Рисование в графическом окне

Public Class Form1
    Dim gr As Graphics
    Dim bmp As Bitmap
    Dim pen As Pen
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
        bmp = New Bitmap(PictureBox1.Width, PictureBox1.Height)
        gr = Graphics.FromImage(bmp)
        PictureBox1.Image = bmp
    End Sub
    Private Sub Button1_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        'рисуем на Bitmap
        pen = New Pen(Color.Red, 10)
        Me.gr.DrawLine(pen, 20, 20, 200, 200)
        pen = New Pen(Color.Green, 10)
        Me.gr.DrawLine(pen, 200, 20, 20, 200)
        'Bitmap на PictureBox
        PictureBox1.Refresh()     'или:        PictureBox1.Image = bmp
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        'рисуем на PictureBox
        Dim grPB As Graphics = PictureBox1.CreateGraphics
        pen = New Pen(Color.Red, 10)
        grPB.DrawLine(pen, 20, 20, 200, 200)
        pen = New Pen(Color.Green, 10)
        grPB.DrawLine(pen, 200, 20, 20, 200)
    End Sub
End Class

Imports System.Runtime.InteropServices
 
Public Class Form1
    <StructLayout(LayoutKind.Sequential)> _
    Public Structure POINTAPI
        Dim x As Integer
        Dim y As Integer
    End Structure
    Public Declare Function SetROP2 Lib "gdi32.DLL" Alias "SetROP2" (
       ByVal hdc As Integer,
       ByVal nDrawMode As Integer) As Integer
    Public Declare Function CreatePen Lib "gdi32.DLL" Alias "CreatePen" (
        ByVal nPenStyle As Integer,
        ByVal nWidth As Integer,
        ByVal crColor As Integer) As Integer
    Public Declare Function SelectObject Lib "gdi32.DLL" Alias "SelectObject" (
        ByVal hdc As Integer,
        ByVal hObject As Integer) As Integer
    Public Declare Function MoveToEx Lib "gdi32.DLL" Alias "MoveToEx" (
        ByVal hdc As Integer,
        ByVal x As Integer,
        ByVal y As Integer,
        ByRef lpPoint As POINTAPI) As Integer
    Public Declare Function LineTo Lib "gdi32.DLL" Alias "LineTo" (
        ByVal hdc As Integer,
        ByVal xEnd As Integer,
        ByVal yEnd As Integer) As Integer
    Dim prevPt As POINTAPI
    Dim bmp As Bitmap
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        bmp = New Bitmap(PictureBox1.Width, PictureBox1.Height)
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        'XOR-рисование  не работает, но линия уже не стирается при перерисовке
        Dim gr As Graphics = Graphics.FromImage(bmp)
 
        Dim hDC As IntPtr = gr.GetHdc  'Получаем дескриптор контекста устройства, связанный с данным объектом Graphics.
        SetROP2(hDC, 7) 'Задаём режим рисования (Copy Pen, Xor Pen, ...)
        Dim pen As IntPtr = CreatePen(0, 10, ColorTranslator.ToWin32(Color.Green))
        SelectObject(hDC, pen)
        MoveToEx(hDC, 100, 100, prevPt)
        LineTo(hDC, 200, 350)
        gr.ReleaseHdc() 'Освобождаем дескриптор контекста устройства Windows.
 
        PictureBox1.Image = bmp
    End Sub
End Class