Police, emergency services, gangs

The wanted level and the crime reports (0x40d640-0x40dc7f, 0x4131d0-0x41429f), the police module (0x464e20-0x46a09f), the emergency services ("sentinels", 0x419000-0x4227a0), the ambulance crews (0x401340-0x401a7f), the scripted helicopter (0x40dc80-0x40e19f) and the Hells Angels gang and the hunting cars (0x431500-0x4325ff), and how the port mirrors them. Addresses are virtual addresses in gta.exe.

Files

File	What
src/game/wanted.c/h	criminal records, Police_ReportCrime, the per-city thresholds, the scanner reports, the pursuit groups (Police_StartPursuit, Police_UpdatePursuits, Police_EndPursuit)
src/game/police.c/h	the criminal record screen, patrol cars, Police_SpawnCar, pursuit membership, roadblocks, Cop_Update
src/game/sentinel.c/h	Emergency_UpdateAll (from the disassembly), Sentinel_DriveCar, the steering and look-ahead probes, warps, the ambulance call queue, the police dispatch list, the chasers, wreck removal
src/game/ambulance.c/h	the ambulance crews: dispatch, the medic, reviving, back to the hospital
src/game/heli.c/h	the mission-end helicopter
src/game/gang.c/h	Gang_* and the hunt table, Hunt_UpdateCar
tests/police_test.c	mission 1: crimes, the wanted level, a pursuit, a roadblock, an arrest, an ambulance; frames in out/police/

The controller table itself (0x507ea0, Sentinel_Get / FindFree / ClearTable / Reset) is ai.c's (struct AiCtl); sentinel.h's Sentinel is the same 0x98 bytes with the field names this part of the port uses. The junction override records (0x505f00) are lights.h's JunctionOvr, Map_FindNearestRoad and Path_Find are path.h's.

The wanted level

A crime is reported with Police_ReportCrime(kind, id, crime, x, y, z): kind 0 a car (its driver must be a player, the car under physics control and not model 0x2f), kinds 1 / 2 a player's ped. Position 0 means "where the reporter is". The record (Criminal, 0x2c bytes at 0x502dd8, four of them) is the one of that ped, else the first free one.

Crime	Wanted points	Score bonus kind	Scanner sample	Counter
2 car hit by a player's car (only above speed 11 or below -5)	2	0x18	0xe	2
3	50	-	0x18	3
4	10	0x1c	0x1c	4
5 car stolen	15	by model, 0x1c..0x24	0x1c	5
6	50	0x25	0x20	6
7	1	-	0x22	7
8 shooting	100	-	0x23	8
9 bank robbery	100	-	0x2a	9

The counters are the player's crime counters (Player_IncKills: shorts at +0xfc this life, +0x110 total; Police_ShowCriminalRecord prints and clears them). Points are capped at 2000 (Player_AddWantedPoints). After the crime the level is recomputed for the city (the MISSION.INI section: 1 / 2 NYC, 0x66 / 0x67 San Andreas, everything else Vice City):

City	level 1	level 2	level 3	level 4	units at levels 1..4
NYC (Police_SetWantedCity1)	151	251	351	501	1, 2, 3, 4
San Andreas (..City2)	101	201	251	376	1, 2, 4, 6
Vice City (..City3)	101	176	251	351	1 at every level

With the no-patrols switch (0x503184) the level is always 0. Level 0 clears the record (and ends its pursuit). Police_UpdatePursuits recomputes the level of every running pursuit's criminal every frame, so wanted points added directly (missions, Player_AddWantedPoints) take effect there too.

A new record's pursuit is pending with a countdown: 200 frames on foot, 100 in a car, 1 when the car last touched a police car (control 3), which also gives a player without a wanted level the points of level 1. Any non-zero level sets the countdown to 1. Each crime also queues a police scanner report (three slots per record, one per area, compass part and crime) said by Police_TickRadioReports after the same delay (Snd_PoliceRadio with the crime sample, the zone part and the nav zone's sample from Area_GetSample).

Quirks kept

• The "at least 3 / 6 units" each crime writes into +0x24 is overwritten by the city's level right after: dead code.
• A car crime first looks for a matching delayed report in the mission's timed table 0x7715d8 indexed by the player number (a mission's "bomb" set on the car): it then only starts that one counting.
• Police_EndPursuit clears the sightings of the criminal record with the pursuit's number.
• Player_IncKills compares a short with 0x7fff, which is always true: the counters wrap.

