-- palverify.lua -- take a real MAME screenshot (video manager -> palette applied)
-- at a chosen frame.  Unlike dump_frame()'s PPM (straight from bitmap pens), a
-- screen:snapshot() renders through the palette, so it is the correct instrument
-- for checking the mono colour ramp.
--
--   PAL_FRAME=<n>  PAL_OUT=<abs path .png>  <mame> ... -autoboot_script palverify.lua

local machine = manager.machine
local dbg = machine.debugger
local screens = machine.screens

local at = tonumber(os.getenv("PAL_FRAME") or "600")
local out = os.getenv("PAL_OUT") or "/home/arti/code/k-space/vt1200/harness/mame/pal_snap.png"

local screen = nil
for tag, s in pairs(screens) do screen = s; break end
if not screen then print("ERROR: no screen device"); machine:exit(); return end

local n = 0
emu.register_frame_done(function()
	n = n + 1
	if n == at then
		local err = screen:snapshot(out)
		print(string.format("SNAP frame=%d -> %s err=%s", n, out, tostring(err)))
		machine:exit()
	end
	if n > at + 5 then machine:exit() end
end, "vt1200-palverify")

if dbg then dbg.execution_state = 'run' end