Draw Rectangle Over UltraGrid

This is some basic stuff about how to draw lines in C#:
Drawing lines in C#

This tries to help with the flickering problem. Didn't get it to work over an UltraGrid:
Don't Flicker! Double Buffer!

This works on a Windows Form but couldn't get it to work over a control containing an UltraGrid, and it uses Win32 API to draw:
C# Rubber Rectangle

This works fine in a Windows Form but gives artifacts over the UltraGrid:
How to draw a rubber band rectangle or a focus rectangle in Visual C#


I also had my own implementation which flickered:

private Point _mouseStart, _mouseCurrent;
private bool _bPaintSelectionRect = false;

private void uGrid_MouseDown(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        _mouseStart = e.Location;
        ...
    }
}

private void uGrid_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        // TODO: Select cells in the rectangle
        _bPaintSelectionRect = false;
    }
}

 private void uGrid_MouseMove(object sender, MouseEventArgs e)
{
    // If user is holding the left button and dragging, draw a rectangle
    if (e.Button == MouseButtons.Left && _mouseStart != null)
    {
        // Save current mouse position as it moves
        _mouseCurrent = e.Location;
        // Allow the paint event to draw the rectangle
        _bPaintSelectionRect = true;
    }

}

private void uGrid_Paint(object sender, PaintEventArgs e)
{
    if (_bPaintSelectionRect)
    {
        Graphics g = e.Graphics;
        Pen solidPen = new Pen(new SolidBrush(Color.Gray));
        //solidPen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dash;
        solidPen.DashPattern = new float[] { 1, 1 };

        // Normalize the rectangle
        int x = _mouseCurrent.X > _mouseStart.X ? _mouseStart.X : _mouseCurrent.X;
        int y = _mouseCurrent.Y > _mouseStart.Y ? _mouseStart.Y : _mouseCurrent.Y;
        int width = Math.Abs(_mouseCurrent.X - _mouseStart.X);
        int height = Math.Abs(_mouseCurrent.Y - _mouseStart.Y);

        g.DrawRectangle(solidPen, x, y, width, height);

        // Force the redraw (causes flicker) - don't call Invalidate() 
        // and you won't see the rectangle
        uGrid.Invalidate();
    }
}