public Winding addBackface() {
if (verts.isEmpty()) {
return this;
}
List<Vector3f> vertsNew = new ArrayList<>();
final int size = verts.size();
for (int i = 0; i < size; i++) {
if (i != 0) {
vertsNew.add(verts.get(i));
}
if (i != size) {
vertsNew.add(verts.get(i));
}
}
return new Winding(vertsNew);
}
/**
* Clips this winding to a plane defined by a normal and distance, removing all vertices in front
* or behind it.
*
* <p>Equals ClipWindingEpsilon() in polylib.cpp
*
* @param normal plane normal
* @param dist plane distance to origin
* @param eps clipping epsilon
* @param back keep vertices behind the plane?
*/
public Winding clipEpsilon(Vector3f normal, float dist, float eps, boolean back) {
// counts number of front, back and on vertices
int[] counts = new int[] {0, 0, 0};
final int size = verts.size();
float[] dists = new float[size + 1];
int[] sides = new int[size + 1];
// determine sides for each point
for (int i = 0; i < size; i++) {
// distance along norm-dirn from origin to vertex
float dot = verts.get(i).dot(normal);
// distance along norm-dirn from clip plane to vertex
dot -= dist;
// store it
dists[i] = dot;
if (dot > eps) {
// vertex in front of plane
sides[i] = SIDE_FRONT;
} else if (dot < -eps) {
// vertex behind plane
sides[i] = SIDE_BACK;
} else {
// vertex on plane (within epsilon)
sides[i] = SIDE_ON;
}
// count relative vertex positions
counts[sides[i]]++;
}
sides[size] = sides[0]; // loop around to 0'th
dists[size] = dists[0];
if (counts[SIDE_FRONT] == 0) {
// no vertices in front - all behind clip plane
if (!back) {
return EMPTY;
} else {
return this;
}
}
if (counts[SIDE_BACK] == 0) {
// no vertices in back - all in front of clip plane
if (back) {
return EMPTY;
} else {
return this;
}
}
List<Vector3f> vertsNew = new ArrayList<Vector3f>();
for (int i = 0; i < size; i++) {
// get i'th vertex
Vector3f p1 = verts.get(i);
if (sides[i] == SIDE_ON) {
vertsNew.add(p1);
continue;
}
if (sides[i] == SIDE_FRONT && !back) {
// add copy the current vertex
vertsNew.add(p1);
}
if (sides[i] == SIDE_BACK && back) {
// add copy the current vertex
vertsNew.add(p1);
}
if (sides[i + 1] == SIDE_ON) {
// next vertex is on the plane, so go to next vertex stat
continue;
}
if (sides[i + 1] == sides[i]) {
// next vertex does not change side, so go to next vertex stat
continue;
}
// otherwise, we are crossing the clip plane between this vertex and the next
// so generate a split point
// will contain the next vertex position
Vector3f p2;
if (i == size - 1) {
// we're the last vertex in the winding
// next vertex is the 0'th one
p2 = verts.get(0);
} else {
// else get the next vertex
p2 = verts.get(i + 1);
}
// dot is fractional position of clip plane between
// this vertex and the next
float dot = dists[i] / (dists[i] - dists[i + 1]);
// vector of the split vertex
Vector3f mv = Vector3f.NULL;
for (int j = 0; j < normal.size; j++) {
// avoid round off error when possible
if (normal.get(j) == 1) {
mv = mv.set(j, dist);
} else if (normal.get(j) == -1) {
mv = mv.set(j, -dist);
} else {
// check it! MSH
mv = mv.set(j, p1.get(j) + dot * (p2.get(j) - p1.get(j)));
}
}
// write the output vertex
vertsNew.add(mv);
}
return new Winding(vertsNew);
}
