Interpolates given points by a bezier curve
/*
* Copyright (c) 2005 David Benson
*
* See LICENSE file in distribution for licensing details of this source file
*/
import java.awt.Point;
import java.awt.geom.Point2D;
/**
* Interpolates given points by a bezier curve. The first
* and the last two points are interpolated by a quadratic
* bezier curve; the other points by a cubic bezier curve.
*
* Let p a list of given points and b the calculated bezier points,
* then one get the whole curve by:
*
* sharedPath.moveTo(p[0])
* sharedPath.quadTo(b[0].x, b[0].getY(), p[1].x, p[1].getY());
*
* for(int i = 2; i < p.length - 1; i++ ) {
* Point b0 = b[2*i-3];
* Point b1 = b[2*i-2];
* sharedPath.curveTo(b0.x, b0.getY(), b1.x, b1.getY(), p[i].x, p[i].getY());
* }
*
* sharedPath.quadTo(b[b.length-1].x, b[b.length-1].getY(), p[n - 1].x, p[n - 1].getY());
*
* @author krueger
*/
public class Bezier {
private static final float AP = 0.5f;
private Point2D[] bPoints;
/**
* Creates a new Bezier curve.
* @param points
*/
public Bezier(Point2D[] points) {
int n = points.length;
if (n < 3) {
// Cannot create bezier with less than 3 points
return;
}
bPoints = new Point[2 * (n - 2)];
double paX, paY;
double pbX = points[0].getX();
double pbY = points[0].getY();
double pcX = points[1].getX();
double pcY = points[1].getY();
for (int i = 0; i < n - 2; i++) {
paX = pbX;
paY = pbY;
pbX = pcX;
pbY = pcY;
pcX = points[i + 2].getX();
pcY = points[i + 2].getY();
double abX = pbX - paX;
double abY = pbY - paY;
double acX = pcX - paX;
double acY = pcY - paY;
double lac = Math.sqrt(acX * acX + acY * acY);
acX = acX /lac;
acY = acY /lac;
double proj = abX * acX + abY * acY;
proj = proj < 0 ? -proj : proj;
double apX = proj * acX;
double apY = proj * acY;
double p1X = pbX - AP * apX;
double p1Y = pbY - AP * apY;
bPoints[2 * i] = new Point((int) p1X, (int) p1Y);
acX = -acX;
acY = -acY;
double cbX = pbX - pcX;
double cbY = pbY - pcY;
proj = cbX * acX + cbY * acY;
proj = proj < 0 ? -proj : proj;
apX = proj * acX;
apY = proj * acY;
double p2X = pbX - AP * apX;
double p2Y = pbY - AP * apY;
bPoints[2 * i + 1] = new Point((int) p2X, (int) p2Y);
}
}
/**
* Returns the calculated bezier points.
* @return the calculated bezier points
*/
public Point2D[] getPoints() {
return bPoints;
}
/**
* Returns the number of bezier points.
* @return number of bezier points
*/
public int getPointCount() {
return bPoints.length;
}
/**
* Returns the bezier points at position i.
* @param i
* @return the bezier point at position i
*/
public Point2D getPoint(int i) {
return bPoints[i];
}
}
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