TabBar: Fixed using more than 32 KB-worth of tab names. (#4176)

docs/CHANGELOG.txt

@@ -36,6 +36,7 @@ HOW TO UPDATE?
 -----------------------------------------------------------------------
 
 Other Changes:
+- TabBar: Fixed using more than 32 KB-worth of tab names. (#4176)
 - Demo: Fixed requirement in 1.83 to link with imgui_demo.cpp if IMGUI_DISABLE_METRICS_WINDOW is not set. (#4171)
   Normally the right way to disable compiling the demo is to set IMGUI_DISABLE_DEMO_WINDOWS, but we want to avoid
   implying that the file is required.

imgui_internal.h

@@ -1952,7 +1952,7 @@ enum ImGuiTabItemFlagsPrivate_
     ImGuiTabItemFlags_Button                    = 1 << 21   // Used by TabItemButton, change the tab item behavior to mimic a button
 };
 
-// Storage for one active tab item (sizeof() 28~32 bytes)
+// Storage for one active tab item (sizeof() 40 bytes)
 struct ImGuiTabItem
 {
     ImGuiID             ID;
@@ -1962,12 +1962,12 @@ struct ImGuiTabItem
     float               Offset;                 // Position relative to beginning of tab
     float               Width;                  // Width currently displayed
     float               ContentWidth;           // Width of label, stored during BeginTabItem() call
-    ImS16               NameOffset;             // When Window==NULL, offset to name within parent ImGuiTabBar::TabsNames
+    ImS32               NameOffset;             // When Window==NULL, offset to name within parent ImGuiTabBar::TabsNames
     ImS16               BeginOrder;             // BeginTabItem() order, used to re-order tabs after toggling ImGuiTabBarFlags_Reorderable
     ImS16               IndexDuringLayout;      // Index only used during TabBarLayout()
     bool                WantClose;              // Marked as closed by SetTabItemClosed()
 
-    ImGuiTabItem()      { memset(this, 0, sizeof(*this)); LastFrameVisible = LastFrameSelected = -1; NameOffset = BeginOrder = IndexDuringLayout = -1; }
+    ImGuiTabItem()      { memset(this, 0, sizeof(*this)); LastFrameVisible = LastFrameSelected = -1; NameOffset = -1; BeginOrder = IndexDuringLayout = -1; }
 };
 
 // Storage for a tab bar (sizeof() 152 bytes)
@@ -2009,7 +2009,7 @@ struct ImGuiTabBar
     int                 GetTabOrder(const ImGuiTabItem* tab) const  { return Tabs.index_from_ptr(tab); }
     const char*         GetTabName(const ImGuiTabItem* tab) const
     {
-        IM_ASSERT(tab->NameOffset != -1 && (int)tab->NameOffset < TabsNames.Buf.Size);
+        IM_ASSERT(tab->NameOffset != -1 && tab->NameOffset < TabsNames.Buf.Size);
         return TabsNames.Buf.Data + tab->NameOffset;
     }
 };

imgui_widgets.cpp

@@ -7765,7 +7765,7 @@ bool    ImGui::TabItemEx(ImGuiTabBar* tab_bar, const char* label, bool* p_open,
     tab->Flags = flags;
 
     // Append name with zero-terminator
-    tab->NameOffset = (ImS16)tab_bar->TabsNames.size();
+    tab->NameOffset = (ImS32)tab_bar->TabsNames.size();
     tab_bar->TabsNames.append(label, label + strlen(label) + 1);
 
     // Update selected tab