/// <summary>
/// Gets the point where the ellipse intersects the line whose end points
/// are the center of the ellipse and the specified point.
/// </summary>
/// <param name="point">A point in either source or destination coordinates.</param>
/// <returns>The point on the graphic closest to the given <paramref name="point"/>.</returns>
/// <remarks>
/// <para>
/// Depending on the value of <see cref="Graphic.CoordinateSystem"/>,
/// the computation will be carried out in either source
/// or destination coordinates.</para>
/// </remarks>
public override PointF GetClosestPoint(PointF point)
{
// Semi major/minor axes
float a = this.Width / 2;
float b = this.Height / 2;
// Center of ellipse
RectangleF rect = this.Rectangle;
float x1 = rect.Left + a;
float y1 = rect.Top + b;
PointF center = new PointF(x1, y1);
return(EllipsePrimitive.IntersectEllipseAndLine(a, b, center, point));
}
internal static PointF GetClosestPoint(
PointF point,
RectangleF boundingBox,
float startAngle,
float sweepAngle)
{
// Semi major/minor axes
float a = boundingBox.Width / 2;
float b = boundingBox.Height / 2;
// Center of ellipse
float x1 = boundingBox.Left + a;
float y1 = boundingBox.Top + b;
// normalize the angles
float normalizedSweepAngle = Math.Sign(sweepAngle) * Math.Min(360, Math.Abs(sweepAngle));
float normalizedStartAngle = startAngle % 360;
if (normalizedStartAngle < 0)
{
normalizedStartAngle += 360;
}
float normalizedEndAngle = (normalizedStartAngle + normalizedSweepAngle);
if (normalizedSweepAngle < 0)
{
//swap start and end angles
float t = normalizedStartAngle;
normalizedStartAngle = normalizedEndAngle;
normalizedEndAngle = t;
//the sweep angle is now positive
normalizedSweepAngle *= -1;
}
// find the closest endpoint
const double degreesToRadians = Math.PI / 180;
PointF center = new PointF(x1, y1);
double normalizedStartAngleRadians = normalizedStartAngle * degreesToRadians;
double normalizedEndAngleRadians = normalizedEndAngle * degreesToRadians;
PointF start = new PointF(center.X + a * (float)Math.Cos(normalizedStartAngleRadians), center.Y + b * (float)Math.Sin(normalizedStartAngleRadians));
PointF end = new PointF(center.X + a * (float)Math.Cos(normalizedEndAngleRadians), center.Y + b * (float)Math.Sin(normalizedEndAngleRadians));
float distanceToStartX = start.X - point.X;
float distanceToStartY = start.Y - point.Y;
float distanceToEndX = end.X - point.X;
float distanceToEndY = end.Y - point.Y;
float squareDistanceToStart = distanceToStartX * distanceToStartX + distanceToStartY * distanceToStartY;
float squareDistanceToEnd = distanceToEndX * distanceToEndX + distanceToEndY * distanceToEndY;
PointF closestPoint = (squareDistanceToStart < squareDistanceToEnd) ? start : end;
float minSquareDistance = Math.Min(squareDistanceToStart, squareDistanceToEnd);
// find the intersection along the ray eminating from center towards point, and calculate its angle from the x-axis
PointF result = EllipsePrimitive.IntersectEllipseAndLine(a, b, center, point);
//Check if the angle between 'start' and 'result' is positive and less than 'sweep'.
double angleStartToPoint = Vector.SubtendedAngle(result, center, start);
if (angleStartToPoint < normalizedSweepAngle && angleStartToPoint > 0)
{
float distanceToResultX = result.X - point.X;
float distanceToResultY = result.Y - point.Y;
float squareDistanceToResult = distanceToResultX * distanceToResultX + distanceToResultY * distanceToResultY;
if (squareDistanceToResult < minSquareDistance)
{
closestPoint = result;
}
}
return(closestPoint);
}