AvaloniaUI/Avalonia · error · ArgumentException

degree should be between {1} and {_maxDegree}

Error message

degree should be between {1} and {_maxDegree}

What it means

Thrown by EstimateError when the requested Bezier degree is less than 1 or greater than the helper's current _maxDegree (set via SetMaxDegree, default 3). The error-estimation branches only handle degrees 1, 2, and 3 up to the configured maximum, so out-of-range degrees have no formula. The message interpolates the actual allowed upper bound, so it reads e.g. 'degree should be between 1 and 3'.

Source

Thrown at src/Avalonia.Base/Media/PreciseEllipticArcHelper.cs:566

            /// <param name="x">Abscissa for which the value should be computed</param>
            /// <param name="c">Coefficients array of the rational function</param>
            /// <returns></returns>
            private static double RationalFunction(double x, double[] c)
            {
                return (x * (x * c[0] + c[1]) + c[2]) / (x + c[3]);
            }

            /// <summary>
            /// Estimate the approximation error for a sub-arc of the instance
            /// </summary>
            /// <param name="degree">Degree of the Bezier curve to use (1, 2 or 3)</param>
            /// <param name="etaA">Start angle of the sub-arc</param>
            /// <param name="etaB">End angle of the sub-arc</param>
            /// <returns>Upper bound of the approximation error between the Bezier curve and the real ellipse</returns>
            public double EstimateError(int degree, double etaA, double etaB)
            {
                if (degree < 1 || degree > _maxDegree)
                    throw new ArgumentException($"degree should be between {1} and {_maxDegree}", nameof(degree));
                double eta = 0.5 * (etaA + etaB);
                if (degree < 2)
                {
                    //start point
                    double aCosEtaA = A * Math.Cos(etaA);
                    double bSinEtaA = B * Math.Sin(etaA);
                    double xA = Cx + aCosEtaA * _cosTheta - bSinEtaA * _sinTheta;
                    double yA = Cy + aCosEtaA * _sinTheta + bSinEtaA * _cosTheta;

                    //end point
                    double aCosEtaB = A * Math.Cos(etaB);
                    double bSinEtaB = B * Math.Sin(etaB);
                    double xB = Cx + aCosEtaB * _cosTheta - bSinEtaB * _sinTheta;
                    double yB = Cy + aCosEtaB * _sinTheta + bSinEtaB * _cosTheta;

                    //maximal error point
                    double aCosEta = A * Math.Cos(eta);
                    double bSinEta = B * Math.Sin(eta);

View on GitHub (pinned to 11c5427268)

Solutions

1. Pass a degree in [1, _maxDegree]; check the current max via the value you set with SetMaxDegree.
2. Loop only over valid degrees: for (int d = 1; d <= maxDegree; d++) ... and pick the smallest whose error is under threshold.
3. Initialize degree explicitly rather than relying on default(int) (0).

Example fix

// before
for (int d = 0; d <= 4; d++)
    err = arc.EstimateError(d, a, b);

// after
for (int d = 1; d <= maxDegree; d++)
    err = arc.EstimateError(d, a, b);

var d = Math.Clamp(degree, 1, maxDegree);
var err = arc.EstimateError(d, etaA, etaB);

static bool IsValidDegree(int d, int max) => d >= 1 && d <= max;

When it happens

Trigger: arc.EstimateError(0, etaA, etaB), arc.EstimateError(4, etaA, etaB), or calling with degree 3 after SetMaxDegree(2).

Common situations: Looping over candidate degrees without bounds; calling EstimateError with a degree higher than the configured max; passing an uninitialized degree variable (0).

Related errors

• maxDegree must be between 1 and 3
• defaultFlatness must be greater than 1.0e-10
• Invalid bool rule.
• Invalid bool rule
• points

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/61c351a8a0a8a7d1. Report an issue: GitHub.