diff --git a/src/gui/widgets/annotation_canvas_widget.py b/src/gui/widgets/annotation_canvas_widget.py
index baff64d..94e03cd 100644
--- a/src/gui/widgets/annotation_canvas_widget.py
+++ b/src/gui/widgets/annotation_canvas_widget.py
@@ -16,8 +16,9 @@ from PySide6.QtGui import (
     QKeyEvent,
     QMouseEvent,
     QPaintEvent,
+    QPolygonF,
 )
-from PySide6.QtCore import Qt, QEvent, Signal, QPoint, QRect
+from PySide6.QtCore import Qt, QEvent, Signal, QPoint, QPointF, QRect
 from typing import Any, Dict, List, Optional, Tuple
 
 from src.utils.image import Image, ImageLoadError
@@ -496,8 +497,10 @@ class AnnotationCanvasWidget(QWidget):
                 )
 
             painter.setPen(pen)
-            for (x1, y1), (x2, y2) in zip(polyline[:-1], polyline[1:]):
-                painter.drawLine(int(x1), int(y1), int(x2), int(y2))
+            # Use QPolygonF for efficient polygon rendering (single call vs N-1 calls)
+            # drawPolygon() automatically closes the shape, ensuring proper visual closure
+            polygon = QPolygonF([QPointF(x, y) for x, y in polyline])
+            painter.drawPolygon(polygon)
 
         # Draw bounding boxes (dashed) if enabled
         if self.show_bboxes and self.original_pixmap is not None and self.bboxes: