private void timer_Tick(object sender, EventArgs e)
{
if (isMouseDown)
{
positionOld = positionCurrent;
positionCurrent = CaptureHelpers.GetZeroBasedMousePosition();
if (positionCurrent != positionOld)
{
SelectionRectangle = CaptureHelpers.CreateRectangle(positionOnClick.X, positionOnClick.Y, positionCurrent.X, positionCurrent.Y);
Refresh();
}
}
}