Ignore the first press after the selection has been cleared

if the selection is cleared with this tool active, there is no way to switch to another tool than to re-select an object (by clicking it) because the tool buttons in the toolbar will have been disabled. The mouse-event happens after the selection is changed, so we need to keep track of what the selection was previously by monitoring the selection state.

plugins/SupportEraser/SupportEraser.py

@@ -4,7 +4,7 @@
 import os
 import os.path
 
-from PyQt5.QtCore import Qt, QUrl
+from PyQt5.QtCore import Qt, QTimer
 
 from UM.Math.Vector import Vector
 from UM.Tool import Tool
@@ -39,10 +39,28 @@ class SupportEraser(Tool):
         self._selection_pass = None
         Application.getInstance().globalContainerStackChanged.connect(self._updateEnabled)
 
+        # Note: if the selection is cleared with this tool active, there is no way to switch to
+        # another tool than to reselect an object (by clicking it) because the tool buttons in the
+        # toolbar will have been disabled. That is why we need to ignore the first press event
+        # after the selection has been cleared.
+        Selection.selectionChanged.connect(self._onSelectionChanged)
+        self._had_selection = False
+        self._skip_press = False
+
+        self._had_selection_timer = QTimer()
+        self._had_selection_timer.setInterval(0)
+        self._had_selection_timer.setSingleShot(True)
+        self._had_selection_timer.timeout.connect(self._selectionChangeDelay)
+
     def event(self, event):
         super().event(event)
 
         if event.type == Event.MousePressEvent and self._controller.getToolsEnabled():
+            if self._skip_press:
+                # The selection was previously cleared, do not add/remove an anti-support mesh but
+                # use this click for selection and reactivating this tool only.
+                self._skip_press = False
+                return
 
             if self._selection_pass is None:
                 # The selection renderpass is used to identify objects in the current view
@@ -119,10 +137,10 @@ class SupportEraser(Tool):
         Application.getInstance().getController().getScene().sceneChanged.emit(node)
 
         # Select the picked node so the group does not get drawn as a wireframe (yet)
-        if Selection.isSelected(group):
-            Selection.remove(group)
         if not Selection.isSelected(parent):
             Selection.add(parent)
+        if Selection.isSelected(group):
+            Selection.remove(group)
 
     def _removeEraserMesh(self, node: CuraSceneNode):
         group = node.getParent()
@@ -138,10 +156,10 @@ class SupportEraser(Tool):
         Application.getInstance().getController().getScene().sceneChanged.emit(node)
 
         # Select the picked node so the group does not get drawn as a wireframe (yet)
-        if Selection.isSelected(group):
-            Selection.remove(group)
         if parent and not Selection.isSelected(parent):
             Selection.add(parent)
+        if Selection.isSelected(group):
+            Selection.remove(group)
 
     def _updateEnabled(self):
         plugin_enabled = False
@@ -151,3 +169,22 @@ class SupportEraser(Tool):
             plugin_enabled = global_container_stack.getProperty("anti_overhang_mesh", "enabled")
 
         Application.getInstance().getController().toolEnabledChanged.emit(self._plugin_id, plugin_enabled)
+
+
+
+    def _onSelectionChanged(self):
+        # When selection is passed from one object to another object, first the selection is cleared
+        # and then it is set to the new object. We are only interested in the change from no selection
+        # to a selection or vice-versa, not in a change from one object to another. A timer is used to
+        # "merge" a possible clear/select action in a single frame
+        if Selection.hasSelection() != self._had_selection:
+            self._had_selection_timer.start()
+
+    def _selectionChangeDelay(self):
+        has_selection = Selection.hasSelection()
+        if not has_selection and self._had_selection:
+            self._skip_press = True
+        else:
+            self._skip_press = False
+
+        self._had_selection = has_selection