Fysik

Structural physics for Valheim building. In vanilla Valheim, a piece only cares about how far it is from the ground. Fysik replaces that with a force calculation in which the shape of your build matters, in the spirit of Poly Bridge and Bridge Constructor:

• Arches carry their load in compression and can span gaps that a flat beam cannot.
• Braces and triangles carry load along their length instead of bending: a diagonal under a balcony halves its stress.
• Cantilevers bend, and the longer they reach, the more they strain.
• An overloaded piece cracks before it falls: it turns red, shakes, creaks and sheds dust, giving you a few seconds to shore it up. Once something gives way, the collapse follows instantly.
• Building an arch works like the real thing: until the last stone closes it, an unfinished arch is just two cantilevers and needs scaffolding. Close it, remove the scaffolding, and it stands.

⚠ Before you install

Fysik is on from the start. As soon as a world loads, every building made by players is checked against the physics Fysik applies, and buildings that do not respect it will crack and fall, including bases you built before installing it. Back up your world first. We recommend starting a new world with Fysik, so everything you build is designed for it from the first post.

Buildings that come with the world (stone towers, abandoned houses, villages, ruins) are not simulated: they keep vanilla support, unless the server sets Structure.WorldBuildings = Physics (see World buildings).

Status

Early access. Material values are still being calibrated. Back up your worlds before trying it.

Installation

Install with a mod manager (r2modman, Thunderstore Mod Manager) or manually:

1. Install BepInExPack_Valheim and Jötunn.
2. Copy plugins/Fysik.dll into BepInEx/plugins/Fysik/.

Fysik must be installed on the server and on every client, with exactly the same version (every player who owns part of a structure must calculate it exactly as the others do). Players without it cannot join a server that has it, and vice versa.

Existing player buildings follow the new rules as soon as the mod is enabled: back up your world, and preferably start a new one. To look at an old base before letting it settle, set Structure.Mode = Sandbox (nothing falls for lack of support) or DisplayOnly (vanilla decides).

Seeing the forces

• Hammer: aim at a piece. It is colored by stress, from blue (relaxed) through green and yellow to red (at its limit), and the value appears next to the crosshair, e.g. Compression 72%, with its material and weight. Light blue means the structure is still being calculated; magenta means it has no path to the ground at all; neutral grey means a world building that Fysik does not simulate (World building · not simulated).
• Placing a piece: the ghost is colored by the stress it would have once placed, with the value next to the crosshair (Preview: Bending 85%). If it would push another piece past its limit, a second line names that piece. When vanilla says the spot is invalid, the ghost stays vanilla red.
• X-ray (F7): colors every piece within 40 m. Ctrl+F7 widens the radius by 10 m, up to 80 m, then back to 40 m.
• Cracking: a piece above 100% pulses red, shakes, creaks and sheds dust. You have CrackWarningSeconds (5 s) to shore it up (add a post, a brace, finish the arch) before it falls. Once something gives way, everything that lost its support comes down with it at once, as debris that bursts on hitting the ground, like a building being imploded; whatever is left overloaded follows without warning. A piece left with no path to the ground at all (you removed its support) has nothing to shore up and falls at once, as in vanilla.
• Furniture: chests, workbenches, torches and similar pieces hold nothing up and add no weight, but still need something to rest on: they fall when the piece under them goes, as in vanilla.

World buildings

Stone towers, abandoned houses, villages, ruins, fortresses and everything else the game places in the world were designed for vanilla support, not for real forces. By default Fysik leaves them alone:

• Only what players build is simulated. World buildings keep vanilla support: they stand as the game built them, and if you break their base, the rest crumbles as in vanilla. Fysik never brings them down.
• They show in neutral grey with the hammer and the X-ray.
• A player build resting on a world building is held as if on rock. If that world building is destroyed, your build is recalculated and may fall.

To simulate world buildings too, the server sets Structure.WorldBuildings = Physics. They are then calculated, colored and brought down like any player build. This changes the game: many of them do not respect the physics and will crack and fall, for good, as soon as someone comes near.

A piece counts as a world building when no player placed it. Pieces spawned with console commands, or by mods that do not record a builder, count as world buildings too.

