Mechanic · combat · shooter

Homing missile

A projectile that picks a target after it is fired and turns toward it in flight.

stubAlso: homing weapon, homing projectile, seeker missile, heat-seeker, homing rocketUpdated 2026-10-22
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A homing missile does its aiming after it is fired. In Descent 3 it searches a cone ahead of it for the visible enemy most nearly in line, and steers at a point a tenth of a second ahead of that enemy1,2.

  • Cone and turnDescent 3 (1999). The target most nearly ahead in the weapon's cone within 500 units, led by a tenth of a second, with robots' missiles turning slower or faster by difficulty.1,2

See also

Mentioned in

Games

GameYearHowNote
Descent 31999Cone and turnthe target most nearly ahead in the weapon's cone within 500 units, led by a tenth of a second, with robots' missiles turning slower or faster by difficulty
Every claim about this mechanic, by game (2)
Descent 3 1999In Descent 3's released source a homing weapon with thrust left starts homing 0.1 s after it is created, unless it is guided. Without a target, it scans every object in a room the missile's room can see: robots, players, and buildings with AI, not its own shooter, not cloaked, and only enemies of the shooter, inside a cone where the dot product of the direction to it with the missile's facing exceeds the weapon's homing_fov. In object order, a chaff chunk ends the scan (by a 1-in-4 roll in single player) and so does anything within 15 units (the distance between centers less both objects' sizes); otherwise the missile takes the object within 500 units most nearly straight ahead with a clear line to it. A target it has is kept while it stays inside the cone and either within 15 units, or within 500 units, in a visible room, with a clear line.Code
Descent 3's released source steers a homing weapon at the target's position plus a tenth of the target's velocity when the target moves under physics or walks. A weapon with rotational drag fires full full_rotthrust left or right and up or down, by which side of the missile the aim point is on, with no roll; one without it turns straight toward the aim point by at most full_rotthrust × the frame time and has its velocity set along its new facing at full_thrust/drag. A weapon whose shooter is not a player has its turning scaled by difficulty: 0.20, 0.70, 1.00, 1.20, and 1.40 from Trainee to Insane.Code

References

  1. ^ abIn Descent 3's released source a homing weapon with thrust left starts homing 0.1 s after it is created, unless it is guided. Without a target, it scans every object in a room the missile's room can see: robots, players, and buildings with AI, not its own shooter, not cloaked, and only enemies of the shooter, inside a cone where the dot product of the direction to it with the missile's facing exceeds the weapon's homing_fov. In object order, a chaff chunk ends the scan (by a 1-in-4 roll in single player) and so does anything within 15 units (the distance between centers less both objects' sizes); otherwise the missile takes the object within 500 units most nearly straight ahead with a clear line to it. A target it has is kept while it stays inside the cone and either within 15 units, or within 500 units, in a visible room, with a clear line.CodeDescentDevelopers/Descent3
    How we know
    1719	if((obj->mtype.phys_info.flags & PF_USES_THRUST) && (obj->ctype.laser_info.thrust_left >= 0.0))
⋮
1721		obj->ctype.laser_info.thrust_left -= Frametime;
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1723		if((obj->creation_time + 0.1f < Gametime) && (obj->mtype.phys_info.flags & PF_HOMING) &&	!(obj->mtype.phys_info.flags & PF_GUIDED))
⋮
1725			obj->ctype.laser_info.last_track_time = Gametime - HOMING_CHECK_VIS_INTERVAL;
1726			HomingDoFrame(obj);
    Descent3/WeaponFire.cpp lines 1719–1726 at 61bb9a3 · upstream ↗
    1461#define MAX_HOMING_DIST	500.0f
1462#define CLOSE_HOMING_DIST 15.0
    Descent3/WeaponFire.cpp lines 1461–1462 at 61bb9a3 · upstream ↗
    1604			for(i = 0; i <= Highest_object_index; i++)
⋮
1606				if(BOA_IsVisible(obj->roomnum, Objects[i].roomnum))
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1608					if((i != OBJNUM(weapon_parent))  && ((Objects[i].type == OBJ_BUILDING && Objects[i].ai_info) || (Objects[i].type == OBJ_ROBOT) || (Objects[i].type == OBJ_PLAYER)))
⋮
1612						if(Objects[i].effect_info && Objects[i].effect_info->type_flags & EF_CLOAKED)
1613							continue;
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1615						if(weapon_parent && !AIObjEnemy(ObjGetUltimateParent(weapon_parent), ObjGetUltimateParent(&Objects[i])))
1616							continue;
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1619						float cur_dot = to_target * obj->orient.fvec;
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1621						if(cur_dot > Weapons[obj->id].homing_fov)
    Descent3/WeaponFire.cpp lines 1604–1621 at 61bb9a3 · upstream ↗
    1623							//Pick chaff over other objects
1624							if ((Objects[i].type == OBJ_ROBOT) && (Objects[i].id == GENOBJ_CHAFFCHUNK)) 
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1634											break;
⋮
1637									else
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1642											break;
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1646								else
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1648									if (ps_rand() < RAND_MAX/4)
1649									{		// 1/4 chance of picking chaff
1650										best_index = i;
1651										break;
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1655							else if(dist_to_target < CLOSE_HOMING_DIST)
⋮
1657								best_index = i;
⋮
    Descent3/WeaponFire.cpp lines 1623–1659 at 61bb9a3 · upstream ↗
    1660							else if(dist_to_target < MAX_HOMING_DIST)
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1662								if(cur_dot > best_dot)
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1677									if(hit_info.hit_type[0] == HIT_NONE)
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1679										best_index = i;
1680										best_dist = dist_to_target;
1681										best_dot = cur_dot;
    Descent3/WeaponFire.cpp lines 1660–1681 at 61bb9a3 · upstream ↗
    1497		else if(to_target * obj->orient.fvec > Weapons[obj->id].homing_fov)
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1509				else
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1539					if(hit_info.hit_type[0] == HIT_NONE)
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1549			if(dist_to_target < CLOSE_HOMING_DIST)
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1551				f_locked = true;
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1553			else if(dist_to_target < MAX_HOMING_DIST)
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1555				if(BOA_IsVisible(obj->roomnum, track_goal->roomnum))
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1572						if(hit_info.hit_type[0] == HIT_NONE)
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1574							f_locked = true;
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1577					else
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1579						f_locked = true;
    Descent3/WeaponFire.cpp lines 1497–1580 at 61bb9a3 · upstream ↗

