contour

Offset curves, skeletons, isolines, and field contours.

Imports

import {
  offsetCurvesOutward,
  offsetCurvesInward,
  medialAxis,
  chordalAxis,
  straightSkeleton,
  straightSkeletonParts,
  centerLine,
  distanceField,
  contrastField,
  distanceTree,
  isolines,
  isolinesFromFunction,
  isolineZeroFromFunction,
  contour,
} from 'pattapatta'

Functions

Function	Description
`offsetCurvesOutward(path, distance)`	Positive buffer
`offsetCurvesInward(path, distance)`	Erosion (may vanish)
`medialAxis(path, axial, distance, area)`	Medial axis with feature pruning (thresholds in `[0,1]`)
`chordalAxis(path)`	Chordal axis from Delaunay triangle classification
`straightSkeleton(path)`	Flat group of faces + branches + bones
`straightSkeletonParts(path)`	Structured `{ faces, branches, bones }`
`centerLine(path, straightness?, smoothing?)`	Longest smoothed medial center line
`distanceField(path, spacing, pole?)`	Isolines of `d_boundary − d_pole` (default pole = MIC)
`contrastField(path, intervals, reference)`	Isolines of `\\|d_boundary − d_reference\\|`
`distanceTree(mesh, source, flatten)`	BFS shortest-path tree on a mesh
`isolines(path, highPoint, spacing)`	Radial isolines from a high point
`isolinesFromFunction(bounds, sample, interval, fn)`	Marching-squares isolines
`isolineZeroFromFunction(bounds, sample, fn)`	Zero level-set

Offset curves

const cross = polygon([/* …cross outline… */])
offsetCurvesOutward(cross, 5)
offsetCurvesInward(cross, 5)

Skeletons

Medial axis Medial axis pruned Chordal axis Straight skeleton

const shape = densify(cross, 2.5)
medialAxis(shape, 0, 0, 0)           // full
medialAxis(shape, 0.15, 0.1, 0.1)    // pruned
chordalAxis(shape)

// Straight skeleton ≈ successive inward offsets (wavefronts above)
let cur = cross
for (let i = 0; i < 5; i++) {
  const next = offsetCurvesInward(cur, 4)
  if (!next.paths.length) break
  cur = next.paths[0]!
}
straightSkeletonParts(cross)         // faces, branches, bones from the same process

Center line

let capsule = union(createRect(22, 40, 56, 20), createCircle(22, 50, 10))
capsule = densify(
  union(capsule.paths[0]!, createCircle(78, 50, 10)).paths[0]!,
  2.5,
)
centerLine(capsule, 0.65, 30)

Fields

Distance field Contrast field Isolines Distance tree

const L = polygon([/* …L outline… */])
distanceField(L, 7)
contrastField(L, 5, vec2(35, 65))
isolines(L, vec2(35, 65), 8)
distanceTree(meshGroup, vec2(35, 65), true)

Notes

Clean-room MIT reimplementations (not ports of PGS / JMedialAxis / grassfire4j).
straightSkeleton uses successive inward offsets (robust approximation); exact kinetic skeletons may follow later.
Densify sparse polygons before medialAxis / centerLine for better quality.