Building guide

The pictures below were computed with Fysik's own solver and the default materials, using the same pieces you build with. In game, pieces snap a little differently, so expect similar, not identical, numbers.

Squeeze, don't bend

A piece is far stronger squeezed or pulled along its length than bent across it. A post under a roof is squeezed and barely notices; a beam reaching out is bent, and the joint where it leaves its support carries the whole reach. The stress grows with the square of the length: half again as far out means more than twice the stress.

• With 4 m core wood logs and floors on top, a balcony 8 m out is comfortable (42%), 12 m out is at the edge (93%) and 16 m out falls.
• A diagonal brace turns the bending into a squeeze: two 45° logs from the ground to the first joint bring the 12 m balcony back to 42%.
• The brace pushes back against whatever it stands on. Give the house a diagonal (or a solid wall), or the push bends its posts instead.

Arches

An arch turns the weight into a squeeze that follows its curve, so it spans far more than a flat beam. This 24 m bridge stands with nothing in the middle; without the arch, the same deck breaks.

• Build it on scaffolding. Until the last piece closes it, half an arch is just a cantilever and will crack. Prop it with plain poles, close it, then remove the poles: it should turn blue and green.
• Hold its feet. An arch pushes outwards where it lands. Here the deck beams tie the two feet together (in tension, about 53 kN); otherwise set the feet against the ground or a heavy wall.
• Hang the deck from it. Poles from the arch down to the deck (hangers) carry the deck in tension.

Stone bridges

Stone is strong squeezed and weak pulled. A pair of stone arches (stone_arch) closes 4 m; wider arches are built out from the piers in steps and closed at the top with a pair of stone arches.

• Pillars every 4 m, a pair of stone arches between each two, stone floors on top: worst piece 27%. At this span the arches are mostly for looks: the same floors laid straight on the pillars hold too (19%).

• With 8 m between the piers the arch does the work: worst piece 48%, while the same piers with a flat deck reach 109% and the deck falls.
• Each arch steps out 1 m and then 2 m from the piers and closes with two stone arches. Before the arches close nothing goes above 39%, so no scaffolding is needed.

Materials

• Stone is very strong squeezed and weak pulled: use it for walls, pillars and arches, not for beams or overhangs. Span an opening in a stone wall with an arch or a wooden beam.
• Core wood (logs) is stronger than wood; iron is strong in every direction.
• Long, thin pieces buckle: a slender post carries less than its material alone would allow.

Tips

• Watch the ghost's color before placing each piece, and check the whole building with the X-ray (F7) after big changes.
• When something cracks, you have a few seconds: put a post under it, add a brace, or remove what it carries.
• Badly damaged pieces (below half health) are weaker; repair them.
• Big bases: structures up to Structure.MaxFrameBodies pieces (2000) get the full calculation. Larger ones use a simpler model that does not recognise arches; raise the limit (up to 5000) if you build arches into a big base.
• Too hard or too easy? Ask your server admin about Structure.Difficulty.

Roadmap

Next:

• Masonry: stone blocks that only hold by pressing on each other, interlocking walls, arches built on wooden centering
• Loads beyond self-weight: furniture, chest contents, snow on roofs

Later:

• Calibration with player builds (feedback welcome)
• Faster recalculation for very large bases
• Translations into every language Valheim supports
• A website to plan and test a build in the browser with the same solver

Configuration

BepInEx/config/menezesbruno.fysik.cfg. Settings marked server are enforced by the server and synced to every client; they can also be edited in game with a configuration manager (F1).

The console command fysik stats, fysik recalc or fysik dump (F5; the game must be started with -console) shows solver statistics, recalculates everything or writes the structure under the hammer to BepInEx/fysik-dump.txt.

Compatibility

Fysik takes over structural integrity, so it is expected to conflict with other mods that change it, such as NoBuildIntegrity, Forever Build or Balrond Better Build. Pieces added by other mods will use conservative default material properties, with a warning in the log for each unknown material.

Links

• Source code and issues: https://github.com/menezesbruno/Fysik
• License: MIT