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Add 'superseded by ImagePresentationComponent' status note; StereoPair: Equatable #2

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Add 'superseded by ImagePresentationComponent' status note; StereoPair: Equatable #2

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24 changes: 24 additions & 0 deletions README.md
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# Stereo Image Display in visionOS

> ## Status (2025): superseded by `ImagePresentationComponent`
>
> This project dates from **June 2024 (visionOS 2.0, Xcode 16.2)**, before the SDK had a purpose-built
> stereo-image API. At the time, driving a `ShaderGraphMaterial` + `CameraIndexSwitch` to feed each eye a
> separate `TextureResource` was a reasonable way to show a stereo pair — but it carries real costs that
> are visible in this code: texture-swap **memory leaks** (worked around by stashing the pair's `id` in the
> entity's `name`), **synchronous `TextureResource.load` on the render thread**, the **grayscale-load bug
> (FB13733823)** patched by painting a blue streak on the NASA Ames frames, **no depth/convergence control**
> (wide-baseline pairs such as several of the Middlebury 2021 scenes are uncomfortably deep with no remedy),
> and a fixed plane whose aspect ratio is locked to the first image.
>
> **As of visionOS 26, prefer `ImagePresentationComponent` with `.spatialStereo`.** Hand it a single spatial
> photo (stereo-pair-group HEIC) via `ImagePresentationComponent(contentsOf:)` and set
> `desiredViewingMode = .spatialStereo`; RealityKit then does per-eye presentation, sizing, and edge
> feathering for you, with comfortable depth driven by the file's baked-in camera metadata (baseline / FOV).
> The grayscale problem is handled once, at conversion time, by producing an RGB spatial HEIC. I've since
> built a productized take on this — a data-driven, multi-app stereo viewer on `ImagePresentationComponent`
> with a pipeline that bakes per-scene calibration and an edge matte into spatial HEICs (reusing these same
> Middlebury scenes) — in a separate `Stereography` project.
>
> This repo is kept as a historical reference for the pre-`ImagePresentationComponent` shader-graph
> technique. The one idea still worth borrowing is the `CameraIndexSwitch` "Mono" fallback for pairs that
> are missing one eye.

This sample project shows my current approach to displaying stereographic image pairs in visionOS. There are a few hiccups.

The shader graph is pretty straightforward. Two named `ImageFile` nodes ("LeftImage" and "RightImage") accept the names of the left and right images, feed to a pair of `Image` nodes, which then feed a `CameraIndexSwitch`. I feed the right image to the "Mono" input, because in the image pairs I'm working with I'll occasionally encounter a missing left image. This pipeline then feeds a named output "StereoImage". In releases through visionOS 2.2, and still in Xcode 16.2's visionOS 2.2 SDK, `TextureResource.load` fails with pure grayscale images, so you will have to convert them to an RGB-based color space (Apple FB 13733823). Size limit is 8192x8192 pixels.
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2 changes: 1 addition & 1 deletion ShaderGraph Stereo/StereoPair.swift
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import Foundation

struct StereoPair: Codable, Identifiable {
struct StereoPair: Codable, Identifiable, Equatable {
let id: String
let leftImageName: String
let rightImageName: String
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