Objects, explosions, fires, power-ups

The object module of the original (0x44c2d0-0x44ee4f), the explosions (0x425170-0x426320), the fire module with its fire engines (0x42e600-0x430400), the power-ups (0x46a0a0-0x46a99f), the block animations (0x402240-0x402610) and the map edits (Map_Set* 0x437b50-0x438020, Map_IsFaceSolid 0x438650, Map_IsCovered 0x438800), and how the port mirrors them. Addresses are virtual addresses in gta.exe.

Files

File	What
src/game/obj.c/h	the object table and record, the object_info records, level start, Obj_Create, Obj_CreateAttached, Obj_CreateAnimated, Obj_Kick, Obj_UpdateAll and its four lists, Obj_Delete and the unlinkers, Obj_IsOnScreen, Obj_OnCarWrecked
src/game/expl.c/h	the 25 explosion slots, Expl_Create, Expl_CarExplode, Expl_AtFaceIfSolid, Expl_UpdateAll, Expl_DamageArea, the delayed explosions
src/game/fire.c/h	the 4 recorded fires: Fire_Init, Fire_Register, Fire_IsNearActive, Fire_Extinguish, Fire_FindNearestUnattended, Fire_HasObjects, Fire_ClearObjects; the fire engines FireEngine_*
src/game/powerup.c/h	the 256 power-ups: PowerUp_Add, _Reveal, _RemoveAt, _ExistsAt, _Collect
src/game/blockanim.c/h	the 64 animated faces (doors)
src/map.c/h, src/game/mapedit.c/h	the copy-on-write map edits, Map_IsFaceSolid, Map_IsCovered (map_covered); mapedit.c is the game's side (the fatal error)
tests/obj_test.c	map edits, a kick, a rocket at a parked car, a blast, a power-up, a door, against mission 1; frames in out/obj/
tests/fire_test.c	a fire, the engine dispatched, driving there, spraying and heading home; frames in out/fire/

The explosions on block faces with debris and fires (0x425520, 0x425780, 0x4258d0) are in mission_obj.c, where the mission thunks 0x475700-0x475720 that call them were ported.

The object record (0x6b40d0, 3500 x 0x88)

Off	Field	Meaning
+0x00	id	own index
+0x02	speed	pixels a frame (moving list), projectiles too
+0x04	life	frames in a state (tumbling, sinking), counters of the 0x40 / 0x4d and projectile types
+0x06	heading	direction of motion (0..1023), separate from the sprite angle
+0x08	weight	object_info +0xe; 3 never moves; 2 * speed >> weight on a kick
+0x0a	type	object_info index
+0x0c	state	the frame state: 0 free; see Obj_UpdateSprite and the moving states below
+0x0e	frame_timer	frames since the last animation step
+0x10	u10	animation cycles done (status 7: timer steps)
+0x12	u12	1: cycles don't count (Obj_SetFlagE2: a recorded fire burns until extinguished)
+0x14	owner	the entity a fire burns on / an attached object rides (-1)
+0x16	param	creation parameter (0x40 / 0x4d: a ped)
+0x18	attach_kind	attached: 0 object, 1 / 5 car (5 also turns the sprite), 2 / 3 train carriage, 4 ped; fires: 0 object, 1 car, else ped
+0x1a / +0x1c	off_fwd / off_side	attached offset in pixels along / across the owner's heading
+0x1e	u1e	projectiles and bombs: the ped that fired / planted it (its player is blamed)
+0x20	in_anim_list
+0x24 / +0x28	next / prev	list links
+0x2c	spr	the sprite (x, y, z, depth key, angle +0x44)

Obj_UpdateSprite 0x44c3a0: the frame of state s is spr_num + s - 1 for 1-8, then three runs of six (9-14, 15-20, 21-26) map to spr_num + 1..6, and 27-31 to spr_num + 8..12.

object_info (style, Obj_LoadInfos 0x44ed60): w, h, depth (16.16 after loading), spr_num, weight, aux (+0x10), status (+0x12), num_into, into[] (the objects it breaks into). The animation code reuses the integer parts of w / h / depth as counts (frames per cycle, frames per frame, cycles).