Pursuits

Four groups (Pursuit, 0x3a bytes at 0x501ac0): the criminal record, up to 20 cop controllers, the lead (the cop nearest the target), the shoot (+0x36, wanted level 3) and shoot-on-sight (+0x35, level 4 and more) flags. Police_StartPursuit 0x40da90 (named Police_SpawnRoadblock in the first names; it spawns nothing) only looks at criminal record 0: when its countdown runs out it takes the first group that isn't running (if it is free) and queues the record's number of units on the dispatch list (0x5058a8), each the nearest patrolling police car (state 199) or none. Emergency_UpdateAll then sends them; Police_UpdatePursuits keeps the flags and the lead and sends the farthest cop home while the group has more cops than the record wants.

Emergency_UpdateAll (0x419880)

The decompiler fails on it; the port follows the disassembly. Every frame, in this order:

1. Police_StartPursuit, Police_UpdatePursuits, Police_FlushObjectDeleteQueue;
2. the ambulance call queue (0x505048): a ped request without a crew gets one (Ambu_AssignVictim, only with the ambulance switch 0x5031cc and while no path search runs); once a crew is assigned the entry is dropped; car entries (id >= 0x26c, wrecks) are removed once off screen and not burning (Car_TryRemoveWreck); the queue is compacted;
3. the police dispatch list: an entry without a car takes the nearest patrol car or a new one from the respawn block (Police_SpawnCarAtTarget); its controller goes to state 200 (chase) with the pursuit, the target's nearest road block as destination, the distance at +0x46, and joins the group; done entries are compacted out;
4. the pursuits: a running group with fewer cops than its record wants (not for a criminal on a train) gets more, found or spawned the same way;
5. the roadblocks (0x50586c): their timer counts down (back to 400 while one of their cars is on a screen); while it runs and a player is wanted (level > 2) they stay; else their unseen cops (state 0x96, control 3) are released (Cop_Release; the scan then restarts at index 1, as the original does), the others leave the list, and an empty roadblock is freed;
6. Police_TickRadioReports, then (tail call) Police_UpdateChasers.

Cop_Update (0x466f10)

The state machine of a police controller (+0x1b; returns 1 when Sentinel_DriveCar should drive on):

State	What it does
1	patrol: siren off, Cop_JoinNearestPursuit, door closed
2	head for the station: released off screen, else a path to the respawn block (Cop_PathToTarget), then 3
3	released off screen, else 0xfe
4	back to the patrol route: on screen a path to its start (then 6), off screen a warp to the first node (then 1); not a patrol car: 2
5	like 2 with sub state 3
6	driving to the route start; off screen a warp, then 1
10 / 0xb	lights overridden near the destination; when the turn ends 4 (patrol car) or 2
0x32, 0x33, 199	idle (199: picked for a pursuit, waiting for the dispatch)
0x6e / 0x6f	the crew gets out (Ped_DriverLeaveCar), placed by the door, then the sub state
0x96	a cop at a roadblock: weapon (2 at wanted level 4), watches the criminal within 5 blocks, then leaves the roadblock, replaces the group's farthest cop, 0xf8
0xbe / 0xbf	a cop on foot walks back and gets in (at once when unseen), then the sub state
200	dispatched: siren; chase directly (0xcb) when close or the group has a lead, else Path_Find mode 3 (0xc9 pending, 0xca found, 0xff failed)
0xc9	waiting for the search
0xca	following the path; within 15 blocks 0xcb
0xcb	chasing: lead election, roadblocks ahead (the lead only), within 5 blocks 0xd1, a warp to a road off screen
0xd0	the cop back in the car, then 4
0xd1	close: both stopped on the same layer: out (0x6e, sub 0xd3); within 3 and the target slow: 0xd2; farther than 4: 0xcb
0xd2	alongside: stop and get out (0x6e, sub 0xd3) or chase on
0xd3	on foot: the target in a car 0xf8 (objective 0x37); on foot 0xe6 (no shooting) or 0xf8 (shooting)
0xd4	running to the target car's door (a bike is stopped); at the door 0xd5
0xd5	pulling him out; then the camera on the ped, criminal +0xe = 4, 0xda
0xd6..0xd8	a criminal on foot gives up; the cop walks him to the car, 0xda
0xd9	the cop back in, Pursuit_RecallCops
0xda	the arrest: single player Player_Busted(0), wanted level and points cleared, the chasers updated, the group recalled; network games: the criminal dies
0xe6	on foot after a criminal on foot (shooting if he is armed)
0xf0	then 0xfc, which has no case: the next step is the fatal default (kept)
0xf8	on foot at the criminal: to his door (0xd4) or shoot; criminal +0xe 3 / 5 recalls the group, 4 sends the cop back (0xd0)
0xf9	the car stopped dead
0xfe	going home: leaves group and roadblock, waits for the cop on foot, then repair + Cop_ResetToPatrol or released
0xff	no path: a warp to the next route node, then 1
other	fatal -0xf5

Criminal +0xe takes the values -1 none, 0 pending, 1 chased, 3 cops recalled, 4 arrested, 5 his car wrecked, 6 shoot on sight.

