matplotlib · joddeepesh-cloud · Feb 24, 2026 · Feb 28, 2026 · Mar 9, 2026 · Mar 25, 2026
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -1772,7 +1772,41 @@ def __init__(self, figure=None):
         figure._original_dpi = getattr(figure, '_original_dpi', figure.dpi)
         self._device_pixel_ratio = 1
         self._blit_backgrounds = {}
+        self._overlay_primitives = []
+
         super().__init__()  # Typically the GUI widget init (if any).
+    def add_overlay_line(self, x1, y1, x2, y2, **style):
+
+     if not hasattr(self, "_overlay_primitives"):
+        self._overlay_primitives = []
+
+        self._overlay_primitives.append(
+          {"type": "line", "coords": (x1, y1, x2, y2), "style": style}
+        )
+
+        print("Added overlay:", self._overlay_primitives)
+
+        self.draw_idle()
+
+    def clear_overlay(self):
+        """
+        Remove all overlay primitives and request a lightweight repaint.
+
+        This clears overlay elements drawn above the rendered figure
+        without triggering a full figure redraw.
+        """
+        self._overlay_primitives.clear()
+        self._request_overlay_draw()
+
+
+    def _request_overlay_draw(self):
+        """
+        Request a lightweight overlay repaint.
+
+        Backends must override this.
+        """
+        raise NotImplementedError
+
 
     callbacks = property(lambda self: self.figure._canvas_callbacks)
     button_pick_id = property(lambda self: self.figure._button_pick_id)

diff --git a/lib/matplotlib/backends/backend_qtagg.py b/lib/matplotlib/backends/backend_qtagg.py
@@ -14,8 +14,64 @@
 
 
 class FigureCanvasQTAgg(FigureCanvasAgg, FigureCanvasQT):
+    def __init__(self, figure):
+        super().__init__(figure)
+
+        self._overlay_lines = []
+        self._overlay_start = None
+        self._overlay_end = None
+        self._drawing_overlay = False
+
+
+    def add_overlay_line(self, x1, y1, x2, y2, **style):
+        """Add a lightweight overlay line drawn directly with Qt."""
+
+        self._overlay_lines.append((x1, y1, x2, y2, style))
+
+        self._request_overlay_draw()
+
+    def clear_overlay(self):
+        """Remove all overlay drawings from the canvas."""
+        self._overlay_lines.clear()
+
+        self._request_overlay_draw()
+
+    def _request_overlay_draw(self):
+        self.update()
+
+    def mousePressEvent(self, event):
+        if event.button() == QtCore.Qt.MouseButton.LeftButton:
+         self._overlay_start = (event.position().x(), event.position().y())
+         self._overlay_end = None
+         self._drawing_overlay = True
+
+
+    def mouseMoveEvent(self, event):
+        if self._drawing_overlay and self._overlay_start:
+         self._overlay_end = (event.position().x(), event.position().y())
+         self._request_overlay_draw()
+
+
+    def mouseReleaseEvent(self, event):
+        if event.button() == QtCore.Qt.MouseButton.LeftButton and self._drawing_overlay:
+         self._overlay_end = (event.position().x(), event.position().y())
+         self._drawing_overlay = False
+
+        # store the finished line
+         x1, y1 = self._overlay_start
+         x2, y2 = self._overlay_end
+         self._overlay_lines.append((x1, y1, x2, y2, {}))
+
+         self._overlay_start = None
+         self._overlay_end = None
+
+         self._request_overlay_draw()
+
+
+
 
     def paintEvent(self, event):
+        print("PAINT EVENT RUNNING")
         """
         Copy the image from the Agg canvas to the qt.drawable.
 
@@ -67,7 +123,17 @@ def paintEvent(self, event):
             if QT_API == "PySide2" and QtCore.__version_info__ < (5, 12):
                 ctypes.c_long.from_address(id(buf)).value = 1
 
-            self._draw_rect_callback(painter)
+           # --- Overlay drawing ---
+            for x1, y1, x2, y2, style in getattr(self, "_overlay_lines", []):
+
+             color = style.get("color", "red")
+             width = style.get("width", 2)
+
+             pen = QtGui.QPen(QtGui.QColor(color), width)
+             painter.setPen(pen)
+
+             painter.drawLine(int(x1), int(y1), int(x2), int(y2))
+
         finally:
             painter.end()
 

diff --git a/lib/mpl_toolkits/mplot3d/axes3d.py b/lib/mpl_toolkits/mplot3d/axes3d.py
@@ -106,12 +106,13 @@ def __init__(
             If None, defaults to 4:4:3
         computed_zorder : bool, default: True
             If True, the draw order is computed based on the average position
-            of the `.Artist`\\s along the view direction.
+            along the view direction for supported artist types (currently
+            Collections and Patches only).
             Set to False if you want to manually control the order in which
             Artists are drawn on top of each other using their *zorder*
             attribute. This can be used for fine-tuning if the automatic order
             does not produce the desired result. Note however, that a manual
-            zorder will only be correct for a limited view angle. If the figure
+            order will only be correct for a limited view angle. If the figure
             is rotated by the user, it will look wrong from certain angles.
 
         **kwargs

diff --git a/overlay_test.py b/overlay_test.py
@@ -0,0 +1,12 @@
+import matplotlib.pyplot as plt
+
+fig, ax = plt.subplots()
+canvas = fig.canvas
+
+plt.show(block=False)
+
+canvas.add_overlay_line(50, 50, 300, 300)
+canvas.add_overlay_line(50, 300, 300, 50)
+
+canvas.draw()
+plt.pause(0.1)