Docking: Tabs use their own identifier (in order to make window->ID refer to whole window in test engine). Also prevents Tab ID from clashing with "" which was common.

docs/CHANGELOG.txt

@@ -232,6 +232,8 @@ Other Changes:
 Docking+Viewports Branch:
 
 - Docking: Fixed a CTRL+TAB crash when aiming at an empty docked window. (#4792)
+- Docking: Tabs use their own identifier instead of the Window identifier.
+  (This will invalidate some stored .ini data such as last selected tab, sorry!)
 - Docking: Fixed size constraints not working on single window holding on a dock id (still doesn't work on docked windows).
 - Viewports, IO: Added io.AddMouseViewportEvent() function to queue hovered viewport change (when known by backend).
 - Viewports: Relaxed specs for backend supporting ImGuiBackendFlags_HasMouseHoveredViewport: it is now _optional_

imgui.cpp

@@ -3264,6 +3264,7 @@ ImGuiWindow::ImGuiWindow(ImGuiContext* context, const char* name) : DrawListInst
     ViewportAllowPlatformMonitorExtend = -1;
     ViewportPos = ImVec2(FLT_MAX, FLT_MAX);
     MoveId = GetID("#MOVE");
+    TabId = GetID("#TAB");
     ScrollTarget = ImVec2(FLT_MAX, FLT_MAX);
     ScrollTargetCenterRatio = ImVec2(0.5f, 0.5f);
     AutoFitFramesX = AutoFitFramesY = -1;
@@ -3541,8 +3542,9 @@ bool ImGui::IsItemHovered(ImGuiHoveredFlags flags)
 
         // Test if another item is active (e.g. being dragged)
         if ((flags & ImGuiHoveredFlags_AllowWhenBlockedByActiveItem) == 0)
-            if (g.ActiveId != 0 && g.ActiveId != g.LastItemData.ID && !g.ActiveIdAllowOverlap && g.ActiveId != window->MoveId)
-                return false;
+            if (g.ActiveId != 0 && g.ActiveId != g.LastItemData.ID && !g.ActiveIdAllowOverlap)
+                if (g.ActiveId != window->MoveId && g.ActiveId != window->TabId)
+                    return false;
 
         // Test if interactions on this window are blocked by an active popup or modal.
         // The ImGuiHoveredFlags_AllowWhenBlockedByPopup flag will be tested here.
@@ -3554,7 +3556,8 @@ bool ImGui::IsItemHovered(ImGuiHoveredFlags flags)
             return false;
 
         // Special handling for calling after Begin() which represent the title bar or tab.
-        // When the window is collapsed (SkipItems==true) that last item will never be overwritten so we need to detect the case.
+        // When the window is skipped/collapsed (SkipItems==true) that last item (always ->MoveId submitted by Begin)
+        // will never be overwritten so we need to detect the case.
         if (g.LastItemData.ID == window->MoveId && window->WriteAccessed)
             return false;
     }
@@ -7299,7 +7302,7 @@ void ImGui::FocusWindow(ImGuiWindow* window)
 
     // Select in dock node
     if (dock_node && dock_node->TabBar)
-        dock_node->TabBar->SelectedTabId = dock_node->TabBar->NextSelectedTabId = window->ID;
+        dock_node->TabBar->SelectedTabId = dock_node->TabBar->NextSelectedTabId = window->TabId;
 
     // Bring to front
     BringWindowToFocusFront(focus_front_window);
@@ -12456,6 +12459,7 @@ static void WindowSettingsHandler_WriteAll(ImGuiContext* ctx, ImGuiSettingsHandl
         buf->appendf("Collapsed=%d\n", settings->Collapsed);
         if (settings->DockId != 0)
         {
+            //buf->appendf("TabId=0x%08X\n", ImHashStr("#TAB", 4, settings->ID)); // window->TabId: this is not read back but writing it makes "debugging" the .ini data easier.
             if (settings->DockOrder == -1)
                 buf->appendf("DockId=0x%08X\n", settings->DockId);
             else
@@ -14063,7 +14067,7 @@ void ImGui::DockContextProcessDock(ImGuiContext* ctx, ImGuiDockRequest* req)
         if (payload_node && payload_node->IsLeafNode())
             next_selected_id = payload_node->TabBar->NextSelectedTabId ? payload_node->TabBar->NextSelectedTabId : payload_node->TabBar->SelectedTabId;
         if (payload_node == NULL)
-            next_selected_id = payload_window->ID;
+            next_selected_id = payload_window->TabId;
     }
 
     // FIXME-DOCK: When we are trying to dock an existing single-window node into a loose window, transfer Node ID as well
@@ -14340,7 +14344,7 @@ int ImGui::DockNodeGetTabOrder(ImGuiWindow* window)
     ImGuiTabBar* tab_bar = window->DockNode->TabBar;
     if (tab_bar == NULL)
         return -1;
-    ImGuiTabItem* tab = TabBarFindTabByID(tab_bar, window->ID);
+    ImGuiTabItem* tab = TabBarFindTabByID(tab_bar, window->TabId);
     return tab ? tab_bar->GetTabOrder(tab) : -1;
 }
 
