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package com.sun.javafx.geom;

import java.util.NoSuchElementException;

import com.sun.javafx.geom.transform.BaseTransform;

A utility class to iterate over the path segments of an arc through the PathIterator interface.
Version:10 Feb 1997
/** * A utility class to iterate over the path segments of an arc * through the PathIterator interface. * * @version 10 Feb 1997 */
class ArcIterator implements PathIterator { double x, y, w, h, angStRad, increment, cv; BaseTransform transform; int index; int arcSegs; int lineSegs; ArcIterator(Arc2D a, BaseTransform at) { this.w = a.width / 2; this.h = a.height / 2; this.x = a.x + w; this.y = a.y + h; this.angStRad = -Math.toRadians(a.start); this.transform = at; double ext = -a.extent; if (ext >= 360.0 || ext <= -360) { arcSegs = 4; this.increment = Math.PI / 2; // btan(Math.PI / 2); this.cv = 0.5522847498307933; if (ext < 0) { increment = -increment; cv = -cv; } } else { arcSegs = (int) Math.ceil(Math.abs(ext) / 90.0); this.increment = Math.toRadians(ext / arcSegs); this.cv = btan(increment); if (cv == 0) { arcSegs = 0; } } switch (a.getArcType()) { case Arc2D.OPEN: lineSegs = 0; break; case Arc2D.CHORD: lineSegs = 1; break; case Arc2D.PIE: lineSegs = 2; break; } if (w < 0 || h < 0) { arcSegs = lineSegs = -1; } }
Return the winding rule for determining the insideness of the path.
See Also:
/** * Return the winding rule for determining the insideness of the * path. * @see #WIND_EVEN_ODD * @see #WIND_NON_ZERO */
public int getWindingRule() { return WIND_NON_ZERO; }
Tests if there are more points to read.
Returns:true if there are more points to read
/** * Tests if there are more points to read. * @return true if there are more points to read */
public boolean isDone() { return index > arcSegs + lineSegs; }
Moves the iterator to the next segment of the path forwards along the primary direction of traversal as long as there are more points in that direction.
/** * Moves the iterator to the next segment of the path forwards * along the primary direction of traversal as long as there are * more points in that direction. */
public void next() { ++index; } /* * btan computes the length (k) of the control segments at * the beginning and end of a cubic bezier that approximates * a segment of an arc with extent less than or equal to * 90 degrees. This length (k) will be used to generate the * 2 bezier control points for such a segment. * * Assumptions: * a) arc is centered on 0,0 with radius of 1.0 * b) arc extent is less than 90 degrees * c) control points should preserve tangent * d) control segments should have equal length * * Initial data: * start angle: ang1 * end angle: ang2 = ang1 + extent * start point: P1 = (x1, y1) = (cos(ang1), sin(ang1)) * end point: P4 = (x4, y4) = (cos(ang2), sin(ang2)) * * Control points: * P2 = (x2, y2) * | x2 = x1 - k * sin(ang1) = cos(ang1) - k * sin(ang1) * | y2 = y1 + k * cos(ang1) = sin(ang1) + k * cos(ang1) * * P3 = (x3, y3) * | x3 = x4 + k * sin(ang2) = cos(ang2) + k * sin(ang2) * | y3 = y4 - k * cos(ang2) = sin(ang2) - k * cos(ang2) * * The formula for this length (k) can be found using the * following derivations: * * Midpoints: * a) bezier (t = 1/2) * bPm = P1 * (1-t)^3 + * 3 * P2 * t * (1-t)^2 + * 3 * P3 * t^2 * (1-t) + * P4 * t^3 = * = (P1 + 3P2 + 3P3 + P4)/8 * * b) arc * aPm = (cos((ang1 + ang2)/2), sin((ang1 + ang2)/2)) * * Let