BeginMenu()/MenuItem(): fixed accidental triggering of child menu items when opening a menu inside a small host window forcing the child menu window to be repositioned under the mouse cursor. (#8233, #9394)

nb: ImGuiSelectableFlags_NoHoldingActiveID is not used anymore. Would remove remove once we remove the unnecessary call to Selectable() from MenuItem().

docs/CHANGELOG.txt

@@ -152,6 +152,13 @@ Other Changes:
     items straying out of columns boundaries. (#7994, #2221)
   - Box-Select + Tables: fixed an issue when calling `BeginMultiSelect()` in a table
     before layout has been locked (first row or headers row submitted). (#8250)
+- Menus:
+  - BeginMenu()/MenuItem(): fixed accidental triggering of child menu items when
+    opening a menu inside a small host window forcing the child menu window to be
+    repositioned under the mouse cursor. (#8233, #9394)
+    Done by reworking BeginMenu()/MenuItem(): they previously avoiding taking
+    ActiveID + key/click ownership (in order to allow releasing button on another item).
+    Now they take them and release them once the mouse is moved outside item boundaries.
 - Inputs:
   - SetItemKeyOwner(): return true if ownership has been requested, which typically
     needs to to checked for gating further tests. This is important as the function

imgui_widgets.cpp

@@ -9391,8 +9391,7 @@ bool ImGui::BeginMenuEx(const char* label, const char* icon, bool enabled)
 
     bool pressed;
 
-    // We use ImGuiSelectableFlags_NoSetKeyOwner to allow down on one menu item, move, up on another.
+    const ImGuiSelectableFlags selectable_flags = ImGuiSelectableFlags_SelectOnClick | ImGuiSelectableFlags_NoAutoClosePopups;
-    const ImGuiSelectableFlags selectable_flags = ImGuiSelectableFlags_NoHoldingActiveID | ImGuiSelectableFlags_NoSetKeyOwner | ImGuiSelectableFlags_SelectOnClick | ImGuiSelectableFlags_NoAutoClosePopups;
     ImGuiMenuColumns* offsets = &window->DC.MenuColumns;
     if (window->DC.LayoutType == ImGuiLayoutType_Horizontal)
     {
@@ -9430,6 +9429,14 @@ bool ImGui::BeginMenuEx(const char* label, const char* icon, bool enabled)
     if (!enabled)
         EndDisabled();
 
+    // Once dragged, release ActiveId + key ownership. This is to allow the idiom of mouse down a menu, dragging elsewhere, up on some other MenuItem(). (#8233, #9394)
+    // Could move logic into lower-level ImGuiButtonFlags_AutoReleaseActiveId + ImGuiButtonFlags_AutoReleaseKeyOwner? Easier once we get rid of the Selectable() middle-man here.
+    if (g.ActiveId == id && g.HoveredId != id && g.ActiveIdSource == ImGuiInputSource_Mouse && IsMouseDragging(0))
+    {
+        ClearActiveID();
+        SetKeyOwner(ImGuiKey_MouseLeft, ImGuiKeyOwner_NoOwner);
+    }
+
     const bool hovered = (g.HoveredId == id) && enabled && !g.NavHighlightItemUnderNav;
     if (menuset_is_open)
         PopItemFlag();
@@ -9510,6 +9517,9 @@ bool ImGui::BeginMenuEx(const char* label, const char* icon, bool enabled)
     IMGUI_TEST_ENGINE_ITEM_INFO(id, label, g.LastItemData.StatusFlags | ImGuiItemStatusFlags_Openable | (menu_is_open ? ImGuiItemStatusFlags_Opened : 0));
     PopID();
 
+    if (g.ActiveId == id && want_open)
+        g.ActiveIdNoClearOnFocusLoss = true;
+
     if (want_open && !menu_is_open && g.OpenPopupStack.Size > g.BeginPopupStack.Size)
     {
         // Don't reopen/recycle same menu level in the same frame if it is a different menu ID, first close the other menu and yield for a frame.
@@ -9602,7 +9612,7 @@ bool ImGui::MenuItemEx(const char* label, const char* icon, const char* shortcut
         BeginDisabled();
 
     // We use ImGuiSelectableFlags_NoSetKeyOwner to allow down on one menu item, move, up on another.
-    const ImGuiSelectableFlags selectable_flags = ImGuiSelectableFlags_NoHoldingActiveID | ImGuiSelectableFlags_SelectOnRelease | ImGuiSelectableFlags_NoSetKeyOwner | ImGuiSelectableFlags_SetNavIdOnHover;
+    const ImGuiSelectableFlags selectable_flags = ImGuiSelectableFlags_SelectOnRelease | ImGuiSelectableFlags_SetNavIdOnHover;
     ImGuiMenuColumns* offsets = &window->DC.MenuColumns;
     if (window->DC.LayoutType == ImGuiLayoutType_Horizontal)
     {
@@ -9645,6 +9655,17 @@ bool ImGui::MenuItemEx(const char* label, const char* icon, const char* shortcut
                 RenderCheckMark(window->DrawList, text_pos + ImVec2(offsets->OffsetMark + stretch_w + g.FontSize * 0.40f, g.FontSize * 0.134f * 0.5f), GetColorU32(ImGuiCol_Text), g.FontSize * 0.866f);
         }
     }
+
+    // Once dragged, release ActiveId + key ownership. This is to allow the idiom of mouse down a menu, dragging elsewhere, up on some other MenuItem(). (#8233, #9394)
+    // Could move logic into lower-level ImGuiButtonFlags_AutoReleaseActiveId + ImGuiButtonFlags_AutoReleaseKeyOwner? Easier once we get rid of the Selectable() middle-man here.
+    const ImGuiID id = g.LastItemData.ID;
+    if (g.ActiveId == id && g.HoveredId != id && g.ActiveIdSource == ImGuiInputSource_Mouse && IsMouseDragging(0))
+    {
+        ClearActiveID();
+        SetKeyOwner(ImGuiKey_MouseLeft, ImGuiKeyOwner_NoOwner);
+    }
+
+
     IMGUI_TEST_ENGINE_ITEM_INFO(g.LastItemData.ID, label, g.LastItemData.StatusFlags | ImGuiItemStatusFlags_Checkable | (selected ? ImGuiItemStatusFlags_Checked : 0));
     if (!enabled)
         EndDisabled();