Optimize snap-to-grid code for drawing items

[b-ehlers]

Is your feature request related to a problem? Please describe.

The current implementation of snap-to-grid for drawing items results in sporadic jitter, when an item is constantly moved a bit, but not far enough to reach the next grid position. This was fixed for nodes in Issue #1599.

Describe the solution you'd like

Implement snap-to-grid like in Issue #1599.

Additional context

Here a patch for v2.2.9:

diff --git a/gns3/items/drawing_item.py b/gns3/items/drawing_item.py
index 204921e9..0d8e7c5e 100644
--- a/gns3/items/drawing_item.py
+++ b/gns3/items/drawing_item.py
@@ -212,14 +212,12 @@ class DrawingItem:
             self._project.delete("/drawings/" + self._id, None, body=self.__json__())

     def itemChange(self, change, value):
-        if change == QtWidgets.QGraphicsItem.ItemPositionHasChanged and self.isActive() and self._main_window.uiSnapToGridAction.isChecked():
+        if change == QtWidgets.QGraphicsItem.ItemPositionChange and self.isActive() and self._main_window.uiSnapToGridAction.isChecked():
             grid_size = self._graphics_view.drawingGridSize()
             mid_x = self.boundingRect().width() / 2
-            tmp_x = (grid_size * round((self.x() + mid_x) / grid_size)) - mid_x
+            value.setX((grid_size * round((value.x()+mid_x)/grid_size)) - mid_x)
             mid_y = self.boundingRect().height() / 2
-            tmp_y = (grid_size * round((self.y() + mid_y) / grid_size)) - mid_y
-            if tmp_x != self.x() and tmp_y != self.y():
-                self.setPos(tmp_x, tmp_y)
+            value.setY((grid_size * round((value.y()+mid_y)/grid_size)) - mid_y)

         if change == QtWidgets.QGraphicsItem.ItemSelectedChange:
             if not value:

[grossmj]

Implemented, thanks 👍