    Checked against the evidence by its author, an AI model, 2026-10-22.

    Checked by a second AI model, 2026-10-22.

    In the claim ledger

  2. ^ abDescent 3's released source steers a homing weapon at the target's position plus a tenth of the target's velocity when the target moves under physics or walks. A weapon with rotational drag fires full full_rotthrust left or right and up or down, by which side of the missile the aim point is on, with no roll; one without it turns straight toward the aim point by at most full_rotthrust × the frame time and has its velocity set along its new facing at full_thrust/drag. A weapon whose shooter is not a player has its turning scaled by difficulty: 0.20, 0.70, 1.00, 1.20, and 1.40 from Trainee to Insane.CodeDescentDevelopers/Descent3
    How we know
    1413	if(target->movement_type == MT_PHYSICS || target->movement_type == MT_WALKING)
⋮
1415		movement = 0.1f * (target->mtype.phys_info.velocity);
⋮
1418	dir_to_target = target->pos + movement - weapon->pos;
    Descent3/WeaponFire.cpp lines 1413–1418 at 61bb9a3 · upstream ↗
    1420	if(weapon->mtype.phys_info.rotdrag > 0.0f)
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1422		if(dir_to_target * weapon->orient.rvec > 0.0)
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1424			weapon->mtype.phys_info.rotthrust.y = weapon->mtype.phys_info.full_rotthrust;
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1431		if(dir_to_target * weapon->orient.uvec > 0.0)
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1433			weapon->mtype.phys_info.rotthrust.x = -weapon->mtype.phys_info.full_rotthrust;
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1440		weapon->mtype.phys_info.rotthrust.z = 0.0;
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1442		if(!ObjGet(weapon->parent_handle) || ObjGet(weapon->parent_handle)->type != OBJ_PLAYER)
1443				weapon->mtype.phys_info.rotthrust *= Diff_homing_strength[DIFF_LEVEL];
    Descent3/WeaponFire.cpp lines 1420–1443 at 61bb9a3 · upstream ↗
    1445	else
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1450		if(!ObjGet(weapon->parent_handle) || ObjGet(weapon->parent_handle)->type != OBJ_PLAYER)
1451			scalar = Diff_homing_strength[DIFF_LEVEL];
1452		else 
1453			scalar = 1.0f;
⋮
1455		AITurnTowardsDir(weapon, &dir_to_target, weapon->mtype.phys_info.full_rotthrust * scalar);
1456		weapon->mtype.phys_info.velocity = weapon->orient.fvec * weapon->mtype.phys_info.full_thrust/weapon->mtype.phys_info.drag;
    Descent3/WeaponFire.cpp lines 1445–1457 at 61bb9a3 · upstream ↗
    2206	max_angle = turn_rate * Frametime;
⋮
2208	if((float)goal_angle > max_angle)
    Descent3/AImain.cpp lines 2206–2208 at 61bb9a3 · upstream ↗
    16float Diff_homing_strength[5]  = {0.20f, 0.70f, 1.00f, 1.20f, 1.40f};
    Descent3/difficulty.cpp line 16 at 61bb9a3 · upstream ↗
    7#define DIFFICULTY_TRAINEE		0
8#define DIFFICULTY_ROOKIE		1
9#define DIFFICULTY_HOTSHOT		2
10#define DIFFICULTY_ACE			3
11#define DIFFICULTY_INSANE		4
    Descent3/difficulty_external.h lines 7–11 at 61bb9a3 · upstream ↗

    Checked against the evidence by its author, an AI model, 2026-10-22.

    Checked by a second AI model, 2026-10-22.

    In the claim ledger

Sources

Code