Roadblocks

They live in the junction override records (JunctionOvr, 0x505f00): a junction's traffic-light object angle (+0xc) names the CMP roadblock vertex set (g_roadblock_sets); +0xe is 1 while a roadblock stands, +0x10 its timer (400 frames), +0x12 its cars (36 shorts), +0x5a their count; the list 0x50586c (at most 0x14 used) holds the junctions with one. Roadblock_TryPlaceAhead (wanted level 3 and more, the lead cop only) scans ahead of the target car for a road and a set; Roadblock_Spawn puts police cars with their cops and barrier objects across the road. A roadblock cop's controller has +0x5e = the junction.

Sentinel_DriveCar and the steering

A sentinel (Sentinel, 0x98 bytes) drives the car whose +0xd8 names it; Cars_UpdateAll calls Sentinel_DriveCar 0x41aed0 for control modes 2, 9, 10, and 3 while the car is owned. Kinds (+0x02): 1 ambulance, 2 police, 5 route follower, 6 fire engine, 9 mission dummy (dummy.c). One step:

1. the controller holding the path search (0x4b3094) only continues it (Sentinel_RecallRoute);
2. state 0xff (dismissed): off screen and not burning the record goes (an ambulance Ambu_Remove, a police car state 0xfe, a fire engine FireEngine_Remove), else the car brakes to a stop;
3. the look-ahead (0x20 pixels ambulances, 0x24 police, the car's half length otherwise) gives the block ahead; a police car of a pursuit measures its distance to the criminal (+0x46);
4. on a route (+0x4a = 0): the current node (path slot +0x44, node number in the car's +0x119) into +0xc..+0xe, the distance to it (+0x14, its minimum +0x16) and to the destination +0x64;
5. the kind's handler (Ambu_Update, Cop_Update, FireEngine_Update, Dummy_Update): 0 ends the step;
6. off a route (+0x4a > 0, a chase): Sentinel_Steer 0x41f290 turns into side roads toward the criminal, lines up beside him and boxes him in, or follows the lane braking for what is ahead (Sentinel_CheckAhead, Sentinel_CheckObstacle, Sentinel_IsLaneClear); a pursuer far from its destination warps after the criminal while unseen;
7. on a route: the node reached advances; the turns toward the next node with lane and stopped-car checks, overtaking (Sentinel_FindOvertakeLane, Map_ScanLaneLength), the stuck recovery (Sentinel_HandleStuck, Car_ReverseLane), warps back onto the road (Sentinel_WarpCar, Sentinel_WarpToNearestRoad), traffic cleared ahead of dummies, the speed.

Emergency vehicles near a junction hold its lights (Sentinel_OverrideLights: the junction override record, timer 0x3c, the saved mode). Unjamming two cars swaps their places (Car_SwapPositions).

Quirks kept (commented in sentinel.c): whether a next route node exists is read from the path slot of the controller's own number, the node itself from +0x44; the junction block comparison of Sentinel_OverrideLights is on signed bytes (blocks past 127 never match); a removal from the call queue skips the entry swapped into the hole; in Sentinel_Steer the "lined up" test for heading +y (ry > 8 && ry < -8) never holds, and the four heading cases differ in small ways (which field is tested, braking, the turn sign); with chase mode 1 the target is in pixels but compared with the car's 16.16 position; the probes query collisions one block behind the block they test.

Ambulances

Peds that die (Ped_Animate) are queued with Ambulance_RequestForPed: the request table 0x50cab0 (10 bytes per ped, then per car + 0x26c for wrecks: block on the nearest road, state, crew) and the call queue 0x505048. Emergency_UpdateAll gives each request a crew (Ambu_AssignVictim): the first crew already out (at most nine victims) whose last victim is within 10 blocks, else a new one (Ambu_Dispatch, at most 10 crews: model 5 on the road at the hospital nearest the victim, control 2, top speed 15, the driver dressed by Ped_GetCopLook). The crew's states (Ambu_Update):

