为了使用户界面更加直观（因为用户很难精确地单击与起点相同的位置），让我们使用以下操作：
- 鼠标左键单击在单击位置的多边形上添加一个点
- 单击鼠标右键完成数据输入，并使程序显示最终填充的多边形
我们需要几个变量来跟踪我们的进度：
- 定义多边形的点的列表。每个点都是一个元组
(x, y)
- 一个布尔标志，表示数据输入何时完成
- 作为奖励，鼠标光标的最后一个已知位置，因此我们可以为当前输入的段（光标后面的一行）设置动画。
当发生适当的鼠标事件时，我们将使用鼠标回调定期更新这些变量：
-
EVENT_MOUSEMOVE-- 鼠标移动了，更新当前位置
-
EVENT_LBUTTONDOWN-- 用户按下鼠标左键，将当前位置添加到点列表中
-
EVENT_RBUTTONDOWN-- 用户按下鼠标右键，将数据输入标记为完成
最后，我们将有一个实现显示循环的函数。
该函数将首先创建一个命名窗口，绘制一个空白画布，并设置鼠标回调。然后它会通过以下方式反复不断更新屏幕：
- 创建一个新的画布图像（在其上绘制）
- 输入点后，使用以下命令绘制连接的线段
cv2.polyline
- 使用不同的颜色绘制从最后输入的点指向当前位置的当前线段
cv2.line.
- 显示新图像。
- 等待一段时间，同时发送窗口消息。
数据输入过程完成后，该函数将绘制最终的填充多边形和干净的画布图像，显示它，并在用户按下某个键时返回最终图像。
代码示例
import numpy as np
import cv2
# ============================================================================
CANVAS_SIZE = (600,800)
FINAL_LINE_COLOR = (255, 255, 255)
WORKING_LINE_COLOR = (127, 127, 127)
# ============================================================================
class PolygonDrawer(object):
def __init__(self, window_name):
self.window_name = window_name # Name for our window
self.done = False # Flag signalling we're done
self.current = (0, 0) # Current position, so we can draw the line-in-progress
self.points = [] # List of points defining our polygon
def on_mouse(self, event, x, y, buttons, user_param):
# Mouse callback that gets called for every mouse event (i.e. moving, clicking, etc.)
if self.done: # Nothing more to do
return
if event == cv2.EVENT_MOUSEMOVE:
# We want to be able to draw the line-in-progress, so update current mouse position
self.current = (x, y)
elif event == cv2.EVENT_LBUTTONDOWN:
# Left click means adding a point at current position to the list of points
print("Adding point #%d with position(%d,%d)" % (len(self.points), x, y))
self.points.append((x, y))
elif event == cv2.EVENT_RBUTTONDOWN:
# Right click means we're done
print("Completing polygon with %d points." % len(self.points))
self.done = True
def run(self):
# Let's create our working window and set a mouse callback to handle events
cv2.namedWindow(self.window_name, flags=cv2.CV_WINDOW_AUTOSIZE)
cv2.imshow(self.window_name, np.zeros(CANVAS_SIZE, np.uint8))
cv2.waitKey(1)
cv2.cv.SetMouseCallback(self.window_name, self.on_mouse)
while(not self.done):
# This is our drawing loop, we just continuously draw new images
# and show them in the named window
canvas = np.zeros(CANVAS_SIZE, np.uint8)
if (len(self.points) > 0):
# Draw all the current polygon segments
cv2.polylines(canvas, np.array([self.points]), False, FINAL_LINE_COLOR, 1)
# And also show what the current segment would look like
cv2.line(canvas, self.points[-1], self.current, WORKING_LINE_COLOR)
# Update the window
cv2.imshow(self.window_name, canvas)
# And wait 50ms before next iteration (this will pump window messages meanwhile)
if cv2.waitKey(50) == 27: # ESC hit
self.done = True
# User finised entering the polygon points, so let's make the final drawing
canvas = np.zeros(CANVAS_SIZE, np.uint8)
# of a filled polygon
if (len(self.points) > 0):
cv2.fillPoly(canvas, np.array([self.points]), FINAL_LINE_COLOR)
# And show it
cv2.imshow(self.window_name, canvas)
# Waiting for the user to press any key
cv2.waitKey()
cv2.destroyWindow(self.window_name)
return canvas
# ============================================================================
if __name__ == "__main__":
pd = PolygonDrawer("Polygon")
image = pd.run()
cv2.imwrite("polygon.png", image)
print("Polygon = %s" % pd.points)
截图
绘图过程中，我们输入了 5 个点，当前线段显示为一条指向鼠标当前位置的深色线：
绘图完成，程序显示整个多边形已填充：
最终图像
控制台输出
Adding point #0 with position(257,144)
Adding point #1 with position(657,263)
Adding point #2 with position(519,478)
Adding point #3 with position(283,383)
Adding point #4 with position(399,126)
Adding point #5 with position(142,286)
Adding point #6 with position(165,38)
Completing polygon with 7 points.
Polygon = [(257, 144), (657, 263), (519, 478), (283, 383), (399, 126), (142, 286), (165, 38)]
