added a full render when event WINDOW_EXPOSED and WINDOW_RESIZED are handled

stopped screen from changing frames when 'Pause' is displayed

src/emucore/EventHandler.cxx

@@ -323,9 +323,8 @@ void EventHandler::handleSystemEvent(SystemEvent e, int, int)
   {
     case SystemEvent::WINDOW_EXPOSED:
     case SystemEvent::WINDOW_RESIZED:
-      //myOSystem.frameBuffer().update(true); // force full update
-      // TODO: test and maybe force a render update instead
-      myOSystem.frameBuffer().update();
+      // Force full render update
+      myOSystem.frameBuffer().update(FrameBuffer::UpdateMode::RERENDER);
       break;
 #ifdef BSPF_UNIX
     case SystemEvent::WINDOW_FOCUS_GAINED:

src/emucore/FrameBuffer.cxx

@@ -311,7 +311,7 @@ FBInitStatus FrameBuffer::createDisplay(const string& title, BufferType type,
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-void FrameBuffer::update(bool forceRedraw)
+void FrameBuffer::update(UpdateMode mode)
 {
   // Onscreen messages are a special case and require different handling than
   // other objects; they aren't UI dialogs in the normal sense nor are they
@@ -322,12 +322,15 @@ void FrameBuffer::update(bool forceRedraw)
   //  - at the bottom of ::update(), to actually draw them (this must come
   //    last, since they are always drawn on top of everything else).
 
+  bool forceRedraw = mode & UpdateMode::REDRAW;
+  bool redraw = forceRedraw;
+
   // Forced render without draw required if messages or dialogs were closed
   // Note: For dialogs only relevant when two or more dialogs were stacked
-  bool rerender = forceRedraw || myPendingRender;
+  bool rerender = (mode & (UpdateMode::REDRAW | UpdateMode::RERENDER))
+    || myPendingRender;
   myPendingRender = false;
 
-  bool redraw = forceRedraw;
   switch(myOSystem.eventHandler().state())
   {
     case EventHandlerState::NONE:
@@ -342,10 +345,10 @@ void FrameBuffer::update(bool forceRedraw)
       {
         myPausedCount = uInt32(7 * myOSystem.frameRate());
         showTextMessage("Paused", MessagePosition::MiddleCenter);
+        myTIASurface->render();
       }
       if(rerender)
         myTIASurface->render();
-
       break;  // EventHandlerState::PAUSE
     }
 
@@ -857,7 +860,7 @@ void FrameBuffer::resetSurfaces()
   freeSurfaces();
   reloadSurfaces();
 
-  update(true); // force full update
+  update(UpdateMode::REDRAW); // force full update
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

src/emucore/FrameBuffer.hxx

@@ -55,6 +55,12 @@ class FrameBuffer
     // Zoom level step interval
     static constexpr float ZOOM_STEPS = 0.25;
 
+    enum UpdateMode {
+      NONE = 0,
+      REDRAW = 1,
+      RERENDER = 2
+    };
+
   public:
     FrameBuffer(OSystem& osystem);
     ~FrameBuffer();
@@ -84,7 +90,7 @@ class FrameBuffer
       Updates the display, which depending on the current mode could mean
       drawing the TIA, any pending menus, etc.
     */
-    void update(bool forceRedraw = false);
+    void update(UpdateMode mode = UpdateMode::NONE);
 
     /**
       There is a dedicated update method for emulation mode.

src/gui/StellaSettingsDialog.cxx

@@ -268,7 +268,7 @@ void StellaSettingsDialog::saveConfig()
   settings.setValue("uipalette",
     myThemePopup->getSelectedTag().toString());
   instance().frameBuffer().setUIPalette();
-  instance().frameBuffer().update(true);
+  instance().frameBuffer().update(FrameBuffer::UpdateMode::REDRAW);
 
   // Dialog position
   settings.setValue("dialogpos", myPositionPopup->getSelectedTag().toString());

src/gui/UIDialog.cxx

@@ -441,7 +441,7 @@ void UIDialog::saveConfig()
   settings.setValue("uipalette",
     myPalettePopup->getSelectedTag().toString());
   instance().frameBuffer().setUIPalette();
-  instance().frameBuffer().update(true);
+  instance().frameBuffer().update(FrameBuffer::UpdateMode::REDRAW);
 
   // Dialog font
   settings.setValue("dialogfont",