无法在picturebox中绘制简单的矩形

Question

我有一个能显示图像的图片框。我希望用户能够点击，拖动，鼠标到图像上的一个矩形。比如“我想用我在这张图片上画的矩形来做一些事情”。如果它们再次单击，我希望前面的矩形消失，然后重新开始，或者当我单击按钮以清除他们绘制的突出显示矩形时。

因此，我从msdn示例中找到了一些很好的启动代码，用于创建一个放大橡皮筋矩形，我在下面编辑了一些代码，但我遇到了一些问题：

       Public bHaveMouse As Boolean
Public ptOriginal As Point
Public ptLast As Point
Public rect As Rectangle
Public b_Redraw As Boolean = False


' and Normalize the points and draw the reversible frame.
Private Sub MyDrawReversibleRectangle(ByVal p1 As Point, ByVal p2 As Point)
    Try
        'clear 

        ' Convert the points to screen coordinates.
        p1 = PointToScreen(p1)
        p2 = PointToScreen(p2)
        ' Normalize the rectangle.
        If (p1.X < p2.X) Then
            rect.X = p1.X
            rect.Width = p2.X - p1.X
        Else
            rect.X = p2.X
            rect.Width = p1.X - p2.X
        End If
        If (p1.Y < p2.Y) Then
            rect.Y = p1.Y
            rect.Height = p2.Y - p1.Y
        Else
            rect.Y = p2.Y
            rect.Height = p1.Y - p2.Y
        End If

        If rect.Width > pbZoneImage.Width Then
            rect.Width = pbZoneImage.Width
        End If

        If rect.Height > pbZoneImage.Height Then
            rect.Height = pbZoneImage.Height
        End If

        ' Draw the reversible frame.
        ControlPaint.DrawReversibleFrame(rect, Color.Red, FrameStyle.Thick)
    Catch ex As Exception

    End Try

End Sub

Private Sub pbZoneImage_MouseDown(sender As Object, e As MouseEventArgs) Handles pbZoneImage.MouseDown
    If e.Button <> Windows.Forms.MouseButtons.Left Then
        Exit Sub
    End If

    Try
        ' Make a note that we "have the mouse".
        bHaveMouse = True
        ' Store the "starting point" for this rubber-band rectangle.

        If b_Redraw Then
            If (ptLast.X <> -1) Then
                '     Dim ptCurrent As Point
                'ptCurrent.X = e.X
                'ptCurrent.Y = e.Y
                MyDrawReversibleRectangle(ptOriginal, ptLast)
            End If
            ' Set flags to know that there is no "previous" line to reverse.
            ptLast.X = -1
            ptLast.Y = -1
            ptOriginal.X = -1
            ptOriginal.Y = -1
        End If

        ptOriginal.X = e.X
        ptOriginal.Y = e.Y
        ' Special value lets us know that no previous
        ' rectangle needs to be erased.
        ptLast.X = -1
        ptLast.Y = -1
    Catch ex As Exception

    End Try

End Sub

Private Sub pbZoneImage_MouseMove(sender As Object, e As MouseEventArgs) Handles pbZoneImage.MouseMove
    Dim ptCurrent As Point
    ptCurrent.X = e.X
    ptCurrent.Y = e.Y
    ' If we "have the mouse", then we draw our lines.
    If (bHaveMouse) Then
        ' If we have drawn previously, draw again in
        ' that spot to remove the lines.
        If (ptLast.X <> -1) Then
            MyDrawReversibleRectangle(ptOriginal, ptLast)
        End If
        ' Update last point.
        ptLast = ptCurrent
        ' Draw new lines.
        MyDrawReversibleRectangle(ptOriginal, ptCurrent)
    End If
End Sub

Private Sub pbZoneImage_MouseUp(sender As Object, e As MouseEventArgs) Handles pbZoneImage.MouseUp

    'Try
    '    ' Set internal flag to know we no longer "have the mouse".
    bHaveMouse = False

End Sub

我的问题：有时在绘图时不会删除以前绘制的矩形，或者如果我悬停在某些按钮上(比如退出按钮)，矩形就会消失！我希望他们留下，以便我可以记录开始和结束点的矩形为其他程序。当我点击清晰的矩形按钮时，我希望它们消失，但我觉得我在一些应该非常简单的事情上感到困惑。

另一个问题是，我试图防止矩形溢出外的图片框(Pbzoneimage)。但它确实改变了颜色。

我哪里出错了？有没有更好的方法来画这个呢？

Answer 1

您需要两个位图，一个用于picturebox (img)，另一个用于清除它并绘制矩形(ImgClone)。

Private mouse_Down As Point
Private img As Bitmap
Private imgClone As Bitmap

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    img = My.Resources..... 'or you can load the image from file

    PictureBox1.Image = img 'with this every time you invalidate it draws img to picturebox

    imgClone = CType(PictureBox1.Image.Clone, Bitmap)

End Sub

Private Sub PictureBox1_MouseDown(sender As System.Object, e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseDown
    mouse_Down = e.Location
End Sub

Private Sub PictureBox1_MouseMove(sender As System.Object, e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseMove
    If e.Button = MouseButtons.Left And e.Location <> mouse_Down Then
        DrawRectangle(e.Location)
    End If
End Sub

Private Sub DrawRectangle(ByVal pnt As Point)
    Dim g As Graphics

    g = Graphics.FromImage(img)

    g.DrawImage(imgClone, 0, 0) 'we are clearing img with imgClone. imgClone contains the original image without the rectangles

    If pnt.X = mouse_Down.X Or pnt.Y = mouse_Down.Y Then
        g.DrawLine(Pens.Firebrick, mouse_Down.X, mouse_Down.Y, pnt.X, pnt.Y)

    Else
        g.DrawRectangle(Pens.Firebrick, Math.Min(mouse_Down.X, pnt.X), Math.Min(mouse_Down.Y, pnt.Y),
                    Math.Abs(mouse_Down.X - pnt.X), Math.Abs(mouse_Down.Y - pnt.Y))

    End If

    g.Dispose()

    PictureBox1.Invalidate() 'draw img to picturebox
End Sub

如果需要清除picturebox：

Dim g As Graphics

g = Graphics.FromImage(img)
g.DrawImage(imgClone, 0, 0)

g.Dispose()

PictureBox1.Invalidate()

瓦尔特