expand leaf nodes (tiling) on the generated json solution

Author: NicolaPerin

src/guillotine/io.py

@@ -104,6 +104,56 @@ def load_problem_json(filepath):
     }
 
 
+def _expand_sequence(seq, w, h, item_sizes):
+    """Recursively expand 'g_X' tiling nodes into explicit X/Y cuts and waste."""
+    if isinstance(seq, str):
+        if seq.startswith("g_"):
+            item_id = int(seq.split("_")[1])
+            iw = item_sizes[0][item_id]
+            ih = item_sizes[1][item_id]
+
+            nx = w // iw
+            ny = h // ih
+
+            if nx < 1 or ny < 1:
+                return "empty"
+
+            used_w = nx * iw
+            used_h = ny * ih
+
+            # Helper to recursively build the grid
+            def build_grid(cols, rows):
+                if cols > 1:
+                    return ("X", iw, build_grid(1, rows), build_grid(cols - 1, rows))
+                if rows > 1:
+                    return ("Y", ih, f"g_{item_id}", build_grid(cols, rows - 1))
+                return f"g_{item_id}"
+
+            tree = build_grid(nx, ny)
+
+            # Trim top waste if the tiling doesn't consume full height
+            if used_h < h:
+                tree = ("Y", used_h, tree, "empty")
+            
+            # Trim right waste if the tiling doesn't consume full width
+            if used_w < w:
+                tree = ("X", used_w, tree, "empty")
+
+            return tree
+        return seq
+
+    direction, z, left, right = seq
+    if direction == "X":
+        return ("X", z,
+                _expand_sequence(left, z, h, item_sizes),
+                _expand_sequence(right, w - z, h, item_sizes))
+    elif direction == "Y":
+        return ("Y", z,
+                _expand_sequence(left, w, z, item_sizes),
+                _expand_sequence(right, w, h - z, item_sizes))
+    return seq
+
+
 def save_solution_json(filepath, value, sequence, item_sizes, defect_sizes, 
                        defect_positions, sheet_size, n_items_orig=None):
     """Save solution to JSON file with all metrics and the full problem definition.
@@ -124,6 +174,9 @@ def save_solution_json(filepath, value, sequence, item_sizes, defect_sizes,
     defect_loss_pct = (defect_area / total_area) * 100
     efficiency_pct = (value / usable_area) * 100 if usable_area > 0 else 0
 
+    # Expand the sequence to explicitly map out tiled items and residual waste
+    expanded_seq = _expand_sequence(sequence, W, H, item_sizes)
+
     output = {
         "problem": _build_problem_dict(item_sizes, defect_sizes, defect_positions, sheet_size),
         "n_items_orig": n_items_orig if n_items_orig is not None else len(item_sizes[0]),
@@ -135,7 +188,7 @@ def save_solution_json(filepath, value, sequence, item_sizes, defect_sizes,
             "utilization": f"{value}/{total_area} ({utilization_pct:.1f}%)",
             "defect_loss": f"{defect_area}/{total_area} ({defect_loss_pct:.1f}%)",
             "efficiency": f"{value}/{usable_area} ({efficiency_pct:.1f}%)",
-            "cut_sequence": _serialize_sequence(sequence)
+            "cut_sequence": _serialize_sequence(expanded_seq)
         }
     }