From 27d0c3afa9327dfdb43c78f02ea3540d5e05dfa3 Mon Sep 17 00:00:00 2001
From: ocornut <omarcornut@gmail.com>
Date: Mon, 21 Sep 2020 19:46:44 +0200
Subject: [PATCH] Tab Bar: Fixed a small bug where scrolling buttons (with
 ImGuiTabBarFlags_FittingPolicyScroll) would generate an unnecessary extra
 draw call.

---
 docs/CHANGELOG.txt |  2 ++
 imgui_widgets.cpp  | 20 ++++++--------------
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 236d278c..1c81c724 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -82,6 +82,8 @@ Other Changes:
   (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 closing a tab that is not selected would leave a tab hole for a frame.
+- Tab Bar: Fixed a small bug where scrolling buttons (with ImGuiTabBarFlags_FittingPolicyScroll) would
+  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]
 - Columns: Fix inverted ClipRect being passed to renderer when using certain primitives inside of
diff --git a/imgui_widgets.cpp b/imgui_widgets.cpp
index a8cc2316..4a7f18c6 100644
--- a/imgui_widgets.cpp
+++ b/imgui_widgets.cpp
@@ -7234,13 +7234,6 @@ static ImGuiTabItem* ImGui::TabBarScrollingButtons(ImGuiTabBar* tab_bar)
     const ImVec2 backup_cursor_pos = window->DC.CursorPos;
     //window->DrawList->AddRect(ImVec2(tab_bar->BarRect.Max.x - scrolling_buttons_width, tab_bar->BarRect.Min.y), ImVec2(tab_bar->BarRect.Max.x, tab_bar->BarRect.Max.y), IM_COL32(255,0,0,255));
 
-    const ImRect avail_bar_rect = tab_bar->BarRect;
-    bool want_clip_rect = !avail_bar_rect.Contains(ImRect(window->DC.CursorPos, window->DC.CursorPos + ImVec2(scrolling_buttons_width, 0.0f)));
-    if (want_clip_rect)
-        PushClipRect(tab_bar->BarRect.Min, tab_bar->BarRect.Max + ImVec2(g.Style.ItemInnerSpacing.x, 0.0f), true);
-
-    ImGuiTabItem* tab_to_select = NULL;
-
     int select_dir = 0;
     ImVec4 arrow_col = g.Style.Colors[ImGuiCol_Text];
     arrow_col.w *= 0.5f;
@@ -7251,30 +7244,29 @@ static ImGuiTabItem* ImGui::TabBarScrollingButtons(ImGuiTabBar* tab_bar)
     const float backup_repeat_rate = g.IO.KeyRepeatRate;
     g.IO.KeyRepeatDelay = 0.250f;
     g.IO.KeyRepeatRate = 0.200f;
-    window->DC.CursorPos = ImVec2(tab_bar->BarRect.Max.x - scrolling_buttons_width, tab_bar->BarRect.Min.y);
+    float x = ImMax(tab_bar->BarRect.Min.x, tab_bar->BarRect.Max.x - scrolling_buttons_width);
+    window->DC.CursorPos = ImVec2(x, tab_bar->BarRect.Min.y);
     if (ArrowButtonEx("##<", ImGuiDir_Left, arrow_button_size, ImGuiButtonFlags_PressedOnClick | ImGuiButtonFlags_Repeat))
         select_dir = -1;
-    window->DC.CursorPos = ImVec2(tab_bar->BarRect.Max.x - scrolling_buttons_width + arrow_button_size.x, tab_bar->BarRect.Min.y);
+    window->DC.CursorPos = ImVec2(x + arrow_button_size.x, tab_bar->BarRect.Min.y);
     if (ArrowButtonEx("##>", ImGuiDir_Right, arrow_button_size, ImGuiButtonFlags_PressedOnClick | ImGuiButtonFlags_Repeat))
         select_dir = +1;
     PopStyleColor(2);
     g.IO.KeyRepeatRate = backup_repeat_rate;
     g.IO.KeyRepeatDelay = backup_repeat_delay;
 
-    if (want_clip_rect)
-        PopClipRect();
-
+    ImGuiTabItem* tab_to_scroll_to = NULL;
     if (select_dir != 0)
         if (ImGuiTabItem* tab_item = TabBarFindTabByID(tab_bar, tab_bar->SelectedTabId))
         {
             int selected_order = tab_bar->GetTabOrder(tab_item);
             int target_order = selected_order + select_dir;
-            tab_to_select = &tab_bar->Tabs[(target_order >= 0 && target_order < tab_bar->Tabs.Size) ? target_order : selected_order]; // If we are at the end of the list, still scroll to make our tab visible
+            tab_to_scroll_to = &tab_bar->Tabs[(target_order >= 0 && target_order < tab_bar->Tabs.Size) ? target_order : selected_order]; // If we are at the end of the list, still scroll to make our tab visible
         }
     window->DC.CursorPos = backup_cursor_pos;
     tab_bar->BarRect.Max.x -= scrolling_buttons_width + 1.0f;
 
-    return tab_to_select;
+    return tab_to_scroll_to;
 }
 
 static ImGuiTabItem* ImGui::TabBarTabListPopupButton(ImGuiTabBar* tab_bar)