public static PrimitiveEllipse Project(PrimitiveEllipse ellipse, Matrix4 transform)
{
// brute-force the endpoints
var fromUnit = Matrix4.CreateScale(1.0, 1.0, 0.0) * transform * ellipse.FromUnitCircle;
var center = transform.Transform(ellipse.Center);
var minPoint = fromUnit.Transform(new Point(MathHelper.COS[0], MathHelper.SIN[0], 0));
var maxPoint = minPoint;
var minDistance = (minPoint - center).LengthSquared;
var maxDistance = minDistance;
for (int i = 1; i < 360; i++)
{
var next = fromUnit.Transform(new Point(MathHelper.COS[i], MathHelper.SIN[i], 0));
var dist = (next - center).LengthSquared;
if (dist < minDistance)
{
minPoint = next;
minDistance = dist;
}
if (dist > maxDistance)
{
maxPoint = next;
maxDistance = dist;
}
}
var majorAxis = maxPoint - center;
var minorAxisRatio = Math.Sqrt(minDistance) / Math.Sqrt(maxDistance);
var startAngle = ellipse.StartAngle;
var endAngle = ellipse.EndAngle;
// projection looks like a circle
if (Math.Abs(maxDistance - minDistance) < MathHelper.Epsilon * 1000) // TODO: need a better way to do this
{
majorAxis = new Vector(majorAxis.Length, 0.0, 0.0); // right vector
minorAxisRatio = 1.0;
}
// correct start/end angles
if (!ellipse.IsClosed)
{
var tempEllipse = new PrimitiveEllipse(center, majorAxis, Vector.ZAxis, minorAxisRatio, 0.0, MathHelper.ThreeSixty, ellipse.Color);
var majorAngle = majorAxis.ToAngle();
var startPoint = transform.Transform(ellipse.StartPoint());
var endPoint = transform.Transform(ellipse.EndPoint());
var toUnit = tempEllipse.FromUnitCircle.Inverse();
var startUnit = (Vector)toUnit.Transform(startPoint);
var endUnit = (Vector)toUnit.Transform(endPoint);
startAngle = (startUnit.ToAngle() - majorAngle).CorrectAngleDegrees();
endAngle = (endUnit.ToAngle() - majorAngle).CorrectAngleDegrees();
}
return(new PrimitiveEllipse(center, majorAxis, Vector.ZAxis, minorAxisRatio, startAngle, endAngle, ellipse.Color));
}
public void EllipseGetPointTest()
{
var el = new PrimitiveEllipse(Point.Origin, 1.0, 0.0, 180.0, Vector.ZAxis);
Assert.True(el.StartPoint().CloseTo(new Point(1.0, 0.0, 0.0)));
Assert.True(el.EndPoint().CloseTo(new Point(-1.0, 0.0, 0.0)));
Assert.True(el.GetPoint(90.0).CloseTo(new Point(0.0, 1.0, 0.0)));
el = new PrimitiveEllipse(new Point(1.0, 1.0, 0.0), 1.0, 0.0, 180.0, Vector.ZAxis);
Assert.True(el.StartPoint().CloseTo(new Point(2.0, 1.0, 0.0)));
Assert.True(el.EndPoint().CloseTo(new Point(0.0, 1.0, 0.0)));
Assert.True(el.GetPoint(90.0).CloseTo(new Point(1.0, 2.0, 0.0)));
}
