System.Drawing.Graphics.drawEllipticalArcToContext C# (CSharp) Method

        public void drawEllipticalArcToContext(int degree, double threshold)
        {
            // find the number of Bézier curves needed
            bool found = false;
            int n = 1;
            while ((!found) && (n < 1024))
            {
                double dEta2 = (eta2 - eta1) / n;
                if (dEta2 <= 0.5 * Math.PI)
                {
                    double etaB2 = eta1;
                    found = true;
                    for (int i = 0; found && (i < n); ++i)
                    {
                        double etaA = etaB2;
                        etaB2 += dEta2;
                        found = (estimateError(degree, etaA, etaB2) <= threshold);
                    }
                }
                n = n << 1;
            }

            double dEta = (eta2 - eta1) / n;
            double etaB = eta1;

            double cosEtaB = Math.Cos(etaB);
            double sinEtaB = Math.Sin(etaB);
            double aCosEtaB = a * cosEtaB;
            double bSinEtaB = b * sinEtaB;
            double aSinEtaB = a * sinEtaB;
            double bCosEtaB = b * cosEtaB;
            double xB = cx + aCosEtaB * cosTheta - bSinEtaB * sinTheta;
            double yB = cy + aCosEtaB * sinTheta + bSinEtaB * cosTheta;
            double xBDot = -aSinEtaB * cosTheta - bCosEtaB * sinTheta;
            double yBDot = -aSinEtaB * sinTheta + bCosEtaB * cosTheta;

            if (isPieSlice)
            {
                context.MoveTo((float)cx, (float)cy);
            }
            else
            {
                context.MoveTo((float)xB, (float)yB);
            }

            double t = Math.Tan(0.5 * dEta);
            double alpha = Math.Sin(dEta) * (Math.Sqrt(4 + 3 * t * t) - 1) / 3;

            for (int i = 0; i < n; ++i)
            {

                //double etaA = etaB;
                double xA = xB;
                double yA = yB;
                double xADot = xBDot;
                double yADot = yBDot;

                etaB += dEta;
                cosEtaB = Math.Cos(etaB);
                sinEtaB = Math.Sin(etaB);
                aCosEtaB = a * cosEtaB;
                bSinEtaB = b * sinEtaB;
                aSinEtaB = a * sinEtaB;
                bCosEtaB = b * cosEtaB;
                xB = cx + aCosEtaB * cosTheta - bSinEtaB * sinTheta;
                yB = cy + aCosEtaB * sinTheta + bSinEtaB * cosTheta;
                xBDot = -aSinEtaB * cosTheta - bCosEtaB * sinTheta;
                yBDot = -aSinEtaB * sinTheta + bCosEtaB * cosTheta;

                if (degree == 1)
                {
                    context.AddLineToPoint((float)xB, (float)yB);
                }
                else if (degree == 2)
                {
                    double k = (yBDot * (xB - xA) - xBDot * (yB - yA))
                        / (xADot * yBDot - yADot * xBDot);
                    context.AddQuadCurveToPoint((float)(xA + k * xADot),(float)(yA + k * yADot),
                                                (float)xB, (float)yB);
                }
                else
                {
                    context.AddCurveToPoint((float)(xA + alpha * xADot), (float)(yA + alpha * yADot),
                                                       (float)(xB - alpha * xBDot), (float)(yB - alpha * yBDot),
                                                       (float)xB, (float)yB);
                }

            }

            if (isPieSlice)
            {
                context.ClosePath();
            }
        }