Tab Bar: Added TabItemButton(), ImGuiTabItemFlags_Leading, ImGuiTabItemFlags_Trailing + demo. (#3291)

(squashed various commits by 2 authors)

docs/CHANGELOG.txt

@@ -86,6 +86,11 @@ Other Changes:
   generate an unnecessary extra draw call.
 - 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]
+- Tab Bar: Added TabItemButton() to submit tab that behave like a button. (#3291) [@Xipiryon]
+- Tab Bar: Added ImGuiTabItemFlags_Leading and ImGuiTabItemFlags_Trailing flags to position tabs or button at
+  either end of the tab bar. Those tabs won't be part of the scrolling region, won't shrink down, and when
+  reordering cannot be moving outside of their section. Most often used with TabItemButton(). (#3291) [@Xipiryon]
+- Tab Bar: Added ImGuiTabItemFlags_NoReorder flag to disable reordering a given tab.
 - Columns: Fix inverted ClipRect being passed to renderer when using certain primitives inside of
   a fully clipped column. (#3475) [@szreder]
 - Popups, Tooltips: Fix edge cases issues with positionning popups and tooltips when they are larger than

imgui.h

@@ -653,8 +653,9 @@ namespace ImGui
     // Tab Bars, Tabs
     IMGUI_API bool          BeginTabBar(const char* str_id, ImGuiTabBarFlags flags = 0);        // create and append into a TabBar
     IMGUI_API void          EndTabBar();                                                        // only call EndTabBar() if BeginTabBar() returns true!
-    IMGUI_API bool          BeginTabItem(const char* label, bool* p_open = NULL, ImGuiTabItemFlags flags = 0);// create a Tab. Returns true if the Tab is selected.
+    IMGUI_API bool          BeginTabItem(const char* label, bool* p_open = NULL, ImGuiTabItemFlags flags = 0); // create a Tab. Returns true if the Tab is selected.
     IMGUI_API void          EndTabItem();                                                       // only call EndTabItem() if BeginTabItem() returns true!
+    IMGUI_API bool          TabItemButton(const char* label, ImGuiTabItemFlags flags = 0);      // create a Tab behaving like a button
     IMGUI_API void          SetTabItemClosed(const char* tab_or_docked_window_label);           // notify TabBar or Docking system of a closed tab/window ahead (useful to reduce visual flicker on reorderable tab bars). For tab-bar: call after BeginTabBar() and before Tab submissions. Otherwise call with a window name.
 
     // Logging/Capture
@@ -954,7 +955,10 @@ enum ImGuiTabItemFlags_
     ImGuiTabItemFlags_SetSelected                   = 1 << 1,   // Trigger flag to programmatically make the tab selected when calling BeginTabItem()
     ImGuiTabItemFlags_NoCloseWithMiddleMouseButton  = 1 << 2,   // Disable behavior of closing tabs (that are submitted with p_open != NULL) with middle mouse button. You can still repro this behavior on user's side with if (IsItemHovered() && IsMouseClicked(2)) *p_open = false.
     ImGuiTabItemFlags_NoPushId                      = 1 << 3,   // Don't call PushID(tab->ID)/PopID() on BeginTabItem()/EndTabItem()
-    ImGuiTabItemFlags_NoTooltip                     = 1 << 4    // Disable tooltip for the given tab
+    ImGuiTabItemFlags_NoTooltip                     = 1 << 4,   // Disable tooltip for the given tab
+    ImGuiTabItemFlags_NoReorder                     = 1 << 5,   // Disable reordering this tab or having another tab cross over this tab
+    ImGuiTabItemFlags_Leading                       = 1 << 6,   // Enforce the tab position to the left of the tab bar (after the tab list popup button) and disable resizing down
+    ImGuiTabItemFlags_Trailing                      = 1 << 7    // Enforce the tab position to the right of the tab bar (before the scrolling buttons) and disable resizing down
 };
 
 // Flags for ImGui::IsWindowFocused()

