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Headless Still Render (renderStill)

Status: Live from v0.1.0 (DD-008 §4.8, E7 phase 5, #132) · consumer: AnyBridge #791.

renderStill produces a single non-interactive image of a toolpath in a headless/offscreen environment — the reusable capability behind AnyBridge's ThumbnailWorker G-code backend. It is a bounded adapter over the same engine the interactive viewer uses (parse → ToolpathIR → ToolpathRenderer), not a second renderer.

import { renderStill } from '@chestnutlabs/gcode-preview-core';

// In a Worker with an OffscreenCanvas, or an Electron hidden window:
const canvas = new OffscreenCanvas(1024, 768);
const { segmentCount } = await renderStill(gcodeBytes, {
  canvas,
  quality: 'tubes',
  buildVolume: machineGeometry // optional; discovered geometry otherwise
});
const png = await canvas.convertToBlob({ type: 'image/png' }); // caller extracts pixels

Input

source is G-code bytes (Uint8Array / ArrayBuffer — a worker parse runs; supply createWorker for the slim/custom worker, else the batteries default) or a pre-parsed ToolpathIR (no worker; AnyBridge can render straight from an IR it already holds).

Options (all neutral — the surface AnyBridge's RenderSpec translates onto)

Option Meaning
canvas (required) OffscreenCanvas or DOM canvas — the render target
width / height output size (defaults to the canvas dimensions)
quality 'auto' (default) / 'tubes' / 'lines'
colorMode single / by-tool / by-feature (feature is capability-gated)
tube tube profile parameters
buildVolume a renderer volume or discovered MachineGeometry
layerRange inclusive [start, end] layer clip
scrub draw up to a segment index (progress-style clip)
showTravel include travel moves (default off)
camera explicit { position, target, fov? } pose; omitted → deterministic bounds framing
createWorker / parseOptions worker + wire options for the bytes path
createRenderer GL-backend injection (tests / exotic hosts)

Returns { canvas, width, height, layerCount, segmentCount, quality, parsed }. The build runs to completion before a single render; the caller reads pixels from canvas in its own environment (convertToBlob, toDataURL, or a WebGL readPixels).

Determinism

Same environment ⇒ identical output. Framing is computed purely from model bounds, the build runs to completion before the one render, and no animation loop is involved. Cross-GPU/driver pixel identity is not promised (antialiasing and rasterization vary by hardware) — cache by job identity, not by pixel hash.

Supported environments

Any Chromium-class WebGL2 context: a Worker OffscreenCanvas, an Electron hidden BrowserWindow, or headless Chromium (CI). The drawing buffer is preserved so the canvas is readable after the render returns.

Out of scope (roadmap): pure-Node GPU-less rendering (software rasterization / a WebGL shim) is a deferred E8-class capability — it would need substantial new infrastructure and is not part of v0.1.0. If a future consumer needs server-side rendering without a Chromium-class context, that opens its own DD.

Ownership boundary (AnyBridge #791)

gcode-preview owns this reusable capability. AnyBridge owns only: its ThumbnailWorker integration, translating its shared RenderSpec into these neutral options, and caching/storage/job-identity/workflow behavior. AnyBridge does not maintain a duplicate rendering harness.