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This draft is a specification for 4D URI's & [hypermediatic](https://github.com/coderofsalvation/hypermediatic) navigation, which links together space, time & text together, for hypermedia browsers with- or without a network-connection.<br>
The specification uses [W3C Media Fragments](https://www.w3.org/TR/media-frags/) and [URI Templates (RFC6570)](https://www.rfc-editor.org/rfc/rfc6570) to promote spatial addressibility, sharing, navigation, filtering and databinding objects for (XR) Browsers.<br>
XR Fragments allows us to better use existing metadata inside 3D scene(files), by connecting it to proven technologies like [URI Fragments](https://en.wikipedia.org/wiki/URI_fragment).
1. addressibility and [hypermediatic](https://github.com/coderofsalvation/hypermediatic) navigation of 3D scenes/objects: [URI Fragments](https://en.wikipedia.org/wiki/URI_fragment) + src/href spatial metadata
Instead of forcing authors to combine 3D/2D objects programmatically (publishing thru a game-editor e.g.), XR Fragments **integrates all** which allows a universal viewing experience.<br>
Fact: our typical browser URL's are just **a possible implementation** of URI's (for untapped humancentric potential of URI's [see interpeer.io](https://interpeer.io))
> XR Fragments does not look at XR (or the web) thru the lens of HTML or URLs.<br>But approaches things from a higherlevel feedbackloop/hypermedia browser-perspective.
XR Fragments itself are [hypermediatic](https://github.com/coderofsalvation/hypermediatic) and HTML-agnostic, though pseudo-XR Fragment browsers **can** be implemented on top of HTML/Javascript.
Pseudo (non-native) browser-implementations (supporting XR Fragments using HTML+JS e.g.) can use the `?` search-operator to address outbound content.<br>
In other words, the URL updates to: `https://me.com?https://me.com/other.glb` when navigating to `https://me.com/other.glb` from inside a `https://me.com` WebXR experience e.g.<br>
That way, if the link gets shared, the XR Fragments implementation at `https://me.com` can load the latter (and still indicates which XR Fragments entrypoint-experience/client was used).
| [W3C Media Fragments](https://www.w3.org/TR/media-frags/) | [media fragment](#media%20fragments%20and%20datatypes) | `#t=0,2&loop` | play (and loop) 3D animation from 0 seconds till 2 seconds|
| **PRESET** | `#<preset>` | string | `#cubes` | evaluates preset (`#foo&bar`) defined in 3D Object metadata (`#cubes: #foo&bar` e.g.) while URL-browserbar reflects `#cubes`. Only works when metadata-key starts with `#` |
| **FOCUS** | `#<tag_or_objectname>` | string | `#person` | (and show) object(s) with `tag: person` or name `person` (XRWG lookup) |
| **FILTERS** | `#[!][-]<tag_or_objectname>[*]` | string | `#person` (`#-person`) | will reset (`!`), show/focus or hide (`-`) focus object(s) with `tag: person` or name `person` by looking up XRWG (`*`=including children) |
| **CAMERASWITCH** | `#<cameraname>` | string | `#cam01` | sets camera with name `cam01` as active camera |
| **MATERIALUPDATE** | `#<tag_or_objectname>[*]=<materialname>` | string=string | `#car=metallic`| sets material of car to material with name `metallic` (`*`=including children)|
| **VARIABLE UPDATE** | `#<variable>=<metadata-key>` | string=string | `#foo=bar` | sets [URI Template](https://www.rfc-editor.org/rfc/rfc6570) variable `foo` to the value `#t=0` from **existing** object metadata (`bar`:`#t=0` e.g.), This allows for reactive [URI Template](https://www.rfc-editor.org/rfc/rfc6570) defined in object metadata elsewhere (`src`:`://m.com/cat.mp4#{foo}` e.g., to play media using [media fragment URI](https://www.w3.org/TR/media-frags/#valid-uri)). NOTE: metadata-key should not start with `#` |
> NOTE: below the word 'play' applies to 3D animations embedded in the 3D scene(file) **but also** media defined in `src`-metadata like audio/video-files (mp3/mp4 e.g.)
> \* = this is extending the [W3C media fragments](https://www.w3.org/TR/media-frags/#mf-advanced) with (missing) playback/viewport-control. Normally `#t=0,2` implies setting start/stop-values AND starting playback, whereas `#s=0&loop` allows pausing a video, speeding up/slowing down media, as well as enabling/disabling looping.
> The rationale for `uv` is that the `xywh` Media Fragment deals with rectangular media, which does not translate well to 3D models (which use triangular polygons, not rectangular) positioned by uv-coordinates.
> NOTE: URI Template variables are immutable and respect scope: in other words, the end-user cannot modify `blue` by entering an URL like `#blue=.....` in the browser URL, and `blue` is not accessible by the plane/media-object (however `{play}` would work).
> It also allows **sourceportation**, which basically means the enduser can teleport to the original XR Document of an `src` embedded object, and see a visible connection to the particular embedded object. Basically an embedded link becoming an outbound link by activating it.
