Python-OpenCV-use the mouse as a pen

table of Contents

Create a mouse callback function

Example-draw a circle at the double-click position

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Create a mouse callback function

This function is executed when a mouse event occurs. There is a specific format for creating a mouse callback function, which is the same everywhere. It differs only in function.

View all mouse events

import cv2 as cv
events = [i for i in dir(cv) if 'EVENT' in i]
print(events)

All events are as follows 

    CV_EVENT_MOUSEMOVE      =0,   //鼠标移动
    CV_EVENT_LBUTTONDOWN    =1,   //按下左键
    CV_EVENT_RBUTTONDOWN    =2,   //按下右键
    CV_EVENT_MBUTTONDOWN    =3,   //按下中键
    CV_EVENT_LBUTTONUP      =4,   //放开左键
    CV_EVENT_RBUTTONUP      =5,   //放开右键
    CV_EVENT_MBUTTONUP      =6,   //放开中键
    CV_EVENT_LBUTTONDBLCLK  =7,   //左键双击
    CV_EVENT_RBUTTONDBLCLK  =8,   //右键双击
    CV_EVENT_MBUTTONDBLCLK  =9,   //中键双击
    CV_EVENT_MOUSEWHEEL     =10,  //滚轮滚动
    CV_EVENT_MOUSEHWHEEL    =11   //横向滚轮滚动（还好我鼠标是G502可以这么干）

    CV_EVENT_FLAG_LBUTTON   =1,   //左键拖拽
    CV_EVENT_FLAG_RBUTTON   =2,   //右键拖拽
    CV_EVENT_FLAG_MBUTTON   =4,   //中键拖拽
    CV_EVENT_FLAG_CTRLKEY   =8,   //按住CTRL拖拽
    CV_EVENT_FLAG_SHIFTKEY  =16,  //按住Shift拖拽
    CV_EVENT_FLAG_ALTKEY    =32   //按住ALT拖拽

Learn the use of cv.setMouseCallback( windowName, onMouse, param=None )

This function always runs in the program, anytime when your mouse moves, this function is called

Example-draw a circle at the double-click position

import cv2 as cv
import numpy as np
def draw_circle(event,x,y,flags,param):   ##定义回调函数
    if event == cv.EVENT_LBUTTONDBLCLK: ##左键双击
        cv.circle(img,(x,y),100,(255,0,0),-1)

if __name__ == '__main__':
    img = np.zeros((512,512,3),np.uint8)  ##创建一个黑色图像
    cv.namedWindow("image")    # 创建图像与窗口并将窗口与回调函数绑定
    cv.setMouseCallback("image",draw_circle)
    while(1):
        cv.imshow("image",img)
        if cv.waitKey(20) & 0xFF==27:  ##27是Esc的ASCII码
            break
    cv.destroyAllWindows()