Toying around with the garbled frames in the Halo 3 trailer for MCC on PC

realign_halo3_pattern.nim

import nimPNG, sequtils, strutils, os, cligen

const startY = 257
const shiftWidth = 78
const shiftHeight = 9
const switch = 548

proc main(input: string,
          output: string,
          start = startY,
          shiftY = shiftHeight,
          shiftX = shiftWidth,
          reverse = switch) =
  let
    pattern = loadPng24(input)
    width = pattern.width
    height = pattern.height
  var data = pattern.data

  template shift(a, b, x, y, w, s: untyped): untyped =
    let frm = y * w * 3 + x
    let to = frm - s
    b[to] = a[frm]
    b[to + 1] = a[frm + 1]
    b[to + 2] = a[frm + 2]

  for y in start ..< height:
    for x in 0 .. (width * 3 - 3):
      let row = (y - start) div shiftY
      let toLeft = row * (shiftX * 3)
      if y < reverse:
        shift(pattern.data, data, x, y, width, toLeft)
      else:
        shift(pattern.data, data, x, y, width, -toLeft)

  echo savePNG24(output, data, width, height)

when isMainModule:
  dispatch main