small artefact in an user control

See more:

C#

.NET

Hi
I created an user control where I intend to do some grafical charts.
I put on the user control border style fixed and inside I plot a white rectangle (my background) where I intend to plot.

My question is why sometimes at the edge of the rectangle (usualy in the top or left area) I see some random grey pixels..why disapear if I do resize? The rectangle is ploted from 0,0 which is top left coordinated of the control.


some code below:

class CPlotGraphUserControl : UserControl

in this class i have:

private void OnUserCtrlResize(object sender, EventArgs e)
{
    //set the relative size
    mGetRelativeControlSize();
    Invalidate();
    Refresh();
}

protected void mInitGraphicalComponents()
{
    offScreenBmp = new Bitmap(xSizeMax, ySizeMax);
    offScreenDC = Graphics.FromImage(offScreenBmp);
    offScreenDC.SmoothingMode = SmoothingMode.AntiAlias;

    mUsedPenDrawGraphics = new Pen(Color.Black, 1);

    //white Backround
    offScreenDC.FillRectangle(backGroundBrush, 0, 0, xSizeMax, ySizeMax);
}

protected override void OnPaint(PaintEventArgs e)
{
    mGetRelativeControlSize();

    mNormalizeMxCoordinates();
    mInitGraphicalComponents();

    //do some drawind here    

    //Draw the image from the memory bitmap object
    e.Graphics.DrawImage(offScreenBmp, new Rectangle(0, 0, xSizeMax, ySizeMax), 0, 0, xSizeMax, ySizeMax, GraphicsUnit.Pixel);

    base.OnPaint(e);
    mDisposeGraphicalComponents();
}