Omniverse Realtime Viewer

Headless SHM CLI

Triggers

Use this skill for headless CLI, SHM automation, ovusd-shm, viewer automation, scripted interaction, CLI testing, non-interactive viewer, screenshot capture, automated scene validation, scripted pick/select sequences, or programmatic stage tree inspection.

Use this with an existing OVRTX server that exposes the ovstream shared-memory transport. The CLI is a local automation client: it does not render USD, host a UI, or replace the viewer server. It attaches to the named SHM stream, reads frames, sends input and JSON viewer messages, and exits with deterministic stdout/stderr behavior suitable for scripts and CI jobs.

Purpose

Build a command-line client for automation, testing, CI pipelines, and scripted interactions with a running OVRTX viewer server through ovstream SHM. Typical uses include:

• capture a rendered frame as PNG, JPEG, or raw BGRA/RGBA bytes

• verify stream health and frame dimensions

• inspect the USD stage hierarchy and selected prim properties

• run scripted camera drags and pick/select workflows

• switch AOVs for validation frames

• pipe raw frames into video encoders or image-diff tools

When To Use This

Choose the headless SHM CLI when:

• an automated test needs to drive a local viewer without opening Electron, Tauri, ovui, or a browser

• CI needs smoke tests against an OVRTX server with --shm enabled

• screenshots or raw frames must be captured from the same renderer path as the desktop viewer

• scene validation needs hierarchy, property, AOV, selection, or pick checks

• scripted interactions should reproduce user workflows such as click, drag, select, inspect, and capture

• Playwright or another e2e harness needs a stable backend for renderer state

Do not use this as a remote browser streaming client. For WebRTC browser delivery, use streaming-server, streaming-client, streaming-messages, and streaming-lifecycle. For an interactive local desktop UI, use electron-shm-viewer, tauri-local-viewer, or local-viewer.

Architecture

Node.js CLI
  -> generated local SHM client module
  -> native Node addon built with node-gyp
  -> libovstream_shm_client.so
  -> libovstream.so
  -> POSIX shared memory frames and control messages
  -> Python OVRTX server started with --shm

The Python server remains the source of truth for USD, ovrtx.Renderer, stage queries, camera state, picking, selection outlines, render settings, and AOVs. The CLI is only a client:

• Frames: wait for the newest SHM frame and write PNG/JPEG/raw output.

• Input: send mouse move/button/wheel events to the server.

• Viewer state: send JSON event_type/payload requests over the SHM control channel and wait for matching responses.

Reference electron-shm-viewer for the server-side SHM lifecycle and streaming-messages for message envelope names. Reference object-selection, stage-hierarchy, stage-attribute-reads, and aov-switching when adding server handlers that the CLI calls.

For ovstream SHM acquisition and runtime setup beyond this CLI pattern, read references/dependencies. Keep the CLI client code local to the generated app.

Use the unified native client API and frame ownership rules. Copy borrowed frames before encoding or retaining them. Build the Node addon for Node's ABI separately from the Electron addon.

Prerequisites

• A Python OVRTX server is already running with SHM enabled, for example --shm.

• The CLI --stream-name matches the server --shm-stream-name.

• Node.js 18 or newer is available.

• LD_LIBRARY_PATH includes the directory containing libovstream.so and any dependent ovstream native libraries.

• A generated local SHM client module exists in the app workspace, for example clients/shm-client/.

• The native addon has been rebuilt for the active Node/Electron ABI with node-gyp.

Example environment:

export LD_LIBRARY_PATH=/path/to/.venv/lib/python3.10/site-packages/ovstream/lib:$LD_LIBRARY_PATH
export OV_SHM_STREAM_NAME=ovrtx-viewer

Command Reference

Commands should be named after actions and produce script-friendly output. Successful commands write the primary result to stdout unless --output is provided. Diagnostics and errors go to stderr. Non-zero exit codes indicate failure.

frame

Capture one frame from SHM.

ovusd-shm frame --output frame.png
ovusd-shm frame --output frame.jpg --format jpeg
ovusd-shm frame --format raw > frame.bgra

Options:

• --output <path> writes to a file instead of stdout.

• --format png|jpeg|raw controls encoding. Infer png or jpeg from --output extension when possible.

Raw output is tightly packed frame data in the native SHM format unless the package explicitly converts it. Include width, height, format, and pitch in info output so raw consumers can decode it correctly.

info

Print stream and latest-frame metadata as JSON.

ovusd-shm info

Include at least stream name, producer liveness, width, height, pixel format, pitch bytes, and sequence number.

tree

Query stage hierarchy rows from the server.

ovusd-shm tree --root /World
ovusd-shm tree --root /World --json

Options:

• --root <path> selects the root prim path. Default to /World only when the server has no loaded root-prim state to report.

• --json prints the raw tree response for machine checks. Without --json, print a readable indented tree with prim paths and types.

click

Send a viewport click using fractional viewport coordinates.

ovusd-shm click 0.40 0.45
ovusd-shm click 0.40 0.45 --wait-select

Arguments are x y in normalized viewport space, clamped to 0..1. --wait-select waits for a selection change and prints the selected prim path or null.

pick

Run a raw pick query without changing selection.

ovusd-shm pick 0.40 0.45

Print the picked prim path or null. Use pickRequest/pickResult on the control channel so the server can distinguish raw pick queries from selection clicks.

drag

Send a scripted viewport drag for orbit or pan behavior.

ovusd-shm drag 0.45 0.50 0.65 0.40 --steps 20 --duration 500

Arguments are x1 y1 x2 y2 in normalized viewport space. Options:

• --steps <n> controls the number of move events.

