Shift the robot centre point to its body's center. Allow offset around it body when moving

app.py

@@ -207,7 +207,7 @@ class Robot:
         if self.png.shape[-1] != 4:
             raise ValueError("Sprite image must have 4 channels (RGBA)")
         self.png = np.array(Image.open(sprite).convert("RGBA").resize((40,40)))
-        self.pos = [0,0]; self.speed=speed
+        self.pos = [20,20]; self.speed=speed
     def step(self, path):
         while path:
             dx, dy = path[0][0] - self.pos[0], path[0][1] - self.pos[1]
@@ -482,26 +482,26 @@ def _pipeline(uid,img_path):
             cv2.circle(frame, (x, y), 6, color, -1)
         # Robot displacement
         robot.step(path)
-        rx, ry = robot.pos
         sp = robot.png
-        # Calculate actual available space (clamp to 640x640)
-        h, w = frame.shape[:2]
-        end_x = min(rx + 40, w)
-        end_y = min(ry + 40, h)
-        crop_w = end_x - rx
-        crop_h = end_y - ry
-        # Crop sprite and alpha accordingly
-        sprite_rgb = sp[:crop_h, :crop_w, :3]
-        alpha = sp[:crop_h, :crop_w, 3] / 255.0
+        sprite_h, sprite_w = sp.shape[:2]
+        rx, ry = robot.pos
+        x1, y1 = rx - sprite_w // 2, ry - sprite_h // 2
+        x2, y2 = x1 + sprite_w, y1 + sprite_h
+        # Clip boundaries to image size
+        x1_clip, x2_clip = max(0, x1), min(frame.shape[1], x2)
+        y1_clip, y2_clip = max(0, y1), min(frame.shape[0], y2)
+        # Adjust sprite crop accordingly
+        sx1, sy1 = x1_clip - x1, y1_clip - y1
+        sx2, sy2 = sprite_w - (x2 - x2_clip), sprite_h - (y2 - y2_clip)
+        sprite_crop = sp[sy1:sy2, sx1:sx2]
+        alpha = sprite_crop[:, :, 3] / 255.0
         alpha = np.stack([alpha] * 3, axis=-1)
-        # Crop background region
-        bgroi = frame[ry:end_y, rx:end_x]
-        blended = (alpha * sprite_rgb + (1 - alpha) * bgroi).astype(np.uint8)
-        # Update frame with blended result
-        frame[ry:end_y, rx:end_x] = blended
+        bgroi = frame[y1_clip:y2_clip, x1_clip:x2_clip]
+        blended = (alpha * sprite_crop[:, :, :3] + (1 - alpha) * bgroi).astype(np.uint8)
+        frame[y1_clip:y2_clip, x1_clip:x2_clip] = blended
         # collection check
         for o in objs:
-            if not o["col"] and np.hypot(o["pos"][0]-rx,o["pos"][1]-ry)<=20:
+            if not o["col"] and np.hypot(o["pos"][0]-robot.pos[0], o["pos"][1]-robot.pos[1]) <= 20:
                 o["col"]=True
         vw.write(frame)
         if all(o["col"] for o in objs): break