Spectacles AI — Reference Guide

The primary bridge between a lens and external AI models on Spectacles is the Remote Service Gateway (RSG). RSG is Snap's managed, authenticated proxy layer that handles auth, rate limiting, and response streaming for any registered endpoint — not just AI endpoints.

Official docs: Spectacles Home · Features Overview (Camera Module for vision input)

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Core Concepts

Remote Service Gateway (RSG)

• Available via require('LensStudio:RemoteServiceModule')
• Makes authenticated calls to registered cloud endpoints defined in your Lens Studio project's Remote Services panel.
• Returns results asynchronously; use callbacks or async/await.

Key APIs on Spectacles

Capability	API / Module	Notes
LLM inference	RSG → your backend or Snap RSG built-in endpoints	Stream tokens with onPartialResponse
Speech-to-Text	AsrModule	40+ languages, accuracy modes, mixed-language
Text-to-Speech	TtsModule	Synthesises audio from a string
Camera frame access	CameraModule	Grab frames for vision model input
AI Vision / object detection	RSG + depth texture / camera frame	Encode frame → send to cloud vision API
Depth texture	DepthTextureProvider	Access per-pixel depth for 3D projection

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Remote Service Gateway — Patterns

Declaring a remote service

In Lens Studio, open Remote Services (Project panel → Remote Services) and add an endpoint. Each service has an ID string you reference in script.

Making a basic call

const remoteServiceModule = require('LensStudio:RemoteServiceModule')

function callLLM(prompt: string, onResult: (text: string) => void): void {
  const request = RemoteServiceHttpRequest.create()
  request.endpoint = 'my-llm-service'   // matches service ID in Remote Services panel
  request.method = RemoteServiceHttpRequest.HttpRequestMethod.Post
  request.body = JSON.stringify({ prompt })

  remoteServiceModule.performHttpRequest(request, (response) => {
    if (response.statusCode === 200) {
      onResult(JSON.parse(response.body).text)
    } else {
      print('RSG error: ' + response.statusCode)
    }
  })
}

Streaming responses (token-by-token)

request.onPartialResponse = (partial: string) => {
  // Update UI in real-time as tokens arrive
  textComponent.text += partial
}

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Speech-to-Text (ASR)

Full example with language and accuracy options

const asrModule = require('LensStudio:AsrModule')

@component
export class VoiceInput extends BaseScriptComponent {
  onAwake(): void {
    const options = AsrModule.Options.create()

    // Language: BCP-47 tag, e.g. 'en-US', 'fr-FR', 'ja-JP'
    // 40+ languages supported. Leave unset for auto-detect.
    options.locale = 'en-US'

    // Accuracy: Balanced (faster, lower power) or High (more accurate, slower)
    options.accuracy = AsrModule.Accuracy.Balanced   // or AsrModule.Accuracy.High

    // Mixed language: allow transcription to switch languages mid-sentence
    options.mixedLanguages = false

    const session = asrModule.startSession(options)

    session.onTranscriptUpdate.add((event: AsrModule.TranscriptUpdateEvent) => {
      print('Transcript: ' + event.transcript)

      if (event.isFinal) {
        // Committed utterance — safe to send to LLM
        print('Final transcript: ' + event.transcript)
        print('Detected language: ' + event.language)
        session.stop()   // IMPORTANT: always stop to free the microphone
      }
    })

    session.onError.add((error) => {
      print('ASR error: ' + error)
      session.stop()  // also stop on error to free the microphone
    })
  }
}

• isFinal = false means a streaming partial result — the word list may still change.
• isFinal = true means the utterance is committed and ready for processing.
• Always call session.stop() when done — leaving ASR open drains battery and blocks the microphone.

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Text-to-Speech (TTS)

const ttsModule = require('LensStudio:TtsModule')

function speak(text: string): void {
  const options = TtsTextToSpeechOptions.create()
  options.text = text

  ttsModule.speak(options, (audioComponent) => {
    audioComponent.play(1)   // play once
  })
}

Cleanup on playback finish

ttsModule.speak(options, (audioComponent) => {
  audioComponent.onPlaybackFinished.add(() => {
    print('TTS finished')
  })
  audioComponent.play(1)
})

• TTS audio competes with other audio sources — set appropriate AudioMixerChannel.
• Calling speak() again before the previous audio finishes will queue the new utterance.

