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fix ai behavior when avoiding ship and weapon shockwaves #6378

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fix ai behavior when avoiding ship and weapon shockwaves #6378

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4 changes: 4 additions & 0 deletions code/ai/ai_flags.h
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,10 @@ namespace AI {
Fix_heat_seeker_stealth_bug,
Fix_linked_primary_bug,
Fix_ramming_stationary_targets_bug,
Fix_avoid_shockwave_bugs, // a) waiting until a homing weapon actually homes before evading;
// b) picking the correct expected impact position for capships;
// c) not clearing shockwave_object for ships;
// d) checking the explosion damage of the correct ship
Force_beam_turret_fov,
Free_afterburner_use,
Glide_decay_requires_thrust,
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5 changes: 5 additions & 0 deletions code/ai/ai_profiles.cpp
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Expand Up @@ -653,6 +653,8 @@ void parse_ai_profiles_tbl(const char *filename)
stuff_float(&profile->rot_fac_multiplier_ply_collisions);
}

set_flag(profile, "$fix avoid-shockwave bugs:", AI::Profile_Flags::Fix_avoid_shockwave_bugs);

// end of options ----------------------------------------

// if we've been through once already and are at the same place, force a move
Expand Down Expand Up @@ -856,4 +858,7 @@ void ai_profile_t::reset()
flags.set(AI::Profile_Flags::Force_beam_turret_fov);
flags.set(AI::Profile_Flags::Guards_ignore_protected_attackers);
}
if (mod_supports_version(25, 0, 0)) {
flags.set(AI::Profile_Flags::Fix_avoid_shockwave_bugs);
}
}
52 changes: 49 additions & 3 deletions code/ai/aicode.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14556,7 +14556,11 @@ static int ai_find_shockwave_ship(object *objp)
shipp = &Ships[A->instance];
// Only look at objects in the process of dying.
if (shipp->flags[Ship::Ship_Flags::Dying]) {
float damage = ship_get_exp_damage(objp);
float damage;
if (The_mission.ai_profile->flags[AI::Profile_Flags::Fix_avoid_shockwave_bugs])
damage = ship_get_exp_damage(A); // A is the object that is actually exploding!
else
damage = ship_get_exp_damage(objp);

if (damage >= EVADE_SHOCKWAVE_DAMAGE_THRESHOLD) { // Only evade quite large blasts
float dist;
Expand All @@ -14576,6 +14580,8 @@ static int ai_find_shockwave_ship(object *objp)

int aas_1(object *objp, ai_info *aip, vec3d *safe_pos)
{
bool fix_bugs = The_mission.ai_profile->flags[AI::Profile_Flags::Fix_avoid_shockwave_bugs];

// MAKE SURE safe_pos DOES NOT TAKE US TOWARD THE A SHIP WE'RE ATTACKING.
if (aip->ai_flags[AI::AI_Flags::Avoid_shockwave_weapon]) {
// If we don't currently know of a weapon to avoid, try to find one.
Expand Down Expand Up @@ -14636,7 +14642,24 @@ int aas_1(object *objp, ai_info *aip, vec3d *safe_pos)
}
}

if (!pos_set) {
if (pos_set) {
// if the object is not a small ship, a surface impact is likely to be some distance away from the ship center, so refine the position
if (fix_bugs && target_ship_obj && !Ship_info[Ships[target_ship_obj->instance].ship_info_index].is_small_ship()) {
mc_info mc;
mc.model_instance_num = Ships[target_ship_obj->instance].model_instance_num;
mc.model_num = Ship_info[Ships[target_ship_obj->instance].ship_info_index].model_num;
mc.orient = &target_ship_obj->orient;
mc.pos = &target_ship_obj->pos;
mc.p0 = &weapon_objp->pos; // Point 1 of ray to check
mc.p1 = &expected_pos; // Point 2 of ray to check
mc.flags = MC_CHECK_MODEL;

model_collide(&mc);
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I'm loathe to add more collision checks unless absolutely necessary, especially since this appears to be called every frame for a thing which is in the average case unlikely to move much (and also this case doesn't need tons of accuracy, some approximation/lag should be fine), so at the very least the result should probably be cached.

Alternatively, have you considered just using the weapon's homing_pos?

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It's a fair point, and I had the same reluctance, but I ended up adding it after seeing how many collision checks were used elsewhere in the code, and due to the difficulty of solving this problem without a collision check. I'm certainly open to suggestions though. And I could cache the result, at the cost of adding some additional fields to ai_info.

