海龟子类不画直线

Question

我正在尝试构建一个继承自 turtle.Turtle 类的子类，并希望创建一个函数来自动绘制多边形。但我发现初始线总是有点倾斜。 不知道哪里出了问题。

代码如下：

import turtle

class Polygon(turtle.Turtle):
    def __init__(self, point_list):
        self.point_list = point_list

    def add_point(self, point):
        self.point_list.append(point)
        return self.point_list

    def over_write_points(self, new_points):
        self.point_list = new_points
        return self.point_list

    def perimeter(self):
        length_peri = 0
        for i in range(len(self.point_list)):
            point1 = self.point_list[i-1]
            point2 = self.point_list[i]
            x1, y1 = point1
            x2, y2 = point2
            length = ((x1 - x2)**2 + (y1 - y2)**2)*0.5
            length_peri += length
        return length_peri

    def area(self):
        area = 0
        for i in range(len(self.point_list)):
            point1 = self.point_list[i-1]
            point2 = self.point_list[i]
            x1, y1 = point1
            x2, y2 = point2
            trapezoid = ((x2 - x1) * (y1 + y2)) / 2
            area = area + trapezoid
        area = abs(area)
        return area

    def bound_points(self):
        unzip_list = list(zip(*self.point_list))
        x_list = unzip_list[0]
        y_list = unzip_list[1]
        bound1 = max(x_list), min(y_list)
        bound2 = max(x_list), max(y_list)
        bound3 = min(x_list), max(y_list)
        bound4 = min(x_list), min(y_list)
        bound_points = [bound1, bound2, bound3, bound4]
        return bound_points

    def move_poly(self, dx, dy):
        new_point_list = []
        for i in self.point_list:
            x = i[0] + dx
            y = i[1] + dy
            new_point = (x, y)
            new_point_list.append(new_point)
        self.point_list = new_point_list
        return self.point_list

    def draw_poly(self, lineColour="green", fillColour="yellow"):
        start = self.point_list[-1]
        turtle.pencolor(lineColour)
        turtle.fillcolor(fillColour)

        turtle.penup()
        turtle.pendown()
        turtle.begin_fill()

        x, y = start
        for point in self.point_list:  # go through a list of points
            dx, dy = point
            turtle.goto(x + dx, y + dy)

        turtle.end_fill()
        turtle.penup()
        turtle.mainloop()
        return f'The polygon is finished'


    test_polygon = Polygon([(50,0), (50,50), (0,50)])
    print(test_polygon.add_point((0, 0)))
    print(test_polygon.over_write_points([(100,0), (100,100), (0,100), (0,0)]))
    print(test_polygon.perimeter())
    print(test_polygon.area())
    print(test_polygon.bound_points())
    print(test_polygon.move_poly(-10,-10))
    print(test_polygon.draw_poly())

Answer 1

您的代码中有几个问题。首先，正如@martineau 所说（+1），您从海龟的起始位置开始绘制，而不是列表中的第一个位置。 （并且您需要通过返回第一个位置来关闭多边形。）

perimeter() 函数中的数学运算似乎有误：

length = ((x1 - x2)**2 + (y1 - y2)**2)*0.5

这应该是**0.5 来计算平方根，而不是一半。您忘记在 __init__ 函数中调用 super()。

另外，您的draw_poly() 正在调用模块turtle 中的函数，而不是调用self 上的方法。这就是为什么我使用import Screen, Turtle 而不是import turtle，只是为了避免这个错误。

以下是通过上述和其他修复对您的代码进行的返工：

from turtle import Turtle

class Polygon(Turtle):
    def __init__(self, point_list):
        super().__init__()

        self.point_list = point_list

    def add_point(self, point):
        self.point_list.append(point)

        return self.point_list

    def over_write_points(self, new_points):
        self.point_list[:] = new_points  # reload existing list

        return self.point_list

    def perimeter(self):
        length_peri = 0

        for i in range(len(self.point_list)):
            point1 = self.point_list[i - 1]
            point2 = self.point_list[i]
            x1, y1 = point1
            x2, y2 = point2
            length = ((x1 - x2)**2 + (y1 - y2)**2)**0.5
            length_peri += length

        return length_peri

    def area(self):
        area = 0

        for i in range(len(self.point_list)):
            point1 = self.point_list[i - 1]
            point2 = self.point_list[i]
            x1, y1 = point1
            x2, y2 = point2
            trapezoid = ((x2 - x1) * (y1 + y2)) / 2
            area += trapezoid

        return abs(area)

    def bound_points(self):
        unzip_list = list(zip(*self.point_list))

        x_list = unzip_list[0]
        y_list = unzip_list[1]

        bound1 = max(x_list), min(y_list)
        bound2 = max(x_list), max(y_list)
        bound3 = min(x_list), max(y_list)
        bound4 = min(x_list), min(y_list)

        return [bound1, bound2, bound3, bound4]

    def move_poly(self, dx, dy):
        new_point_list = []

        for x, y in self.point_list:
            new_point = (x + dx, y + dy)
            new_point_list.append(new_point)

        return self.over_write_points(new_point_list)

    def draw_poly(self, lineColour='green', fillColour='yellow'):
        self.pencolor(lineColour)
        self.fillcolor(fillColour)

        start, *remaining_points = self.point_list

        self.penup()
        self.goto(start)
        self.pendown()

        self.begin_fill()

        for point in remaining_points:  # go through a list of points
            self.goto(point)

        self.goto(start)
        self.end_fill()
        self.penup()

        return 'The polygon is finished'

if __name__ == '__main__':
    from turtle import Screen

    screen = Screen()

    test_polygon = Polygon([(50, 0), (50, 50), (0, 50)])
    print(test_polygon.add_point((0, 0)))
    print(test_polygon.over_write_points([(100, 0), (100, 100), (0, 100), (0, 0)]))
    print(test_polygon.perimeter(), "pixels")
    print(test_polygon.area(), "pixels squared")
    print(test_polygon.bound_points())
    print(test_polygon.move_poly(-10, -10))
    print(test_polygon.draw_poly())

    screen.exitonclick()