@@ -14444,7 +14448,7 @@ static void ImGui::DockNodeRemoveWindow(ImGuiDockNode* node, ImGuiWindow* window
     node->WantHiddenTabBarUpdate = true;
     if (node->TabBar)
     {
-        TabBarRemoveTab(node->TabBar, window->ID);
+        TabBarRemoveTab(node->TabBar, window->TabId);
         const int tab_count_threshold_for_tab_bar = node->IsCentralNode() ? 1 : 2;
         if (node->Windows.Size < tab_count_threshold_for_tab_bar)
             DockNodeRemoveTabBar(node);
@@ -14627,7 +14631,7 @@ static void ImGui::DockNodeUpdateFlagsAndCollapse(ImGuiDockNode* node)
         bool node_was_active = (node->LastFrameActive + 1 == g.FrameCount);
         bool remove = false;
         remove |= node_was_active && (window->LastFrameActive + 1 < g.FrameCount);
-        remove |= node_was_active && (node->WantCloseAll || node->WantCloseTabId == window->ID) && window->HasCloseButton && !(window->Flags & ImGuiWindowFlags_UnsavedDocument);  // Submit all _expected_ closure from last frame
+        remove |= node_was_active && (node->WantCloseAll || node->WantCloseTabId == window->TabId) && window->HasCloseButton && !(window->Flags & ImGuiWindowFlags_UnsavedDocument);  // Submit all _expected_ closure from last frame
         remove |= (window->DockTabWantClose);
         if (remove)
         {
@@ -15159,7 +15163,7 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
             if (is_focused || root_node->VisibleWindow == NULL)
                 root_node->VisibleWindow = node->VisibleWindow;
             if (node->TabBar)
-                node->TabBar->VisibleTabId = node->VisibleWindow->ID;
+                node->TabBar->VisibleTabId = node->VisibleWindow->TabId;
         }
         return;
     }
@@ -15210,7 +15214,7 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
     for (int window_n = 0; window_n < node->Windows.Size; window_n++)
     {
         ImGuiWindow* window = node->Windows[window_n];
-        if (TabBarFindTabByID(tab_bar, window->ID) == NULL)
+        if (TabBarFindTabByID(tab_bar, window->TabId) == NULL)
             TabBarAddTab(tab_bar, ImGuiTabItemFlags_Unsorted, window);
     }
 
@@ -15255,7 +15259,7 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
     if (tab_bar_is_recreated && TabBarFindTabByID(tab_bar, node->SelectedTabId) != NULL)
         tab_bar->SelectedTabId = tab_bar->NextSelectedTabId = node->SelectedTabId;
     else if (tab_bar->Tabs.Size > tabs_count_old)
-        tab_bar->SelectedTabId = tab_bar->NextSelectedTabId = tab_bar->Tabs.back().Window->ID;
+        tab_bar->SelectedTabId = tab_bar->NextSelectedTabId = tab_bar->Tabs.back().Window->TabId;
 
     // Begin tab bar
     ImGuiTabBarFlags tab_bar_flags = ImGuiTabBarFlags_Reorderable | ImGuiTabBarFlags_AutoSelectNewTabs; // | ImGuiTabBarFlags_NoTabListScrollingButtons);
@@ -15275,7 +15279,7 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
     for (int window_n = 0; window_n < node->Windows.Size; window_n++)
     {
         ImGuiWindow* window = node->Windows[window_n];
-        if ((closed_all || closed_one == window->ID) && window->HasCloseButton && !(window->Flags & ImGuiWindowFlags_UnsavedDocument))
+        if ((closed_all || closed_one == window->TabId) && window->HasCloseButton && !(window->Flags & ImGuiWindowFlags_UnsavedDocument))
             continue;
         if (window->LastFrameActive + 1 >= g.FrameCount || !node_was_active)
         {
@@ -15290,11 +15294,12 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
             for (int color_n = 0; color_n < ImGuiWindowDockStyleCol_COUNT; color_n++)
                 g.Style.Colors[GWindowDockStyleColors[color_n]] = ColorConvertU32ToFloat4(window->DockStyle.Colors[color_n]);
 
+            // Note that TabItemEx() calls TabBarCalcTabID() so our tab item ID will ignore the current ID stack (rightly so)
             bool tab_open = true;
             TabItemEx(tab_bar, window->Name, window->HasCloseButton ? &tab_open : NULL, tab_item_flags, window);
             if (!tab_open)
-                node->WantCloseTabId = window->ID;
-            if (tab_bar->VisibleTabId == window->ID)
+                node->WantCloseTabId = window->TabId;
+            if (tab_bar->VisibleTabId == window->TabId)
                 node->VisibleWindow = window;
 
             // Store last item data so it can be queried with IsItemXXX functions after the user Begin() call
@@ -15303,7 +15308,7 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
 
