Flutter PrismSDK Capture Wrapper Guide

This guide explains how to build a Flutter plugin - prism_capture - that wraps the body-scan capture experience only of PrismSDK for both iOS and Android behind one unified Dart API. The plugin presents the full-screen capture UX, receives the output zip, and performs a direct PUT upload to an S3 presigned URL that your backend obtains from the Prism API. No Prism API credentials are needed on the device; all REST calls (user management, scan records, measurements, health reports) remain on the backend and are out of scope for this plugin.

Scope - What This Wraps / What It Doesn't

Wraps:

Full-screen capture UX: volume check → (face guidance, iOS only) → device leveling → body positioning → posing → recording → processing → optional review → finished.
Output: a .zip file written to local storage.
Zip upload: a direct HTTP PUT to an S3 presigned URL (Content-Type: application/zip).

Does NOT wrap:

The Prism REST API (user creation, scan lifecycle, measurements, health reports). These live on your backend server.
Any authentication or API key management. Capture requires no PrismSDK-Info.plist on iOS and no API credentials on Android.

Unified Architecture

Dart Layer
  └── PrismCapture (lib/prism_capture.dart)
        ├── MethodChannel  "tech.prismlabs.prism_capture/methods"   ← commands
        └── EventChannel   "tech.prismlabs.prism_capture/events"    ← typed event stream
              ├── iOS: PrismCapturePlugin.swift
              │         FlutterPlugin + FlutterStreamHandler
              │         presents PrismSessionViewController via UIHostingController
              │         FileUploader (PrismLink) for background S3 PUT
              └── Android: PrismCapturePlugin.kt
                            FlutterPlugin + MethodCallHandler + StreamHandler + ActivityAware
                            launches PrismCaptureActivity (ComponentActivity + Compose)
                            PrismSessionView Composable wraps PrismSession controller
                            Ktor client for S3 PUT

The plugin uses the present native full-screen via method channel + stream events back model: startCaptureSession instructs the native side to present a new full-screen VC (iOS) or launch a new Activity (Android); the Future returned by startCaptureSession completes when the command is accepted, not when the UI finishes presenting. Events - status changes, archive delivery, upload progress - flow back through the EventChannel stream as typed maps. This gives the capture surface full access to camera hardware and native animations without embedding a PlatformView.

PlatformView alternative: If your app needs the capture surface inline (e.g., inside a tab layout), you can host it as a UiKitView (iOS) or AndroidView (Android) instead. That requires the native plugin class to register a FlutterPlatformViewFactory and is more complex to size and lifecycle-manage. The method-channel + full-screen model is strongly preferred for capture.

Plugin Contract

Methods

Dart Method	What it does	Platform notes
`startCaptureSession({CaptureOptions? options})`	Presents the full-screen capture flow. Returns `Future<void>` when the command is accepted (not when the UI finishes presenting).	Both platforms
`dismissCaptureSession()`	Programmatically dismisses the capture UI. Returns `Future<void>`.	Both platforms
`uploadCapture(String filePath, String presignedUrl)`	Uploads the zip at `filePath` via HTTP PUT to `presignedUrl`. Returns `Future<void>`.	Both; see platform differences
`setupUploader()`	Resumes interrupted background uploads from a previous app session. Returns `Future<void>`.	iOS only. On Android this is a documented no-op.