fix: Use combo bounding boxes for offset calculations

Fixes #70

keymap_drawer/draw/combo.py

@@ -50,13 +50,13 @@ def _draw_line_dendron(self, p_1: Point, p_2: Point, shorten: float) -> None:
         line = f"l{round(diff.x)},{round(diff.y)}"
         self.out.write(f'<path d="{start} {line}" class="combo"/>\n')
 
-    def print_combo(self, combo: ComboSpec, combo_ind: int) -> Point:
+    def print_combo(self, combo: ComboSpec, combo_ind: int) -> tuple[Point, Point]:  # pylint: disable=too-many-locals
         """
         Print SVG code for a rectangle with text representing a combo specification, which contains the key positions
         that trigger it and what it does when triggered. The position of the rectangle depends on the alignment
         specified, along with whether dendrons are drawn going to each key position from the combo.
 
-        Returns the midpoint of the combo box, for bounding box calculations.
+        Returns top-left/bottom-right coordinates of bounding box that contains the combo.
         """
         p_keys = [self.layout.keys[p] for p in combo.key_positions]
         width, height = combo.width or self.cfg.combo_w, combo.height or self.cfg.combo_h
@@ -156,7 +156,11 @@ def print_combo(self, combo: ComboSpec, combo_ind: int) -> Point:
             self.out.write("</g>\n")
 
         self.out.write("</g>\n")
-        return p
+
+        # calculate bounding box coordinates by creating a temporary PhysicalKey
+        combo_key = PhysicalKey(p, width, height, combo.rotation)
+        dims = 0.5 * Point(combo_key.bounding_width, combo_key.bounding_height)
+        return p - dims, p + dims
 
     def print_combos_for_layer(self, combos: Sequence[ComboSpec]) -> tuple[float | None, float | None]:
         """
@@ -166,7 +170,7 @@ def print_combos_for_layer(self, combos: Sequence[ComboSpec]) -> tuple[float | N
         combo_pts = []
         for combo_ind, combo_spec in enumerate(combos):
             combo_pts.append(self.print_combo(combo_spec, combo_ind))
-        return min((p.y for p in combo_pts), default=None), max((p.y for p in combo_pts), default=None)
+        return min((p.y for p, _ in combo_pts), default=None), max((p.y for _, p in combo_pts), default=None)
 
     def create_combo_diagrams(
         self, scale_factor: int, ghost_keys: Sequence[int] | None = None