1. the Y-coordinate of `pos` identifies the floorposition. This means that desktop-projections usually need to add 1.5m (average person height) on top (which is done automatically by VR/AR headsets).
1. set the position of the camera accordingly to the vector3 values of `#pos`
1.`rot` sets the rotation of the camera (only for non-VR/AR headsets)
An XR Fragment-compatible browser viewing this scene, allows the end-user to interact with the `buttonA` and `buttonB`.<br>
In case of `buttonA` the end-user will be teleported to another location and time in the **current loaded scene**, but `buttonB` will **replace the current scene** with a new one, like `other.fbx`, and assume `pos=0,0,0`.
1. IF a `#cube` matches a custom property-key (of an object) in the 3D file/scene (`#cube`: `#......`) <b>THEN</b> execute that predefined_view.
2. IF scene operators (`pos`) and/or animation operator (`t`) are present in the URL then (re)position the camera and/or animation-range accordingly.
3. IF no camera-position has been set in <b>step 1 or 2</b> update the top-level URL with `#pos=0,0,0` ([example](https://github.com/coderofsalvation/xrfragment/blob/main/src/3rd/js/three/navigator.js#L31]]))
4. IF a `#cube` matches the name (of an object) in the 3D file/scene then draw a line from the enduser('s heart) to that object (to highlight it).
5. IF a `#cube` matches anything else in the XR Word Graph (XRWG) draw wires to them (text or related objects).
An XR Fragment-compatible browser viewing this scene, lazy-loads and projects `painting.png` onto the (plane) object called `canvas` (which is copy-instanced in the bed and livingroom).<br>
Also, after lazy-loading `ocean.com/aquarium.gltf`, only the queried objects `fishbowl` (and `bass` and `tuna`) will be instanced inside `aquariumcube`.<br>
> Instead of cherrypicking a rootobject `#fishbowl` with `src`, additional filters can be used to include/exclude certain objects. See next chapter on filtering below.
2.<b>local</b>`src` values (`#...` e.g.) starting with a non-negating filter (`#cube` e.g.) will (deep)reparent that object (with name `cube`) as the new root of the scene at position 0,0,0
3.<b>local</b>`src` values should respect (negative) filters (`#-foo&price=>3`)
4. the instanced scene (from a `src` value) should be <b>scaled accordingly</b> to its placeholder object or <b>scaled relatively</b> based on the scale-property (of a geometry-less placeholder, an 'empty'-object in blender e.g.). For more info see Chapter Scaling.
5.<b>external</b>`src` values should be served with appropriate mimetype (so the XR Fragment-compatible browser will now how to render it). The bare minimum supported mimetypes are:
6.`src` values should make its placeholder object invisible, and only flush its children when the resolved content can succesfully be retrieved (see [broken links](#links))
7.<b>external</b>`src` values should respect the fallback link mechanism (see [broken links](#broken-links)
8. when the placeholder object is a 2D plane, but the mimetype is 3D, then render the spatial content on that plane via a stencil buffer.
9. src-values are non-recursive: when linking to an external object (`src: foo.fbx#bar`), then `src`-metadata on object `bar` should be ignored.
12. when the enduser clicks an href with `#t=1,0,0` (play) will be applied to all src mediacontent with a timeline (mp4/mp3 e.g.)
13. a non-euclidian portal can be rendered for flat 3D objects (using stencil buffer e.g.) in case ofspatial `src`-values (an object `#world3` or URL `world3.fbx` e.g.).
2. relocation/reorientation should happen locally for local URI's (`#pos=....`)
3. navigation should not happen ''immediately'' when user is more than 2 meter away from the portal/object containing the href (to prevent accidental navigation e.g.)
4. URL navigation should always be reflected in the client (in case of javascript: see [[here](https://github.com/coderofsalvation/xrfragment/blob/dev/src/3rd/js/three/navigator.js) for an example navigator).
7. In XR mode, the navigator back/forward-buttons should be always visible (using a wearable e.g., see [[here](https://github.com/coderofsalvation/xrfragment/blob/dev/example/aframe/sandbox/index.html#L26-L29) for an example wearable)
8. in case of navigating to a new [[pos)ition, ''first'' navigate to the ''current position'' so that the ''back-button'' of the ''browser-history'' always refers to the previous position (see [[here](https://github.com/coderofsalvation/xrfragment/blob/main/src/3rd/js/three/xrf/href.js#L97))
11. the end-user navigator back/forward buttons should repeat a back/forward action until a `pos=...` primitive is found (the inbetween interaction URI's are only for UX research purposes)
How does the scale of the object (with the embedded properties) impact the scale of the referenced content?<br>
> Rule of thumb: visible placeholder objects act as a '3D canvas' for the referenced scene (a plane acts like a 2D canvas for images e, a cube as a 3D canvas e.g.).
