试图在 OpenCV 读取的图像上画线，但没有画线

Question

I build a simple code that showing image through openCV window and using setmousecallback function, I want to draw a horizontal line on the open cv image. However even though there is no error alarm, no line was shown on the image. I think I made mistake, but as I know I can't find. please let me know why a line can't be drawn on the "src" image.

import cv2 
import numpy as np 

x_start, y_start, x_end, y_end = -1,-1,-1,-1
drawing = False

def line_draw(event, x,y, flags, param):

    global x_start, y_start, x_end, y_end, drawing  

    if event == cv2.EVENT_LBUTTONDOWN:
        drawing = True
        x_start, y_start = x,y
        print("up")
    elif event == cv2.EVENT_MOUSEMOVE:
        if drawing == True:
            cv2.line(src,(10,y),(500,y),(255,0,0),1)
            print("move")

    elif event == cv2.EVENT_LBUTTONUP:
        drawing = False
        cv2.line(src,(10,y),(500,y),(255,0,0),1)
        print("up")


src = cv2.imread("d:/sample.jpg")
cv2.namedWindow("image_window")
cv2.imshow("image_window", src)
cv2.setMouseCallback("image_window", line_draw)

cv2.waitKey(0)
cv2.destroyAllWindows()

Answer 1

Try this:

...
...
    elif event == cv2.EVENT_MOUSEMOVE:
        if drawing == True:
            src = cv2.line(src,(10,y),(500,y),(255,0,0),1)
            print("move")