Mouse as a Paint-Brush

1回调函数

cv2.setMouseCallback(windowName, onMouse [, param])

• windowName：显示窗口名称
• onMouse：鼠标响应处理函数

鼠标回调函数，该函数在鼠标事件发生时执行。 鼠标事件可以是与鼠标相关的任何内容，如左键向下，左键向上，左键双击等。它为我们提供了每个鼠标事件的坐标（x，y）。 通过这个活动和地点，我们可以做任何我们喜欢的事情。

下面代码输出了鼠标事件的种类
代码：

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

输出

['EVENT_FLAG_ALTKEY', 'EVENT_FLAG_CTRLKEY', 'EVENT_FLAG_LBUTTON', 'EVENT_FLAG_MBUTTON', 'EVENT_FLAG_RBUTTON', 'EVENT_FLAG_SHIFTKEY', 'EVENT_LBUTTONDBLCLK', 'EVENT_LBUTTONDOWN', 'EVENT_LBUTTONUP', 'EVENT_MBUTTONDBLCLK', 'EVENT_MBUTTONDOWN', 'EVENT_MBUTTONUP', 'EVENT_MOUSEHWHEEL', 'EVENT_MOUSEMOVE', 'EVENT_MOUSEWHEEL', 'EVENT_RBUTTONDBLCLK', 'EVENT_RBUTTONDOWN', 'EVENT_RBUTTONUP']

应用一

创建了一个简单的应用程序，只要我们双击它就可以在图像上绘制一个圆圈.
代码：

import numpy as np
import cv2# mouse callback function
def draw_circle(event,x,y,flags,param):if event == cv2.EVENT_LBUTTONDBLCLK:cv2.circle(img,(x,y),100,(255,0,0),-1)# Create a black image, a window and bind the function to window
img = np.zeros((512,512,3), np.uint8)
cv2.namedWindow('image')
cv2.setMouseCallback('image',draw_circle)while(1):cv2.imshow('image',img)if cv2.waitKey(20) & 0xFF == 27:break
cv2.destroyAllWindows()

双击鼠标左键：

应用二

通过拖动鼠标绘制矩形或圆形（取决于我们选择的模式），就像在Paint应用程序中一样。 所以我们的鼠标回调函数有两个部分，一个用于绘制矩形，另一个用于绘制圆形.在主循环中，设置键'm'设置键盘绑定以在矩形和圆之间切换.

代码：

import numpy as np
import cv2drawing = False # true if mouse is pressed
mode = True # if True, draw rectangle. Press 'm' to toggle to curve
ix,iy = -1,-1# mouse callback function
def draw_circle(event,x,y,flags,param):global ix,iy,drawing,modeif event == cv2.EVENT_LBUTTONDOWN:drawing = Trueix,iy = x,yelif event == cv2.EVENT_MOUSEMOVE:if drawing == True:if mode == True:cv2.rectangle(img,(ix,iy),(x,y),(0,255,0),-1)else:cv2.circle(img,(x,y),5,(0,0,255),-1)elif event == cv2.EVENT_LBUTTONUP:drawing = Falseif mode == True:cv2.rectangle(img,(ix,iy),(x,y),(0,255,0),-1)else:cv2.circle(img,(x,y),5,(0,0,255),-1)img = np.zeros((512,512,3), np.uint8)
cv2.namedWindow('image')
cv2.setMouseCallback('image',draw_circle)while(1):cv2.imshow('image',img)k = cv2.waitKey(1) & 0xFFif k == ord('m'):mode = not modeelif k == 27:breakcv2.destroyAllWindows()

按住鼠标左键滑动

按“m”键，再次按住鼠标左键滑动