Combat maneuvers¶

How a ship fights. The order Fight (105) runs one maneuver after another against its target: "loop the loop", "defend dodge1", "attack pursue" and seven more. Each maneuver is a script in a small language of the developers' own, which the payload compiles line by line as it first runs each line, and a table picks the next maneuver by where the two ships are.

aidefend.zig and aifight.zig define the structures, aidefend/maneuvers.zig holds the maneuvers, their scripts and the handlers of each opcode, which make maneuver-tables transcribes from the executable, and aidefend/script.zig compiles the scripts as the payload does. The build compiles every script, so a script the compiler cannot read fails it. The names below are those make ghidra-annotate gives the Ghidra project; the source file the asserts name is aidefend.cpp.

The maneuvers¶

maneuvers (0x4E1070) holds a 16-byte ManeuverRecord for each maneuver:

A script is a list of 8-byte ManeuverScriptLine records ending with one without text: the line's text, and a pointer to its compiled instruction, null until the line first runs. "loop the loop" reads:

Cloak(on)
SetAfterburner(off)
SetPitch(1)
SetYaw(0)
SetRoll(0)
SetSpeed(0.5)
loop:
    Wait(1000)
    Goto loop

and "attack pursue":

Cloak(off)
SetAfterburner(off)
loop:
    If Goingtocrash
        Avoid(300)
    Endif
    Attack(25)
    Goto loop

The language¶

Each line is one command: a word, then for some commands arguments in parentheses, separated by commas. A word is letters, digits and _ . : -; spaces and tabs around words are skipped. Commands compare without regard to case. A line whose first word ends in : is a label.

maneuver_compile_line (0x00405010) compiles a line into maneuver_code (0x515DA4) at maneuver_code_end: a byte of opcode, then what the command needs. It reads arguments with script_read_arguments (0x00404F80), four at most. Where a command takes a range, one argument gives both ends. It stops with a fatal error on a command it does not know ("Syntax error %s"), arguments that do not open with ( or are not separated by commas ("Syntax error"), a Goto to a label no line holds ("Invalid goto"), and an If or Else with no Endif ("no endif for if").

Running a maneuver¶

maneuver_handlers (0x4E0CC0) holds a start and a run routine for each opcode, either of which may be null. maneuver_run (0x004069B0) runs the Fight order's maneuver for an update, keeping the line it is on and whether that line waits in the order's state, a FightState:

1. While no line waits, it moves to the next line, compiles it if it has not been, and calls its opcode's start routine, which returns true for an instruction that waits.
2. It then calls the waiting line's run routine, which returns true while the instruction still waits.

So a script's commands run one after another in the same update until one waits, and a loop without a waiting command in it would never return. Commands that wait keep a timer in the state, min + random * (max - min) ticks after frame_start, which maneuver_start_timer (0x00405B20) sets. What each does:

ai_escape_direction sums, over each box of the collision trees of the parts in the ship's root's child list, every part whatever it is linked to, taken as a sphere as wide as its half-size, a push away from the box for each whose edge is within 20000 units of the point, the harder the nearer, and normalizes the sum.

The commands that fly to a point (maneuver_steer_to_point, 0x00405C60) go at full throttle and steer with ai_steer at the pilot's turn limit and no ease, flags 0xB, unless there is something to avoid, when they steer at full limit with flags 0x3. Once the point is within 26 degrees of the nose, the ship pitches at its full rate until it is 45 degrees off, then steers at it again, so it weaves.

Choosing a maneuver¶

fight_choose_maneuver (0x0040A3A0) chooses the next maneuver into the order's data, a FightData, which Fight starts on its next update. It runs when Fight starts and whenever the maneuver's time is up.

• Against a target with components: "attack massive object", for 20000 ticks.
• For a ship with components: "attack medium fighter", for 10000 ticks.
• For a ship outside the action sphere whose target is not a player's and is either within 200000 units of it or outside the sphere as well, with no player's ship within 100000 units: "out of action sphere", for 500 ticks. The AI's first setup (ai_first_setup, 0x0040C9B0) puts the sphere around slot 0 with a radius of 220000 units; a mission's SetActionCentre (command 0x25) moves it (action_sphere_center, 0x515D78, and action_sphere_radius, 0x515D74), back to 220000 for a radius of 0.
• Otherwise, fight_choose_by_position (0x0040A000):
• Farther from the target than pursue_distances (0x4E193C), 300000, 200000 or 100000 units by the pilot's skill, times the target's speed over its top speed but at least a quarter: "attack pursue". Fix: the table holds three, and the game indexes it with the skill as a signed word, reading past it or before it, so that some other skills never pursue and others always do. OpenReliant never pursues by distance for a skill outside the table.
• With the target behind the ship, one time in ten, "run to ship" toward the nearest friendly ship with components and combat class 2 or 3, unless the ship is already within 50000 units of one, its radius aside (fight_find_ship_to_run_to, 0x00409F00).
• Within 10000 units of the target: "defend runaway".
• Otherwise a random maneuver from maneuver_choices (0x4E1918), by where the target is from the ship's nose (ahead within 60 degrees, behind more than 120 degrees off it, or abeam between), then where the ship is from the target's (ahead within 60 degrees, behind more than 96 degrees off it, or abeam between): "attack pursue" when the ship is behind the target, or when the target is ahead and the ship abeam of it, and otherwise one of "defend runaway", the three dodges and "loop the loop".

