Wiresheet: keep the half-and-half knob's white centre centred

Pushed into the wire-coloured half, the centre filled almost all of it: that
half is only KNOB_RADIUS wide and the centre is KNOB_CORE_RADIUS, so at the
real 8px knob size the wire colour was reduced to a sliver and the marker read
as plain grey. Centred, both halves keep enough colour to tell apart.

Found on a slot carrying two links on its own sheet plus one leaving it, which
is the only arrangement that produces this knob and did not occur in testSax
until now.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app_state.py

@@ -44,6 +44,9 @@ selected_canvas_tag = None    # Tracks the currently clicked/highlighted canvas
 selected_tree_item_id = None  # Tracks the currently right-clicked Treeview item
 link_mark_element = None      # Component marked as a link endpoint via "Link Mark"
 selected_link_tag = None      # Canvas tag of the currently selected (red-highlighted) link wire
+unroutable_link_count = 0     # Links drawn as knobs because no wire could avoid a component
+meta_scale = DEFAULT_GRID_SIZE  # Pixels per meta coordinate step on the painted sheet
+knob_link_ends = {}           # wire tag -> (x1, y1, x2, y2) for a link shown as two knobs
 canvas_link_map = {}          # Canvas link tag -> ET.Element (<link>)
 xml_root_element = None       # Keep a persistent root reference to redraw tree layouts cleanly
 current_sheet_parent = None   # Element whose children are painted; None means the app root

main.py

@@ -42,6 +42,9 @@ def do_save(event=None):
     return "break"
 
 
+NL = chr(10)   # newline, for the multi-line message boxes
+
+
 def do_tidy_layout(event=None):
     """Menu command: re-flow the open sheet so nothing overlaps."""
     if not app_state.canvas_comp_map:
@@ -49,15 +52,28 @@ def do_tidy_layout(event=None):
         return "break"
 
     moved, clamped = wiresheet.tidy_layout()
+    multiplier = app_state.meta_scale // app_state.GRID_SIZE
+
     if moved == 0:
         messagebox.showinfo("Tidy Layout", "Nothing to move — no boxes overlap.")
     elif clamped:
         messagebox.showwarning(
             "Tidy Layout",
             f"Repositioned {moved} component(s).\n\n"
-            f"{clamped} hit the coordinate limit of {wiresheet.META_COORD_MAX} grid units "
-            "and were clamped, because meta stores x and y in one byte each. "
-            "Lower the grid size in Preferences to fit more in."
+            f"{clamped} still hit the coordinate limit of {wiresheet.META_COORD_MAX} "
+            "steps, because meta stores x and y in one byte each. This sheet is already "
+            f"laid out at {multiplier} grid squares per step, the widest meta can reach, "
+            "so it does not fit however it is spaced. Split it across sub-sheets."
+        )
+    elif multiplier > 1:
+        messagebox.showinfo(
+            "Tidy Layout",
+            f"Repositioned {moved} component(s)." + NL + NL +
+            f"This sheet needs more width than meta's {wiresheet.META_COORD_MAX} "
+            f"coordinate steps allow at one grid square each, so it is laid out at "
+            f"{multiplier} grid squares per step ({app_state.meta_scale} px). Boxes "
+            f"settle on every {multiplier} grid lines rather than every one. Your grid "
+            "size in Preferences is unchanged."
         )
     return "break"
 
@@ -179,6 +195,12 @@ def on_canvas_click(event):
         app_state.drag_data["y"] = cy
         app_state.selected_canvas_tag = group_tag
 