             // Update navigation ID on menu layer
             if (g.NavWindow && g.NavWindow->RootWindow == window && (window->DC.NavLayersActiveMask & (1 << ImGuiNavLayer_Menu)) == 0)
-                host_window->NavLastIds[1] = window->ID;
+                host_window->NavLastIds[1] = window->TabId;
         }
     }
 
@@ -15317,7 +15322,7 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
             root_node->VisibleWindow = node->VisibleWindow;
 
     // Close button (after VisibleWindow was updated)
-    // Note that VisibleWindow may have been overrided by CTRL+Tabbing, so VisibleWindow->ID may be != from tab_bar->SelectedTabId
+    // Note that VisibleWindow may have been overrided by CTRL+Tabbing, so VisibleWindow->TabId may be != from tab_bar->SelectedTabId
     const bool close_button_is_enabled = node->HasCloseButton && node->VisibleWindow && node->VisibleWindow->HasCloseButton;
     const bool close_button_is_visible = node->HasCloseButton;
     //const bool close_button_is_visible = close_button_is_enabled; // Most people would expect this behavior of not even showing the button (leaving a hole since we can't claim that space as other windows in the tba bar have one)
@@ -16931,7 +16936,7 @@ void ImGui::BeginDocked(ImGuiWindow* window, bool* p_open)
     if (node->TabBar && window->WasActive)
         window->DockOrder = (short)DockNodeGetTabOrder(window);
 
-    if ((node->WantCloseAll || node->WantCloseTabId == window->ID) && p_open != NULL)
+    if ((node->WantCloseAll || node->WantCloseTabId == window->TabId) && p_open != NULL)
         *p_open = false;
 
     // Update ChildId to allow returning from Child to Parent with Escape

imgui_internal.h

@@ -2231,6 +2231,7 @@ struct IMGUI_API ImGuiWindow
     float                   WindowBorderSize;                   // Window border size at the time of Begin().
     int                     NameBufLen;                         // Size of buffer storing Name. May be larger than strlen(Name)!
     ImGuiID                 MoveId;                             // == window->GetID("#MOVE")
+    ImGuiID                 TabId;                              // == window->GetID("#TAB")
     ImGuiID                 ChildId;                            // ID of corresponding item in parent window (for navigation to return from child window to parent window)
     ImVec2                  Scroll;
     ImVec2                  ScrollMax;

imgui_widgets.cpp

@@ -7584,7 +7584,7 @@ static ImU32   ImGui::TabBarCalcTabID(ImGuiTabBar* tab_bar, const char* label, I
     {
         IM_UNUSED(tab_bar);
         IM_ASSERT(tab_bar->Flags & ImGuiTabBarFlags_DockNode);
-        ImGuiID id = ImHashStr(label);
+        ImGuiID id = docked_window->TabId;
         KeepAliveID(id);
         return id;
     }
@@ -7629,14 +7629,14 @@ ImGuiTabItem* ImGui::TabBarFindMostRecentlySelectedTabForActiveWindow(ImGuiTabBa
 void ImGui::TabBarAddTab(ImGuiTabBar* tab_bar, ImGuiTabItemFlags tab_flags, ImGuiWindow* window)
 {
     ImGuiContext& g = *GImGui;
-    IM_ASSERT(TabBarFindTabByID(tab_bar, window->ID) == NULL);
+    IM_ASSERT(TabBarFindTabByID(tab_bar, window->TabId) == NULL);
     IM_ASSERT(g.CurrentTabBar != tab_bar);  // Can't work while the tab bar is active as our tab doesn't have an X offset yet, in theory we could/should test something like (tab_bar->CurrFrameVisible < g.FrameCount) but we'd need to solve why triggers the commented early-out assert in BeginTabBarEx() (probably dock node going from implicit to explicit in same frame)
 
     if (!window->HasCloseButton)
         tab_flags |= ImGuiTabItemFlags_NoCloseButton;       // Set _NoCloseButton immediately because it will be used for first-frame width calculation.
 
     ImGuiTabItem new_tab;
-    new_tab.ID = window->ID;
+    new_tab.ID = window->TabId;
     new_tab.Flags = tab_flags;
     new_tab.LastFrameVisible = tab_bar->CurrFrameVisible;   // Required so BeginTabBar() doesn't ditch the tab
     if (new_tab.LastFrameVisible == -1)
@@ -8209,7 +8209,7 @@ bool    ImGui::TabItemEx(ImGuiTabBar* tab_bar, const char* label, bool* p_open,
         flags |= ImGuiTabItemFlags_NoCloseWithMiddleMouseButton;
 
     // Render tab label, process close button
-    const ImGuiID close_button_id = p_open ? GetIDWithSeed("#CLOSE", NULL, id) : 0;
+    const ImGuiID close_button_id = p_open ? GetIDWithSeed("#CLOSE", NULL, docked_window ? docked_window->ID : id) : 0;
     bool just_closed;
     bool text_clipped;
     TabItemLabelAndCloseButton(display_draw_list, bb, flags, tab_bar->FramePadding, label, id, close_button_id, tab_contents_visible, &just_closed, &text_clipped);