import cv2
import numpy as np

cap = cv2.VideoCapture(0)

cap.set(3, 320)
cap.set(4, 240)
cap.set(cv2.CAP_PROP_BUFFERSIZE, 1)

ret, prev_frame = cap.read()
prev_gray = cv2.cvtColor(prev_frame, cv2.COLOR_BGR2GRAY)
prev_gray = cv2.GaussianBlur(prev_gray, (5,5), 0)

while True:
    ret, frame = cap.read()
    if not ret:
        break

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    gray = cv2.GaussianBlur(gray, (5,5), 0)

    # 帧差
    diff = cv2.absdiff(prev_gray, gray)
    diff = cv2.convertScaleAbs(diff, alpha=2.5)

    _, thresh = cv2.threshold(diff, 20, 255, cv2.THRESH_BINARY)

    contours, _ = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

    # ===== 核心：选最大目标 =====
    target = None
    max_area = 0

    for cnt in contours:
        area = cv2.contourArea(cnt)

        if area < 300:  # 过滤噪声
            continue

        if area > max_area:
            max_area = area
            target = cnt

    # ===== 只处理一个目标 =====
    if target is not None:
        x, y, w, h = cv2.boundingRect(target)
        cx = x + w // 2
        cy = y + h // 2

        cv2.rectangle(frame, (x, y), (x+w, y+h), (0, 255, 0), 2)
        cv2.circle(frame, (cx, cy), 5, (0, 0, 255), -1)

        print("唯一目标:", cx, cy, "area:", max_area)

    cv2.imshow("tracking", frame)

    prev_gray = gray.copy()

    if cv2.waitKey(1) & 0xFF == 27:
        break

cap.release()
cv2.destroyAllWindows()