Operation for constructing a grid of points & respective draw order using an unbroken line of two zig zags - most efficient for larger grids

zig-zag.java

 int length = 5;

 float[] vertices = new float[length * length * 3];
 short[] drawOrder = new short[(length * length * 2) - 1];

 // building up grid points
 {
    int position = 0;
    for (float i = 0f; i < length; i++) {
       for (float j = 0f; j < length; j++) {
          vertices[position++] = i * unitSize;
          vertices[position++] = 0f;
          vertices[position++] = j * unitSize;
       }
    }
 }

 // building up the draw order
 {
    boolean up = true, right = true;

    // horizontal zig zag
    for (int vertexIndex = 0, i = 0, max = length * length; i < max; i++) {


       drawOrder[i] = (short) vertexIndex;

       if (vertexIndex >= ((length * length) - length) && right) {
          right = false;
          vertexIndex++;

       } else if (vertexIndex < length && !right) {
          right = true;
          vertexIndex++;

       } else {
          vertexIndex += (right ? length : -length);
       }
    }

    // vertical zig zag
    for (int vertexIndex = 0, i = (length * length * 2) - 2, max = length * length;
       i >= max; i--) {

       drawOrder[i] = (short) vertexIndex;

       if ((vertexIndex + 1) % length == 0 && up) {
          up = false;
          vertexIndex += length;

       } else if (vertexIndex % length == 0 && !up) {
          up = true;
          vertexIndex += length;

       } else {
          vertexIndex += (up ? 1 : -1);
       }
    }
 }