PathDrawer

A Unity 6 path input, spline, and trajectory engine. Convert a pointer trace into a simplified path, distance-spaced spline or ballistic arc, terrain projection, blocker result, and a Burst-generated ribbon. Runtime buffers are preallocated; the warmed geometry and full frame-loop EditMode probes report 0 B managed GC.

Unity 6000.6.3f1 · URP 17.6 · Burst · Collections · Mathematics · Input System 1.18

Engineering X-Ray

Subsystem	Implementation	What it does
01 Path input	PathInputDecimator	Fixed-capacity pointer samples, distance/turn hysteresis, iterative stack-based RDP.
02 Path geometry	CentripetalCatmullRomResampler	α = 0.5 Catmull–Rom, cumulative arc-length LUT, binary-search distance sampling, ballistic integration.
03 Line Renderer	PathRenderAdapter, BurstRibbonMeshBuilder	NativeArray LineRenderer submission and writable MeshData ribbon with miter/bevel joins and continuous UVs.
04 Trajectory view	TrajectoryPhysicsValidator	Batched terrain raycasts, blocker sphere casts, first-impact split, distance-based travel evaluation.

flowchart LR
    I[01 Pointer samples] --> R[RDP controls]
    R --> G[02 Spline or ballistic LUT]
    G --> P[04 Terrain projection + blocker batches]
    P --> L[03 Reachable / blocked lines]
    P --> M[03 Burst ribbon mesh]

Loading

Performance

Editor benchmark: Unity 6000.6.3f1 on an Intel Core i3-13100F, 30 measured samples after Burst warmup. Times include input simplification, spline/LUT work, and writable ribbon generation.

Input points	RDP points	Output points	RDP median (µs)	Spline + LUT median (µs)	Ribbon median (µs)	Total median (µs)	Total P95 (µs)
100	10	110	115.3	115.7	29.0	256.8	276.5
500	42	552	1022.7	628.1	119.1	1854.0	2186.9
2000	172	2211	5203.6	2402.1	251.9	7802.9	9430.1

These are measurements from the checked-in Editor benchmark report, not a cross-device guarantee. The EditMode suite includes warmed 1,000-rebuild geometry and 500-iteration full-pipeline zero-managed-allocation checks. MeshData allocation and GPU upload still consume native memory and time.

Sampling model

Centripetal Catmull–Rom sets knot intervals using Δt = ||Pᵢ₊₁ − Pᵢ||^0.5. Nonuniform intervals reduce overshoot around tight turns. A preallocated lookup stores cumulative segment length; a binary search locates each requested travel distance, then bounded refinement keeps the emitted Euclidean step within the configured spacing. The same LUT and uniform-distance resampler serve ballistic trajectories.

The demo uses 0.20 m spline spacing, a continuous 80×80 terrain mesh, and synchronous capture rebuilds. Input gestures use batched terrain and obstacle queries; the showcase builds and validates deterministically before updating the view.

Run it

Open the repository in Unity 6000.6.3f1. The checked-in Assets/Scenes/SampleScene.unity is the runnable sample. Use the HUD buttons or keyboard: LMB draw, S spline, B ballistic, Space arc preview, R restore Auto-Showcase.

The runtime owners are constructed once and disposed with their controller:

input.TryAddSample(worldPosition);
int controls = input.Simplify(tolerance, simplifiedControls);
geometry.RebuildSpline(simplifiedControls, controls, 16, 0.20f).Complete();
physics.ScheduleValidation(geometry, geometry.Count);
physics.ScheduleBlockerCasts();
physics.CompleteValidation();
ribbon.Build(mesh, geometry.Positions, physics.PathDistances, geometry.Count, width: 0.42f);

Run Window → General → Test Runner → EditMode → Run All. The Unity Editor menu Tools → PathDrawer rebuilds the sample scene, exports fresh benchmark metrics, captures the 1080p showcase, and builds a WebGL ZIP for itch.io. Install the matching WebGL Build Support module in Unity Hub before using menu item 4.

Editor command	Output
1. Build & Save Ready-to-Play SampleScene	Assets/Scenes/SampleScene.unity and generated terrain/material assets.
2. Run Benchmark Sweep & Export Markdown	PathDrawer-Benchmark-Results.md plus updated README metrics.
3. Capture 1080p Portfolio Screenshot	docs/screenshots/pathdrawer-game-view.png, with content assertions before saving.
4. Build WebGL for itch.io (ZIP)	Builds/WebGL-ItchIo/ and a ZIP whose root contains index.html.

License

MIT. See LICENSE.