-- Native-size identity study, not a motion atlas. One scale across all views.
local source=app.open(app.params.source)
local pixels=Image(source.cels[1].image)
for pixel in pixels:pixels() do
  local value=pixel()
  if app.pixelColor.rgbaA(value)>=192 then
    pixel(app.pixelColor.rgba(app.pixelColor.rgbaR(value),app.pixelColor.rgbaG(value),app.pixelColor.rgbaB(value),255))
  else pixel(0) end
end
local boxes=dofile(app.params.boxes)
assert(#boxes==4, 'Expected exactly four poses: south, west, east, north')
local maxw,maxh=0,0
for _,box in ipairs(boxes) do maxw,maxh=math.max(maxw,box.w),math.max(maxh,box.h) end
local factor=math.min(40/maxw,tonumber(app.params.height)/maxh)
local sheet=Image(192,64,ColorMode.RGB)
for i,box in ipairs(boxes) do
  local crop=Image(box.w,box.h,ColorMode.RGB)
  crop:drawImage(pixels,Point(-box.x,-box.y))
  local tmp=Sprite(box.w,box.h,ColorMode.RGB)
  tmp.cels[1].image=crop
  local w,h=math.floor(box.w*factor+.5),math.floor(box.h*factor+.5)
  app.command.SpriteSize{ui=false,width=w,height=h,method='nearest-neighbor'}
  local anchor=math.floor((box.foot_x or box.w/2)*factor+.5)
  local frame=Image(48,64,ColorMode.RGB)
  frame:drawImage(tmp.cels[1].image,Point(24-anchor,61-h))
  sheet:drawImage(frame,Point((i-1)*48,0))
  tmp:close()
end
source:close()
local out=Sprite(192,64,ColorMode.RGB)
out.cels[1].image=sheet
out:saveAs(app.params.output)
out:close()
print('Four static views exported; uniform scale '..factor)