diff --git a/scanslicer/canvas_render.py b/scanslicer/canvas_render.py
index 9329f31..0eff838 100644
--- a/scanslicer/canvas_render.py
+++ b/scanslicer/canvas_render.py
@@ -4,3 +4,71 @@ from PySide6.QtGui import QColor, QFont, QPainter, QPen
 
 
 # CanvasRenderMixin: class definition for ScanSlicer behavior.
+class CanvasRenderMixin:
+    # paintEvent: function definition for ScanSlicer behavior.
+    def paintEvent(self, event):
+        painter = QPainter(self)
+        painter.fillRect(self.rect(), self.OFF_CANVAS_COLOR)
+
+        if self.image is None:
+            return
+
+        img_rect = self._image_rect_view()
+        painter.drawImage(img_rect, self.image)
+
+        label_font = QFont(painter.font())
+        label_font.setPointSize(18)
+        label_font.setBold(True)
+
+        for si, s in enumerate(self.slices):
+            points = [self._image_to_view(p) for p in s.bbox]
+
+            for i in range(4):
+                a = points[i]
+                b = points[(i + 1) % 4]
+                if i == 0:
+                    color = QColor("red")
+                else:
+                    color = QColor("blue") if s.locked else QColor("lightgreen")
+                painter.setPen(QPen(color, 3))
+                painter.drawLine(a, b)
+
+            painter.setPen(QPen(QColor("blue"), 2))
+            painter.setBrush(QColor(128, 128, 128, 170))
+            for p in points:
+                painter.drawRect(QRectF(p.x() - 5, p.y() - 5, 10, 10))
+
+            center = np.mean(s.bbox, axis=0)
+            center_view = self._image_to_view(center)
+            if si == self.active_slice_index:
+                text_color = QColor("gold")
+            else:
+                text_color = QColor("blue") if s.locked else QColor("lightgreen")
+            painter.setPen(QPen(text_color, 1))
+            painter.setFont(label_font)
+            painter.drawText(
+                QRectF(center_view.x() - 20, center_view.y() - 16, 40, 32),
+                Qt.AlignCenter,
+                str(si),
+            )
+
+            if s.side_handles_enabled and s.is_perfect_rectangle():
+                handle_color = QColor("orange") if si == self.active_slice_index else QColor(255, 170, 0)
+                painter.setPen(QPen(handle_color, 2))
+                painter.setBrush(QColor(handle_color.red(), handle_color.green(), handle_color.blue(), 170))
+                handle_size = (
+                    float(getattr(self, "SIDE_HANDLE_SIZE_ACTIVE", 11.0))
+                    if si == self.active_slice_index
+                    else float(getattr(self, "SIDE_HANDLE_SIZE_INACTIVE", 9.0))
+                )
+                for ei in range(4):
+                    mid = (s.bbox[ei] + s.bbox[(ei + 1) % 4]) / 2.0
+                    mid_view = self._image_to_view(mid)
+                    painter.drawRect(
+                        QRectF(
+                            mid_view.x() - handle_size / 2.0,
+                            mid_view.y() - handle_size / 2.0,
+                            handle_size,
+                            handle_size,
+                        )
+                    )