code: float[] dtRotate2D(float[] v, float ang) {
          float[] dest = new float[3];
          float c = (float) Math.cos(ang);
          float s = (float) Math.sin(ang);
          dest[0] = v[0] * c - v[2] * s;
          dest[2] = v[0] * s + v[2] * c;
          dest[1] = v[1];
          return dest;
      }
docs: vector normalization that ignores the y-component.