Wiresheet: left-drag rectangle selection, group move, Ctrl+A select all

Rectangle selection moves to the left button on bare sheet (Ctrl adds);
right-click is the menu again. Dragging a selected box by its title bar
moves the whole selection as one undoable step.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

link_drag.py

@@ -11,9 +11,9 @@ either end. While dragging, the cursor points along the flow of the link over a
 would take it, and turns into a no-entry sign over one that would not, so a bad drop is
 visible before the button is released.
 
-A right press that never moves still opens the component's context menu. A right drag
-that starts off a slot row draws a selection rectangle instead, and selects the boxes
-wholly inside it on release; with Ctrl held they join the current selection. A left press
+A right press that never moves still opens the component's context menu. A left drag
+that starts on bare sheet draws a selection rectangle, and selects the boxes wholly
+inside it on release; with Ctrl held they join the current selection. A left press
 anywhere on a box selects it, but only a press on its title bar moves it; on a slot row
 it draws a link instead, as in Workbench.
 """
@@ -41,7 +41,7 @@ CTRL_MASK = 0x0004
 _cursors = {}                   # role -> Tk cursor spec, built on first use
 _press = None                   # pending right press: {"hit", "x", "y", "event"}
 _drag = None                    # live link drag: {"hit", "anchor"}
-_marquee = None                 # right press off a slot: {"x", "y", "cx", "cy", "state", "active"}
+_marquee = None                 # left press on bare sheet: {"x", "y", "cx", "cy", "state", "active"}
 _menu_callback = None           # opens the ordinary right-click menu for an event
 _select_boxes = None            # makes a list of comp tags the box selection
 _link_dialog = None             # opens the Link dialog: (source, target, src_slot, tgt_slot)
@@ -434,9 +434,34 @@ def _finish(event):
     return "link"
 
 
-# Right button: on a slot it drags a link. Anywhere else, dragging pulls out a selection
-# rectangle that selects every box wholly inside it on release (Ctrl adds them to the
-# current selection). A press that never moves is the menu.
+# Right button: on a slot it drags a link, and a press that never moves is the menu.
+
+def on_right_press(event):
+    if _start_press(event) is None:
+        _menu_callback(event)
+
+
+def on_right_motion(event):
+    _drag_motion(event)
+
+
+def on_right_release(event):
+    if _finish(event) == "click":
+        _menu_callback(event)
+
+
+# Left button on bare sheet: dragging pulls out a selection rectangle that selects every
+# box wholly inside it on release (Ctrl adds them to the current selection).
+
+def _on_bare_sheet(cx, cy):
+    """True if no box or link lies under a canvas point."""
+    canvas = app_state.canvas
+    for item in canvas.find_overlapping(cx - 3, cy - 3, cx + 3, cy + 3):
+        tags = canvas.gettags(item)
+        if "component" in tags or "link" in tags:
+            return False
+    return True
+
 
 def _marquee_motion(event):
     """Draws the selection rectangle once the pointer has moved far enough."""
@@ -486,30 +511,6 @@ def _marquee_finish(event):
     return True
 
 
-def on_right_press(event):
-    global _marquee
-    _marquee = None
-    if _start_press(event) is None:
-        canvas = app_state.canvas
-        _marquee = {"x": event.x, "y": event.y, "cx": canvas.canvasx(event.x),
-                    "cy": canvas.canvasy(event.y), "state": event.state, "active": False}
-
-
-def on_right_motion(event):
-    if _marquee is not None:
-        _marquee_motion(event)
-    else:
-        _drag_motion(event)
-
-
-def on_right_release(event):
-    if _marquee is not None:
-        if not _marquee_finish(event):
-            _menu_callback(event)
-    elif _finish(event) == "click":
-        _menu_callback(event)
-
-
 # Left button: anywhere on a box selects it. Only the title bar moves it; a slot row
 # drags out a link, and the rest of the box does nothing more than select.
 
@@ -519,6 +520,19 @@ def _on_title_bar(comp_tag, cy):
 
 
 def on_left_press(event):
+    global _marquee
+    _marquee = None
+    canvas = app_state.canvas
+    cx, cy = canvas.canvasx(event.x), canvas.canvasy(event.y)
+    if _on_bare_sheet(cx, cy):
+        app_state.drag_data["tag"] = None
+        if not event.state & CTRL_MASK:
+            # A plain click on bare sheet still clears the selection, drag or not.
+            wiresheet.deselect_link()
+            _select_boxes([])
+        _marquee = {"x": event.x, "y": event.y, "cx": cx, "cy": cy,
+                    "state": event.state, "active": False}
+        return
     _box_handlers["press"](event)               # selection, and arms a box move
     if _start_press(event) is not None:
         app_state.canvas.delete("slot_hover")
@@ -528,14 +542,18 @@ def on_left_press(event):
 
 
 def on_left_motion(event):
-    if _press is not None or _drag is not None:
+    if _marquee is not None:
+        _marquee_motion(event)
+    elif _press is not None or _drag is not None:
         _drag_motion(event)
     else:
         _box_handlers["motion"](event)
 
 
 def on_left_release(event):
-    if _finish(event) is None:
+    if _marquee is not None:
+        _marquee_finish(event)
+    elif _finish(event) in (None, "click"):
         _box_handlers["release"](event)