angb = (ang2 - ang1)/2; angb is half of the angle * between ang1 and ang2. * * Solve the equation bPm == aPm * * a) For xm coord: * x1 + 3*x2 + 3*x3 + x4 = 8*cos((ang1 + ang2)/2) * * cos(ang1) + 3*cos(ang1) - 3*k*sin(ang1) + * 3*cos(ang2) + 3*k*sin(ang2) + cos(ang2) = * = 8*cos((ang1 + ang2)/2) * * 4*cos(ang1) + 4*cos(ang2) + 3*k*(sin(ang2) - sin(ang1)) = * = 8*cos((ang1 + ang2)/2) * * 8*cos((ang1 + ang2)/2)*cos((ang2 - ang1)/2) + * 6*k*sin((ang2 - ang1)/2)*cos((ang1 + ang2)/2) = * = 8*cos((ang1 + ang2)/2) * * 4*cos(angb) + 3*k*sin(angb) = 4 * * k = 4 / 3 * (1 - cos(angb)) / sin(angb) * * b) For ym coord we derive the same formula. * * Since this formula can generate "NaN" values for small * angles, we will derive a safer form that does not involve * dividing by very small values: * (1 - cos(angb)) / sin(angb) = * = (1 - cos(angb))*(1 + cos(angb)) / sin(angb)*(1 + cos(angb)) = * = (1 - cos(angb)^2) / sin(angb)*(1 + cos(angb)) = * = sin(angb)^2 / sin(angb)*(1 + cos(angb)) = * = sin(angb) / (1 + cos(angb)) * */ private static double btan(double increment) { increment /= 2.0; return 4.0 / 3.0 * Math.sin(increment) / (1.0 + Math.cos(increment)); }
Returns the coordinates and type of the current path segment in the iteration. The return value is the path segment type: SEG_MOVETO, SEG_LINETO, SEG_QUADTO, SEG_CUBICTO, or SEG_CLOSE. A float array of length 6 must be passed in and may be used to store the coordinates of the point(s). Each point is stored as a pair of float x,y coordinates. SEG_MOVETO and SEG_LINETO types will return one point, SEG_QUADTO will return two points, SEG_CUBICTO will return 3 points and SEG_CLOSE will not return any points.
See Also:
/** * Returns the coordinates and type of the current path segment in * the iteration. * The return value is the path segment type: * SEG_MOVETO, SEG_LINETO, SEG_QUADTO, SEG_CUBICTO, or SEG_CLOSE. * A float array of length 6 must be passed in and may be used to * store the coordinates of the point(s). * Each point is stored as a pair of float x,y coordinates. * SEG_MOVETO and SEG_LINETO types will return one point, * SEG_QUADTO will return two points, * SEG_CUBICTO will return 3 points * and SEG_CLOSE will not return any points. * @see #SEG_MOVETO * @see #SEG_LINETO * @see #SEG_QUADTO * @see #SEG_CUBICTO * @see #SEG_CLOSE */
public int currentSegment(float[] coords) { if (isDone()) { throw new NoSuchElementException("arc iterator out of bounds"); } double angle = angStRad; if (index == 0) { coords[0] = (float) (x + Math.cos(angle) * w); coords[1] = (float) (y + Math.sin(angle) * h); if (transform != null) { transform.transform(coords, 0, coords, 0, 1); } return SEG_MOVETO; } if (index > arcSegs) { if (index == arcSegs + lineSegs) { return SEG_CLOSE; } coords[0] = (float) x; coords[1] = (float) y; if (transform != null) { transform.transform(coords, 0, coords, 0, 1); } return SEG_LINETO; } angle += increment * (index - 1); double relx = Math.cos(angle); double rely = Math.sin(angle); coords[0] = (float) (x + (relx - cv * rely) * w); coords[1] = (float) (y + (rely + cv * relx) * h); angle += increment; relx = Math.cos(angle); rely = Math.sin(angle); coords[2] = (float) (x + (relx + cv * rely) * w); coords[3] = (float) (y + (rely - cv * relx) * h); coords[4] = (float) (x + relx * w); coords[5] = (float) (y + rely * h); if (transform != null) { transform.transform(coords, 0, coords, 0, 3); } return SEG_CUBICTO; } }