Reference for ultralytics/solutions/object_counter.py

def display_frames(self):
    """Displays the current frame with annotations and regions in a window."""
    if self.env_check:
        cv2.namedWindow(self.window_name)
        if len(self.reg_pts) == 4:  # only add mouse event If user drawn region
            cv2.setMouseCallback(self.window_name, self.mouse_event_for_region, {"region_points": self.reg_pts})
        cv2.imshow(self.window_name, self.im0)
        # Break Window
        if cv2.waitKey(1) & 0xFF == ord("q"):
            return

def extract_and_process_tracks(self, tracks):
    """Extracts and processes tracks for object counting in a video stream."""
    # Annotator Init and region drawing
    annotator = Annotator(self.im0, self.tf, self.names)

    # Draw region or line
    annotator.draw_region(reg_pts=self.reg_pts, color=(104, 0, 123), thickness=self.tf * 2)

    if tracks[0].boxes.id is not None:
        boxes = tracks[0].boxes.xyxy.cpu()
        clss = tracks[0].boxes.cls.cpu().tolist()
        track_ids = tracks[0].boxes.id.int().cpu().tolist()

        # Extract tracks
        for box, track_id, cls in zip(boxes, track_ids, clss):
            # Draw bounding box
            annotator.box_label(box, label=f"{self.names[cls]}#{track_id}", color=colors(int(track_id), True))

            # Store class info
            if self.names[cls] not in self.class_wise_count:
                self.class_wise_count[self.names[cls]] = {"IN": 0, "OUT": 0}

            # Draw Tracks
            track_line = self.track_history[track_id]
            track_line.append((float((box[0] + box[2]) / 2), float((box[1] + box[3]) / 2)))
            if len(track_line) > 30:
                track_line.pop(0)

            # Draw track trails
            if self.draw_tracks:
                annotator.draw_centroid_and_tracks(
                    track_line,
                    color=colors(int(track_id), True),
                    track_thickness=self.tf,
                )

            prev_position = self.track_history[track_id][-2] if len(self.track_history[track_id]) > 1 else None

            # Count objects in any polygon
            if len(self.reg_pts) >= 3:
                is_inside = self.counting_region.contains(Point(track_line[-1]))

                if prev_position is not None and is_inside and track_id not in self.count_ids:
                    self.count_ids.append(track_id)

                    if (box[0] - prev_position[0]) * (self.counting_region.centroid.x - prev_position[0]) > 0:
                        self.in_counts += 1
                        self.class_wise_count[self.names[cls]]["IN"] += 1
                    else:
                        self.out_counts += 1
                        self.class_wise_count[self.names[cls]]["OUT"] += 1

            # Count objects using line
            elif len(self.reg_pts) == 2:
                if prev_position is not None and track_id not in self.count_ids:
                    # Check if the object's movement segment intersects the counting line
                    if LineString([(prev_position[0], prev_position[1]), (box[0], box[1])]).intersects(
                        self.counting_line_segment
                    ):
                        self.count_ids.append(track_id)

                        # Determine the direction of movement (IN or OUT)
                        direction = (box[0] - prev_position[0]) * (
                            self.counting_region.centroid.x - prev_position[0]
                        )
                        if direction > 0:
                            self.in_counts += 1
                            self.class_wise_count[self.names[cls]]["IN"] += 1
                        else:
                            self.out_counts += 1
                            self.class_wise_count[self.names[cls]]["OUT"] += 1

    labels_dict = {}

    for key, value in self.class_wise_count.items():
        if value["IN"] != 0 or value["OUT"] != 0:
            if not self.view_in_counts and not self.view_out_counts:
                continue
            elif not self.view_in_counts:
                labels_dict[str.capitalize(key)] = f"OUT {value['OUT']}"
            elif not self.view_out_counts:
                labels_dict[str.capitalize(key)] = f"IN {value['IN']}"
            else:
                labels_dict[str.capitalize(key)] = f"IN {value['IN']} OUT {value['OUT']}"

    if labels_dict:
        annotator.display_analytics(self.im0, labels_dict, (104, 31, 17), (255, 255, 255), 10)

def mouse_event_for_region(self, event, x, y, flags, params):
    """
    Handles mouse events for defining and moving the counting region in a real-time video stream.

    Args:
        event (int): The type of mouse event (e.g., cv2.EVENT_MOUSEMOVE, cv2.EVENT_LBUTTONDOWN, etc.).
        x (int): The x-coordinate of the mouse pointer.
        y (int): The y-coordinate of the mouse pointer.
        flags (int): Any associated event flags (e.g., cv2.EVENT_FLAG_CTRLKEY,  cv2.EVENT_FLAG_SHIFTKEY, etc.).
        params (dict): Additional parameters for the function.
    """
    if event == cv2.EVENT_LBUTTONDOWN:
        for i, point in enumerate(self.reg_pts):
            if (
                isinstance(point, (tuple, list))
                and len(point) >= 2
                and (abs(x - point[0]) < 10 and abs(y - point[1]) < 10)
            ):
                self.selected_point = i
                self.is_drawing = True
                break

    elif event == cv2.EVENT_MOUSEMOVE:
        if self.is_drawing and self.selected_point is not None:
            self.reg_pts[self.selected_point] = (x, y)
            self.counting_region = Polygon(self.reg_pts)

    elif event == cv2.EVENT_LBUTTONUP:
        self.is_drawing = False
        self.selected_point = None

def start_counting(self, im0, tracks):
    """
    Main function to start the object counting process.

    Args:
        im0 (ndarray): Current frame from the video stream.
        tracks (list): List of tracks obtained from the object tracking process.
    """
    self.im0 = im0  # store image
    self.extract_and_process_tracks(tracks)  # draw region even if no objects

    if self.view_img:
        self.display_frames()
    return self.im0