拖拽一条参考线时，感觉反应迟钝，如何改进？

        private bool zg1_MouseDownEvent(ZedGraphControl control, MouseEventArgs e)

        {

            // point-dragging is activated by an 'Alt' key and mousedown combination

            if (Control.ModifierKeys == Keys.Alt)

            {

                GraphPane myPane = control.GraphPane;

                PointF mousePt = new PointF(e.X, e.Y);



                // find the point that was clicked, and make sure the point list is editable

                // and that it's a primary Y axis (the first Y or Y2 axis)

                if (myPane.FindNearestPoint(mousePt, out dragCurve, out dragIndex) &&

                         dragCurve.Points is PointPairList &&

                         dragCurve.YAxisIndex == 0)

                {

                    // save the starting point information

                    startPt = mousePt;

                    startPair = dragCurve.Points[dragIndex];

                    // indicate a drag operation is in progress

                    isDragPoint = true;

                    // get the scale values for the start of the drag

                    //double startY2;

                    myPane.ReverseTransform(mousePt, out startX, out startY);

                    // if it's a Y2 axis, use that value instead of Y

                    //if (dragCurve.IsY2Axis)

                    //    startY = startY2;



                    return true;

                }

            }



            return false;

        }



        private bool zg1_MouseMoveEvent(ZedGraphControl control, MouseEventArgs e)

        {

            GraphPane myPane = control.GraphPane;

            PointF mousePt = new PointF(e.X, e.Y);



            // see if a dragging operation is underway

            if (isDragPoint)

            {

                // get the scale values that correspond to the current point

                double curX, curY; //, curY2;

                myPane.ReverseTransform(mousePt, out curX, out curY);

                // if it's a Y2 axis, use that value instead of Y

                //if (dragCurve.IsY2Axis)

                //    curY = curY2;

                // calculate the new scale values for the point

                PointPair newPt = new PointPair(startPair.X + curX - startX, startPair.Y + curY - startY);

                // save the data back to the point list

                (dragCurve.Points as PointPairList)[dragIndex] = newPt;

                // force a redraw

                control.Refresh();

                // tell the ZedGraphControl not to do anything else with this event

                return true;

            }

            else

            {

                //change the cursor if the mouse is sufficiently close to a point

                if (myPane.FindNearestPoint(mousePt, out dragCurve, out dragIndex) &&

                         dragCurve.Points is PointPairList &&

                         dragCurve.YAxisIndex == 0)

                {

                    zg1.Cursor = Cursors.SizeAll;

                }

                else

                {

                    zg1.Cursor = Cursors.Default;

                }

            }



            // since we didn't handle the event, tell the ZedGraphControl to handle it

            return false;

        }



        private bool zg1_MouseUpEvent(ZedGraphControl control, MouseEventArgs e)

        {

            if (isDragPoint)

            {

                // dragging operation is no longer active

                isDragPoint = false;

            }



            return false;

        }