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package tesseract.forces;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import javax.media.j3d.Transform3D;
import javax.vecmath.Quat4f;
import javax.vecmath.Vector2f;
import javax.vecmath.Vector3f;
import tesseract.objects.PhysicalObject;
public class AirDrag extends Force {
private static final float COEFFICIENT = 20f;
@Override
protected Vector3f calculateForce(PhysicalObject obj) {
if (obj.isNodeNull() || obj.getVelocity().length() == 0) {
return new Vector3f();
}
Vector3f v = new Vector3f(obj.getVelocity());
Vector3f p = new Vector3f(obj.getPosition());
p.negate();
Vector3f c = new Vector3f();
c.sub(new Vector3f(0, 1, 0), v);
Quat4f r = new Quat4f(c.x, c.y, c.z, 0);
r.normalize();
Vector3f com = new Vector3f(-obj.getCenterOfMass().x, -obj.getCenterOfMass().y, -obj.getCenterOfMass().z);
com.negate();
Transform3D tmp = new Transform3D();
tmp.setTranslation(com);
Transform3D tmp2 = new Transform3D();
tmp2.setRotation(r);
com.negate();
com.add(p);
tmp2.setTranslation(com);
tmp2.mul(tmp);
ArrayList<Vector3f> vertices = obj.getVertices();
ArrayList<Vector2f> points = new ArrayList<Vector2f>();
for (Vector3f point : vertices) {
tmp2.transform(point);
Vector2f newPoint = new Vector2f(point.x, point.z);
// Place min y at front of arraylist if it's the minimum
if (points.size() == 0) {
points.add(newPoint);
} else if (newPoint.y < points.get(0).y
|| (newPoint.y == points.get(0).y
&& newPoint.x < points.get(0).x)) {
Vector2f oldPoint = points.get(0);
points.set(0, newPoint);
points.add(oldPoint);
} else {
points.add(newPoint);
}
}
List<Vector2f> hull = convexHull(points);
float surfaceArea = areaOfHull(hull);
float force = 0.5f * v.lengthSquared() * COEFFICIENT * surfaceArea;
v.normalize();
v.scale(-force);
return v;
}
/**
*
* @param hull vector list.
* @return area
*/
private float areaOfHull(final List<Vector2f> hull) {
float area = 0;
Vector2f p = hull.get(0);
for (int i = 2; i < hull.size(); i++) {
// Area of triangle p0 - p(i-1) - p(i)
Vector2f ab = new Vector2f();
Vector2f ac = new Vector2f();
ab.sub(hull.get(i - 1), p);
ac.sub(hull.get(i), p);
area += 0.5f * (ab.x * ac.y - ac.x * ab.y);
}
return area;
}
/**
* Graham's convex hull algorithm from pseudocode on wikipedia.
* @param points point list.
* @return point list.
*/
private List<Vector2f> convexHull(final ArrayList<Vector2f> points) {
Collections.sort(points, new Vector2fAngleCompare(points.get(0)));
points.set(0, points.get(points.size() - 1));
int m = 2;
for (int i = m + 1; i < points.size(); i++) {
try {
while (i < points.size() - 1 && ccw(points.get(m - 1),
points.get(m), points.get(i)) <= 0) {
if (m == 2) {
final Vector2f vec = points.get(m);
points.set(m, points.get(i));
points.set(i, vec);
i++;
} else {
m--;
}
}
} catch (Exception e) {
System.out.println(e);
}
m++;
final Vector2f vec = points.get(m);
points.set(m, points.get(i));
points.set(i, vec);
}
return points.subList(0, m + 1);
}
/**
*
* @param v1 vector.
* @param v2 vector.
* @param v3 vector.
* @return result
*/
private float ccw(final Vector2f v1, final Vector2f v2, final Vector2f v3) {
return (v2.x - v1.x) * (v3.y - v1.y) - (v2.y - v1.y) * (v3.x - v1.x);
}
/**
*
*
*
*/
private class Vector2fAngleCompare implements Comparator<Vector2f> {
/**
* Base vector.
*/
Vector2f base;
/**
* constructor.
* @param theBase the base.
*/
public Vector2fAngleCompare(final Vector2f theBase) {
base = theBase;
}
/**
* @param o1 vector to compare
* @param o2 vector2 to compare
* @return comparison
*/
public int compare(final Vector2f o1, final Vector2f o2) {
return (int) Math.signum(vecAngle(o1) - vecAngle(o2));
}
/**
*
* @param vector to look at.
* @return result
*/
private float vecAngle(final Vector2f vector) {
final Vector2f v = new Vector2f();
v.sub(vector, base);
return v.y / (v.x * v.x + v.y * v.y);
}
}
}
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