Docking: Demo: Fixed docking document window into parent window. (#2286)

imgui_demo.cpp

@@ -4205,24 +4205,32 @@ void ShowExampleAppDocuments(bool* p_open)
 {
     static ExampleAppDocuments app;
 
-    if (!ImGui::Begin("Example: Documents", p_open, ImGuiWindowFlags_MenuBar))
-    {
-        ImGui::End();
-        return;
-    }
-
     // Options
     enum Target
     {
         Target_None,
-        Target_Tab,     // Create document as a local tab into a local tab bar
-        Target_Window   // Create document as a regular window
+        Target_Tab,                 // Create documents as local tab into a local tab bar
+        Target_DockspaceAndWindow   // Create documents as regular windows, and create an embedded dockspace
     };
     static Target opt_target = Target_Tab;
     static bool   opt_reorderable = true;
     static ImGuiTabBarFlags opt_fitting_flags = ImGuiTabBarFlags_FittingPolicyDefault_;
 
-    // Menu
+    // When (opt_target == Target_DockspaceAndWindow) there is the possibily that one of our child Document window (e.g. "Eggplant")
+    // that we emit gets docked into the same spot as the parent window ("Example: Documents").
+    // This would create a problematic feedback loop because selecting the "Eggplant" tab would make the "Example: Documents" tab
+    // not visible, which in turn would stop submitting the "Eggplant" window.
+    // We avoid this problem by submitting our documents window even if our parent window is not currently visible.
+    // Another solution may be to make the "Example: Documents" window use the ImGuiWindowFlags_NoDocking.
+
+    bool window_contents_visible = ImGui::Begin("Example: Documents", p_open, ImGuiWindowFlags_MenuBar);
+    if (!window_contents_visible && opt_target != Target_DockspaceAndWindow)
+    {
+        ImGui::End();
+        return;
+    }
+
+    // Menu Bar
     if (ImGui::BeginMenuBar())
     {
         if (ImGui::BeginMenu("File"))
@@ -4267,8 +4275,8 @@ void ShowExampleAppDocuments(bool* p_open)
     ImGui::Combo("Output", (int*)&opt_target, "None\0TabBar+Tabs\0DockSpace+Window\0");
     ImGui::PopItemWidth();
     bool redock_all = false;
-    if (opt_target == Target_Tab)    { ImGui::SameLine(); ImGui::Checkbox("Reorderable Tabs", &opt_reorderable); }
-    if (opt_target == Target_Window) { ImGui::SameLine(); redock_all = ImGui::Button("Redock all"); }
+    if (opt_target == Target_Tab)                { ImGui::SameLine(); ImGui::Checkbox("Reorderable Tabs", &opt_reorderable); }
+    if (opt_target == Target_DockspaceAndWindow) { ImGui::SameLine(); redock_all = ImGui::Button("Redock all"); }
 
     ImGui::Separator();
 
@@ -4313,7 +4321,7 @@ void ShowExampleAppDocuments(bool* p_open)
             ImGui::EndTabBar();
         }
     }
-    else if (opt_target == Target_Window)
+    else if (opt_target == Target_DockspaceAndWindow)
     {
         if (ImGui::GetIO().ConfigFlags & ImGuiConfigFlags_DockingEnable)
         {
@@ -4357,6 +4365,13 @@ void ShowExampleAppDocuments(bool* p_open)
         }
     }
 
+    // Early out other contents
+    if (!window_contents_visible)
+    {
+        ImGui::End();
+        return;
+    }
+
     // Update closing queue
     static ImVector<MyDocument*> close_queue;
     if (close_queue.empty())