如何仅截取椭圆内的区域？

Question

我正在VB.NET中创建一个类似于剪切工具的小程序，我可以截屏任何我想要的区域，前提是它是一个矩形区域。我选择屏幕中的区域并将其另存为图像。这很容易。

我的问题是我希望能够不仅截取矩形（标准矩形区域），而且选择/绘制椭圆并截取其内部部分。见下图：

有没有办法实现这个或任何我可以使用的库？

这是我目前的代码：

Public Class Form3
    Private _bRubberBandingOn As Boolean = False 
    Private _pClickStart As New Point 
    Private _pClickStop As New Point 
    Private _pNow As New Point 

    Private Sub Form3_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseDown
        Me._bRubberBandingOn = Not _bRubberBandingOn

        If Me._bRubberBandingOn Then
            If _pClickStart = Nothing Then _pClickStart = New Point
            _pClickStart.X = e.X
            _pClickStart.Y = e.Y
            _pNow.X = e.X
            _pNow.Y = e.Y
        End If
        Me.Invalidate()
    End Sub

    Private Sub Form3_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove

        If Me._bRubberBandingOn Then
            If _pNow = Nothing Then _pNow = New Point
            Me._pNow.X = e.X
            Me._pNow.Y = e.Y
            Me.Invalidate()
        End If
    End Sub

    Private Sub Form3_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseUp

        Me._bRubberBandingOn = Not Me._bRubberBandingOn
        If Not Me._bRubberBandingOn Then
            If _pClickStop = Nothing Then _pClickStop = New Point
            _pClickStop.X = e.X
            _pClickStop.Y = e.Y
            Me.Invalidate()

        End If
    End Sub

    Private Sub Form3_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
        Dim _rRectangle As New Rectangle
        Dim _penNew As New Pen(Color.Black, 2)

        _rRectangle.X = _pClickStart.X
        _rRectangle.Y = _pClickStart.Y

        If Me._bRubberBandingOn Then
            _rRectangle.Width = Me._pNow.X - _pClickStart.X
            _rRectangle.Height = Me._pNow.Y - _pClickStart.Y
        Else 
            _rRectangle.Width = Me._pClickStop.X - _pClickStart.X
            _rRectangle.Height = Me._pClickStop.Y - _pClickStart.Y

        End If
        _penNew.DashStyle = Drawing2D.DashStyle.Solid
        e.Graphics.DrawEllipse(_penNew, _rRectangle)

    End Sub
End Class

有没有办法实现这个或任何我可以使用的库？ 有没有办法获得绘制的线条/形状的句柄，然后用它来创建截图？我实际上搜索了这个，但没有找到任何有意义的东西。 提前感谢您的时间。

Answer 1

将您正在绘制椭圆的图像放在上面并执行以下操作：

Dim theBitmap As Bitmap = DirectCast(Image.FromFile("PathToFileYouAreDrawingEllipseOn.bmp"), Bitmap)
Dim theEllipseBitmap As New Bitmap(theBitmap.Width, theBitmap.Height)
Dim theGraphics As Graphics = Graphics.FromImage(theEllipseBitmap)
Dim theGraphicsPath As New GraphicsPath()

' The (10,10) coordinates here are made up, you will need to take what is drawn by the user (starting x,y; ending x,y, etc.)
theGraphicsPath.AddEllipse(10, 10, theBitmap.Width - 20, theBitmap.Height - 20)
theGraphics.Clear(Color.Magenta)
theGraphics.SetClip(theGraphicsPath)
theGraphics.DrawImage(theBitmap, New Rectangle(0, 0, theBitmap.Width, theBitmap.Height), 0, 0, theBitmap.Width, theBitmap.Height, _
GraphicsUnit.Pixel)
theGraphics.Dispose()
theEllipseBitmap.MakeTransparent(Color.Magenta)

' Save the ellipse bitmap to a PNG file format
string fileName = "PathToYourDesiredOutput.png"
theEllipseBitmap.Save(fileName, System.Drawing.Imaging.ImageFormat.Png)