2022/12/09(Fri) 04:27:45 編集(投稿者)

■No35275に返信(ま〜さんの記事)
>>高 DPI 環境で実行している場合は、ズレる可能性がありますね。
> まさにこれが原因でした。凄いです感激です。

これ動きますか？
ちょっと問題があって、画像を縮小するせいか、少しぼやけた感じになります。
,NET Framework 4.7 以上なら RichTextBox の DrawToBitmap を使ったほうがいいかもしれません。

Imports System.Runtime.InteropServices

Public Class Form1

    <DllImport("User32.dll")>
    Public Shared Function LogicalToPhysicalPointForPerMonitorDPI(ByVal hwnd As IntPtr, ByRef point As Point) As Boolean
    End Function

    Private Shared Function LogicalToPhysicalRectangleForPerMonitorDPI(ByVal hwnd As IntPtr, ByVal r As Rectangle) As Rectangle
        Dim p1 As Point = r.Location
        Dim p2 As Point = New Point(r.Right, r.Bottom)
        LogicalToPhysicalPointForPerMonitorDPI(hwnd, p1)
        LogicalToPhysicalPointForPerMonitorDPI(hwnd, p2)
        Return Rectangle.FromLTRB(p1.X, p1.Y, p2.X, p2.Y)
    End Function

    Private Function LogicalToPhysicalRectangleForPerMonitorDPI(ByVal r As Rectangle) As Rectangle
        Return LogicalToPhysicalRectangleForPerMonitorDPI(Handle, r)
    End Function

    Public Sub New()
        InitializeComponent()
        PictureBox1.SizeMode = PictureBoxSizeMode.Zoom
        PictureBox1.Size = RichTextBox1.Size
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim rectangle1 = RectangleToScreen(RichTextBox1.Bounds)
        Dim rectangle2 = LogicalToPhysicalRectangleForPerMonitorDPI(rectangle1)
        Dim bmp = New Bitmap(rectangle2.Width, rectangle2.Height)
        Using g = Graphics.FromImage(bmp)
            g.CopyFromScreen(rectangle2.Location, Point.Empty, rectangle2.Size)
        End Using
        If PictureBox1.Image IsNot Nothing Then
            PictureBox1.Image.Dispose()
        End If
        PictureBox1.Image = bmp
    End Sub

End Class