Obj_UpdateAll 0x44d790

Four lists, then Proj_UpdateAll (projectiles are objects too, proj.c):

• Moving (0x6b40bc): what Obj_Kick set going (statuses 0, 8, 9 only; the bomb 0x16 explodes instead, the signs 0x21 / 0x22 stay). An object moves speed pixels along its heading (at most 48) unless a corner of its box is over a building (state 7, speed 0); tumbling ones (states 8-25) knock peds down (anim 0x2c), a ped walking into a light one (weight 0) stops it. States: 2-6 slide, 7 bounce, 8-13 tumble, 14-19 in the air, 20-25 tumble again, 26-31 sink (status 8 floats at 26). Each frame it spins 0x40 (less in the air) and steps through a fixed table of state changes. Over an edge (the ground 8 pixels lower) it falls 5 pixels a frame and nearby peds panic. Landing on water sinks it; elsewhere it lands (status 0: state 7, or 2 when it breaks), and an object with into entries breaks into them, each kicked on with speed 3 in a random direction. Speed drops by 2 a frame; at 0 it settles on the ground, leaves the list and kicks a ped standing on it.
• Status 7 (0x6b40c0): timers. Every h frames a step; after depth steps the object is deleted and explodes (a pixel up), blamed on its ped's player.
• Animated (0x728430, statuses 5 and 9): fires (0x12, 0x13, 0x2e) make peds panic, leave smoke (type 10) on frame 1, follow their owner (an object, a car, a ped; a car parked at the map's corner puts it out) or, without one, set a ped walking into them on fire (object 0x2e, health - 10) and add 5 damage to a car on them. Smoke (10, 0x33) rises a pixel a frame and drifts to +x / -y. Type 0x3f spawns a 0x40 on its first frame in state 5; 0x40 / 0x4d live until their ped dies (then 1000 frames). Status 9 cycles 1..aux, a frame every 3; the others a frame every h over w frames, and with a depth for depth cycles (unless u12): then they go (a fire 0x12 leaving a dying fire 0x13 and adding to its car's burning count), unlinked only when aux is 1.
• Attached (0x6b40c4): back onto the owner at the offset (cars 2 pixels under, peds 1 over). The car lights 0x35 cycle 1-11, the object lights 0x30 / 0x31 1-8. Obj_ListRotate (used by the tank) moves the second entry to the head.

Explosions (0x50f7e8, 25 x 0x64)

A slot is a sprite (kind 0xc in the collision grid; the renderer draws the owner as the sprite) plus a frame (+0x5c) and a tick (+0x5e). Expl_Create takes the first group of four consecutive free slots (groups 0..21), plays sample 0x27, applies the blast, and places four quarters of a 64 x 64 picture around (x, y): frames 1, 13, 25, 37 of the explosion sprite group (0x774ef4). The picture floats 16..31 pixels (random) above z, its depth key a layer higher. Every 2 frames a slot steps; the first quarter leaves smoke (0x33) on frame 10; frames 12 / 24 / 36 / 48 free the quarters. Expl_CarExplode explodes at the car and the four corners of its box (8 pixels under the corners' ground).

Expl_DamageArea 0x425ca0, over everything of the 3 x 3 cells touching the layer of z:

• peds (alive, not dead / in a car, at most a layer below) within 60 pixels are thrown (speed 16, away by quadrant); within 35 they die (anim 0x5a), further out they catch fire (object 0x2e, sample 0x18, health - 10). The owner scores (Score_PedKilled cause 2) and the police hear of it (crime 8). In single player a ped seen lately counts for the player.
• objects without an owner at rest within 75 pixels are kicked away (speed 10); a gas tank (0x45) within 25 goes off 5 frames later (the 25 delayed explosions at 0x50f610). Crates (0x54) open.
• cars within 64 pixels are wrecked (damage 100) and blamed on the owner (crime 7); the tank (0x25) only takes 4 damage.