State
200	wait for the path search, then plan the route to the victim (1)
1	driving; at the victim's block (or within 5 and stopped) with no route left: stop (0x50)
0x50	the rear door opens (0x5a); nobody near a screen: 0x6c
0x5a	the medic gets out at the rear wheels (Ped_CreateSpecial)
0x5b, 0x5c	he walks behind the car, then to the victim (100)
100	he follows the victim until touching it (0x66) or arriving (0x65)
0x65	75 frames later the victim is revived: health 100, walking (state 2, objective 0x19)
0x66, 0x67, 0x6a, 0x6b	the medic walks back behind the car and into it
0x6c, 0x6d	the medic gone, a still dead victim's body removed, the rear door closes; then 2
2	the next victim (0x50 within 6 blocks, else 200); none: back to the hospital (3)
3, 4	Ambu_SendToHospital (path mode 3, then 2); at the hospital the crew is removed
0xfe	told to leave: once the medic is off screen he and the record go (the car stays)

A stolen ambulance makes the crew leave (0xfe); a victim that recovers, isn't lying for the medic or has been dead over 950 frames ends the call; a dead medic sends the crew back to the hospital.

Quirk kept: a new crew records itself only in its own victim list, not in the request (+8 stays -1).

The helicopter

Heli_Spawn (the CHOPPER command; one at a time, a second is fatal -0xf8) puts it at a point with its landing point; its shadow is an object of type 0x5c 17 pixels ahead, a block below; the sprite is the car info sprite of model 88; it is entity kind 0x1e in the grid. Heli_Update: turn to the landing point (4 a frame), fly (speed to 15), slow over the block, descend 2 pixels a frame to 66 pixels above the ground, wait 40 frames, take the player (his ped leaves the grid, the camera follows the heli: target kind 5), climb to z = 2, fly to the exit point (CHOPPER_ENDPOINT, speed to 39), freeze the camera there (kind 4) and end the level 30 frames later (Event_ScheduleExit(30, 1)).

Quirk kept: Heli_TurnTowards masks the heading only when it turns again, so a heading of -4..-1 or 0x400..0x403 is used once; below the sine table lies the tan table, which the port reads in that case.

The gang and the hunters

A mission's gang cars (Gang_AddCar, ten) hunt a player who rides one of them (a bike, model 3) for 30 frames (Hunt_AddCarTarget mode 6). While he is on a bike Gang_Update (from the mission's trigger update) also gives every gang car an extra Hunt_UpdateCar step: the gang drives twice per frame.

The hunt table (Hunt, 0x1c bytes at 0x5132a0, 20 entries) drives cars with control 0x32 (Hunt_UpdateCar from Cars_UpdateAll): to a block (modes 4 / 10) or after a ped (other modes, its car's block when it drives). A hunter chasing a car accelerates (bikes to the top speed, model 0x2f 3 a frame, others to 10 above the target's speed), otherwise it slows to 7; off the road and unseen it warps onto the nearest road; within 2 blocks it turns toward the target; else at each junction it takes the exit (left, right, ahead) whose direction is nearest the target's. A car that hasn't moved since the last step stops unless it can push the car in its way off screen.

How the chase plays out

Police_UpdatePursuits makes the nearest cop the group's lead every frame, so dispatched cops go straight to the chase (0xcb) and are steered greedily toward the criminal (Sentinel_Steer) rather than along a Path_Find route. On the one-way grid around a criminal who stands still they can circle for a long time (mission 1's start block: within about 8 blocks, never closer). What brings them is the criminal moving: once he is 12 blocks from where a cop was sent, the unseen cop is warped there (Sentinel_WarpCar) and sent on. tests/police_test.c therefore moves the player between two blocks 13 apart; at wanted level 2 (no shooting) a cop then gets out and arrests him.

The helicopter takes the player by pointing his camera at it (kind 5). A player on foot whose ped is walking (state 2, action 2) has Ped_UpdateAll copy the camera target into the controlled kind (Player_ControlViewTarget), and kind 5 is fatal in Player_UpdateAll (-0x4a); the original does the same, so in the shipped missions the player is presumably not in that state when the heli lands (open question). The test boards it from a car.

Port deviations

• The original reads outside its tables in a few places (criminal -1, ped -1, a cache layer below 0, the player record of a ped that is no player); the port guards them (documented at each place).
• Car_SteerTowards 0x40bc70 is car.c's, Area_GetSample 0x44b7b0 the area module's (src/hud/area.c), Player_IncKills / Player_SetViewFixed4 / Player_AwardBonus player.c's, Ref_GetKind1PosRect 0x45fb60 ped.c's. The fire engines (kind 6) are fire.c's: see Objects.
• The dispatch list stores car / ped ids where the original stores record pointers.