在 PictureBox 上绘制矩形

Question

接下来的代码让您可以用鼠标在窗体中绘制矩形。 为什么不，或者如何在 PictureBox 上绘制？

Public Class Form1
Dim SelectRect As Rectangle = New Rectangle()
Dim ps As Point = New Point()
Dim pe As Point = New Point()

这会捕获矩形的第一次点击、起点或角

Private Sub Form1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseDown
    SelectRect.Width = 0
    SelectRect.Height = 0
    SelectRect.X = e.X
    SelectRect.Y = e.Y
    ps.X = e.X
    ps.Y = e.Y
    pe = ps
End Sub

这部分决定了矩形的宽高：

Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
    If (e.Button = MouseButtons.Left) Then
        ControlPaint.DrawReversibleFrame(Me.RectangleToScreen(SelectRect), Color.Black, FrameStyle.Dashed)
        SelectRect.Width = e.X - SelectRect.X
        SelectRect.Height = e.Y - SelectRect.Y
        ControlPaint.DrawReversibleFrame(Me.RectangleToScreen(SelectRect), Color.Black, FrameStyle.Dashed)
    End If

End Sub

这部分确定最后一个坐标，矩形的第二个角：

Private Sub Form1_MouseUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles MyBase.MouseUp
    Dim g As Graphics = Me.CreateGraphics()
    Dim p As Pen = New Pen(Color.Blue, 2)
    ControlPaint.DrawReversibleFrame(Me.RectangleToScreen(SelectRect), Color.Black, FrameStyle.Dashed)
    g.DrawRectangle(p, SelectRect)
    g.Dispose()
End Sub
   End Class

Answer 1

在Control.DrawReversibleFrame() 提供的指南的帮助下，您的代码使用控件（在本例中为表单）鼠标事件来启用矩形形状的绘制。
您只需为不同的、可绘制的控件（如 PictureBox）定义相同的事件，然后或多或少地重复相同的过程（在清理之后）。

正如许多所说，在这里和之前，使用 Graphics 对象 Paint 事件请提供，以便您的绘图将持续存在。
您从 Control.CreateGraphics() 获得的 Graphics 对象不是 持久性，并且可以在您不想要时擦除/剪切。
仅当您确实计划这样做时才使用它 你知道的原因。

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我添加了一个事件处理程序，用于检查是否按下了 Control Key。
如果按下Control，则添加一个矩形，如果没有，则仅绘制一个矩形。
作为示例，我还包括了一行填充矩形的代码。我认为这很有趣，因为您必须控制无效区域的大小。
注释掉这些代码行以仅绘制框架：

SelectRect.Inflate(CInt(-_pen.Width / 2), CInt(-_pen.Width / 2))
e.Graphics.FillRectangle(_brush, SelectRect)

Dim SelectRect As Rectangle = New Rectangle()
Dim _pen As Pen = New Pen(Color.Green, 4)
Dim _brush As SolidBrush = New SolidBrush(Color.Orange)
Dim _ControlPressed As Boolean = False

Private Sub Form1_KeyDown(sender As Object, e As KeyEventArgs) Handles MyBase.KeyDown
    _ControlPressed = (e.Modifiers And Keys.Control) = Keys.Control
End Sub

Private Sub Form1_KeyUp(sender As Object, e As KeyEventArgs) Handles Me.KeyUp
    _ControlPressed = (e.Modifiers And Keys.Control) = Keys.Control
End Sub


Private Sub PictureBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseDown
    SelectRect.Location = e.Location
    SelectRect.Size = New Size(0, 0)
End Sub

Private Sub PictureBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseMove
    If (e.Button = MouseButtons.Left) Then
        ControlPaint.DrawReversibleFrame(PictureBox1.RectangleToScreen(SelectRect), PictureBox1.BackColor, FrameStyle.Dashed)
        SelectRect.Width = e.X - SelectRect.X
        SelectRect.Height = e.Y - SelectRect.Y
        ControlPaint.DrawReversibleFrame(PictureBox1.RectangleToScreen(SelectRect), PictureBox1.BackColor, FrameStyle.Dashed)
    End If
End Sub

Private Sub PictureBox1_MouseUp(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseUp

    If (e.Y < SelectRect.Y) Then
        SelectRect.Location = If(SelectRect.Location.X > e.X,
                                 New Point(e.X, e.Y), New Point(SelectRect.X, e.Y))
        SelectRect.Size = New Size(Math.Abs(SelectRect.Width), Math.Abs(SelectRect.Height))
    Else
        If SelectRect.Location.X > SelectRect.Right Then
            SelectRect.Location = New Point(e.X, SelectRect.Y)
            SelectRect.Size = New Size(Math.Abs(SelectRect.Width), Math.Abs(SelectRect.Height))
        End If
    End If

    If _ControlPressed Then
        Dim _InflatedRect As Rectangle = New Rectangle(SelectRect.Location, SelectRect.Size)
        _InflatedRect.Inflate(CInt(_pen.Width / 2), CInt(_pen.Width / 2))
        PictureBox1.Invalidate(_InflatedRect)
    Else
        PictureBox1.Invalidate()
    End If

End Sub

Private Sub PictureBox1_Paint(sender As Object, e As PaintEventArgs) Handles PictureBox1.Paint
    'Draw the outer rectangle with the color of _pen
    e.Graphics.DrawRectangle(_pen, SelectRect)

    'Fill the rectangle with the color of _brush
    'It's half Pen.Width smaller so it doesn't erase the contour
    SelectRect.Inflate(CInt(-_pen.Width / 2), CInt(-_pen.Width / 2))
    e.Graphics.FillRectangle(_brush, SelectRect)

End Sub