Enhance marker item behavior: add context manager for symbol management and synchronize movable/resizable states

Author: PierreRaybaut

CHANGELOG.md

@@ -37,6 +37,10 @@
 * Edit tools (Edit data, center image position):
   * Exclude read-only items from the list of editable items
   * It is no longer possible to use those tools on read-only items
+* Marker items (markers, cursors):
+  * Setting item movable state now also sets the resizable state:
+    * The PlotPy event system won't prevent the user from moving the item by dragging the handles if the item is just not movable: it has to be not resizable, which is not intuitive.
+    * This is now fixed
 
 Other changes:
 

plotpy/items/shape/marker.py

@@ -3,7 +3,8 @@
 from __future__ import annotations
 
 import math
-from typing import TYPE_CHECKING
+from contextlib import contextmanager
+from typing import TYPE_CHECKING, Generator
 
 from guidata.dataset import update_dataset
 from guidata.utils.misc import assert_interfaces_valid
@@ -28,6 +29,27 @@
     from plotpy.styles.base import ItemParameters
 
 
+@contextmanager
+def no_symbol_context(
+    item: QwtPlotMarker, condition: bool
+) -> Generator[None, None, None]:
+    """Context manager for temporarily changing a marker's symbol
+
+    Args:
+        item: The marker object whose symbol might be changed
+        condition: If True, the symbol will be changed to None temporarily
+    """
+    old_symbol = None
+    if condition:
+        old_symbol = item.symbol()
+        item.setSymbol(None)
+    try:
+        yield
+    finally:
+        if condition and old_symbol is not None:
+            item.setSymbol(old_symbol)
+
+
 class Marker(QwtPlotMarker):
     """Marker shape
 
@@ -137,7 +159,8 @@ def draw(
             x, y = self.center_handle(self.xValue(), self.yValue())
             self.setValue(x, y)
         self.update_label()
-        QwtPlotMarker.draw(self, painter, xMap, yMap, canvasRect)
+        with no_symbol_context(self, not self.can_resize()):
+            QwtPlotMarker.draw(self, painter, xMap, yMap, canvasRect)
 
     # ------IBasePlotItem API----------------------------------------------------
     def get_icon_name(self) -> str:
@@ -180,6 +203,14 @@ def set_movable(self, state: bool) -> None:
             state: True if item is movable, False otherwise
         """
         self._can_move = state
+        # For a marker, setting the movable state to False means that, obviously,
+        # it cannot be moved. However, due to the way the event system works,
+        # the marker can still be moved by the user: it has to be not resizable
+        # to prevent the user from moving it by dragging the handles, which is not
+        # intuitive for a marker (from a user point of view, a marker is a point
+        # or a line, not a shape with handles).
+        # So, we set the resizable state to the same value as the movable state:
+        self.set_resizable(state)
 
     def set_rotatable(self, state: bool) -> None:
         """Set item rotatable state