static Arc ComputeArc(double x0, double y0,
double rx, double ry,
double angle,
bool largeArcFlag,
bool sweepFlag,
double x, double y)
{
//from Apache2, https://xmlgraphics.apache.org/
/**
* This constructs an unrotated Arc2D from the SVG specification of an
* Elliptical arc. To get the final arc you need to apply a rotation
* transform such as:
*
* AffineTransform.getRotateInstance
* (angle, arc.getX()+arc.getWidth()/2, arc.getY()+arc.getHeight()/2);
*/
//
// Elliptical arc implementation based on the SVG specification notes
//
// Compute the half distance between the current and the final point
double dx2 = (x0 - x) / 2.0;
double dy2 = (y0 - y) / 2.0;
// Convert angle from degrees to radians
angle = ((angle % 360.0) * Math.PI / 180f);
double cosAngle = Math.Cos(angle);
double sinAngle = Math.Sin(angle);
//
// Step 1 : Compute (x1, y1)
//
double x1 = (cosAngle * dx2 + sinAngle * dy2);
double y1 = (-sinAngle * dx2 + cosAngle * dy2);
// Ensure radii are large enough
rx = Math.Abs(rx);
ry = Math.Abs(ry);
double Prx = rx * rx;
double Pry = ry * ry;
double Px1 = x1 * x1;
double Py1 = y1 * y1;
// check that radii are large enough
double radiiCheck = Px1 / Prx + Py1 / Pry;
if (radiiCheck > 1)
{
rx = Math.Sqrt(radiiCheck) * rx;
ry = Math.Sqrt(radiiCheck) * ry;
Prx = rx * rx;
Pry = ry * ry;
}
//
// Step 2 : Compute (cx1, cy1)
//
double sign = (largeArcFlag == sweepFlag) ? -1 : 1;
double sq = ((Prx * Pry) - (Prx * Py1) - (Pry * Px1)) / ((Prx * Py1) + (Pry * Px1));
sq = (sq < 0) ? 0 : sq;
double coef = (sign * Math.Sqrt(sq));
double cx1 = coef * ((rx * y1) / ry);
double cy1 = coef * -((ry * x1) / rx);
//
// Step 3 : Compute (cx, cy) from (cx1, cy1)
//
double sx2 = (x0 + x) / 2.0;
double sy2 = (y0 + y) / 2.0;
double cx = sx2 + (cosAngle * cx1 - sinAngle * cy1);
double cy = sy2 + (sinAngle * cx1 + cosAngle * cy1);
//
// Step 4 : Compute the angleStart (angle1) and the angleExtent (dangle)
//
double ux = (x1 - cx1) / rx;
double uy = (y1 - cy1) / ry;
double vx = (-x1 - cx1) / rx;
double vy = (-y1 - cy1) / ry;
double p, n;
// Compute the angle start
n = Math.Sqrt((ux * ux) + (uy * uy));
p = ux; // (1 * ux) + (0 * uy)
sign = (uy < 0) ? -1d : 1d;
double angleStart = (sign * Math.Acos(p / n)); // Math.toDegrees(sign * Math.Acos(p / n));
// Compute the angle extent
n = Math.Sqrt((ux * ux + uy * uy) * (vx * vx + vy * vy));
p = ux * vx + uy * vy;
sign = (ux * vy - uy * vx < 0) ? -1d : 1d;
double angleExtent = (sign * Math.Acos(p / n));// Math.toDegrees(sign * Math.Acos(p / n));
if (!sweepFlag && angleExtent > 0)
{
angleExtent -= 360f;
}
else if (sweepFlag && angleExtent < 0)
{
angleExtent += 360f;
}
//angleExtent %= 360f;
//angleStart %= 360f;
//
// We can now build the resulting Arc2D in double precision
//
//Arc2D.Double arc = new Arc2D.Double();
//arc.x = cx - rx;
//arc.y = cy - ry;
//arc.width = rx * 2.0;
//arc.height = ry * 2.0;
//arc.start = -angleStart;
//arc.extent = -angleExtent;
Arc arc = new Arc();
arc.Init(x, y, rx, ry, -(angleStart), -(angleExtent));
return(arc);
}
