permute_palette_colours.lua

-- Aseprite script for permuting the palette
-- permute_palette_colours.lua
-- by increpare - public domain
-- This script randomly permutes the color palette in the active indexed sprite.

-- Ensure there is an active sprite
local sprite = app.activeSprite
if not sprite then
  app.alert("There is no active sprite.")
  return
end

-- Only work in Indexed mode
if sprite.colorMode ~= ColorMode.INDEXED then
  app.alert("The sprite must be in Indexed mode to permute its palette.")
  return
end

local palette = sprite.palettes[1]

-- Read all palette colors into a table
local colors = {}
for i = 0, #palette - 1 do
  table.insert(colors, palette:getColor(i))
end

-- Seed random number generator
math.randomseed(os.time())

-- Perform a Fisher-Yates shuffle on the colors table
for i = #colors, 2, -1 do
  local j = math.random(i)
  colors[i], colors[j] = colors[j], colors[i]
end

-- Apply the new shuffled palette colors in a transaction
app.transaction(function()
  for i = 0, #palette - 1 do
    palette:setColor(i, colors[i+1])
  end
  app.refresh()
end)