#创建画布
img=np.zeros((300,512,3),np.uint8)
#给画布命名——需要提供给Trackbar
cv.namedWindow("image")
#创建RGB三种颜色的Trackbar，返回函数不需要做任何动作
cv.createTrackbar("R","image",0,255,nothing)
cv.createTrackbar("G","image",0,255,nothing)
cv.createTrackbar("B","image",0,255,nothing)
#由于OpenCv里面无按钮函数，所以用0/1来表示开关
switch="0:OFF\n1:ON"
cv.createTrackbar(switch,"image",0,1,nothing)
#回调函数，不需要做任何操作
def nothing(x):
 pass

#设置一个是否开始画画的开关
drawing=False
#定义画画函数
def draw(event,x,y,flag,param):
 #将画画开关作为全局变量，以便于在每次动作以后改变它的值
 global drawing
 #使用函数cv.EVENT_LBUTTONDOWN，如果鼠标左键按下，画圆，同时drawing为真
 if event==cv.EVENT_LBUTTONDOWN:
  cv.circle(img,(x,y),3,(g,b,r),-1)
  drawing=True
 #如果鼠标移动，进行下面操作
 elif event==cv.EVENT_MOUSEMOVE:
  #如果drawing为真，开始画圆
  if drawing==True:
   cv.circle(img, (x, y), 3, (g, b, r), -1)
 #如果鼠标左键抬起，画最后一个圆，并将drawing设为False，此时就会停止画画
 elif event==cv.EVENT_LBUTTONUP:
  cv.circle(img,(x,y),3,(g,b,r),-1)
  drawing=False

while(1):
 #展示画布
 cv.imshow("image",img)
 #设置终止按钮，为了保证在32/64位系统或者在不是ASCII编码的键盘上有正常的操作，使用&0xFF取低八位
 k=cv.waitKey(1)&0xFF
 #如果k为27，即键盘上Esc的ASCII编码序号，退出画板
 if k==27:
  break
 #获取每个Trackbar中的值
 r=cv.getTrackbarPos("R","image")
 g = cv.getTrackbarPos("G", "image")
 b = cv.getTrackbarPos("B", "image")
 s = cv.getTrackbarPos(switch, "image")
 #如果开关是0，清空画板并禁止画画，如果是1，则允许
 if s==0:
  img[:]=0
 else:
  cv.setMouseCallback("image", draw)
#最后不要忘记销毁窗口
cv.destroyAllWindows()

import cv2 as cv
import numpy as np

def nothing(x):
 pass
img=np.zeros((300,512,3),np.uint8)
cv.namedWindow("image")
cv.createTrackbar("R","image",0,255,nothing)
cv.createTrackbar("G","image",0,255,nothing)
cv.createTrackbar("B","image",0,255,nothing)
switch="0:OFF\n1:ON"
cv.createTrackbar(switch,"image",0,1,nothing)

drawing=False
def draw(event,x,y,flag,param):
 global drawing
 if event==cv.EVENT_LBUTTONDOWN:
  cv.circle(img,(x,y),3,(g,b,r),-1)
  drawing=True
 elif event==cv.EVENT_MOUSEMOVE:
  if drawing==True:
   cv.circle(img, (x, y), 3, (g, b, r), -1)
 elif event==cv.EVENT_LBUTTONUP:
  cv.circle(img,(x,y),3,(g,b,r),-1)
  drawing=False

while(1):
 cv.imshow("image",img)
 k=cv.waitKey(1)&0xFF
 if k==27:
  break
 r=cv.getTrackbarPos("R","image")
 g = cv.getTrackbarPos("G", "image")
 b = cv.getTrackbarPos("B", "image")
 s = cv.getTrackbarPos(switch, "image")
 if s==0:
  img[:]=0
 else:
  cv.setMouseCallback("image", draw)
cv.destroyAllWindows()