+        # Where the box starts out. The drag is measured as an offset from this pair
+        # rather than accumulated per motion event, so repeated snapping cannot drift.
+        origin = wiresheet.get_box_origin(group_tag)
+        app_state.drag_data["box_x"] = origin[0] if origin else None
+        app_state.drag_data["box_y"] = origin[1] if origin else None
+
         # Snapshot the pre-drag meta so the move can be pushed as one undoable step.
         dragged = app_state.canvas_comp_map.get(group_tag)
         meta_prop = dragged.find("prop[@name='meta']") if dragged is not None else None
@@ -444,18 +466,40 @@ def on_canvas_drag(event):
         return
 
     canvas = app_state.canvas
+    group_tag = app_state.drag_data["tag"]
     cx = canvas.canvasx(event.x)
     cy = canvas.canvasy(event.y)
 
-    delta_x = cx - app_state.drag_data["x"]
-    delta_y = cy - app_state.drag_data["y"]
-
-    canvas.move(app_state.drag_data["tag"], delta_x, delta_y)
+    box_x = app_state.drag_data.get("box_x")
+    origin = wiresheet.get_box_origin(group_tag)
 
+    if box_x is None or origin is None:
+        # Nothing to align against, so the box just follows the pointer one to one.
+        canvas.move(group_tag, cx - app_state.drag_data["x"], cy - app_state.drag_data["y"])
         app_state.drag_data["x"] = cx
         app_state.drag_data["y"] = cy
+        wiresheet.draw_links()
+        return
 
-    # Wires are not part of the dragged group, so they are re-routed against the new positions.
+    # Snap to whole meta steps, which is the grid on an ordinary sheet and a multiple of
+    # it on one too wide for meta's range -- a position between steps cannot be stored.
+    step = app_state.meta_scale
+    margin = wiresheet.layout_margin(step)
+
+    # Follow the pointer, but land the box on a step every step of the way, and keep it
+    # out of the margin strip along the top and left canvas edges.
+    wanted_x = box_x + (cx - app_state.drag_data["x"])
+    wanted_y = app_state.drag_data["box_y"] + (cy - app_state.drag_data["y"])
+    target_x = max(margin, round(wanted_x / step) * step)
+    target_y = max(margin, round(wanted_y / step) * step)
+
+    shift_x = target_x - origin[0]
+    shift_y = target_y - origin[1]
+
+    if shift_x or shift_y:
+        canvas.move(group_tag, shift_x, shift_y)
+        # Wires are not part of the dragged group, so they are re-routed against the
+        # new positions.
         wiresheet.draw_links()
 
 
@@ -464,16 +508,16 @@ def on_canvas_release(event):
         return
 
     canvas = app_state.canvas
-    grid_size = app_state.GRID_SIZE
+    step = app_state.meta_scale
     group_tag = app_state.drag_data["tag"]
-    outline_item = canvas.find_withtag(f"{group_tag} && block_outline")
+    origin = wiresheet.get_box_origin(group_tag)
 
-    if outline_item:
-        coords = canvas.coords(outline_item[0])
-        current_x, current_y = coords[0], coords[1]
+    if origin is not None:
+        current_x, current_y = origin
 
-        snapped_x = round(current_x / grid_size) * grid_size
-        snapped_y = round(current_y / grid_size) * grid_size
+        margin = wiresheet.layout_margin(step)
+        snapped_x = max(margin, round(current_x / step) * step)
+        snapped_y = max(margin, round(current_y / step) * step)
 
         shift_x = snapped_x - current_x
         shift_y = snapped_y - current_y
@@ -482,8 +526,8 @@ def on_canvas_release(event):
             canvas.move(group_tag, shift_x, shift_y)
             app_state.mark_dirty()
 
-        raw_x = int(snapped_x / grid_size)
-        raw_y = int(snapped_y / grid_size)
+        raw_x = min(wiresheet.META_COORD_MAX, int(round(snapped_x / step)))
+        raw_y = min(wiresheet.META_COORD_MAX, int(round(snapped_y / step)))
 
         comp_element = app_state.canvas_comp_map.get(group_tag)
         if comp_element is not None:
@@ -591,6 +635,22 @@ def open_preferences_dialog():
                     f"{app_state.MAX_ALLOWED_BOX_WIDTH} pixels."
                 )
 