Expl_AtFaceIfSolid 0x425960 (rockets against walls): an explosion on a side face of a block when the face is there (Map_IsFaceSolid), plus two fires beside it where World_AnyThingAt finds none.

Fires (0x511988, 4 x 0x24)

{object, x, y, z (the road block next to it, pixels), engine (its car id), objects[10] (the water jet; the last one counts the spraying frames), extra}. Fire_Register (from the creators of fire objects) records a type 0x12 fire when the record, fire and engine counts allow, no recorded fire with an engine is within 40 blocks and it doesn't burn on the cars 0xb / 0xd: within 2 blocks of a recorded fire it becomes that fire's extra (and burns on: u12); otherwise the nearest road (Map_FindNearestRoad) on its layer within 4 blocks gets a fire engine (FireEngine_Dispatch). No engine to send: the record is dropped again.

Fire engines (0x42e870-0x430400)

A fire engine is a sentinel of kind 6 (Police) driving car model 0x2a. FireEngine_Dispatch 0x42ec70 takes a free record (Sentinel_FindFree) and spawns the engine (FireEngine_Spawn 0x42e920) at the nearest (Manhattan) of the 4 fire stations of the CMP's locations, else at each in turn: Car_SpawnOnRoad with a driver (control type 6), car control 9, cruise speed 6; the record listed in engines[] (0x511a1c, 3) with 2500 frames to stay out (0x511978), and the hose (object 0x32) attached 1 left and 6 back, turning with the car (its id also at car +0x11c, so the siren code leaves it alone). With 3 out and no free engines[] slot an engine heading home is sent instead (quirk: only sentinels 0..2 are looked at, each against its own engines[] slot). FireEngine_SetDestination 0x42ea90 puts the siren on and starts a route search (mode 5) to the road block next to the fire.

Sentinel_DriveCar drives it along the route and calls FireEngine_Update 0x42f460 every frame, a state machine on the record's +0x1b:

State
5, 2	waiting for the path search (another controller holds it), the search running
1	driving to the fire; stops (-> 10) within 4 blocks (Chebyshev, another layer counting 500 more) unless still moving and the next block is closer, or at the end of the route
10, 0x14	braking to a stop; the hose stops turning with the car
0x64	the hose turns 3 a frame toward the fire object (FireEngine_AimHoseAtObject 0x42f240)
0x6e	the jet: n = (d - 52) / 32 + 1 objects (d the hose-to-fire distance in pixels, at most 320 and n below 9): 0x30, each 0x1e ahead of the previous (the first 0x24 ahead of the hose), and a 0x31 end, shortened by the rest of the division; the fire object is deleted (its record keeps the position)
0x82	spraying: 262 frames while the fire object's record stays where it was
0x97, 0xa0	the jet deleted; the hose turns back to the car (FireEngine_AimHoseAtCar 0x42f2d0), turns with it again, the fire record is dropped (Fire_Extinguish)
0x1e	the nearest unattended fire (FireEngine_ArriveCheck 0x42ebe0: more than 2 blocks away it drives there) or home (FireEngine_ReturnToBase 0x42ee40: siren off, a route to the nearest station)
0x23, 0x28	the search home running, driving home; an unattended fire on the way is taken; at the end of the route 0xff
0x27, 0xaa	giving the fire up (its object and record go) -> 0xff; a wall in the jet's way -> 0x97
0xff	dismissed: Sentinel_DriveCar removes it (FireEngine_Remove 0x42e870: hose, car, record) once off screen

A burnt-out engine (damage 100) or one out for 2500 frames gives its fire up; burnt out, its hose is deleted and the fire dropped every frame. tests/fire_test.c lights a fire 8 blocks from a station in NYC: the engine stops 4 blocks from it after about 530 frames, sprays a jet of 9 objects and heads home at frame 910.

Port notes: engines[] is filled at engine_count, which FireEngine_Remove decrements whatever slot it frees, so a spawn after an engine left from a lower slot overwrites a live one (which then keeps no timer and is never removed from the list): kept. Object -1 (the hose after a burn-out) and the request of the victim slot -1 (FireEngine_ReturnToBase writes one, 0x50caae, unused memory) are read as a blank object and not written.

