Tab Bar: Made it possible to append to an existing tab bar by calling BeginTabBar()/EndTabBar() again.

docs/CHANGELOG.txt

@@ -54,6 +54,7 @@ Breaking Changes:
 
 Other Changes:
 
+- Tab Bar: Made it possible to append to an existing tab bar by calling BeginTabBar()/EndTabBar() again.
 - Docs: Split examples/README.txt into docs/BACKENDS.md and docs/EXAMPLES.md improved them.
 - Docs: Consistently renamed all occurences of "binding" and "back-end" to "backend" in comments and docs.
 

imgui_internal.h

@@ -1754,7 +1754,8 @@ struct ImGuiTabBar
     int                 CurrFrameVisible;
     int                 PrevFrameVisible;
     ImRect              BarRect;
-    float               LastTabContentHeight;   // Record the height of contents submitted below the tab bar
+    float               CurrTabsContentsHeight;
+    float               PrevTabsContentsHeight; // 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               ScrollingAnim;
@@ -1770,8 +1771,9 @@ struct ImGuiTabBar
     bool                WantLayout;
     bool                VisibleTabWasSubmitted;
     bool                TabsAddedNew;           // Set to true when a new tab item or button has been added to the tab bar during last frame
-    short               LastTabItemIdx;         // Index of last BeginTabItem() tab for use by EndTabItem() 
+    short               LastTabItemIdx;         // Index of last BeginTabItem() tab for use by EndTabItem()
     ImVec2              FramePadding;           // style.FramePadding locked at the time of BeginTabBar()
+    ImVec2              TabsContentsMin;
     ImGuiTextBuffer     TabsNames;              // For non-docking tab bar we re-append names in a contiguous buffer.
 
     ImGuiTabBar();

imgui_widgets.cpp

@@ -6805,7 +6805,7 @@ ImGuiTabBar::ImGuiTabBar()
     ID = 0;
     SelectedTabId = NextSelectedTabId = VisibleTabId = 0;
     CurrFrameVisible = PrevFrameVisible = -1;
-    LastTabContentHeight = 0.0f;
+    CurrTabsContentsHeight = PrevTabsContentsHeight = 0.0f;
     WidthAllTabs = WidthAllTabsIdeal = 0.0f;
     ScrollingAnim = ScrollingTarget = ScrollingTargetDistToVisibility = ScrollingSpeed = 0.0f;
     ScrollingRectMinX = ScrollingRectMaxX = 0.0f;
@@ -6877,10 +6877,10 @@ bool    ImGui::BeginTabBarEx(ImGuiTabBar* tab_bar, const ImRect& tab_bar_bb, ImG
     g.CurrentTabBarStack.push_back(GetTabBarRefFromTabBar(tab_bar));
     g.CurrentTabBar = tab_bar;
 
+    // Append with multiple BeginTabBar()/EndTabBar() pairs.
     if (tab_bar->CurrFrameVisible == g.FrameCount)
     {
-        //IMGUI_DEBUG_LOG("BeginTabBarEx already called this frame\n", g.FrameCount);
-        IM_ASSERT(0);
+        window->DC.CursorPos = tab_bar->TabsContentsMin;
         return true;
     }
 
@@ -6899,12 +6899,15 @@ bool    ImGui::BeginTabBarEx(ImGuiTabBar* tab_bar, const ImRect& tab_bar_bb, ImG
     tab_bar->WantLayout = true; // Layout will be done on the first call to ItemTab()
     tab_bar->PrevFrameVisible = tab_bar->CurrFrameVisible;
     tab_bar->CurrFrameVisible = g.FrameCount;
+    tab_bar->PrevTabsContentsHeight = tab_bar->CurrTabsContentsHeight;
+    tab_bar->CurrTabsContentsHeight = 0.0f;
     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;
-    window->DC.CursorPos.y = tab_bar->BarRect.Max.y + g.Style.ItemSpacing.y;
+    tab_bar->TabsContentsMin.x = tab_bar->BarRect.Min.x;
+    tab_bar->TabsContentsMin.y = tab_bar->BarRect.Max.y + g.Style.ItemSpacing.y;
+    window->DC.CursorPos = tab_bar->TabsContentsMin;
 
     // Draw separator
     const ImU32 col = GetColorU32((flags & ImGuiTabBarFlags_IsFocused) ? ImGuiCol_TabActive : ImGuiCol_TabUnfocusedActive);
@@ -6930,15 +6933,22 @@ void    ImGui::EndTabBar()
         IM_ASSERT_USER_ERROR(tab_bar != NULL, "Mismatched BeginTabBar()/EndTabBar()!");
         return;
     }
-    if (tab_bar->WantLayout) // Fallback in case no TabItem have been submitted
+
+    // Fallback in case no TabItem have been submitted
+    if (tab_bar->WantLayout)
         TabBarLayout(tab_bar);
 
     // Restore the last visible height if no tab is visible, this reduce vertical flicker/movement when a tabs gets removed without calling SetTabItemClosed().
     const bool tab_bar_appearing = (tab_bar->PrevFrameVisible + 1 < g.FrameCount);
     if (tab_bar->VisibleTabWasSubmitted || tab_bar->VisibleTabId == 0 || tab_bar_appearing)
-        tab_bar->LastTabContentHeight = ImMax(window->DC.CursorPos.y - tab_bar->BarRect.Max.y, 0.0f);
+    {
+        tab_bar->CurrTabsContentsHeight = ImMax(window->DC.CursorPos.y - tab_bar->BarRect.Max.y, tab_bar->CurrTabsContentsHeight);
+        window->DC.CursorPos.y = tab_bar->BarRect.Max.y + tab_bar->CurrTabsContentsHeight;
+    }
     else
-        window->DC.CursorPos.y = tab_bar->BarRect.Max.y + tab_bar->LastTabContentHeight;
+    {
+        window->DC.CursorPos.y = tab_bar->BarRect.Max.y + tab_bar->PrevTabsContentsHeight;
+    }
 
     if ((tab_bar->Flags & ImGuiTabBarFlags_DockNode) == 0)
         PopID();