Kotlin Multiplatform port of @glandais/virtual-cyclist: physics-based cycling simulator that turns a static GPS trace into a virtualized ride with realistic speeds, times and power estimates. Inspired by gpx2web (Java) for the physics model and the @glandais/elevation TypeScript library for elevation data.

                        ┌──────────────┐
        sample.gpx ────▶│ GpxParser    │
                        └──────┬───────┘
                               ▼
            ┌─────────────────────────────────────────┐
            │  Enhancer (orchestrator)                │
            │  ├─ PointPerDistance(-1, 30)            │
            │  ├─ fixElevation (Terrarium tiles)*     │
            │  ├─ PointPerDistance(1, 2)              │
            │  ├─ smoothElevation (150 m kernel)      │
            │  ├─ MaxSpeedComputer (cornering+braking)│
            │  ├─ VirtualizeService (1 Hz physics)    │
            │  ├─ PointPerSecond (uniform sampling)   │
            │  └─ PathSimplifier (Douglas-Peucker 3D) │
            └──────────────────┬──────────────────────┘
                               ▼
                        ┌──────────────┐
                        │ GpxWriter    │────▶ output.gpx
                        └──────────────┘
            (*) optional — needs an ElevationProvider

npm install @glandais/vcyclist-engine          # Kotlin/JS bundle
npm install @glandais/vcyclist-engine-wasm     # Kotlin/Wasm bundle
npm install @glandais/vcyclist-elevation       # Kotlin/JS bundle
npm install @glandais/vcyclist-elevation-wasm  # Kotlin/Wasm bundle

// Gradle Kotlin DSL
dependencies {
    implementation("io.github.glandais:vcyclist-engine:1.0.0")    // pulls -jvm / -js / -wasm-js per target
    implementation("io.github.glandais:vcyclist-elevation:1.0.0")
}

Replace 1.0.0 by the latest version shown in the badges above. KMP consumers automatically get the platform-specific variant (-jvm, -js, -wasm-js) for their target.

See docs/publishing.md for the release process.

# Enhance a GPX file with the default cyclist (80 kg / 280 W) and bike (Crr 0.004) :
./gradlew :engine:run -Pargs="enhance path/to/input.gpx -o /tmp/output.gpx"

The CLI runs the full enhancement pipeline (no elevation correction — no HTTP) and writes the simulated trace back to a GPX file. See engine/src/jvmMain/.../EngineCli.kt.

# Kotlin/Wasm demo
./gradlew :elevation:wasmJsBrowserDevelopmentRun
# Kotlin/JS demo (sibling, same UI)
./gradlew :elevation:jsBrowserDevelopmentRun

Both demos share the original TS demo UI (Leaflet + Chart.js + GPX upload). See elevation/README.md for details.

import io.github.glandais.engine.Enhancer
import io.github.glandais.engine.gpx.GpxParser
import io.github.glandais.engine.gpx.firstTrackAsPath

suspend fun virtualize(xml: String): String {
    val path = GpxParser.parse(xml).firstTrackAsPath()
    val out = Enhancer.enhanceCourseDefault(path)  // pure physics, no HTTP
    return io.github.glandais.engine.gpx.GpxWriter.write(
        out.toGpxDocument(trackName = "virtualized")
    )
}

generateTypeScriptDefinitions() is enabled on both js(IR) and wasmJs, so you get a .d.ts next to the bundle in build/dist/{js,wasmJs}/productionExecutable/vcyclist-engine.d.{ts,mts}.

The Kotlin/JS variant (@glandais/vcyclist-engine, @glandais/vcyclist-elevation) runs in both browser and Node.js / Bun. The Wasm variants (*-wasm) are browser-only.

import { parseGpx, enhance, writeGpx, pathSize, pathTotalDistance } from '@glandais/vcyclist-engine';

const handle = parseGpx(gpxXml);
console.log('input points:', pathSize(handle));
const out = await enhance(handle, null);                    // physics only, no HTTP
console.log('output:', pathSize(out), pathTotalDistance(out), 'm');
const xml = writeGpx(out);

import { parseGpx, enhance, writeGpx } from '@glandais/vcyclist-engine';

const handle = parseGpx(gpxXml);
const out = await enhance(handle, { fixElevation: true });  // fetches DEM tiles, decodes WebP
const xml = writeGpx(out);

enhance(..., { fixElevation: true }) auto-instantiates a default ElevationProvider (mapterhorn Terrarium tiles) and runs the full pipeline (densify → fix elevation → smooth → max speeds → virtualize → resample → simplify).

