grid over jpg - continued

Well you could start by removing lines 90 and 91 (in the code posted on your previous question), which does the actual reset (shown in context here):

    Private Sub Rows_Cols_ValueChanged(sender As Object, e As System.EventArgs) Handles Rows.ValueChanged, Cols.ValueChanged
        GridOffsetX = 0 ' line 90
        GridOffsetY = 0 ' line 91
        PB.Refresh()
    End Sub

Select allOpen in new window

But like I said in a later comment, without that code the grid appears to jump when sliding it again after changing rows or columns.

That could possibly be remedied by remembering (in another global class variable) where you actually positioned the grid last but that would have to be based on the assumption that you actually click on a point of the grid that you want positioned on an exact spot. Then a bit of adding and subtracting should make it possible to reset the offsets (to something other than 0) to make sure that with the new rows/columns setting the grid actually stays put at that point, but only for that point.

EDIT: maybe even simpler by using that last clicked point as grid origin point instead of using offsets.

Yeah, probably the easiest way to do it:

Public Class Form1

    Private GridColor As Color = Color.Black
    ' additional members for grid offset
    Private GridOffsetX As Integer = 0
    Private GridOffsetY As Integer = 0
    Private GridOffsetPrvX As Integer = -1
    Private GridOffsetPrvY As Integer = -1
    Private GridMoving As Boolean = False

    Private WithEvents PB As New PictureBox
    Private WithEvents Rows As New NumericUpDown
    Private WithEvents Cols As New NumericUpDown
    Private WithEvents btnSelectFile As New Button
    Private WithEvents btnSelectColor As New Button

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        Rows.Minimum = 2
        Cols.Minimum = 2

        Dim TLB As New TableLayoutPanel
        TLB.RowCount = 2
        TLB.RowStyles.Add(New RowStyle(SizeType.AutoSize))
        TLB.RowStyles.Add(New RowStyle(SizeType.Percent, 100))
        TLB.ColumnCount = 6
        TLB.ColumnStyles.Add(New ColumnStyle(SizeType.Percent, 20))
        TLB.ColumnStyles.Add(New ColumnStyle(SizeType.Percent, 20))
        TLB.ColumnStyles.Add(New ColumnStyle(SizeType.Percent, 20))
        TLB.ColumnStyles.Add(New ColumnStyle(SizeType.Percent, 20))
        TLB.ColumnStyles.Add(New ColumnStyle(SizeType.Percent, 20))
        TLB.ColumnStyles.Add(New ColumnStyle(SizeType.Percent, 20))

        Dim lbl As New Label
        lbl.Text = "Rows:"
        lbl.TextAlign = ContentAlignment.TopRight
        lbl.Dock = DockStyle.Bottom
        TLB.Controls.Add(lbl, 0, 0)
        TLB.Controls.Add(Rows, 1, 0)

        lbl = New Label
        lbl.Text = "Cols:"
        lbl.TextAlign = ContentAlignment.TopRight
        lbl.Dock = DockStyle.Bottom
        TLB.Controls.Add(lbl, 2, 0)
        TLB.Controls.Add(Cols, 3, 0)

        btnSelectFile.Text = "Pic"
        btnSelectFile.AutoSize = True
        btnSelectFile.Dock = DockStyle.Fill
        TLB.Controls.Add(btnSelectFile, 4, 0)

        btnSelectColor.Text = "Color"
        btnSelectColor.AutoSize = True
        btnSelectColor.Dock = DockStyle.Fill
        TLB.Controls.Add(btnSelectColor, 5, 0)

        PB.Dock = DockStyle.Fill
        PB.SizeMode = PictureBoxSizeMode.Zoom
        PB.BorderStyle = BorderStyle.FixedSingle
        TLB.Controls.Add(PB, 0, 1)
        TLB.SetColumnSpan(PB, 6)

        TLB.Dock = DockStyle.Fill
        Me.Controls.Add(TLB)
        Me.Text = "Image Grid Tool"
    End Sub

