Tab Bar: Fixed a small bug where toggling a tab bar from Reorderable to not Reorderable would leave tabs reordered in the tab list popup.

docs/CHANGELOG.txt

@@ -53,6 +53,8 @@ Other Changes:
   and amends the change done in 1.76 which only affected cases were _OpenOnArrow flag was set.
   (This is also necessary to support full multi/range-select/drag and drop operations.)
 - Tab Bar: Keep tab item close button visible while dragging a tab (independent of hovering state).
+- Tab Bar: Fixed a small bug where toggling a tab bar from Reorderable to not Reorderable would leave
+  tabs reordered in the tab list popup. [@Xipiryon]
 - Metrics: Various tweaks, listing windows front-to-back, greying inactive items when possible.
 - Demo: Add simple InputText() callbacks demo (aside from the more elaborate ones in 'Examples->Console').
 - Examples: Vulkan: Reworked buffer resize handling, fix for Linux/X11. (#3390, #2626) [@RoryO]

imgui_internal.h

@@ -1710,9 +1710,10 @@ struct ImGuiTabItem
     float               Width;                  // Width currently displayed
     float               ContentWidth;           // Width of actual contents, stored during BeginTabItem() call
     ImS16               NameOffset;             // When Window==NULL, offset to name within parent ImGuiTabBar::TabsNames
+    ImS8                BeginOrder;             // BeginTabItem() order, used to re-order tabs after toggling ImGuiTabBarFlags_Reorderable
     bool                WantClose;              // Marked as closed by SetTabItemClosed()
 
-    ImGuiTabItem()      { ID = 0; Flags = ImGuiTabItemFlags_None; LastFrameVisible = LastFrameSelected = -1; NameOffset = -1; Offset = Width = ContentWidth = 0.0f; WantClose = false; }
+    ImGuiTabItem()      { ID = 0; Flags = ImGuiTabItemFlags_None; LastFrameVisible = LastFrameSelected = -1; NameOffset = -1; Offset = Width = ContentWidth = 0.0f; BeginOrder = -1; WantClose = false; }
 };
 
 // Storage for a tab bar (sizeof() 92~96 bytes)
@@ -1737,9 +1738,10 @@ struct ImGuiTabBar
     ImGuiTabBarFlags    Flags;
     ImGuiID             ReorderRequestTabId;
     ImS8                ReorderRequestDir;
+    ImS8                TabsActiveCount;        // Number of tabs submitted this frame.
     bool                WantLayout;
     bool                VisibleTabWasSubmitted;
-    short               LastTabItemIdx;         // For BeginTabItem()/EndTabItem()
+    short               LastTabItemIdx;         // Index of last BeginTabItem() tab for use by EndTabItem() 
     ImVec2              FramePadding;           // style.FramePadding locked at the time of BeginTabBar()
     ImGuiTextBuffer     TabsNames;              // For non-docking tab bar we re-append names in a contiguous buffer.
 

imgui_widgets.cpp

@@ -6782,15 +6782,16 @@ ImGuiTabBar::ImGuiTabBar()
     Flags = ImGuiTabBarFlags_None;
     ReorderRequestTabId = 0;
     ReorderRequestDir = 0;
+    TabsActiveCount = 0;
     WantLayout = VisibleTabWasSubmitted = false;
     LastTabItemIdx = -1;
 }
 
-static int IMGUI_CDECL TabItemComparerByVisibleOffset(const void* lhs, const void* rhs)
+static int IMGUI_CDECL TabItemComparerByBeginOrder(const void* lhs, const void* rhs)
 {
     const ImGuiTabItem* a = (const ImGuiTabItem*)lhs;
     const ImGuiTabItem* b = (const ImGuiTabItem*)rhs;
-    return (int)(a->Offset - b->Offset);
+    return (int)(a->BeginOrder - b->BeginOrder);
 }
 
 static ImGuiTabBar* GetTabBarFromTabBarRef(const ImGuiPtrOrIndex& ref)
@@ -6842,10 +6843,9 @@ bool    ImGui::BeginTabBarEx(ImGuiTabBar* tab_bar, const ImRect& tab_bar_bb, ImG
         return true;
     }
 
-    // When toggling back from ordered to manually-reorderable, shuffle tabs to enforce the last visible order.
-    // Otherwise, the most recently inserted tabs would move at the end of visible list which can be a little too confusing or magic for the user.
-    if ((flags & ImGuiTabBarFlags_Reorderable) && !(tab_bar->Flags & ImGuiTabBarFlags_Reorderable) && tab_bar->Tabs.Size > 1 && tab_bar->PrevFrameVisible != -1)
-        ImQsort(tab_bar->Tabs.Data, tab_bar->Tabs.Size, sizeof(ImGuiTabItem), TabItemComparerByVisibleOffset);
+    // When toggling ImGuiTabBarFlags_Reorderable flag, ensure tabs are ordered based on their submission order.
+    if ((flags & ImGuiTabBarFlags_Reorderable) != (tab_bar->Flags & ImGuiTabBarFlags_Reorderable) && tab_bar->Tabs.Size > 1)
+        ImQsort(tab_bar->Tabs.Data, tab_bar->Tabs.Size, sizeof(ImGuiTabItem), TabItemComparerByBeginOrder);
 
     // Flags
     if ((flags & ImGuiTabBarFlags_FittingPolicyMask_) == 0)
@@ -6857,6 +6857,7 @@ bool    ImGui::BeginTabBarEx(ImGuiTabBar* tab_bar, const ImRect& tab_bar_bb, ImG
     tab_bar->PrevFrameVisible = tab_bar->CurrFrameVisible;
     tab_bar->CurrFrameVisible = g.FrameCount;
     tab_bar->FramePadding = g.Style.FramePadding;
+    tab_bar->TabsActiveCount = 0;
 
     // Set cursor pos in a way which only be used in the off-chance the user erroneously submits item before BeginTabItem(): items will overlap
     window->DC.CursorPos.x = tab_bar->BarRect.Min.x;
@@ -7362,6 +7363,7 @@ bool    ImGui::TabItemEx(ImGuiTabBar* tab_bar, const char* label, bool* p_open,
     }
     tab_bar->LastTabItemIdx = (short)tab_bar->Tabs.index_from_ptr(tab);
     tab->ContentWidth = size.x;
+    tab->BeginOrder = tab_bar->TabsActiveCount++;
 
     const bool tab_bar_appearing = (tab_bar->PrevFrameVisible + 1 < g.FrameCount);
     const bool tab_bar_focused = (tab_bar->Flags & ImGuiTabBarFlags_IsFocused) != 0;