perf(modeling): Excessive vec3.create() allocations in extrudeWalls.js

[jbroll]

Summary

extrudeWalls.js creates new vec3 arrays inside nested loops, causing GC pressure during extrusions.

Usage Frequency: HIGH

Called by extrudeFromSlices() which powers all extrusion operations:

• extrudeLinear() / extrudeLinearGeom2()
• extrudeRotate()
• extrudeHelical()

Typical model usage: Every extruded shape. A model with 5 extrusions with 32 segments each = 160+ calls to extrudeWalls, each creating many vec3 arrays.

Problem

File: packages/modeling/src/operations/extrusions/extrudeWalls.js
Lines: 32-39

edges.forEach((edge) => {
  const increment = vec3.subtract(vec3.create(), edge[1], edge[0])  // New array
  vec3.divide(increment, increment, divisor)

  let prev = edge[0]
  for (let i = 1; i <= multiple; ++i) {
    const next = vec3.add(vec3.create(), prev, increment)  // New array in inner loop
    newEdges.push([prev, next])
    prev = next
  }
})

For each edge, this creates 1 + multiple vec3 arrays. With many edges and multiple > 1, this generates significant allocations.

Suggested Fix

Reuse temporary vectors:

const tempIncrement = vec3.create()
edges.forEach((edge) => {
  vec3.subtract(tempIncrement, edge[1], edge[0])
  vec3.divide(tempIncrement, tempIncrement, divisor)

  let prev = edge[0]
  for (let i = 1; i <= multiple; ++i) {
    const next = vec3.clone(prev)  // Still need new arrays for storage
    vec3.add(next, next, tempIncrement)
    newEdges.push([prev, next])
    prev = next
  }
})

Note: The inner loop still needs allocations since edges are stored, but the increment calculation can be reused.

Impact

Medium - contributes to GC pressure during extrusion operations. More noticeable with high segment counts.