Menus: Some renaming, comments, add to demo. Amend 0342a3c. (#1207)

imgui.cpp

@@ -3623,7 +3623,7 @@ void ImGui::NewFrame()
     g.FrameCount += 1;
     g.TooltipOverrideCount = 0;
     g.WindowsActiveCount = 0;
-    g.RenderedMenusId.resize(0);
+    g.MenusIdSubmittedThisFrame.resize(0);
 
     // Setup current font and draw list shared data
     g.IO.Fonts->Locked = true;
@@ -3915,6 +3915,7 @@ void ImGui::Shutdown(ImGuiContext* context)
     g.ShrinkWidthBuffer.clear();
 
     g.PrivateClipboard.clear();
+    g.MenusIdSubmittedThisFrame.clear();
     g.InputTextState.ClearFreeMemory();
 
     g.SettingsWindows.clear();

imgui.h

@@ -559,7 +559,8 @@ namespace ImGui
 
     // Widgets: Menus
     // - Use BeginMenuBar() on a window ImGuiWindowFlags_MenuBar to append to its menu bar.
-    // - Use BeginMainMenuBar() to create a menu bar at the top of the screen.
+    // - Use BeginMainMenuBar() to create a menu bar at the top of the screen and append to it.
+    // - Use BeginMenu() to create a menu. You can call BeginMenu() multiple time with the same identifier to append more items to it.
     IMGUI_API bool          BeginMenuBar();                                                     // append to menu-bar of current window (requires ImGuiWindowFlags_MenuBar flag set on parent window).
     IMGUI_API void          EndMenuBar();                                                       // only call EndMenuBar() if BeginMenuBar() returns true!
     IMGUI_API bool          BeginMainMenuBar();                                                 // create and append to a full screen menu-bar.

imgui_demo.cpp

@@ -288,6 +288,27 @@ void ImGui::ShowDemoWindow(bool* p_open)
     // Menu Bar
     if (ImGui::BeginMenuBar())
     {
+        if (ImGui::BeginMenu("Foo"))
+        {
+            if (ImGui::BeginMenu("AAA"))
+            {
+                ImGui::EndMenu();
+            }
+            if (ImGui::BeginMenu("BBB"))
+            {
+                ImGui::EndMenu();
+            }
+            if (ImGui::BeginMenu("AAA"))
+            {
+                ImGui::EndMenu();
+            }
+            if (ImGui::BeginMenu("BBB"))
+            {
+                ImGui::EndMenu();
+            }
+            ImGui::EndMenu();
+        }
+
         if (ImGui::BeginMenu("Menu"))
         {
             ShowExampleMenuFile();
@@ -3580,6 +3601,7 @@ static void ShowExampleMenuFile()
     }
     if (ImGui::MenuItem("Save", "Ctrl+S")) {}
     if (ImGui::MenuItem("Save As..")) {}
+
     ImGui::Separator();
     if (ImGui::BeginMenu("Options"))
     {
@@ -3591,13 +3613,12 @@ static void ShowExampleMenuFile()
         ImGui::EndChild();
         static float f = 0.5f;
         static int n = 0;
-        static bool b = true;
         ImGui::SliderFloat("Value", &f, 0.0f, 1.0f);
         ImGui::InputFloat("Input", &f, 0.1f);
         ImGui::Combo("Combo", &n, "Yes\0No\0Maybe\0\0");
-        ImGui::Checkbox("Check", &b);
         ImGui::EndMenu();
     }
+
     if (ImGui::BeginMenu("Colors"))
     {
         float sz = ImGui::GetTextLineHeight();
@@ -3612,6 +3633,17 @@ static void ShowExampleMenuFile()
         }
         ImGui::EndMenu();
     }
+
+    // Here we demonstrate appending again to the "Options" menu (which we already created above)
+    // Of course in this demo it is a little bit silly that this function calls BeginMenu("Options") twice.
+    // In a real code-base using it would make senses to use this feature from very different code locations.
+    if (ImGui::BeginMenu("Options")) // <-- Append!
+    {
+        static bool b = true;
+        ImGui::Checkbox("SomeOption", &b);
+        ImGui::EndMenu();
+    }
+
     if (ImGui::BeginMenu("Disabled", false)) // Disabled
     {
         IM_ASSERT(0);

imgui_internal.h

@@ -1159,7 +1159,7 @@ struct ImGuiContext
     float                   ScrollbarClickDeltaToGrabCenter;    // Distance between mouse and center of grab box, normalized in parent space. Use storage?
     int                     TooltipOverrideCount;
     ImVector<char>          PrivateClipboard;                   // If no custom clipboard handler is defined
-    ImVector<ImGuiID>       RenderedMenusId;                    // A list of menu IDs that were rendered at least once
+    ImVector<ImGuiID>       MenusIdSubmittedThisFrame;          // A list of menu IDs that were rendered at least once
 
     // Platform support
     ImVec2                  PlatformImePos;                     // Cursor position request & last passed to the OS Input Method Editor

imgui_widgets.cpp

@@ -6223,25 +6223,26 @@ bool ImGui::BeginMenu(const char* label, bool enabled)
     const ImGuiStyle& style = g.Style;
     const ImGuiID id = window->GetID(label);
     bool menu_is_open = IsPopupOpen(id);
-    ImGuiWindowFlags flags = ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoSavedSettings | ImGuiWindowFlags_NoNavFocus;
 
     // Sub-menus are ChildWindow so that mouse can be hovering across them (otherwise top-most popup menu would steal focus and not allow hovering on parent menu)
-    if (window->Flags & (ImGuiWindowFlags_Popup|ImGuiWindowFlags_ChildMenu))
+    ImGuiWindowFlags flags = ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoSavedSettings | ImGuiWindowFlags_NoNavFocus;
+    if (window->Flags & (ImGuiWindowFlags_Popup | ImGuiWindowFlags_ChildMenu))
         flags |= ImGuiWindowFlags_ChildWindow;
 
-    if (g.RenderedMenusId.contains(id))
+    // If a menu with same the ID was already submitted, we will append to it, matching the behavior of Begin().
+    // We are relying on a O(N) search - so O(N log N) over the frame - which seems like the most efficient for the expected small amount of BeginMenu() calls per frame.
+    // If somehow this is ever becoming a problem we can switch to use e.g. a ImGuiStorager mapping key to last frame used.
+    if (g.MenusIdSubmittedThisFrame.contains(id))
     {
-        // Menu with same ID was already created - append to it.
         if (menu_is_open)
             menu_is_open = BeginPopupEx(id, flags); // menu_is_open can be 'false' when the popup is completely clipped (e.g. zero size display)
-        if (!menu_is_open)
-            g.NextWindowData.ClearFlags();          // We behave like Begin() and need to consume those values
+        else
+            g.NextWindowData.ClearFlags();          // we behave like Begin() and need to consume those values
         return menu_is_open;
     }
-    else
-    {
-        g.RenderedMenusId.push_back(id);            // Tag menu as used. Next time BeginMenu() with same ID is called it will append to existing menu.
-    }
+
+    // Tag menu as used. Next time BeginMenu() with same ID is called it will append to existing menu
+    g.MenusIdSubmittedThisFrame.push_back(id);
 
     ImVec2 label_size = CalcTextSize(label, NULL, true);
     bool pressed;