Flag unreachable as yellow:

app.py

@@ -137,7 +137,13 @@ def build_masks(seg):
     return water_mask, garbage_mask, movable_mask
 
 # Garbage mask can be highlighted in red
-def highlight_chunk_masks_on_frame(frame, labels, objs, color_uncollected=(0, 0, 128), color_collected=(0, 128, 0), alpha=0.8):
+def highlight_chunk_masks_on_frame(
+    frame, labels, objs,
+    color_uncollected=(0, 0, 128),
+    color_collected=(0, 128, 0),
+    color_unreachable=(0, 255, 255), 
+    alpha=0.8
+):
     """
     Overlays semi-transparent colored regions for garbage chunks on the frame.
     `objs` must have 'pos' and 'col' keys. The collection status changes the overlay color.
@@ -150,8 +156,13 @@ def highlight_chunk_masks_on_frame(frame, labels, objs, color_uncollected=(0, 0,
             continue
         mask = (labels == lab).astype(np.uint8)
         contours, _ = cv2.findContours(mask, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
-        color = color_collected if obj["col"] else color_uncollected
-        # drawContours on overlay
+        # Choose color based on status
+        if obj.get("unreachable"):
+            color = color_unreachable
+        elif obj["col"]:
+            color = color_collected
+        else:
+            color = color_uncollected        # drawContours on overlay
         cv2.drawContours(overlay, contours, -1, color, thickness=cv2.FILLED)
     # Blend overlay with original frame using alpha
     return cv2.addWeighted(overlay, alpha, frame, 1 - alpha, 0)
@@ -201,32 +212,29 @@ def knn_path(start, targets, occ):
     reachable = []; unreachable = []
     while todo:
         # KNN follow a Greedy approach, which may not guarantee shortest path, hence only use A*
-        # nbrs = NearestNeighbors(n_neighbors=1).fit(todo)
-        # _,idx = nbrs.kneighbors([cur]); nxt=tuple(todo[idx[0][0]])
-        # seg  = astar(cur, nxt, occ)
-        # if seg:
-        #     if path and seg[0]==path[-1]: seg=seg[1:]
-        #     path.extend(seg)
-        # cur  = nxt; todo.remove(list(nxt))
         best = None
         best_len = float('inf')
         best_seg = []
         # Try A* to each target, find shortest actual path
         for t in todo:
             seg = astar(cur, tuple(t), occ)
-            if seg: # and len(seg) < best_len: # index error?
+            if seg and len(seg) < best_len: # index error?
                 best = tuple(t)
                 best_len = len(seg)
                 best_seg = seg
         if not best:
-            print("⚠️ Some garbage unreachable")
-            break  # stop if no reachable targets left
+            # All remaining in `todo` are unreachable
+            for u in todo:
+                print(f"⚠️ Garbage unreachable at {u}")
+                unreachable.append(u)
+            break  # no more reachable targets   
         if path and path[-1] == best_seg[0]:
-            best_seg = best_seg[1:]  # avoid duplicate point
+            best_seg = best_seg[1:]  # skip duplicate
         path.extend(best_seg)
+        reachable.append(list(best))
         cur = best
         todo.remove(list(best))
-    return path
+    return path, unreachable
 
 
 # ── Robot sprite/class -──────────────────────────────────────────────────
@@ -488,18 +496,28 @@ def _pipeline(uid,img_path):
     robot = Robot(SPRITE)
     # Robot will be spawn on the closest movable mask to top-left
     robot.pos = [spawn_x, spawn_y]
-    path  = knn_path(robot.pos, centres, movable_mask)
+    path, unreachable  = knn_path(robot.pos, centres, movable_mask)
+    if unreachable:
+        print(f"⚠️ Unreachable garbage chunks at: {unreachable}")
 
     # 4- Video synthesis
     out_tmp=f"{OUTPUT_DIR}/{uid}_tmp.mp4"
     vw=cv2.VideoWriter(out_tmp,cv2.VideoWriter_fourcc(*"mp4v"),10.0,(640,640))
-    objs=[{"pos":p,"col":False} for p in centres]
+    objs = [{"pos": p, "col": False, "unreachable": False} for p in centres if p not in unreachable]
+    objs += [{"pos": p, "col": False, "unreachable": True} for p in unreachable]
     bg = bgr.copy()
     for _ in range(15000): # safety frames
         frame=bg.copy()
         # Draw garbage chunk masks in red-to-green (semi-transparent)
-        frame = highlight_chunk_masks_on_frame(frame, labels, objs)                               # 🔴 garbage overlay
-        frame = highlight_water_mask_on_frame(frame, water_mask)  # 🔵 water overlay
+        frame = highlight_chunk_masks_on_frame(
+            frame,
+            labels,
+            objs,
+            color_uncollected=(0, 0, 128),     # 🔴
+            color_collected=(0, 128, 0),       # 🟢
+            color_unreachable=(0, 255, 255)    # 🟡
+        )                                                        # 🔴 garbage overlay
+        frame = highlight_water_mask_on_frame(frame, water_mask) # 🔵 water overlay
         # Draw object detections as red (to green) dots
         for o in objs:
             color = (0, 0, 128) if not o["col"] else (0, 128, 0)