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Calcs
(
aka
the
Code,
Math
and
You:
A
Beginner’s
Guide)
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Collision
Calcs
(
aka
the
Code,
Math
and
You:
A
Beginner’s
Guide)
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1. Unit-vs-Unit Collision
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1. Unit-vs-Unit Collision
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Handled by the DoCollisionDamage() function, triggered when weaponDefID == -3 and an attackerID is present.
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Handled by the DoCollisionDamage() function, triggered when weaponDefID == -3 and an attackerID is present.
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Step 1, Speed check: Collision damage only activates if either unit's speed exceeds UNIT_UNIT_SPEED (5.5 elmos/frame).
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Step 1, Speed check: Collision damage only activates if either unit's speed exceeds UNIT_UNIT_SPEED (5.5 elmos/frame).
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Step 2, Relative speed: The relative velocity between the two units is calculated as:
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Step 2, Relative speed: The relative velocity between the two units is calculated as:
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relativeSpeed = sqrt((oVx-myVx)² + (oVy-myVy)² + (oVz-myVz)²)
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relativeSpeed = sqrt((oVx-myVx)² + (oVy-myVy)² + (oVz-myVz)²)
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Step 3, Damage per unit: Each unit's damage is calculated using LocalSpeedToDamage():
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Step 3, Damage per unit: Each unit's damage is calculated using LocalSpeedToDamage():
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if relativeSpeed > velocityDamageThreshold (3):
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if relativeSpeed > velocityDamageThreshold (3):
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damage = (relativeSpeed - 3) × (mass × 0.6)
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damage = (relativeSpeed - 3) × (mass × 0.6)
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Buildings get a ×10 multiplier on their velocityDamageScale since they're treated as far more massive.
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Buildings get a ×10 multiplier on their velocityDamageScale since they're treated as far more massive.
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Step 4, Final damage dealt: The game deals the lesser of the two units' computed damages, multiplied by UNIT_UNIT_DAMAGE_FACTOR (0.8) so the smaller/lighter unit sets the damage ceiling. Both units take this same amount.
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Step 4, Final damage dealt: The game deals the lesser of the two units' computed damages, multiplied by UNIT_UNIT_DAMAGE_FACTOR (0.8) so the smaller/lighter unit sets the damage ceiling. Both units take this same amount.
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Step 5, Multipliers & immunity: The final damage is scaled by each unit's collisionDamageMult (set per-unit by other gadgets). Units can be immune (e.g. during jump/teleport), and allied units are protected from "no-ally-damage" flags.
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Step 5, Multipliers & immunity: The final damage is scaled by each unit's collisionDamageMult (set per-unit by other gadgets). Units can be immune (e.g. during jump/teleport), and allied units are protected from "no-ally-damage" flags.
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Step 6, Velocity correction: After collision, both units' velocities are blended toward a shared momentum-conserving average (a weighted sum based on their masses), simulating an inelastic collision. GitHub
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Step 6, Velocity correction: After collision, both units' velocities are blended toward a shared momentum-conserving average (a weighted sum based on their masses), simulating an inelastic collision. GitHub
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2. Unit-vs-Ground Collision (Fall Damage)
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2. Unit-vs-Ground Collision (Fall Damage)
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Triggered when weaponDefID == -2 with no attacker. This is the classic "fall damage."
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Triggered when weaponDefID == -2 with no attacker. This is the classic "fall damage."
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Step 1, Decompose velocity into normal and tangent: The unit's velocity is split into a component normal to the terrain surface and a tangential component (sliding along it).
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Step 1, Decompose velocity into normal and tangent: The unit's velocity is split into a component normal to the terrain surface and a tangential component (sliding along it).
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Step 2, Bounce physics: The normal component is reflected and scaled by elasticity (default 0.3), and the tangential component is scaled by friction (default 0.8), then an impulse is applied to simulate the bounce.
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Step 2, Bounce physics: The normal component is reflected and scaled by elasticity (default 0.3), and the tangential component is scaled by friction (default 0.8), then an impulse is applied to simulate the bounce.
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Step 3, Damage speed calculation:
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Step 3, Damage speed calculation:
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damageSpeed = magnitude of (normal + tangent × TANGENT_DAMAGE)
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damageSpeed = magnitude of (normal + tangent × TANGENT_DAMAGE)
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where TANGENT_DAMAGE = 0.5, so sliding impacts count for half.
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where TANGENT_DAMAGE = 0.5, so sliding impacts count for half.
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Step 4, Convert speed to damage (same LocalSpeedToDamage() as above):
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Step 4, Convert speed to damage (same LocalSpeedToDamage() as above):
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if damageSpeed > 3:
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if damageSpeed > 3:
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damage = (damageSpeed - 3) × (mass × 0.6)
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damage = (damageSpeed - 3) × (mass × 0.6)
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Step 5, Out-of-map bonus damage: If the unit is outside the map boundaries, additional damage is added proportional to how far out of bounds the unit is, scaled by unit.health / 800.
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Step 5, Out-of-map bonus damage: If the unit is outside the map boundaries, additional damage is added proportional to how far out of bounds the unit is, scaled by unit.health / 800.
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Step 6, Multiplier applied: Final damage × collisionDamageMult[unitID] (or 1 if unset).
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Step 6, Multiplier applied: Final damage × collisionDamageMult[unitID] (or 1 if unset).
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3. Unit-vs-Wreck/Feature Collision
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3. Unit-vs-Wreck/Feature Collision
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Triggered when weaponDefID == -3 and
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Triggered when weaponDefID == -3 and
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attackerID == nil (no unit attacker — a feature like debris).
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attackerID == nil (no unit attacker — a feature like debris).
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The engine's native damage value is taken and multiplied by DEBRIS_SPRING_DAMAGE_MULTIPLIER = 10 (described in the code as "tweaked arbitrarily"), then scaled by collisionDamageMult. The unit also gets a velocity-scaling impulse of 0.3 (i.e. it loses 70% of its speed).
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The engine's native damage value is taken and multiplied by DEBRIS_SPRING_DAMAGE_MULTIPLIER = 10 (described in the code as "tweaked arbitrarily"), then scaled by collisionDamageMult. The unit also gets a velocity-scaling impulse of 0.3 (i.e. it loses 70% of its speed).
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Note: Feature collisions still use the native engine value as a base, unlike unit-unit and ground collisions which are calculated entirely from scratch.
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Note: Feature collisions still use the native engine value as a base, unlike unit-unit and ground collisions which are calculated entirely from scratch.
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Qrow Esoterica