Aseprite script to copy multiple sprites into the active one (each sprite as a layer)

Copy-Frames-From-Files.lua

local filenames = {
  "/Users/david/piano00.png",
  "/Users/david/drums00.png",
  "/Users/david/bass00.png"
}

local spr = app.activeSprite
if not spr then return app.alert "No active sprite" end

for _,fn in ipairs(filenames) do
  local newLayer = spr:newLayer()
  newLayer.name = app.fs.fileTitle(fn)

  app.command.OpenFile{ filename=fn, sequence="agree" }
  local subSprite = app.activeSprite
  for _,cel in ipairs(subSprite.cels) do
    while #spr.frames < cel.frameNumber do
      spr:newEmptyFrame()
    end
    spr:newCel(newLayer, cel.frameNumber, cel.image, cel.position)
  end
  subSprite:close()
end