-- Same as show_frame.lua, but sets a REAL 256x256 CRTC mode instead of
-- borrowing the IPL's 768x512 text timing.  Proves the mode table in
-- crtc_mode.lua and removes the x=512 wrap of FINDINGS 22.5.
M=manager.machine; SP=M.devices[":maincpu"].spaces["program"]; SUB=nil

local function load_mode()
  for _,p in ipairs{"../tools/bench/crtc_mode.lua","tools/bench/crtc_mode.lua","crtc_mode.lua"} do
    local f=loadfile(p); if f then return f() end
  end
  error("crtc_mode.lua not found")
end
local MODE = load_mode()

local GVRAM, GPAL = 0xC00000, 0xE82000

local f=io.open("frame256.bin","rb"); local d=f:read("a"); f:close()
local function B(i) return string.byte(d,i) end
local W,H = B(5)*256+B(6), B(7)*256+B(8)
local PAL0, PIX0 = 9, 9+256*3
local YOFF = (MODE.height - H) // 2        -- letterbox 192 rows inside 256

-- GGGGGRRRRRBBBBBI, confirmed from x68k_v.cpp.  The LSB "I" is SHARED by all
-- three channels: each renders as pal6bit((field<<1)|I).  Hardcoding I=1 (as
-- show_frame.lua does) makes true black unreachable -- pal6bit(1) = 4 -- so I
-- is chosen per entry to minimise summed squared error over R,G,B.
local function pal6(v) return ((v<<2)|(v>>4)) & 0xff end
local function pack(r,g,b)
  local f = {r>>3, g>>3, b>>3}
  local best, bestI = nil, 1
  for I=0,1 do
    local e=0
    for c=1,3 do
      local want = ({r,g,b})[c]
      local d = pal6((f[c]<<1)|I) - want
      e = e + d*d
    end
    if best==nil or e<best then best,bestI = e,I end
  end
  return (f[2]<<11)|(f[1]<<6)|(f[3]<<1)|bestI
end
local function T() local t=M.time; return t.seconds+t.attoseconds/1e18 end
local st,tp="wait",nil

SUB = emu.add_machine_frame_notifier(function()
  local t=T()
  if st=="wait" then
    if t<3.0 then return end
    MODE.apply(SP)
    -- clear the letterbox rows: GVRAM holds IPL leftovers, not zeros
    for y=0,MODE.height-1 do
      if y<YOFF or y>=YOFF+H then
        local base=GVRAM+y*1024
        for x=0,MODE.width-1 do SP:write_u16(base+x*2,0) end
      end
    end
    for c=0,255 do
      local o=PAL0+c*3
      SP:write_u16(GPAL+c*2, pack(B(o),B(o+1),B(o+2)))
    end
    for y=0,H-1 do
      local row,base = PIX0+y*W, GVRAM+(y+YOFF)*1024
      for x=0,W-1 do SP:write_u16(base+x*2, B(row+x)) end
    end
    print(string.format("[256] R00-R08 %d %d %d %d %d %d %d %d %d  R20=%04X yoff=%d t=%.3f",
      SP:read_u16(0xE80000),SP:read_u16(0xE80002),SP:read_u16(0xE80004),SP:read_u16(0xE80006),
      SP:read_u16(0xE80008),SP:read_u16(0xE8000A),SP:read_u16(0xE8000C),SP:read_u16(0xE8000E),
      SP:read_u16(0xE80010),SP:read_u16(0xE80028), YOFF, t))
    st,tp="painted",t
  elseif st=="painted" and t>tp+0.30 then
    M.video:snapshot(); print("[256] snapshot"); st="done"; M:exit()
  end
end)