sendQueuedEvents()
   {
     const auto& event_pair = event_queue.front();
     setQueued(*event_pair.second, false);
-    sendEvent(event_pair.first, event_pair.second);
+    sendEvent(event_pair.first, event_pair.second.get());
     event_queue.pop_front();
   }
 }
@@ -285,10 +285,7 @@ auto FApplication::eventInQueue() const -> bool
 //----------------------------------------------------------------------
 auto FApplication::removeQueuedEvent (const FObject* receiver) -> bool
 {
-  if ( ! eventInQueue() )
-    return false;
-
-  if ( ! receiver )
+  if ( ! receiver || ! eventInQueue() )
     return false;
 
   bool retval{false};
@@ -313,6 +310,31 @@ void FApplication::queueDraw (FWidget* widget)
 {
   // Queue the widget for redrawing
   draw_queue.push_back(widget);
+
+  // We only need one draw event to redraw all the widgets in the queue
+  if ( need_widget_redraw )
+    return;
+
+  need_widget_redraw = true;
+
+  auto ev = std::make_unique<FEvent>(Event::Draw);
+  FApplication::queueEvent(this, std::move(ev));
+}
+
+//----------------------------------------------------------------------
+auto FApplication::removeQueuedDraw (const FWidget* widget) -> bool
+{
+  if ( ! widget || draw_queue.empty() )
+    return false;
+
+  const auto queue_end = draw_queue.end();
+  const auto last = std::remove (draw_queue.begin(), queue_end, widget);
+  draw_queue.erase(last, queue_end);
+
+  if ( draw_queue.empty() )
+    need_widget_redraw = false;
+
+  return true;
 }
 
 //----------------------------------------------------------------------
@@ -425,6 +447,30 @@ void FApplication::processExternalUserEvent()
   // This method can be overloaded and replaced by own code
 }
 
+//----------------------------------------------------------------------
+auto FApplication::event (FEvent* ev) -> bool
+{
+  const auto event_type = ev->getType();
+
+  if ( event_type == Event::Draw )
+  {
+    onDraw (ev);
+    return true;
+  }
+
+  return FWidget::event(ev);
+}
+
+//----------------------------------------------------------------------
+void FApplication::onDraw (FEvent*)
+{
+  // This event handler can be reimplemented in a subclass
+  // to receive draw events
+
+  processRedraw();
+  need_widget_redraw = false;
+}
+
 
 // private methods of FApplication
 //----------------------------------------------------------------------
@@ -1378,7 +1424,7 @@ void FApplication::processRedraw()
   // Sort the queue by hierarchy depth
   std::sort ( processing_queue.begin()
             , processing_queue.end()
-            , [] (FWidget* lhs, FWidget* rhs)
+            , [] (const FWidget* lhs, const FWidget* rhs)
               {
                 return lhs->getDepth() < rhs->getDepth();
               } );
@@ -1445,7 +1491,6 @@ auto FApplication::processNextEvent() -> bool
     processResizeEvent();  // when the terminal size has changed
     processDialogResizeMove();
     sendQueuedEvents();
-    processRedraw();
     processTerminalUpdate();  // for changed regions on the terminal
     flush();  // Flush output buffer (via an instance of FOutput)
     processLogger();

final/fapplication.h

@@ -142,11 +142,12 @@ class FApplication : public FWidget
     static void  exit (int = EXIT_SUCCESS);
     void         quit() const;
     static auto  sendEvent (FObject*, FEvent*) -> bool;
-    void         queueEvent (FObject*, FEvent*);
+    void         queueEvent (FObject*, std::unique_ptr<FEvent>&&);
     void         sendQueuedEvents();
     auto         eventInQueue() const -> bool;
     auto         removeQueuedEvent (const FObject*) -> bool;
     void         queueDraw (FWidget*);
+    auto         removeQueuedDraw (const FWidget*) -> bool;
     void         registerMouseHandler (const FMouseHandler&);
     void         initTerminal() override;
     static void  setDefaultTheme();
@@ -161,10 +162,14 @@ class FApplication : public FWidget
   protected:
     virtual void processExternalUserEvent();
 
