Minor tweaks/comments. Note that the reordering the one subtraction caused subtle havoc before the patch in 9ac8820ee2.

imgui.cpp

@@ -4404,7 +4404,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
                 else if (held)
                 {
                     // We don't use an incremental MouseDelta but rather compute an absolute target size based on mouse position
-                    size_target = (g.IO.MousePos - g.ActiveIdClickOffset + resize_rect.GetSize()) - window->Pos;
+                    size_target = (g.IO.MousePos - g.ActiveIdClickOffset - window->Pos) + resize_rect.GetSize();
                 }
 
                 if (size_target.x != FLT_MAX && size_target.y != FLT_MAX)
@@ -10456,8 +10456,8 @@ void ImGui::EndColumns()
         {
             float x = window->Pos.x + GetColumnOffset(i);
             const ImGuiID column_id = window->DC.ColumnsSetId + ImGuiID(i);
-            const float column_w = 4.0f; // Width for interaction
+            const float column_hw = 4.0f; // Half-width for interaction
-            const ImRect column_rect(ImVec2(x - column_w, y1), ImVec2(x + column_w, y2));
+            const ImRect column_rect(ImVec2(x - column_hw, y1), ImVec2(x + column_hw, y2));
             if (IsClippedEx(column_rect, column_id, false))
                 continue;
             
@@ -10468,7 +10468,7 @@ void ImGui::EndColumns()
                 if (hovered || held)
                     g.MouseCursor = ImGuiMouseCursor_ResizeEW;
                 if (held && g.ActiveIdIsJustActivated)
-                    g.ActiveIdClickOffset.x -= column_w; // Store from center of column line (we used a 8 wide rect for columns clicking). This is used by GetDraggedColumnOffset().
+                    g.ActiveIdClickOffset.x -= column_hw; // Store from center of column line (we used a 8 wide rect for columns clicking). This is used by GetDraggedColumnOffset().
                 if (held)
                     dragging_column = i;
             }