Chain reactions

Propagation lets a destroyed object deliver a bounded radial hit to nearby destructibles. It is disabled by default on every profile.

Heavy Prop
   ↓
Crate
  ↙ ↘
Pot Pot

Enabling it

On the profile of the object that should start a chain when it dies:

Property	Default	Meaning
bAllowDestructionPropagation	false	Master switch
PropagationRadius	250.0	Sphere radius searched for neighbours
PropagationDamage	100.0	Damage delivered to each neighbour
PropagationPower	Light	Destruction power of the propagated hit
PropagationImpulse	600.0	Impulse magnitude of the propagated hit
MaxPropagationDepth	2	Hard depth cap when this profile starts a chain

What a propagated hit looks like

Each neighbour receives a normal FSDFDestructionHit:

• Damage = the source profile’s PropagationDamage;
• DestructionPower = PropagationPower;
• ImpulseStrength = PropagationImpulse;
• ImpactDirection = outward, from the source toward the neighbour;
• PropagationDepth = parent depth + 1;
• RandomSeed = derived deterministically (see below).

The neighbour evaluates it against its own profile like any other hit. A pot with MinimumDestructionPower = VeryLight breaks; a statue requiring Heavy ignores a Light propagation.

Cycle prevention

The subsystem keeps a visited set of Actors for the duration of a logical chain. An Actor that has already been visited is never queued again, so A → B → A is impossible. The number of such suppressions is reported as TargetsIgnoredAlreadyVisited.

The chain is processed as a queue, not as recursion, which keeps the call stack flat regardless of how many objects are involved.

Deterministic ordering and seeds

Candidates are gathered and placed in a stable order before any hit is delivered, so the same scene produces the same chain every run.

CalculatePropagationSeed(ParentSeed, SourceDepth, SourceActor) derives each event’s seed from its parent seed and stable source context. Given the same root seed, a chain replays identically — useful for capturing a bug, and for deterministic automated tests.

Chain diagnostics

When a chain completes, OnPropagationChainCompleted broadcasts an FSDFPropagationChainResult. GetLastPropagationChainResult returns the same data on demand.

Field	Meaning
bExecuted	A chain actually ran
RootActor	The object that started it
RootSeed	Seed the chain was derived from
TargetsDiscovered	Compatible neighbours found
HitsPropagated	Hits actually delivered
DestroyedTargets	Neighbours destroyed by the chain
MaximumDepthReached	Deepest level reached
TargetsIgnoredAlreadyVisited	Suppressed by the visited set
TargetsIgnoredByMaximumDepth	Neighbours skipped because the cap was reached
SourcesBlockedByMaximumDepth	Sources that could not propagate further
UniqueActorsVisited	Size of the visited set
HitResults	Per-hit records: source, target, depth, seed, destruction result

Each FSDFPropagationHitResult contains the full FSDFDestructionResult of that target, so a chain can be audited hit by hit.

Budgets still apply

Propagated destruction is normal destruction. It competes for the same per-frame destruction event admission and the same Chaos representation budget as player-caused destruction, and it falls back to SwapAndScatter under pressure exactly the same way. A chain in a crowded scene degrades instead of spiking. See Performance.

Tuning guidance

• Start with PropagationRadius slightly larger than the visual footprint of the source object. A radius that reaches across a corridor turns one crate into a room-wide cascade.
• Give the chain a lower PropagationPower than the player’s heavy attack. Chains that break everything read as a bug rather than as a reaction.
• Keep MaxPropagationDepth at 2 unless you are building an intentional set piece.
• Use the chain result counters while tuning: a high TargetsIgnoredByMaximumDepth means the layout wants a smaller radius, not a bigger cap.

Radial versus propagation

They deliver similar payloads but are triggered differently:

	Radial	Propagation
Trigger	Your gameplay code calls ApplyRadialDestruction	An object with propagation enabled is destroyed
Configuration	Per call, in the request	On the source object’s profile
Depth	You set PropagationDepth on the request	Managed by the chain
Result	FSDFRadialDestructionResult	FSDFPropagationChainResult

See Radial destruction.