+    // Event handlers
+    auto         event (FEvent*) -> bool override;
+    virtual void onDraw (FEvent*);
+
   private:
     // Using-declaration
     using CmdOption = struct option;
-    using EventPair = std::pair<FObject*, FEvent*>;
+    using EventPair = std::pair<FObject*, std::unique_ptr<FEvent>>;
     using FEventQueue = std::deque<EventPair>;
     using FDrawQueue = std::vector<FWidget*>;
     using FMouseHandlerList = std::vector<FMouseHandler>;
@@ -249,6 +254,7 @@ class FApplication : public FWidget
     FDrawQueue        draw_queue{};
     FMouseHandlerList mouse_handler_list{};
     bool              has_terminal_resized{false};
+    bool              need_widget_redraw{false};
     static uInt64     next_event_wait;
     static TimeValue  time_last_event;
     static rdbuf      default_clog_rdbuf;

final/fc.h

@@ -75,6 +75,7 @@ enum class Event : uInt8
   WindowLowered,     // Lower window
   Accelerator,       // Keyboard accelerator
   Resize,            // Terminal resize
+  Draw,              // Widget redraw
   Show,              // Widget is shown
   Hide,              // Widget is hidden
   Close,             // Widget close

final/fobject.cpp

@@ -99,7 +99,7 @@ auto FObject::getDepth() const noexcept -> std::size_t
     depth++;
   }
 
-  return depth; // 0 means it has no parent (root object)
+  return depth;  // 0 means it has no parent (root object)
 }
 
 //----------------------------------------------------------------------

final/fwidget.cpp

@@ -112,6 +112,7 @@ FWidget::~FWidget()  // destructor
   processDestroy();
   delCallback();
   removeQueuedEvent();
+  removeQueuedDraw();
 
   // unset clicked widget
   if ( this == getClickedWidget() )
@@ -1516,7 +1517,7 @@ inline void FWidget::mapKeyEvents()
     { Event::KeyDown,
       [this] (FEvent* ev)
       {
-        KeyDownEvent(static_cast<FKeyEvent*>(ev));
+        KeyDownEvent (static_cast<FKeyEvent*>(ev));
       }
     }
   } );
@@ -2279,6 +2280,15 @@ void FWidget::removeQueuedEvent() const
     app_object->removeQueuedEvent(this);
 }
 
+//----------------------------------------------------------------------
+void FWidget::removeQueuedDraw() const
+{
+  auto app_object = FApplication::getApplicationObject();
+
+  if ( app_object )
+    app_object->removeQueuedDraw(this);
+}
+
 //----------------------------------------------------------------------
 void FWidget::setStatusBarText (bool enable) const
 {

final/fwidget.h

@@ -484,6 +484,7 @@ class FWidget : public FVTerm
     static auto  isDefaultTheme() -> bool;
     static void  initColorTheme();
     void  removeQueuedEvent() const;
+    void  removeQueuedDraw() const;
     void  setStatusBarText (bool = true) const;
 
     // Data members

test/fwidget-test.cpp

@@ -792,6 +792,7 @@ void FWidgetTest::noArgumentTest()
   CPPUNIT_ASSERT ( wdgt.getFlags().feature.minimizable == false );
   CPPUNIT_ASSERT ( wdgt.getFlags().visibility.modal == false );
   CPPUNIT_ASSERT ( wdgt.getFlags().visibility.visible_cursor == false );
+  CPPUNIT_ASSERT ( ! wdgt.needsRedraw() );
   CPPUNIT_ASSERT ( wdgt.getFlags().visibility.needs_redraw == false );
   CPPUNIT_ASSERT ( ! wdgt.hasVisibleCursor() );
   CPPUNIT_ASSERT ( wdgt.getFlags().type.window_widget == false );