如何在tkinter中获取<Motion>的方向？

Question

<Motion>我正在尝试了解 tkinter （实际上）事件的方向<B1-Motion>。

\n\n

我已经尝试使用event.direction（错误），event.keysym（??）并且事件本身给了我一些坐标。

\n\n

这是到目前为止我的代码：

\n\n

def holdanddrag(event):\n    print('Direction: '+event.   \xe2\x80\xa6 ) # here I need some help\nWidget.bind('<B1-Motion>', holdanddrag)\n

\n\n

有人知道该怎么办吗？提前致谢！

\n

Answer 1

为了确定方向，您必须存储 a previous position，并使用它来计算 的运动方向（标准化向量）actual position。这些变量必须随着运动的发生而更新。

这是一个小例子，在画布上绘制与鼠标拖动方向相对应的矢量（箭头）：

import math
import tkinter as tk
from collections import deque


class Vector:
    """small class for vector arithmetic convenience
    """ 
    def __init__(self, x: float=0, y: float=0) -> None:
        self.x = x
        self.y = y
    def __str__(self) -> str:
        return f'({self.x}, {self.y})'
    def __mul__(self, scalar: float) -> 'Vector':
        return Vector(self.x * scalar, self.y * scalar)
    def magnitude(self) -> float:
        return math.hypot(self.x, self.y)
    def normalize(self) -> 'Vector':
        mag = self.magnitude()
        return Vector(self.x / mag, self.y / mag) if mag != 0 else Vector()
    def __repr__(self) -> str:
        return str(self)
    def __iter__(self) -> float:
        yield self.x
        yield self.y


class Point:
    """small class for point arithmetic convenience
    """ 
    def __init__(self, x: float, y: float):
        self.x = x
        self.y = y        
    def __sub__(self, other: 'Point') -> Vector:
        return Vector(other.x - self.x, other.y - self.y)
    def __add__(self, vec: Vector) -> 'Point':
        return Point(self.x + vec.x, self.y + vec.y)
    def __str__(self) -> str:
        return f'({self.x}, {self.y})'
    def __repr__(self) -> str:
        return str(self)
    def __iter__(self) -> float:
        yield self.x
        yield self.y

def draw_dir(canvas, start_point: Point, _vid=[None]) -> None:
    """draws and updates the scaled normalized direction vector
    on the canvas.
    Keeps track of the id of the canvas item last drawn 
    """
    if _vid[0] is not None:
        canvas.delete(_vid[0])
    normed_scaled_v = direct.normalize() * -50
    end_point = start_point + normed_scaled_v
    _vid[0] = canvas.create_line(*start_point, *end_point, arrow=tk.LAST)

_maxlen = 4

def direction(event, _direct=deque([Vector(0, 0) for _ in range(_maxlen)], maxlen=_maxlen)) -> None:
    """stores previous position, and uses it to calculate the direction
    from the current position.
    updates these variables
    """
    global direct
    _direct.append(Point(event.x, event.y))
    p0, p1 = _direct[0], _direct[-1]
    direct = p1 - p0
    draw_dir(canvas, p1)    
#     print(_direct, direct)

direct = Vector(0, 0)

root = tk.Tk()
canvas = tk.Canvas(root, bg='cyan')
canvas.pack()
canvas.bind('<B1-Motion>', direction)
root.mainloop()