The weapon's homing_pos will work if the missile is homing on a subsystem, but will not work if the weapon is homing on the actual ship, since the position will be at the center of the ship.

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On a large ship, the homing_pos shouldn't be the center of the ship, see the usage of ai_big_pick_attack_point in weapon_home. They tend to spread themselves over the hull surface on the side facing the missile.

if (mc.num_hits > 0) {
expected_pos = mc.hit_point_world;
}
}
} else {
float time_scale;

if (wip->lifetime - weaponp->lifeleft > 5.0f) {
Expand Down Expand Up @@ -14682,12 +14705,13 @@ int aas_1(object *objp, ai_info *aip, vec3d *safe_pos)
Assert(aip->shockwave_object > -1);
object *ship_objp = &Objects[aip->shockwave_object];
if (ship_objp == objp) {
aip->shockwave_object = -1;
aip->shockwave_object = -1; // this one was already present in retail
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@Baezon Baezon Oct 11, 2024 •
edited
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There are some additional weapon cases above which also return 0, but don't seem to reset shockwave_object, should those be updated as well?

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The shockwave_object field should be reset when, and only when, an Avoid_shockwave_ flag is removed, not necessarily when the function returns 0.

There is of course the interesting // See if too far away to care about shockwave. case which returns 0 but does not remove the flag, as the flag is commented out -- even though the equivalent distance case for ship shockwaves removes the flag. The fact that the line is commented out makes me think Volition had a good reason for not clearing the flag. I'll give that another test. There's always the possibility of another separate AI profiles flag for that specific line.

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Ok. I'm fine with whatever you go with, I figured I'd bring it up.

return 0;
}

if (ship_objp->type != OBJ_SHIP) {
aip->ai_flags.remove(AI::AI_Flags::Avoid_shockwave_ship);
if (fix_bugs) aip->shockwave_object = -1;
return 0;
}

Expand All @@ -14701,6 +14725,7 @@ int aas_1(object *objp, ai_info *aip, vec3d *safe_pos)

if (vm_vec_dist_quick(&objp->pos, &ship_objp->pos) > outer_rad*1.5f) {
aip->ai_flags.remove(AI::AI_Flags::Avoid_shockwave_ship);
if (fix_bugs) aip->shockwave_object = -1;
return 0;
}

Expand All @@ -14720,16 +14745,37 @@ int aas_1(object *objp, ai_info *aip, vec3d *safe_pos)
int ai_avoid_shockwave(object *objp, ai_info *aip)
{
vec3d safe_pos;
bool fix_bugs = The_mission.ai_profile->flags[AI::Profile_Flags::Fix_avoid_shockwave_bugs];

// BIG|HUGE do not respond to shockwaves
// Goober5000 - let's treat shockwave response the same way whether from weapon or ship
if (!Ship_info[Ships[objp->instance].ship_info_index].avoids_shockwaves()) {
// don't come here again
aip->ai_flags.remove(AI::AI_Flags::Avoid_shockwave_ship);
aip->ai_flags.remove(AI::AI_Flags::Avoid_shockwave_weapon);
if (fix_bugs) aip->shockwave_object = -1;
return 0;
}

// Don't try to evade a homing weapon until it starts homing
if (fix_bugs && aip->ai_flags[AI::AI_Flags::Avoid_shockwave_weapon] && !(aip->ai_flags[AI::AI_Flags::Avoid_shockwave_started])) {
// since the "don't all react right away" timer should only start when the weapon begins homing, we need the actual weapon now...
// so choose the weapon ahead of time using the same technique aas_1() would normally use later
if (aip->shockwave_object == -1) {
aip->shockwave_object = ai_find_shockwave_weapon(objp);
if (aip->shockwave_object == -1) {
aip->ai_flags.remove(AI::AI_Flags::Avoid_shockwave_weapon);
return 0;
}
}

// if this is a homing weapon that isn't homing, don't react yet
auto wp = &Weapons[Objects[aip->shockwave_object].instance];
if (Weapon_info[wp->weapon_info_index].is_homing() && IS_VEC_NULL(&wp->homing_pos)) {
return 0;
}
}

// Don't all react right away.
if (!(aip->ai_flags[AI::AI_Flags::Avoid_shockwave_started])) {
float evadeChance = (aip->ai_shockwave_evade_chance == FLT_MIN)
Expand Down
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