On Node.js / Bun, tile decoding uses @jsquash/webp (a pure-WASM WebP decoder, ~50 KB, listed as a runtime dependency of @glandais/vcyclist-engine and @glandais/vcyclist-elevation). It is loaded lazily via eval('require'), so browser bundlers do not pull it into the browser build. Requires Node ≥ 18 (globalThis.fetch is built-in since Node 18 / Bun) ; Node 22+ recommended for ESM require() support.

The demo/ module is a Vue 3 + Vite frontend that exercises the Kotlin/JS engine end-to-end in a browser (GPX upload, configurable cyclist / bike / wind / power, chart + map, hover sync).

./gradlew :demo:assemble
python -m http.server -d demo/dist 8000  # or any static file server

See demo/README.md for the dev workflow and architecture.

./gradlew check                         # full build + all tests on all targets
./gradlew :engine:allTests              # engine tests across JVM / JS Node / JS browser / Wasm browser
./gradlew :elevation:allTests           # elevation tests
./gradlew :elevation:jvmTest --tests '*Integration*' \
          -PINTEGRATION=1               # live HTTP tests against tiles.mapterhorn.com
./gradlew ktlintCheck                   # lint

vcyclist/
├── settings.gradle.kts          # multi-module Gradle KMP project
├── gradle/libs.versions.toml    # version catalog (Kotlin 2.3.21, coroutines 1.11, xmlutil 0.91, …)
├── docs/
│   ├── PLAN.md                  # task-by-task progress (Phases 1-2bis)
│   ├── parity.md                # parity strategy vs the TS reference
│   ├── elevation-integration.md # how to run live HTTP integration tests
│   ├── kotlin-wasm-jvm-webp.md  # Kotlin/Wasm ↔ JS interop guide
│   └── tasks/                   # one Markdown per implementation task (00-31, + bonus demos)
├── elevation/                   # :elevation KMP module
├── engine/                      # :engine KMP module (depends on :elevation)
└── codegen/                     # :codegen JVM helper for Path accessor generation

• ✅ Phase 1 — :elevation module port (tasks 00-09) : Terrarium tiles, Haversine, ECEF, Douglas-Peucker 3D, smoother, LRU cache + TileManager, ElevationProvider, live HTTP integration.
• ✅ Phase 2 — :engine module port (tasks 10-28) : Path model, Cyclist/Bike/Course, GPX I/O, full physics, simulation, post-processing, Enhancer, CLI, @JsExport façades.
• ✅ Phase 2bis — pipeline fidelity fixes (tasks 29-31) : VirtualizeService last-point timestamp, PointPerDistance port, integration into Enhancer.
• ✅ Phase 3 — Node.js / Bun support (tasks 32-33) : runtime-detection in TileFetcher.js.kt (browser path unchanged, Node path uses globalThis.fetch + @jsquash/webp WASM decoder loaded via lazy eval('require')), webpack externals to keep the browser bundle free of @jsquash/webp, ElevationProvider auto-instantiation in EngineJsApi.enhance when opts.fixElevation is true (JS + Wasm façades), 6 jsTest classes gated by INTEGRATION=1.

Total :engine test coverage : 32 test classes / ~326 commonTest cases / 4 targets = ~1300 green executions, plus JVM-only smoke tests for the CLI and the full pipeline.

End-to-end smoke (after Phase 2bis) : sample.gpx (3569 source points, 130 km, ~4550 m gain) runs through the complete Enhancer pipeline in ~1.7 s on JVM, producing ~1000 simplified output points covering ~128.6 km / ~5.3 h of simulated ride.

• docs/PLAN.md — task-by-task plan with commit hashes for every step.
• docs/tasks/ — detailed Markdown spec for each task (00-31 + bonus demos).
• docs/parity.md — TS↔Kotlin parity approach and tolerances.
• docs/kotlin-wasm-jvm-webp.md — Kotlin/Wasm ↔ JS interop guide that underpins the @JsExport façades and the WebP tile decoding.
• docs/publishing.md — release flow (Maven Central + npm via semantic-release on push to develop).
• elevation/README.md — :elevation module details + browser demos.

develop is the default and only long-lived branch — there is no main. Open PRs against develop using Conventional Commits : feat: triggers a minor release, fix: a patch, anything else is a no-op release-wise. Every push to develop runs the full multi-target test suite via .github/workflows/release.yml and, if green, lets semantic-release tag a new version, publish to Maven Central + npm, and commit the version bump back to develop with [skip ci]. See docs/publishing.md for the full flow.

Apache License 2.0, aligned with the upstream gpx2web project. See the Maven Central POM metadata in engine/build.gradle.kts and elevation/build.gradle.kts. A top-level LICENSE file will be added before the first public release.