# png.ludic - the renderer writes a frame as a PPM; the lab keeps it as a PNG, stored rather than
# compressed (png_write.ludic: a PNG anything opens, with no zlib here).

# a PPM's header: "P6", width, height, maxval, each after white space; returns the pixel offset
function lp_ppm_header(lab_st: mut LabState, d: []byte) -> int {
  var i = 2
  var got = 0
  var vals = new []int
  while got < 3 and i < len(d) {
    while i < len(d) and (d[i] == 32 or d[i] == 10 or d[i] == 13 or d[i] == 9) { i += 1 }
    var v = 0
    while i < len(d) and d[i] >= 48 and d[i] <= 57 {
      v = v * 10 + (d[i] - 48)
      i += 1
    }
    push(vals, v)
    got += 1
  }
  lab_st.lp_w = vals[0]
  lab_st.lp_h = vals[1]
  return i + 1
}
# the PPM at `ppm` as a PNG at `png`; the PPM is removed
export function lab_ppm_to_png(lab_st: mut LabState, ppm: string, png: string) -> bool {
  let d = Fs.read_bytes(ppm)
  if d == null or len(d) < 8 { return false }
  let px = lp_ppm_header(lab_st, d)
  let w = lab_st.lp_w
  let h = lab_st.lp_h
  if px + w * h * 3 > len(d) { return false }
  let out = buffer(lp_png_size(w, h, 3))
  let n = lp_encode(lab_st.lp_table, w, h, 3, d, px, out)
  if not Fs.write_bytes(png, out, n) { return false }
  Fs.remove(ppm)
  return true
}