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Missile.cpp: yield based damage #4927

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Missile.cpp: yield based damage #4927

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77e7fb1
Update Missile.cpp: yield based damage
PtrMan Jul 20, 2020
463bc37
Update Missile.cpp
PtrMan Jul 20, 2020
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47 changes: 37 additions & 10 deletions src/Missile.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -172,24 +172,51 @@ bool Missile::OnDamage(Object *attacker, float kgDamage, const CollisionContact
return true;
}

double calcAreaSphere(const double r) {
return 4.0*M_PI*r*r;
}

double calcAreaCircle(const double r) {
return M_PI*r*r;
}

void Missile::Explode()
{
Pi::game->GetSpace()->KillBody(this);

const double damageRadius = 200.0;
const double kgDamage = 10000.0;
double kgYield = 200.0; // yield of the used explosive in kg
const double jEnergyPerKgExplosive = 4.184e6; // energy density of explosive, here it's TNT

const double jYield = kgYield * jEnergyPerKgExplosive; // how much energy was converted in the explosion?

double queryRadius = 2000.0; // hardcoded to 2 km, this is sufficient for most explosions
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Why such a large distance compared to the old one?

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This is just the query distance, not the "real" explosion distance. There is no real explosion distance due to the nature of an explosion in empty space. The spatial data structure which is queried has to know a maximum query distance.
I've chosen a relatively large distance to allow for a bigger yield without modifying the queryDistance too.
Note here that this doesn't have any effect on the performance because the query is done once and because space is relatively empty anyways. Not an issue in my opinion here.

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May I suggest adding a comment to that effect?

Suggested change
double queryRadius = 2000.0; // hardcoded to 2 km, this is sufficient for most explosions
// The radius in which to search for possible recipients of the damages
// Hardcoded to 2 km, this should be sufficient for most explosions
const double queryRadius = 2000.0;

CollisionContact dummy;
Space::BodyNearList nearby = Pi::game->GetSpace()->GetBodiesMaybeNear(this, damageRadius);
Space::BodyNearList nearby = Pi::game->GetSpace()->GetBodiesMaybeNear(this, queryRadius);
for (Body *body : nearby) {
if (body->GetFrame() != GetFrame()) continue;
double dist = (body->GetPosition() - GetPosition()).Length();
if (dist < damageRadius) {
// linear damage decay with distance
body->OnDamage(m_owner, kgDamage * (damageRadius - dist) / damageRadius, dummy);
if (body->IsType(Object::SHIP))
LuaEvent::Queue("onShipHit", dynamic_cast<Ship *>(body), m_owner);
}
double dist = (body->GetPosition() - GetPosition()).Length(); // distance from explosion in meter

double targetRadius = 6.0; // radius of the hit target in meter
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double areaSphere = calcAreaSphere(dist);
double crossSectionTarget = calcAreaCircle(targetRadius);
double ratioArea = crossSectionTarget / areaSphere; // compute ratio of areas to know how much energy was transfered to target
ratioArea = std::min(ratioArea, 1.0); // we must limit received energy to finite amount

double jReceivedEnergy = ratioArea * jYield; // compute received energy by blast

//Output("dist %f\n", dist);
//Output("area sphere %f\n", areaSphere);
//Output("crossSectionTarget %f\n", crossSectionTarget);
//Output("ratio %f\n", ratioArea);
//Output("received energy %f\n", jReceivedEnergy);

double kgDamage = jReceivedEnergy * 0.000022; // received energy back to damage in pioneer "kg" unit
//Output("dmg %f\n", kgDamage);

body->OnDamage(m_owner, kgDamage, dummy);
if (body->IsType(Object::SHIP))
LuaEvent::Queue("onShipHit", dynamic_cast<Ship *>(body), m_owner);
}

SfxManager::Add(this, TYPE_EXPLOSION);
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