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Camera Access for Vision

const cameraModule = require('LensStudio:CameraModule')

const request = CameraModule.createCameraRequest()
request.cameraId = CameraModule.CameraId.Default_Color
const cameraTexture = cameraModule.requestCamera(request)

// Encode for transmission
const encodeOptions = EncodeTextureOptions.create()
Base64.encodeTextureAsync(cameraTexture, encodeOptions, (base64: string) => {
  callVisionAPI(base64)
})

Depth Cache pattern

Cache multiple depth frames for richer 3D analysis:

• Capture frames on a timer using DelayedCallbackEvent
• Store frames in a ring buffer (const buffer: string[] = [])
• On user interaction, select the most relevant cached frame and send to a cloud vision model

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Agentic Loop Pattern

For autonomous multi-step AI interactions (as in the Agentic Playground sample):

1. User speaks → ASR transcription
2. Transcription sent to LLM via RSG
3. LLM returns a tool call (e.g., { "action": "show_object", "params": {} })
4. Lens executes the action in the AR scene
5. Lens sends a tool result back to the LLM for the next turn
6. Loop continues until LLM returns a final response

Key design notes:

• Store conversation history in a typed array and include it in each request body.
• Use a thinking or loading UI state while waiting for LLM responses.
• Implement a hard iteration cap (e.g., max 10 tool calls) to avoid infinite loops.

interface Message { role: 'user' | 'assistant'; content: string }

const history: Message[] = []
const MAX_HISTORY = 20   // trim to avoid leaking earlier turns and hitting size limits
const MAX_TOOL_CALLS = 10 // hard cap to prevent runaway loops
let toolCallCount = 0

async function chat(userText: string): Promise<void> {
  if (toolCallCount++ >= MAX_TOOL_CALLS) {
    displayText('Reached iteration limit')
    return
  }

  history.push({ role: 'user', content: userText })
  // Keep only the last MAX_HISTORY messages
  if (history.length > MAX_HISTORY) history.splice(0, history.length - MAX_HISTORY)

  const request = RemoteServiceHttpRequest.create()
  request.endpoint = 'my-llm'
  request.method = RemoteServiceHttpRequest.HttpRequestMethod.Post
  request.body = JSON.stringify({ messages: history })

  remoteServiceModule.performHttpRequest(request, (response) => {
    const reply = JSON.parse(response.body).content as string
    history.push({ role: 'assistant', content: reply })
    displayText(reply)
  })
}

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AI Music Generation (Lyria / Gemini)

Pattern from the AI Music Gen sample:

ASR → Gemini text → Lyria audio → AudioComponent → 3D mesh driven by FFT

1. User describes genre/vibe via ASR
2. Description sent to Gemini via RSG for tag extraction
3. Tags forwarded to Lyria endpoint to generate an audio clip
4. Clip played through AudioComponent
5. 3D visualiser driven by AudioSpectrum FFT data

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Gesture + Vision: Crop Pattern

From the Crop sample — pinch to define a region, send to vision model:

1. Track hand pinch position with SIK HandInputData
2. Convert screen position to UV coordinates
3. Crop the camera texture at those UVs
4. Encode cropped region and send to RSG vision endpoint
5. Display result in a world-space panel near the gesture origin

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Permissions & Privacy

Combining camera, microphone, or location with internet connectivity triggers Snap's Transparent Permission system: the OS shows a consent dialog on launch and the device LED blinks during capture.

Important exception: Calls via the Remote Service Gateway (RSG) do not count as external connectivity. You can freely combine camera or microphone with RSG (LLMs, ASR, TTS, vision APIs) in a published lens without triggering the Transparent Permission prompt. This is the recommended pattern for AI-powered lenses.

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Common Gotchas

• RSG is not available in the Lens Studio simulator — test AI features on-device.
• Large base64 payloads can hit RSG body-size limits; resize or downsample images before encoding.
• ASR leaves the microphone open until you call session.stop() — always stop on both isFinal and onError to protect privacy and battery.
• ASR accuracy modes: Balanced is faster; High gives better results for commands with technical vocabulary.
• TTS and game audio share a mixer — prioritise with AudioMixerChannel.
• Use async/await to avoid callback pyramids in complex agentic loops.
• Always handle response.statusCode !== 200 cases — network errors are common on Spectacles (the device moves around).
• Agentic loops: always enforce a hard iteration cap in code (not just in comments) and trim conversation history to avoid leaking earlier sensitive user input.

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Reference Examples

• APIKeyHint.ts - A standard pattern for providing API key context.
• ModelGenBridge.ts - Example usage of handling Remote Service module prompts.