TabBar: Tweak shrinking policy so that while resizing tabs that don't need shrinking keep their initial width more precisely.

Has been the case before but adding support for SetNextItemWidth() ocornut#5262 made this more noticeable.

Author: ocornut

docs/CHANGELOG.txt

@@ -106,6 +106,8 @@ Other Changes:
 - Inputs: Fixed IsMouseClicked() repeat mode rate being half of keyboard repeat rate.
 - ColorEdit: Fixed text baseline alignment after a SameLine() after a ColorEdit() with visible label.
 - TabBar: TabItem() now reacts to SetNextItemWidth() and SetNextItemOpen(true). (#5262)
+- TabBar: Tweak shrinking policy so that while resizing tabs that don't need shrinking keep their
+  initial width more precisely (without the occasional +1 worth of width).
 - Menus: Adjusted BeginMenu() closing logic so hovering void or non-MenuItem() in parent window
   always lead to menu closure. Fixes using items that are not MenuItem() or BeginItem() at the root
   level of a popup with a child menu opened.

imgui_internal.h

@@ -1150,6 +1150,7 @@ struct ImGuiShrinkWidthItem
 {
     int         Index;
     float       Width;
+    float       InitialWidth;
 };
 
 struct ImGuiPtrOrIndex

imgui_widgets.cpp

@@ -1540,7 +1540,7 @@ void ImGui::ShrinkWidths(ImGuiShrinkWidthItem* items, int count, float width_exc
         width_excess -= width_to_remove_per_item * count_same_width;
     }
 
-    // Round width and redistribute remainder left-to-right (could make it an option of the function?)
+    // Round width and redistribute remainder
     // Ensure that e.g. the right-most tab of a shrunk tab-bar always reaches exactly at the same distance from the right-most edge of the tab bar separator.
     width_excess = 0.0f;
     for (int n = 0; n < count; n++)
@@ -1549,10 +1549,13 @@ void ImGui::ShrinkWidths(ImGuiShrinkWidthItem* items, int count, float width_exc
         width_excess += items[n].Width - width_rounded;
         items[n].Width = width_rounded;
     }
-    if (width_excess > 0.0f)
+    while (width_excess > 0.0f)
         for (int n = 0; n < count; n++)
-            if (items[n].Index < (int)(width_excess + 0.01f))
+            if (items[n].Width + 1.0f <= items[n].InitialWidth)
+            {
                 items[n].Width += 1.0f;
+                width_excess -= 1.0f;
+            }
 }
 
 //-------------------------------------------------------------------------
@@ -7557,9 +7560,9 @@ static void ImGui::TabBarLayout(ImGuiTabBar* tab_bar)
 
         // Store data so we can build an array sorted by width if we need to shrink tabs down
         IM_MSVC_WARNING_SUPPRESS(6385);
-        int shrink_buffer_index = shrink_buffer_indexes[section_n]++;
-        g.ShrinkWidthBuffer[shrink_buffer_index].Index = tab_n;
-        g.ShrinkWidthBuffer[shrink_buffer_index].Width = tab->ContentWidth;
+        ImGuiShrinkWidthItem* shrink_width_item = &g.ShrinkWidthBuffer[shrink_buffer_indexes[section_n]++];
+        shrink_width_item->Index = tab_n;
+        shrink_width_item->Width = shrink_width_item->InitialWidth = tab->ContentWidth;
 
         IM_ASSERT(tab->ContentWidth > 0.0f);
         tab->Width = tab->ContentWidth;