Draw on a picturebox image using mouse vb.net

Question

如何使用vb.net中的鼠标在线条或画笔上绘制图片框图像？

Answer 1

Converted a similar question from C# to VB.NET, using a line - tested and working:

Private _Previous As System.Nullable(Of Point) = Nothing
Private Sub pictureBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseDown
  _Previous = e.Location
  pictureBox1_MouseMove(sender, e)
End Sub

Private Sub pictureBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseMove
  If _Previous IsNot Nothing Then
    If PictureBox1.Image Is Nothing Then
      Dim bmp As New Bitmap(PictureBox1.Width, PictureBox1.Height)
      Using g As Graphics = Graphics.FromImage(bmp)
        g.Clear(Color.White)
      End Using
      PictureBox1.Image = bmp
    End If
    Using g As Graphics = Graphics.FromImage(PictureBox1.Image)
      g.DrawLine(Pens.Black, _Previous.Value, e.Location)
    End Using
    PictureBox1.Invalidate()
    _Previous = e.Location
  End If
End Sub

Private Sub pictureBox1_MouseUp(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseUp
  _Previous = Nothing
End Sub

Answer 2

I have modified your code to place a "dot", which can be moved (overwritten) on mouse click

What I need is this to be used for more than one "dot", say four.

The user selects a marker from the list, and places it on the picture box, they then select another and place in a different location, however it overwrites the previous marker.

Marker = Lst_Markers.SelectedIndex + 1
If _Previous IsNot Nothing Then
  For i As Integer = 0 To Marker
    Dim bmp As New Bitmap(PictureBox1.Width, PictureBox1.Height)
    PictureBox1.Image = bmp
  Next
  Select Case Marker
    Case 1
      'PictureBox1.Image = bmp1
      Using g As Graphics = Graphics.FromImage(PictureBox1.Image)
        g.FillEllipse(Brushes.Red, e.X, e.Y, 10, 10)
      End Using
    Case 2
      'PictureBox1.Image = bmp2
      Using g As Graphics = Graphics.FromImage(PictureBox1.Image)
        g.FillEllipse(Brushes.Yellow, e.X, e.Y, 10, 10)
      End Using
    Case 3
      'PictureBox1.Image = bmp3
      Using g As Graphics = Graphics.FromImage(PictureBox1.Image)
        g.FillEllipse(Brushes.Green, e.X, e.Y, 10, 10)
      End Using
    Case 4
      'PictureBox1.Image = bmp4
      Using g As Graphics = Graphics.FromImage(PictureBox1.Image)
        g.FillEllipse(Brushes.Blue, e.X, e.Y, 10, 10)
      End Using
    Case Else
      MsgBox("Select a marker")
  End Select
  PictureBox1.Invalidate()
  _Previous = e.Location
End If