int i1 = index++;
int i2 = index++;
int i3 = index++;
assert(i1 < hull.numIndices () &&
i2 < hull.numIndices () &&
i3 < hull.numIndices ());
int index1 = idx.get(i1);
int index2 = idx.get(i2);
int index3 = idx.get(i3);
assert(index1 < hull.numVertices () &&