Doom demos (id Software's linuxdoom-1.10 source)

In the Linux 1.10 source, a Doom demo starts with a 13-byte header: the version (110), skill, episode, map, the deathmatch, respawn, fast, and no-monsters options, the recording player's number, and one in-game flag for each of the 4 players. Then, for every tic and every player in the game, come 4 bytes: forward move, side move, the high byte of the turn, and the buttons. A byte of 0x80 ends it. A one-player demo takes 140 bytes a second at 35 tics a second (computed). doom-demo/lump-format

About: Doom Demo playback

{
 "header": 13,
 "bytesPerPlayerTic": 4,
 "endMarker": 128,
 "version": 110
}

Cited by: Demo playback

Playback goes through the same path as play. Each tic, G_Ticker copies every player's command (ticcmd_t) from the network buffer, then, during a demo, overwrites its move, turn, and buttons from the demo; the player code then acts on that command as on a live one. doom-demo/ticcmd-path

About: Doom Demo playback

Cited by: Demo playback

A demo keeps only the turn's high byte, rounded, so a recorded turn moves in steps of 1/256 of a full circle, about 1.4 degrees (computed). While recording, the game writes the command and reads it straight back ("make SURE it is exactly the same"), so the recording player also plays with the rounded turn and the recording matches what the player saw. doom-demo/turn-rounding

About: Doom Demo playback

{
 "turnStep": 0.00390625
}

Cited by: Demo playback

Playing a demo restores the recorded skill, episode, map, and options from its header and starts the level through G_InitNew, which resets both random indices to 0, as a recording started from the command line also does. A demo whose version byte isn't 110 is refused with "Demo is from a different game version!". doom-demo/determinism

About: Doom Demo playback

Cited by: Demo playback

Playback ends at the 0x80 byte. A demo given with -playdemo then quits the game, and one given with -timedemo reports the tics and the real time taken. Otherwise the attract loop moves on: the title picture, demo1, the credits, demo2, a third page, demo3, and, in the retail Ultimate Doom only, demo4. During an attract demo, a key press that the menu doesn't take first, or a mouse or joystick button, opens the menu, and the demo keeps running behind it. doom-demo/end-and-loop

About: Doom Demo playback

Cited by: Demo playback

Recording (-record) ends when the player presses Q, when the buffer, 128 KiB unless -maxdemo sets another size in KiB, is within 16 bytes of full, when a player leaves a net game, or when the game stops on an error (I_Error); the game then writes the 0x80 byte and the file <name>.lmp, and exits with "Demo <name>.lmp recorded". doom-demo/recording-end

About: Doom Demo playback

{
 "defaultBufferBytes": 131072
}

Cited by: Demo playback