+            # The width cap is applied after each box is fitted to its text, so a cap
+            # that is not a multiple of the grid leaves the widest boxes off-grid.
+            proposed = wiresheet.suggest_box_width_for_grid(width, val)
+            if proposed != width:
+                if not messagebox.askyesno(
+                    "Box Width Off Grid",
+                    f"A box width of {width} px is not a multiple of the {val} px grid, "
+                    f"so the widest boxes would not line up with it.\n\n"
+                    f"Change the box width to {proposed} px?",
+                    parent=dialog,
+                ):
+                    return
+                width = proposed
+                entry_box_width.delete(0, tk.END)
+                entry_box_width.insert(0, str(width))
+
             app_state.BOX_WIDTH = width
             app_state.GRID_SIZE = val
             app_state.ADD_TIMESTAMP = var_timestamp.get()
@@ -693,6 +753,21 @@ def verify_startup_configurations():
             "before trying to view or load profile source files."
         )
         open_preferences_dialog()
+        return
+
+    # editor.properties can be hand-edited, so the pair is reconciled here too.
+    proposed = wiresheet.suggest_box_width_for_grid(app_state.BOX_WIDTH, app_state.GRID_SIZE)
+    if proposed != app_state.BOX_WIDTH and messagebox.askyesno(
+        "Box Width Off Grid",
+        f"The saved box width of {app_state.BOX_WIDTH} px is not a multiple of the "
+        f"{app_state.GRID_SIZE} px grid, so the widest boxes will not line up with it.\n\n"
+        f"Change the box width to {proposed} px?",
+    ):
+        app_state.BOX_WIDTH = proposed
+        app_state.save_preferences()
+        wiresheet.draw_grid()
+        if app_state.active_components_list:
+            wiresheet.render_components(app_state.active_components_list)
 
 
 # --- UI Setup ---
@@ -767,6 +842,8 @@ menu_edit.add_command(label="Undo", command=do_undo, accelerator=f"{accel_mod}+Z
 menu_edit.add_command(label="Redo", command=do_redo, accelerator=f"{accel_mod}+Y")
 menu_edit.add_separator()
 menu_edit.add_command(label="Delete Component", command=delete_selected_component, accelerator="Del")
+menu_edit.add_separator()
+menu_edit.add_command(label="Tidy Layout", command=do_tidy_layout)
 menu_bar.add_cascade(label="Edit", menu=menu_edit)
 
 menu_kits = tk.Menu(menu_bar, tearoff=0)
@@ -776,10 +853,6 @@ menu_kits.add_command(
 )
 menu_bar.add_cascade(label="Kits", menu=menu_kits)
 
-menu_layout = tk.Menu(menu_bar, tearoff=0)
-menu_layout.add_command(label="Tidy Layout", command=do_tidy_layout)
-menu_bar.add_cascade(label="Layout", menu=menu_layout)
-
 menu_app_info = tk.Menu(menu_bar, tearoff=0)
 menu_app_info.add_command(label="App Info", command=show_app_info)
 menu_bar.add_cascade(label="App", menu=menu_app_info)
@@ -993,9 +1066,10 @@ def on_palette_release(event):
     drop_x = canvas.canvasx(event.x_root - canvas.winfo_rootx())
     drop_y = canvas.canvasy(event.y_root - canvas.winfo_rooty())
 
-    grid_size = app_state.GRID_SIZE
-    grid_x = max(0, min(wiresheet.META_COORD_MAX, round(drop_x / grid_size)))
-    grid_y = max(0, min(wiresheet.META_COORD_MAX, round(drop_y / grid_size)))
+    step = app_state.meta_scale
+    min_step = wiresheet.layout_margin(step) // step
+    grid_x = max(min_step, min(wiresheet.META_COORD_MAX, round(drop_x / step)))
+    grid_y = max(min_step, min(wiresheet.META_COORD_MAX, round(drop_y / step)))
 
     sax_file.add_component(kit_name, type_name, grid_x, grid_y)