Its length is what the choice gives, or min + random % (max - min) ticks from the maneuver's range, with the ship's own random number.

When Fight starts (order_fight_init, 0x0040A4D0) it chooses the first maneuver, draws the wait for the first missile, sets the ship's fighting to the target, counts one more in the target's fought_by, and zeroes the ship's recent_damage. When it starts a chosen maneuver it clears its state, puts the script before its first line, picks the inputs to mirror, and sets the tick it ends at.

Each update¶

Fight's update (order_fight, 0x0040A5E0) pops the order when its target is no longer valid, chooses a new maneuver when the last one's time is up and starts one chosen, and then:

1. Aims (fight_aim, 0x00409BE0). Every pilot's aim_interval ticks it aims afresh: ahead of the target where ai_lead_aim (0x00401280) can lead it with the fastest of the guns it fires together, and otherwise at the target, or at its part for a component. ai_lead_aim_with_gun (0x00401180) leads it along its heading by its speed times the time the gun's shot takes to reach it, where that is within a quarter of the gun's lifetime, three times its lifetime for a Turret Flak. Fix: the game reads each gun's turret kind as its type, so it leads every ship's shots as a Laser Cannon's; OpenReliant leads by the fastest gun's own type. Fix: for the Turret Flak the game takes the Laser Cannon's lifetime, the table's first gun's, which leads flak past the life of its own shells; OpenReliant the flak's own. The aim point's velocity is a quarter of the target's, turned by the target's per-update turn half aim_interval times. Each update the aim point moves by that velocity times frame_duration.
2. Fires (fight_fire, 0x004096B0), unless the ship is cloaked, or its target is cloaked and stands within both radii and 10000 units of it (cloak_target_far, 0x00463BD0), which the order's target never is. Once the pilot's pause has passed since it last looked, it looks again: where the aim point is within fire_spread times the target's radius (or its part's) of the line along the ship's nose, and the part is within a quarter of a laser cannon's range (its speed times its lifetime), it fires for the pilot's burst ticks. A friendly ship holds its fire while a player's ship is ahead of it within 50000 units and within a tenth of that distance, plus the player's radius and 500 units, of the line along its nose. It then locks and launches its missiles, timed from the pilot's missiles range, and drops its countermeasures, timed from its countermeasures range, while a missile homes on it (Missiles).
3. Calls for help (fight_call_for_help, 0x00409D10). When the target is the player, the player hit the ship last, its recent_damage has reached 1.2 times its armor class, and one of its armor values is below 3 times its armor class, about half what it starts with, it zeroes recent_damage and pushes Fight, aimed at the player, on the nearest ship of its side with combat class 1 whose order is Fight or Mill. The first milling ship in the slots takes over from any fighting ship found before it, however near; from there the nearest wins.
4. Cloaks (fight_update_cloak, 0x00409EC0) as the maneuver's Cloak asked.
5. Runs the maneuver.

The pilot¶

The Fight order and its maneuvers read the ship's pilot, a record of pilot_stats that pilotstats.bin's tiers fill (pilots.zig):

Unknown: what the game calls these.

In OpenReliant¶

The Fight order and every command run as described, but for multiplayer, where the host chooses the maneuvers (#55).

Where the game would stop, hang or read past its tables, OpenReliant goes on:

• Fix: a script that runs off its end ends the maneuver, so Fight chooses another, where the game stops with a syntax error.
• Fix: a loop that starts 256 lines in one update without one waiting is left for the next update, where the game hangs.
• Fix: a maneuver number past the table runs nothing, where the game reads past it.
• Fix: a range with no span gives its least, where the game divides by zero.
• Fix: Fight's init leaves a target past the objects for the update to pop, where the game takes its index as a ship's slot whatever it holds, and fights with the pilot the ship's number gives, where the game stops with "pilot not setup for %s" for a ship with no pilot record.