Damage, Ruins & Explosions¶

You do not need this page to build a custom city

Everything required to author content lives in Reference and Concepts. This page covers the mechanism behind keys you are already setting on the Profile page, for tuning them with intent rather than by trial and error.

TL;DR

Each chunk independently rolls for explosions, then breaks blocks around each centre. notbreakable-tagged blocks never break and easybreakable-tagged ones break more easily. Ruins are a separate destruction pass on top of a fully placed building. Both run after part selection has finished. code review code review

Explosions are per-chunk, independent rolls¶

Every city chunk independently rolls for a normal explosion, with explosionChance, a radius from explosionMinRadius and explosionMaxRadius, and a height from explosionMinHeight and explosionMaxHeight. It separately rolls a mini explosion, with miniExplosionChance and its own radius and height range. code review

One chunk can end up with several overlapping explosions, either by rolling more than one type or by catching a neighbouring chunk's blast, and damage from every overlapping source accumulates rather than only the strongest applying. explosionsInCitiesOnly restricts where a blast's centre can roll, not how far it reaches, so a blast centred just inside a city can still tear into non-city terrain at its edge. code review

What actually breaks¶

Whether a block breaks under nearby damage is not a flat roll. Block identity matters. code review

Tag	Effect
`lostcities:notbreakable`	Never breaks, whatever the explosion strength. Bedrock, end portal, end portal frame and end gateway by default
`lostcities:easybreakable`	Breaks more readily than an untagged block. `forge:glass` by default
(untagged)	Normal odds, roughly proportional to distance from the blast centre and its strength
code review

When a block does break, the palette entry's damaged key decides what it becomes: rubble, a broken variant, or whatever else was authored there. A character with no damaged value breaks to air. game test

damaged covers the rubble band, not the ruined section

Measured rather than assumed, and narrower than this page once claimed. See Palette Reference. game test

Debris spreads into neighbouring chunks¶

Damage does not stop cleanly at a chunk border. debrisToNearbyChunkFactor controls how much of a damaged chunk's rubble bleeds into its neighbours, and the relationship is inverse: higher values mean less spillover. Scattered rubble just outside the chunk that rolled the explosion is expected, not a sign of a misconfiguration. code review

Ruins are a separate pass, after the building already exists¶

Ruin generation is gated on ruinChance and destroys a band of the building's height between ruinMinlevelPercent and ruinMaxlevelPercent. It runs strictly after the building's parts have been selected and placed, so part selection never knows it is about to be ruined and ruin state cannot bias which variant of a floor was picked. It only removes blocks from what was already going to generate. code review

The ruin pass is also what consumes a palette's rubble character. A character used nowhere else appeared 40 times with ruins on and never with ruins off. game test

Ruins and explosions are not the same phase, despite being described together

The distinction changes what each one can touch. code review

Ruins run inside the city-chunk pass, immediately after the building and street are placed:

generateBuilding -> generateStreet -> generateRuins -> highways
  -> generateStreetDecorations -> generateHighways -> generateRubble -> generateStuff

Explosions and debris run much later, back in the top-level chunk pass, after railways and the torch fixup, just before the chunk is flushed. code review

So anything generated after generateRuins in that list is not ruined. Street decorations, highways, rubble and stuff objects all land on top of an already-ruined building and survive intact, while explosion damage, running later still, does reach them. A half-collapsed building with pristine street furniture around it is expected. See The Generation Pipeline. code review

You cannot exempt one building from ruin¶

A Building asset has no key that protects it from the ruin pass. No preventruins, no noruin, and no equivalent under another name. code review

What you want	How to get it
A specific landmark left intact	Place it through a Predefined City and set `preventruins: true` on that entry. The only per-building exemption in the mod game test
Fewer ruined buildings everywhere	Lower `ruinChance` in the Profile
No ruined buildings at all	Set `ruinChance` to `0`
Specific blocks to survive	Add them to the `lostcities:notbreakable` tag. That protects the blocks, not the building code review
code review

Ruin chance is profile-wide and cannot vary by city style

A city style can override explosionchance, and there is no city style key for ruin chance, so one district cannot be ruined while another stays pristine through city styles. A predefined city is the only per-place control. code review

The asymmetry is easy to miss, because the two are usually described together even though they run in different phases. code review