Trackbar

1.1

回调函数

定义：由系统调用，由用户实现

1.2

信号和消息循环

Ø GUI 编程中常用消息循环阻塞主线程，使其一直处于侦听事件状态

Ø 利用消息路由机制分辨出用户触发了哪类消息，用来调用用户自己实现回

调函数

import cv2 as cv
import argparse

alpha_slider_max=100
title_window='Linear Blend'
def on_trackbar(val):
    alpha=val/alpha_slider_max
    beta=(1.0-alpha)
    dst=cv.addWeighted(src1,alpha,src2,beta,0.0)
    cv.imshow(title_window,dst)

src1=cv.imread('D:/lena.jpg')
src2=cv.imread('D:/box.png')
if src1 is None:
    print('Could not open or find the image:',args.input1)
    exit(0)
if src2 is None:
    print('Could not open or find the image:',args.input2)
    exit(0)

src2=cv.resize(src2,(500,496))
cv.namedWindow(title_window)
trackbar_name='Alpha x %d'%alpha_slider_max
cv.createTrackbar(trackbar_name,title_window,0,alpha_slider_max,on_trackbar)
# Show some stuff
on_trackbar(0)
# Wait untill user press some key
cv.waitKey()