• --duration <ms> spreads the drag over the given duration.

Default to left-button drag for orbit unless the CLI adds an explicit button or mode option that maps to the server's camera controls.

select

Select a prim by absolute USD path.

ovusd-shm select /World/Cube

Send selectPrimsRequest {paths:[path]} and wait for stageSelectionChanged. Print the confirmed path or resulting selected paths.

props

Print properties for a prim.

ovusd-shm props /World/Cube
ovusd-shm props /World/Cube --json

Without --json, print tab-separated name, type, and value rows. With --json, print the server response as structured JSON. Cap large payloads on the server and preserve any truncated flag.

aov

List or switch render AOVs.

ovusd-shm aov --list
ovusd-shm aov --set LdrColor

Options:

• --list prints available AOV names, one per line.

• --set <name> sends changeAOVRequest and prints the resulting active AOV state as JSON.

Expose only render vars that map to real full-resolution image data.

stream

Continuously write frames to stdout for video capture or external tools.

ovusd-shm stream --format raw > frames.bgra
ovusd-shm stream --format png > frames.pngstream

Default to raw output for predictable throughput. Handle SIGINT and SIGTERM by closing the SHM client cleanly.

Common Options

All commands accept:

• --stream-name <name>: SHM stream name. Default to OV_SHM_STREAM_NAME or the app default such as ovrtx-viewer.

• --timeout <ms>: operation timeout in milliseconds. Default to 15000.

Timeouts should apply to stream attachment, frame waits, request/response round-trips, and --wait-select unless the command documents a shorter selection-specific timeout.

Building From Source

Build the shared SHM client against the selected SDK headers and libraries, then build the CLI using the generated project's scripts. Share the client implementation with desktop and test clients, while building each native addon for its host runtime ABI. Follow the SDK's loader setup through dependencies and package the required runtime libraries with the app.

The generated local SHM client module should provide:

• TypeScript types for frames, prim nodes, prim properties, input events, AOV state, and request options

• a ShmViewerClient class that owns its connection and frame pump

• PNG encoding without requiring browser APIs

• optional JPEG encoding through a Node dependency such as sharp

• native addon loading from installed and source-tree locations

• a clear error when libovstream.so or libovstream_shm_client.so cannot be loaded

The native addon should:

• wrap libovstream_shm_client.so

• build with node-gyp

• expose blocking frame waits through a safe JS API for CLI use

• validate frame dimensions, pitch, format, and byte lengths

• close native handles on process exit or thrown errors

• avoid exposing raw pointers or file descriptors to JavaScript

Playwright And E2E Testing

Use the headless CLI as the renderer/test backend when Playwright is responsible for UI checks or orchestration:

import { execFile } from 'node:child_process';
import { promisify } from 'node:util';
import { expect, test } from '@playwright/test';

const run = promisify(execFile);
const streamName = process.env.OV_SHM_STREAM_NAME ?? 'ovrtx-viewer';

test('selects a prim through the OVRTX backend', async () => {
  await run('ovusd-shm', ['frame', '--output', 'before.png', '--stream-name', streamName]);
  const { stdout } = await run('ovusd-shm', [
    'click', '0.50', '0.50', '--wait-select', '--stream-name', streamName,
  ]);
  expect(stdout.trim()).toMatch(/^\/World\//);
  await run('ovusd-shm', ['frame', '--output', 'after.png', '--stream-name', streamName]);
});

Testing guidance:

• start the Python server as a fixture and wait for shmReady before running CLI commands

• use unique stream names per parallel worker

• treat the CLI as the source of renderer truth for frame capture, selection, hierarchy, properties, and AOV state

• keep browser DOM assertions separate from renderer-state assertions

• preserve captured frames as test artifacts on failure

Example Automation Script

#!/usr/bin/env bash
set -euo pipefail

STREAM_NAME="${OV_SHM_STREAM_NAME:-ovrtx-viewer}"
TARGET="${1:-/World/Cube}"

ovusd-shm info --stream-name "$STREAM_NAME"
ovusd-shm frame --stream-name "$STREAM_NAME" --output before.png

picked="$(ovusd-shm pick --stream-name "$STREAM_NAME" 0.50 0.50)"
echo "picked=${picked}"

ovusd-shm select --stream-name "$STREAM_NAME" "$TARGET"
selected="$(ovusd-shm click --stream-name "$STREAM_NAME" 0.50 0.50 --wait-select)"
test -n "$selected"
test "$selected" != "null"

ovusd-shm props --stream-name "$STREAM_NAME" "$selected" --json > selected-props.json
ovusd-shm frame --stream-name "$STREAM_NAME" --output after.png

This pattern captures a baseline frame, performs a pick/select interaction, verifies that selection state is observable, records selected prim properties, and captures a post-selection frame for visual diffing.

Gotchas

• LD_LIBRARY_PATH must be set before Node starts. Changing it inside the process is too late for native dynamic loading.

• --stream-name must exactly match the server --shm-stream-name.

• Coordinates are 0..1 fractional viewport coordinates, not CSS pixels. The client converts them to render-product pixels after reading a frame.

• Use the fixed server render resolution for input mapping. Do not use browser DOM size or Electron window size in the CLI.

• Wait for at least one frame before sending fractional input so width and height are known.

• Keep JSON control messages small. Do not send frame bytes through JSON.

• Server callbacks should enqueue work; only the server render owner should call renderer.step(), reset/load scenes, or write live attributes.

• Raw frame streams need out-of-band width, height, format, and pitch metadata. Capture info alongside raw artifacts.

• In CI, use unique stream names and clean up stale POSIX SHM segments owned by the current test run only.