Move window relayout before inserting the window to the manager (fix #3746)

This is necessary to prevent the manager to invalidate a window whose relayout is not finished. This can happen when a script opens a new window when another is currently opening. For instance a script whose canvas.onpaint handler opens another dialog.

src/app/ui/preview_editor.cpp

@@ -183,6 +183,7 @@ PreviewEditorWindow::PreviewEditorWindow()
   , m_refFrame(0)
   , m_aniSpeed(1.0)
   , m_relatedEditor(nullptr)
+  , m_opening(false)
 {
   setAutoRemap(false);
   setWantFocus(false);
@@ -343,6 +344,9 @@ Editor* PreviewEditorWindow::previewEditor() const
 
 void PreviewEditorWindow::updateUsingEditor(Editor* editor)
 {
+  if (m_opening)
+    return;
+
   if (!m_isEnabled || !editor) {
     hideWindow();
     m_relatedEditor = nullptr;
@@ -357,8 +361,11 @@ void PreviewEditorWindow::updateUsingEditor(Editor* editor)
   Doc* document = editor->document();
   Editor* miniEditor = (m_docView ? m_docView->editor(): nullptr);
 
-  if (!isVisible())
+  if (!isVisible()) {
+    m_opening = true;
     openWindow();
+    m_opening = false;
+  }
 
   // Document preferences used to store the preferred zoom/scroll point
   auto& docPref = Preferences::instance().document(document);

src/app/ui/preview_editor.h

@@ -70,6 +70,10 @@ namespace app {
     doc::frame_t m_refFrame;
     double m_aniSpeed;
     Editor* m_relatedEditor;
+    // This flag indicates that the preview editor is being opened, it is used to avoid
+    // an infinite recursive loop when PreviewEditorWindow::updateUsingEditor calls the
+    // openWindow() method.
+    bool m_opening;
   };
 
 } // namespace app

src/ui/manager.cpp

@@ -1334,6 +1334,16 @@ void Manager::_openWindow(Window* window, bool center)
     freeFocus();
   }
 
+  // Relayout before inserting the window to the list of children widgets prevents
+  // the manager to invalidate a window currently being laid out when
+  // ui::Manager::getDefault()->invalidate() is called. This situation could happen,
+  // for instance, when a script opens a dialog whose canvas.onpaint handler opens
+  // another dialog, because the onpaint handler is executed during window layout.
+  if (center)
+    window->centerWindow(parentDisplay);
+  else
+    window->layout();
+
   // Add the window to manager.
   insertChild(0, window);
 
@@ -1343,12 +1353,6 @@ void Manager::_openWindow(Window* window, bool center)
     window->sendMessage(&msg);
   }
 
-  // Relayout
-  if (center)
-    window->centerWindow(parentDisplay);
-  else
-    window->layout();
-
   // If the window already was set a display, we don't setup it
   // (i.e. in the case of combobox popup/window the display field is
   // set to the same display where the ComboBox widget is located)