/**
* Compute the (inward) normal at each node by averaging the unit direction vectors of the two
* edges connected to it.
*/
private void computeNormals() {
for (int i = 0, n = nodeList.size(); i < n; i++) {
Node prevNode = nodeList.get(i);
Node curNode = nodeList.get((i + 1) % n);
Node nextNode = nodeList.get((i + 2) % n);
Vector2D prevEdge = curNode.getPosition().subtract(prevNode.getPosition());
Vector2D nextEdge = nextNode.getPosition().subtract(curNode.getPosition());
double crossProd = prevEdge.crossMag(nextEdge);
Vector2D normal =
prevEdge.normalize().subtract(nextEdge.normalize()).scaleTo(Math.signum(crossProd));
normals.put(curNode, normal);
}
}
public void update() {
Vector2D prevVector = main.getPosition().subtract(previous.getPosition());
Vector2D nextVector = next.getPosition().subtract(main.getPosition());
double angleRad =
Math.acos(prevVector.dot(nextVector) / (prevVector.norm() * nextVector.norm()));
double angle = Math.toDegrees(angleRad);
if (prevVector.crossMag(nextVector) > 0) {
angle = 360.0 - angle;
}
double forceMag = ANGLE_CONSTANT * (angle - 90.0);
forces.put(previous, prevVector.rotate270().scaleTo(NEIGHBOR_ANGLE_SCALE * forceMag));
forces.put(main, normals.get(main).scaleTo(forceMag));
forces.put(next, nextVector.rotate270().scaleTo(NEIGHBOR_ANGLE_SCALE * forceMag));
}