    Private Sub btnSelectFile_Click(sender As Object, e As System.EventArgs) Handles btnSelectFile.Click
        Static OFD As New OpenFileDialog
        OFD.Title = "Select an Image File"
        OFD.Filter = "Image Files(*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|All files (*.*)|*.*"
        If OFD.ShowDialog = Windows.Forms.DialogResult.OK Then
            Try
                PB.Image = New Bitmap(Image.FromFile(OFD.FileName))
            Catch ex As Exception
                MessageBox.Show("File: " & OFD.FileName & vbCrLf & vbCrLf & ex.ToString, "Error Opening Image", MessageBoxButtons.OK, MessageBoxIcon.Error)
            End Try
        End If
    End Sub

    Private Sub btnSelectColor_Click(sender As Object, e As System.EventArgs) Handles btnSelectColor.Click
        Static CD As New ColorDialog
        If CD.ShowDialog = Windows.Forms.DialogResult.OK Then
            GridColor = CD.Color
            PB.Refresh()
        End If
    End Sub

    Private Sub Rows_Cols_ValueChanged(sender As Object, e As System.EventArgs) Handles Rows.ValueChanged, Cols.ValueChanged
        PB.Refresh()
    End Sub

    Private Sub PB_SizeChanged(sender As Object, e As System.EventArgs) Handles PB.SizeChanged
        PB.Refresh()
    End Sub

    Private Sub PB_Paint(sender As Object, e As System.Windows.Forms.PaintEventArgs) Handles PB.Paint
        Using pn As New Pen(GridColor)
            Dim xValue, yValue As Integer
            For y As Integer = 1 To Rows.Value
                yValue = (y / Rows.Value * PB.Height + GridOffsetY) Mod PB.Height
                If yValue > 0 And yValue < PB.Height - 3 Then ' don't draw line right up against top or bottom border
                    e.Graphics.DrawLine(pn, 0, yValue, PB.Width, yValue)
                End If
            Next
            For x As Integer = 1 To Cols.Value
                xValue = (x / Cols.Value * PB.Width + GridOffsetX) Mod PB.Width
                If xValue > 0 And xValue < PB.Width - 3 Then ' don't draw line right up against left or right border
                    e.Graphics.DrawLine(pn, xValue, 0, xValue, PB.Height)
                End If
            Next
        End Using
    End Sub

    Private Sub PB_MouseDown(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles PB.MouseDown
        If e.Button = Windows.Forms.MouseButtons.Left Then
            GridMoving = True
            GridOffsetPrvX = e.X
            GridOffsetPrvY = e.Y
        End If
    End Sub

    Private Sub PB_MouseUp(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles PB.MouseUp
        GridMoving = False
        GridOffsetX = e.X
        GridOffsetY = e.Y
    End Sub

    Private Sub PB_MouseMove(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles PB.MouseMove
        If GridMoving Then
            GridOffsetX += e.X - GridOffsetPrvX
            GridOffsetY += e.Y - GridOffsetPrvY
            ' keep it positive for the 'mod' to work in PB_Paint
            While GridOffsetX < 0
                GridOffsetX += PB.Width
            End While
            While GridOffsetY < 0
                GridOffsetY += PB.Height
            End While
            ' remember new position for next move
            GridOffsetPrvX = e.X
            GridOffsetPrvY = e.Y
            PB.Refresh()
        End If
    End Sub

End Class

Select allOpen in new window

so in case you wonder; the last point is now set directly as the new offset on MouseUp which means the actual point where you release the mouse becomes the exact offset position with the effect of keeping the grid static, pinned to that point as it were, when changing rows/columns afterwards.

couple of notes:
- resize has a funky effect... (may want to put the reset back in for that?)
- the zoomstyle of the picturebox can have the visual effect of changing the actual position of the grid over the picture. If you elaborate on how you do the positioning and if you need to keep that 'static' as well, if needed it would be possible to do the calculations for that.

many thanks - again - Robert!