private IEnumerable <PdfPathCommand> GetCommands(double theta, double startAngle)
{
if (theta <= 0.0)
{
yield break;
}
// from http://www.tinaja.com/glib/bezcirc2.pdf
var x0 = Math.Cos(theta * 0.5);
var y0 = -Math.Sin(theta * 0.5);
var x3 = x0;
var y3 = -y0;
var x1 = (4.0 - x0) / 3.0;
var y1 = ((1.0 - x0) * (3.0 - x0)) / (3.0 * y0);
var x2 = x1;
var y2 = -y1;
var p0 = new PdfPoint(PdfMeasurement.Points(x0), PdfMeasurement.Points(y0));
var p1 = new PdfPoint(PdfMeasurement.Points(x1), PdfMeasurement.Points(y1));
var p2 = new PdfPoint(PdfMeasurement.Points(x2), PdfMeasurement.Points(y2));
var p3 = new PdfPoint(PdfMeasurement.Points(x3), PdfMeasurement.Points(y3));
// now rotate points by (theta / 2) + startAngle
var rotTheta = theta * 0.5 + startAngle;
p0 = p0.RotateAboutOrigin(rotTheta);
p1 = p1.RotateAboutOrigin(rotTheta);
p2 = p2.RotateAboutOrigin(rotTheta);
p3 = p3.RotateAboutOrigin(rotTheta);
// multiply by the radius
p0 = new PdfPoint(p0.X * RadiusX, p0.Y * RadiusY);
p1 = new PdfPoint(p1.X * RadiusX, p1.Y * RadiusY);
p2 = new PdfPoint(p2.X * RadiusX, p2.Y * RadiusY);
p3 = new PdfPoint(p3.X * RadiusX, p3.Y * RadiusY);
// do final rotation
p0 = p0.RotateAboutOrigin(RotationAngle);
p1 = p1.RotateAboutOrigin(RotationAngle);
p2 = p2.RotateAboutOrigin(RotationAngle);
p3 = p3.RotateAboutOrigin(RotationAngle);
// offset for the center
p0 += Center;
p1 += Center;
p2 += Center;
p3 += Center;
yield return(new PdfPathMoveTo(p0));
yield return(new PdfCubicBezier(p1, p2, p3));
}
