Proxies

A proxy is a placeholder inside one model that says “render another model right here.” It’s how a rifle shows whatever optic is attached, how a vest shows its pouches, how a car shows its wheels. Instead of baking every variant into one giant model, you leave a marked spot and let the engine drop the right sub-model into it at runtime.

This builds on P3D setup and selections & naming — a proxy is a special kind of named selection, so read those first if the terms are new.

Proxy vs baked-in geometry

Use a proxy when the attached part is interchangeable or optional:

A weapon’s optic, muzzle device, or light — the player swaps them.
A vest’s pouches, a backpack’s add-ons — different loadouts.
A vehicle’s wheels and removable parts — they come off, get damaged, get replaced.

Bake the geometry in when the part is permanent and never swapped — there’s no reason to pay the proxy’s indirection for a fixed handle or a welded bracket. The test is simple: can the player remove or change this part? If yes, proxy; if no, bake it.

What a proxy is, physically

In the P3D, a proxy is a single triangle in a Visual LOD, assigned to a named selection whose name starts with proxy:. The triangle isn’t drawn — its three vertices define a coordinate frame where the attached model is placed:

vertex 0  →  origin   (where the sub-model's pivot lands)
vertex 1  →  one axis  (orientation)
vertex 2  →  another axis (orientation)

So the proxy carries both a position and a rotation. Object Builder creates proxies for you (Create Proxy), so you place and orient them visually rather than entering coordinates — but knowing it’s “an oriented triangle” explains why a mis-placed proxy points an attachment the wrong way instead of just offsetting it.

The proxy triangle should reference no texture and no material — it’s a marker, not geometry.

How the engine resolves a proxy

The selection name is the link to the model. Its form:

proxy:\path\to\submodel.NNN

proxy: — the literal prefix that marks the selection as a proxy.
\path\to\submodel — the path to the sub-model’s P3D, relative to the P: drive (no .p3d extension here).
.NNN — a three-digit index (.001, .002, …). Multiple instances of the same sub-model get incrementing indices, so a vest with four grenade slots has .001 through .004.

At load, the engine reads that path, finds the sub-model’s P3D, and renders it in the proxy’s frame. For swappable attachments (an optic that changes), the proxy slot is wired through config rather than hard-pointing at one model — the config’s attachment slot decides which model fills the proxy. For fixed decorative sub-models, the path can point straight at the one model.

Common uses

Weapons. An optics rail, a muzzle slot, and an underbarrel/light slot are proxies on the weapon model. Each accepts a category of attachment defined in config. The attachment’s own model then lines up using its memory points.
Vehicles. Wheels are proxies, which is what lets a wheel be removed, damaged, and re-fitted as a separate item. Other removable parts (doors, hoods on some setups) follow the same idea.
Clothing. Vests and backpacks proxy their pouches and add-on containers.

Pitfalls

Proxies fail quietly, and almost always for one of these reasons:

Broken path. The proxy:\… path doesn’t match where the sub-model’s P3D actually packs to. Result: nothing renders at the slot, no error you’ll notice. Check the path against the packed location, not your source-folder spelling.
Wrong or missing index. Two proxies sharing .001, or a config expecting .002 that isn’t there. Instances must be uniquely indexed.
Proxy in the wrong LOD. A proxy only does its job in the LODs that need to show the attachment (typically the Visual LODs). Forgetting to add it to a lower Visual LOD makes the attachment vanish at distance.
Mis-oriented triangle. The attachment appears but points sideways or sits rotated — the proxy triangle’s vertices define orientation, so a flipped triangle flips the part.
Attachment’s own points missing. The proxy places the sub-model; the sub-model still needs its own correct memory points and origin to line up. A scope that sits 2 cm too high is usually the scope’s eye/origin, not the rifle’s proxy.

Selections & naming — a proxy is a proxy:-prefixed selection.
P3D setup — where proxies live among the LODs.
Memory points — how the attached model aligns itself.
Configs — the attachment-slot side that fills swappable proxies.
Inventory & attachments — the runtime model of slots and attachments.