Columns: Fixed boundary of clipping being off by 1 pixel within the left column.

docs/CHANGELOG.txt

@@ -51,6 +51,7 @@ Other Changes:
 - 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)
 - Window: Window close button is horizontally aligned with style.FramePadding.x.
+- Columns: Fixed boundary of clipping being off by 1 pixel within the left column.
 - Misc: Added IM_MALLOC/IM_FREE macros mimicking IM_NEW/IM_DELETE so user doesn't need to revert
   to using the ImGui::MemAlloc()/MemFree() calls directly.
 - Metrics: Added "Show windows rectangles" tool to visualize the different rectangles.

imgui.cpp

@@ -8542,7 +8542,7 @@ void ImGui::BeginColumns(const char* str_id, int columns_count, ImGuiColumnsFlag
     {
         // Compute clipping rectangle
         ImGuiColumnData* column = &columns->Columns[n];
-        float clip_x1 = ImFloor(0.5f + window->Pos.x + GetColumnOffset(n) - 1.0f);
+        float clip_x1 = ImFloor(0.5f + window->Pos.x + GetColumnOffset(n));
         float clip_x2 = ImFloor(0.5f + window->Pos.x + GetColumnOffset(n + 1) - 1.0f);
         column->ClipRect = ImRect(clip_x1, -FLT_MAX, clip_x2, +FLT_MAX);
         column->ClipRect.ClipWith(window->ClipRect);