imgui_demo.cpp

@@ -2354,6 +2354,91 @@ static void ShowDemoWindowLayout()
             ImGui::Separator();
             ImGui::TreePop();
         }
+
+        if (ImGui::TreeNode("TabItem Button"))
+        {
+            static int next_id = 0;
+            static ImVector<int> tabs_list;
+            if (next_id == 0) // Initialize with a default tab
+                for (int i = 0; i < 9; i++)
+                    tabs_list.push_back(next_id++);
+
+            static ImGuiTabBarFlags tab_bar_flags = ImGuiTabBarFlags_Reorderable | ImGuiTabBarFlags_FittingPolicyResizeDown;
+            ImGui::CheckboxFlags("ImGuiTabBarFlags_Reorderable", (unsigned int*)&tab_bar_flags, ImGuiTabBarFlags_Reorderable);
+            ImGui::CheckboxFlags("ImGuiTabBarFlags_TabListPopupButton", (unsigned int*)&tab_bar_flags, ImGuiTabBarFlags_TabListPopupButton);
+            if (ImGui::CheckboxFlags("ImGuiTabBarFlags_FittingPolicyResizeDown", (unsigned int*)&tab_bar_flags, ImGuiTabBarFlags_FittingPolicyResizeDown))
+                tab_bar_flags &= ~(ImGuiTabBarFlags_FittingPolicyMask_ ^ ImGuiTabBarFlags_FittingPolicyResizeDown);
+            if (ImGui::CheckboxFlags("ImGuiTabBarFlags_FittingPolicyScroll", (unsigned int*)&tab_bar_flags, ImGuiTabBarFlags_FittingPolicyScroll))
+                tab_bar_flags &= ~(ImGuiTabBarFlags_FittingPolicyMask_ ^ ImGuiTabBarFlags_FittingPolicyScroll);
+
+            static bool show_leading_button = true;
+            static bool show_trailing_button = true;
+            ImGui::Checkbox("Show Leading TabItemButton()", &show_leading_button);
+            ImGui::Checkbox("Show Trailing TabItemButton()", &show_trailing_button);
+            static bool enable_position = false;
+            ImGui::Checkbox("Enable Leading/Trailing TabItem()", &enable_position);
+
+            if (ImGui::BeginTabBar("MyTabBar", tab_bar_flags))
+            {
+                if (show_leading_button)
+                {
+                    if (ImGui::TabItemButton("+", ImGuiTabItemFlags_Leading | ImGuiTabItemFlags_NoTooltip))
+                        tabs_list.push_back(next_id++);
+                    if (ImGui::IsItemHovered())
+                        ImGui::SetTooltip("Add a new TabItem() in the tab bar");
+
+                    // Popup Context also works with TabItemButton
+                    if (ImGui::BeginPopupContextItem())
+                    {
+                        ImGui::Text("I'm a popup!");
+                        if (ImGui::Button("Close"))
+                            ImGui::CloseCurrentPopup();
+                        ImGui::EndPopup();
+                    }
+                }
+
+                bool close_current_tab = false;
+                if (show_trailing_button)
+                {
+                    if (ImGui::TabItemButton("X", ImGuiTabItemFlags_Trailing | ImGuiTabItemFlags_NoTooltip))
+                        close_current_tab = true;
+                    if (ImGui::IsItemHovered())
+                        ImGui::SetTooltip("Close the currently selected TabItem()");
+                }
+
+                for (int n = 0; n < tabs_list.Size; )
+                {
+                    int mod = tabs_list[n] % 3;
+                    ImGuiTabItemFlags flags = mod == 0 ? 0 : mod == 1 ? ImGuiTabItemFlags_Leading : ImGuiTabItemFlags_Trailing;
+                    if (!enable_position)
+                        flags = 0;
+
+                    char name[16];
+                    snprintf(name, IM_ARRAYSIZE(name), "%04d", tabs_list[n]);
+                    bool open = true;
+                    if (ImGui::BeginTabItem(name, &open, flags))
+                    {
+                        ImGui::Text("This is the %s tab!", name);
+                        ImGui::EndTabItem();
+
+                        if (close_current_tab)
+                        {
+                            open = false;
+                            ImGui::SetTabItemClosed(name);
+                        }
+                    }
+
+                    if (!open)
+                        tabs_list.erase(tabs_list.Data + n);
+                    else
+                        ++n;
+                }
+
+                ImGui::EndTabBar();
+           }
+            ImGui::Separator();
+            ImGui::TreePop();
+        }
         ImGui::TreePop();
     }
 

imgui_internal.h

@@ -1703,7 +1703,8 @@ enum ImGuiTabBarFlagsPrivate_
 // Extend ImGuiTabItemFlags_
 enum ImGuiTabItemFlagsPrivate_
 {
-    ImGuiTabItemFlags_NoCloseButton             = 1 << 20   // Track whether p_open was set or not (we'll need this info on the next frame to recompute ContentWidth during layout)
+    ImGuiTabItemFlags_NoCloseButton             = 1 << 20,  // Track whether p_open was set or not (we'll need this info on the next frame to recompute ContentWidth during layout)
+    ImGuiTabItemFlags_Button                    = 1 << 21   // [Internal] Used by TabItemButton, change the tab item behavior to mimic a button
 };
 
 // Storage for one active tab item (sizeof() 28~32 bytes)
@@ -1737,7 +1738,8 @@ struct ImGuiTabBar
     float               LastTabContentHeight;   // Record the height of contents submitted below the tab bar
     float               WidthAllTabs;           // Actual width of all tabs (locked during layout)
     float               WidthAllTabsIdeal;      // Ideal width if all tabs were visible and not clipped
-    float               OffsetNextTab;          // Distance from BarRect.Min.x, incremented with each BeginTabItem() call, not used if ImGuiTabBarFlags_Reorderable if set.
+    float               LeadingWidth;           // Total width used by leading button
+    float               TrailingWidth;          // Total width used by trailing button
     float               ScrollingAnim;
     float               ScrollingTarget;
     float               ScrollingTargetDistToVisibility;