def log2(n):
    return {
        1: 0,
        2: 1,
        4: 2,
        8: 3,
        16: 4,
        32: 5,
        64: 6,
        128: 7,
        256: 8,
        512: 9,
        1024: 10,
    }[n]

def from_xy(x, y, width, height):
  # maximum texture size       : 1024x1024
  # maximum 1-dimensional index: 0xfffff
  # bits                       : 19-0

  # y bits: 0, 2, 4, 6, 8, 10, 12, 14, 16, 18
  # x bits: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19

  width_max = log2(width)
  height_max = log2(height)

  twiddle_ix = 0
  for i in range(20 // 2):
      if (i < width_max and i < height_max):
          twiddle_ix |= ((y >> i) & 1) << (i * 2 + 0)
          twiddle_ix |= ((x >> i) & 1) << (i * 2 + 1)
      elif (i < width_max):
          twiddle_ix |= ((x >> i) & 1) << (i + height_max)
      elif (i < height_max):
          twiddle_ix |= ((y >> i) & 1) << (i + width_max)
      else:
          break

  return twiddle_ix

def npot(v):
    v -= 1;
    v |= v >> 1;
    v |= v >> 2;
    v |= v >> 4;
    v |= v >> 8;
    v |= v >> 16;
    v += 1;
    return v

def texture(dst, src, width, height):
    #pot_height = npot(height)
    max_twiddle_ix = -1
    for y in range(height):
        for x in range(width):
            twiddle_ix = from_xy(x, y, width, height)
            value = src[y * width + x]
            dst[twiddle_ix] = value
            if twiddle_ix > max_twiddle_ix:
                max_twiddle_ix = twiddle_ix
    return max_twiddle_ix