private Bitmap DrawTangentAndNormal(float t)
{
tangentAndNormal = true;
Bitmap bmp = new Bitmap(onlyTractrix);
Graphics graphics = Graphics.FromImage(bmp);
if (t != 90)
{
List <PointF> points = curve.TangentLine(t);
PointF TangentText = curve.Tangent(curve.FindPoint(t).X - 20, t);
PointF NormalText = curve.Normal(curve.FindPoint(t).X - 20, t);
graphics.DrawString("Tangent", new Font("Calibri", 10), Brushes.Turquoise, viewport.FactToLogic(TangentText));
graphics.DrawString("Normal", new Font("Calibri", 10), Brushes.Orange, viewport.FactToLogic(NormalText));
graphics.DrawLine(new Pen(Color.Turquoise, 1), viewport.FactToLogic(points[0]), viewport.FactToLogic(points[1]));
points = curve.NormalLine(t);
graphics.DrawLine(new Pen(Color.Orange, 1), viewport.FactToLogic(points[0]), viewport.FactToLogic(points[1]));
PointF p = viewport.FactToLogic(curve.Tangent(curve.FindPoint(t).X, t));
int s = 3;
graphics.DrawEllipse(new Pen(Color.Red, 1), p.X - s, p.Y - s, s * 2, s * 2);
}
return(bmp);
}
