Separator: Declare its thickness (1.0f) to the layout, making items around separator more symmetrical.

docs/CHANGELOG.txt

@@ -62,7 +62,8 @@ Other Changes:
 - GetMouseDragDelta(): verify that mouse positions are valid otherwise returns zero.
 - Inputs: Also add support for horizontal scroll with Shift+Mouse Wheel. (#2424, #1463) [@LucaRood]
 - PlotLines, PlotHistogram: Ignore NaN values when calculating min/max bounds. (#2485)
-- Columns: Fixed boundary of clipping being off by 1 pixel within the left column.
+- Columns: Fixed boundary of clipping being off by 1 pixel within the left column. (#125)
+- Separator: Declare its thickness (1.0f) to the layout, making items around separator more symmetrical.
 - Combo, Slider, Scrollbar: Improve rendering in situation when there's only a few pixels available (<3 pixels).
 - Nav: Fixed Drag/Slider functions going into text input mode when keyboard CTRL is held while pressing NavActivate.
 - Misc: Added IM_MALLOC/IM_FREE macros mimicking IM_NEW/IM_DELETE so user doesn't need to revert

imgui_widgets.cpp

@@ -1203,7 +1203,7 @@ void ImGui::Separator()
         return;
     ImGuiContext& g = *GImGui;
 
-    // Those flags should eventually be overridable by the user
+    // Those flags should eventually be overrideable by the user
     ImGuiSeparatorFlags flags = (window->DC.LayoutType == ImGuiLayoutType_Horizontal) ? ImGuiSeparatorFlags_Vertical : ImGuiSeparatorFlags_Horizontal;
     IM_ASSERT(ImIsPowerOfTwo(flags & (ImGuiSeparatorFlags_Horizontal | ImGuiSeparatorFlags_Vertical)));   // Check that only 1 option is selected
     if (flags & ImGuiSeparatorFlags_Vertical)
@@ -1222,7 +1222,7 @@ void ImGui::Separator()
         x1 += window->DC.Indent.x;
 
     const ImRect bb(ImVec2(x1, window->DC.CursorPos.y), ImVec2(x2, window->DC.CursorPos.y+1.0f));
-    ItemSize(ImVec2(0.0f, 0.0f)); // NB: we don't provide our width so that it doesn't get feed back into AutoFit, we don't provide height to not alter layout.
+    ItemSize(ImVec2(0.0f, 1.0f)); // NB: we don't provide our width so that it doesn't get feed back into AutoFit
     if (!ItemAdd(bb, 0))
     {
         if (window->DC.CurrentColumns)
@@ -1252,7 +1252,7 @@ void ImGui::VerticalSeparator()
     float y1 = window->DC.CursorPos.y;
     float y2 = window->DC.CursorPos.y + window->DC.CurrentLineSize.y;
     const ImRect bb(ImVec2(window->DC.CursorPos.x, y1), ImVec2(window->DC.CursorPos.x + 1.0f, y2));
-    ItemSize(ImVec2(bb.GetWidth(), 0.0f));
+    ItemSize(ImVec2(1.0f, 0.0f));
     if (!ItemAdd(bb, 0))
         return;