Columns: Made the right-most edge reaches up to the clipping rectangl…

…e (removing WindowPadding.x*0.5 worth of asymmetrical/extraneous padding). (#125, #2666)

+ Moved a few things in BeginColumns().

docs/CHANGELOG.txt

@@ -58,6 +58,9 @@ Other Changes:
 - TabBar: Fixed unfocused tab bar separator color (was using ImGuiCol_Tab, should use ImGuiCol_TabUnfocusedActive).
 - Columns: Fixed a regression from 1.71 where the right-side of the contents rectangle within each column
   would wrongly use a WindowPadding.x instead of ItemSpacing.x like it always did. (#125, #2666)
+- Columns: Made the right-most edge reaches up to the clipping rectangle (removing half of WindowPadding.x
+  worth of asymmetrical/extraneous padding, note that there's another half that conservatively has to offset
+  the right-most column, otherwise it's clipping width won't match the other column). (#125, #2666)
 - Word-wrapping: Fixed overzealous word-wrapping when glyph edge lands exactly on the limit. Because
   of this, auto-fitting exactly unwrapped text would make it wrap. (fixes initial 1.15 commit, 78645a7d).
 - Scrolling: Added SetScrollHereX(), SetScrollFromPosX() for completeness. (#1580) [@kevreco]

imgui_widgets.cpp

@@ -7304,13 +7304,13 @@ void ImGui::BeginColumns(const char* str_id, int columns_count, ImGuiColumnsFlag
     columns->HostWorkRect = window->WorkRect;
 
     // Set state for first column
+    // We aim so that the right-most column will have the same clipping width as other after being clipped by parent ClipRect
     const float column_padding = g.Style.ItemSpacing.x;
+    const float half_clip_extend_x = ImFloor(ImMax(window->WindowPadding.x * 0.5f, window->WindowBorderSize));
     columns->OffMinX = window->DC.Indent.x - column_padding;
-    columns->OffMaxX = window->WorkRect.Max.x - window->Pos.x;
+    columns->OffMaxX = window->WorkRect.Max.x + half_clip_extend_x - window->Pos.x;
     columns->OffMaxX = ImMax(columns->OffMaxX, columns->OffMinX + 1.0f);
     columns->LineMinY = columns->LineMaxY = window->DC.CursorPos.y;
-    window->DC.ColumnsOffset.x = 0.0f;
-    window->DC.CursorPos.x = (float)(int)(window->Pos.x + window->DC.Indent.x + window->DC.ColumnsOffset.x);
 
     // Clear data if columns count changed
     if (columns->Columns.Size != 0 && columns->Columns.Size != columns_count + 1)
@@ -7346,10 +7346,13 @@ void ImGui::BeginColumns(const char* str_id, int columns_count, ImGuiColumnsFlag
         PushColumnClipRect(0);
     }
 
+    // We don't generally store Indent.x inside ColumnsOffset because it may be manipulated by the user.
     float offset_0 = GetColumnOffset(columns->Current);
     float offset_1 = GetColumnOffset(columns->Current + 1);
     float width = offset_1 - offset_0;
     PushItemWidth(width * 0.65f);
+    window->DC.ColumnsOffset.x = 0.0f;
+    window->DC.CursorPos.x = (float)(int)(window->Pos.x + window->DC.Indent.x + window->DC.ColumnsOffset.x);
     window->WorkRect.Max.x = window->Pos.x + offset_1 - column_padding;
 }