vtk自定义一个带箭头的直线2d的actor，可设置方向和长度

以下是一个简单的vtk自定义直线2D带箭头的actor示例代码：

import vtk

class ArrowLineActor2D(vtk.vtkActor2D):
    def __init__(self, length=1.0, direction=[1.0, 0.0], arrow_size=0.1):
        super().__init__()
        
        # 创建直线
        self.line_source = vtk.vtkLineSource()
        self.line_source.SetPoint1(0, 0, 0)
        self.line_source.SetPoint2(length*direction[0], length*direction[1], 0)
        
        # 创建箭头
        self.arrow_source = vtk.vtkArrowSource()
        self.arrow_source.SetTipLength(arrow_size)
        self.arrow_source.SetShaftRadius(0.01)
        
        # 创建mapper和actor
        self.mapper = vtk.vtkPolyDataMapper2D()
        self.mapper.SetInputConnection(self.line_source.GetOutputPort())
        self.arrow_mapper = vtk.vtkPolyDataMapper2D()
        self.arrow_mapper.SetInputConnection(self.arrow_source.GetOutputPort())
        self.arrow_actor = vtk.vtkActor2D()
        self.arrow_actor.SetMapper(self.arrow_mapper)
        
        # 设置箭头位置和方向
        arrow_pos = length*direction
        arrow_pos -= arrow_size*direction
        self.arrow_actor.SetPosition(arrow_pos[0], arrow_pos[1])
        self.arrow_actor.SetOrientation(vtk.vtkMath.DegreesFromRadians(
            vtk.vtkMath.AngleBetweenVectors([1, 0, 0], direction)))
        
        # 添加actor
        self.AddPart(self.arrow_actor)
        self.SetMapper(self.mapper)
        
    def SetLength(self, length):
        self.line_source.SetPoint2(length*self.line_source.GetDirection())
        arrow_pos = length*self.line_source.GetDirection()
        arrow_pos -= self.arrow_source.GetTipLength()*self.line_source.GetDirection()
        self.arrow_actor.SetPosition(arrow_pos[0], arrow_pos[1])
        
    def SetDirection(self, direction):
        self.line_source.SetPoint2(self.line_source.GetPoint1() + self.line_source.GetLength()*direction)
        arrow_pos = self.line_source.GetLength()*direction
        arrow_pos -= self.arrow_source.GetTipLength()*direction
        self.arrow_actor.SetPosition(arrow_pos[0], arrow_pos[1])
        self.arrow_actor.SetOrientation(vtk.vtkMath.DegreesFromRadians(
            vtk.vtkMath.AngleBetweenVectors([1, 0, 0], direction)))

这个actor可以通过`SetLength`和`SetDirection`方法来设置长度和方向。例如，可以创建一个长度为2，方向为[1, 1]的箭头直线并添加到vtkRenderer中：

renderer = vtk.vtkRenderer()
renderer.SetBackground(0.2, 0.2, 0.2)

actor = ArrowLineActor2D(length=2.0, direction=[1.0, 1.0])
renderer.AddActor(actor)

render_window = vtk.vtkRenderWindow()
render_window.AddRenderer(renderer)

render_interactor = vtk.vtkRenderWindowInteractor()
render_interactor.SetRenderWindow(render_window)

render_window.Render()
render_interactor.Start()