PoC: GUI-native crosshair cursor

timhoffm · timhoffm · commit 1568a439383f · 2025-09-05T01:12:17.000+02:00
Addresses #30515
diff --git a/lib/matplotlib/backends/backend_qt.py b/lib/matplotlib/backends/backend_qt.py
@@ -239,6 +239,7 @@ def __init__(self, figure=None):
 
         self.setAttribute(QtCore.Qt.WidgetAttribute.WA_OpaquePaintEvent)
         self.setMouseTracking(True)
+        self.mouse_xy = (0, 0)
         self.resize(*self.get_width_height())
 
         palette = QtGui.QPalette(QtGui.QColor("white"))
@@ -344,8 +345,10 @@ def mouseDoubleClickEvent(self, event):
     def mouseMoveEvent(self, event):
         if self.figure is None:
             return
+        self.mouse_xy = self.mouseEventCoords(event)
+        self.repaint()
         MouseEvent("motion_notify_event", self,
-                   *self.mouseEventCoords(event),
+                   *self.mouse_xy,
                    buttons=self._mpl_buttons(event.buttons()),
                    modifiers=self._mpl_modifiers(),
                    guiEvent=event)._process()
diff --git a/lib/matplotlib/backends/backend_qtagg.py b/lib/matplotlib/backends/backend_qtagg.py
@@ -68,6 +68,19 @@ def paintEvent(self, event):
                 ctypes.c_long.from_address(id(buf)).value = 1
 
             self._draw_rect_callback(painter)
+
+            figx = self.mouse_xy[0] / rect.width()
+            figy = 1 - self.mouse_xy[1] / rect.height()
+            x0 = rect.left()
+            x1 = rect.left() + rect.width()
+            y0 = rect.top()
+            y1 = rect.top() + rect.height()
+            x = rect.left() + int(figx * rect.width())
+            y = rect.top() + int(figy * rect.height())
+            painter.setPen(QtGui.QPen(QtCore.Qt.GlobalColor.red))
+            painter.drawLine(x0, y, x1, y)
+            painter.drawLine(x, y0, x, y1)
+
         finally:
             painter.end()
 