Power-ups (0x74f858, 256 x 0x1c)

{x, y, z, object, visible (1 crate, 2 revealed), type, value}. PowerUp_Add puts a crate (0x54; help signs, type 14, as 0x5f at once). PowerUp_Reveal (rockets, cars, punches, blasts) replaces the crate with the power-up's object (types 1-4: 0x4e-0x51, 6: 0x61, 9: 0x65, 10: 0x60, 11: 100, 12: 0x62, 13 / 15: 99; the others none: the record is cleared) and a broken crate (0x55). Touching the object (ped and car collision code) calls PowerUp_Collect: weapons (default ammo from the exe table 0x4a8c18 when the value is 0, the value if below 100, else a temporary weapon for value - 100 frames; refused at 99 ammo or with a temporary weapon), speed-up (in a car Car_DampThrust, on foot fast walking for 0x177 frames), bribe (wanted level cleared), armour (3 hits; refused when full), multiplier + 1, get out of jail free (refused when held), extra life (15 with a voice), help text "help<value>". The local player sees the item's text; a sample plays (2 weapons, 3 odd types, 4 even).

Block animations (0x4bbc70, 64 x 0x74)

{which (1 lid, 0 side), tile, active, tick, speed, index, event type, event arg, n, frames[10] of {kind, tile}}. BlockAnim_Create gives a door's face a fresh tile number past the style's tiles (Style_AllocSide / Style_AllocLid: the style's counts grow) and points the face at it (Map_SetBlockFace), showing the old tile. StartForward / StartReverse fill the frames with ascending / descending tiles of a kind (2 = aux tiles); BlockAnim_Tick steps every speed frames (Style_SetTileFrame sets what the tile shows) and dispatches the event (2 / 3: door opened / closed) on reaching the last frame.

Map edits (0x437b50-0x438020)

The loaded map is shared data; an edit first copies the block's column (7 - h shorts) into the column change area (0x2000 bytes after data_end + 0x2000) and the block (8 bytes) into the block change area (0x2000 bytes at data_end), repoints the column entry and the base table, then changes the copy; later edits of the same block change the copy in place. Overflow is fatal (-0x15, "Map change overflow"). Map_SetBlockType / _SetBlockKind / _OrBlockFlags update the type cache; Map_SetBlockFace doesn't.

Quirks kept

• Obj_Kick pushes onto the moving list without setting prev; when an object settles, the list is unlinked through prev (NULL), so the head becomes the next object and the ones before it stop being moved.
• Obj_Kick compares the angle with itself plus / minus 0x20 to turn it by 0x40: never true.
• Moving objects give Map_SlopeDelta the block kind (0..7) instead of a type map: no slope speeds them up.
• Obj_CreateAttached tests the attach kind, not the type, against the blended types.
• Obj_CreateAnimated initialises the sprite with the owner as its angle (then sets 0); callers that pass a heading as the last argument set the attach kind to it.
• Obj_DeleteByOwner deletes free slots whose stale owner matches (the smashable count drops again).
• Fire_IsNearActive ignores fires whose engine id is 0; Fire_Register compares against every record, the free ones (at block 0) too.
• Expl_AtFaceIfSolid explodes without testing the face outside blocks 1..255 / 0..255, and gives World_AnyThingAt block coordinates for the first fire.
• In Expl_Create the quarters copy z from the first slot, even when the first was outside the world.
• Map_SetBlockKind ORs the new type bits in on a block's first edit (it reads the source block after clearing the copy) and replaces them on later edits.
• A blast in single player credits every later kill of the same blast to the player once a ped seen lately died.
• Status 4 objects turn their heading on landing without wrapping it (see the deviations).

Port deviations

• Out-of-range headings (status 4 landings) index the sine table wrapped; the original reads the tan table before it or memory after it.
• PowerUp_Reveal on a record without an object doesn't delete object -1 (the original indexes before the table).
• The block animation frame list stops at the end of the table (the original writes on into the next record, and past the last one).
• Map_IsCovered answers false outside the map (unchecked in the original).