1.<b>IF</b> an embedded property (`src` e.g.) is set on an non-empty placeholder object (geometry of >2 vertices):
* calculate the <b>bounding box</b> of the ''placeholder'' object (maxsize=1.4 e.g.)
* hide the ''placeholder'' object (material e.g.)
* instance the `src` scene as a child of the existing object
* calculate the <b>bounding box</b> of the instanced scene, and scale it accordingly (to 1.4 e.g.)
> REASON: non-empty placeholder object can act as a protective bounding-box (for remote content of which might grow over time e.g.)
* see [an (outdated) example video here](https://coderofsalvation.github.io/xrfragment.media/queries.mp4) which used a dedicated `q=` variable (now deprecated and usable directly)
> NOTE 1: after an external embedded object has been instanced (`src: https://y.com/bar.fbx#room` e.g.), filters do not affect them anymore (reason: local tag/name collisions can be mitigated easily, but not in case of remote content).
> NOTE 2: depending on the used 3D framework, toggling objects (in)visible should happen by enabling/disableing writing to the colorbuffer (to allow children being still visible while their parents are invisible).
> An example filter-parser (which compiles to many languages) can be [found here](https://github.com/coderofsalvation/xrfragment/blob/main/src/xrfragment/Filter.hx)
The obvious approach for this, is to consult the XRWG ([example](https://github.com/coderofsalvation/xrfragment/blob/feat/macros/src/3rd/js/XRWG.js)), which basically has all these things already collected/organized for you during scene-load.
> The XR Fragments does this by collapsing space into a **Word Graph** (the **XRWG** [example](https://github.com/coderofsalvation/xrfragment/blob/feat/macros/src/3rd/js/XRWG.js)), augmented by Bib(s)Tex.
Instead of just throwing together all kinds media types into one experience (games), what about their tagged/semantical relationships?<br>
Perhaps the following question is related: why is HTML adopted less in games outside the browser?
Through the lens of constructive lazy game-developers, ideally metadata must come **with** text, but not **obfuscate** the text, or **spawning another request** to fetch it.<br>
> Why Bib(s)Tex? Because its seems to be the lowest common denominator for an human-curated XRWG (extendable by speech/scanner/writing/typing e.g, see [further motivation here](https://github.com/coderofsalvation/hashtagbibs#bibs--bibtex-combo-lowest-common-denominator-for-linking-data))
1. XR Fragments promotes (de)serializing a scene to the XRWG ([example](https://github.com/coderofsalvation/xrfragment/blob/feat/macros/src/3rd/js/XRWG.js))
5. Like Bibs, XR Fragments generalizes the BibTex author/title-semantics (`author{title}`) into **this** points to **that** (`this{that}`)
6. The XRWG should be recalculated when textvalues (in `src`) change
7. HTML/RDF/JSON is still great, but is beyond the XRWG-scope (they fit better in the application-layer)
8. Applications don't have to be able to access the XRWG programmatically, as they can easily generate one themselves by traversing the scene-nodes.
9. The XR Fragment focuses on fast and easy-to-generate end-user controllable word graphs (instead of complex implementations that try to defeat word ambiguity)
> both `#john@baroque`-bib and BibTex `@baroque{john}` result in the same XRWG, however on top of that 2 tages (`house` and `todo`) are now associated with text/objectname/tag 'baroque'.
> [hashtagbibs](https://github.com/coderofsalvation/hashtagbibs) potentially allow the enduser to annotate text/objects by **speaking/typing/scanning associations**, which the XR Browser saves to remotestorage (or localStorage per toplevel URL). As well as, referencing BibTags per URI later on: `https://y.io/z.fbx#@baroque@todo` e.g.
9. The XR Browser needs to adjust tag-scope based on the endusers needs/focus (infinite tagging only makes sense when environment is scaled down significantly)
10. The XR Browser should always allow the human to view/edit the metadata, by clicking 'toggle metadata' on the 'back' (contextmenu e.g.) of any XR text, anywhere anytime.
13. Default font (unless specified otherwise) is a modern monospace font, for maximized tabular expressiveness (see [the core principle](#core-principle)).
14. anti-pattern: hardcoupling an XR Browser with a mandatory **markup/scripting-language** which departs from onubtrusive plain text (HTML/VRML/Javascript) (see [the core principle](#core-principle))
> The simplicity of appending metadata (and leveling the metadata-playfield between humans and machines) is also demonstrated by [visual-meta](https://visual-meta.info) in greater detail.
* lines beginning with `@` will not be rendered verbatim by default ([read more](https://github.com/coderofsalvation/hashtagbibs#hashtagbib-mimetypes))
* the XRWG should expand bibs to BibTex occurring in text (`#contactjohn@todo@important` e.g.)
> This significantly expands expressiveness and portability of human tagged text, by **postponing machine-concerns to the end of the human text** in contrast to literal interweaving of content and markupsymbols (or extra network requests, webservices e.g.).
> additional tagging using [bibs](https://github.com/coderofsalvation/hashtagbibs): to tag spatial object `note_canvas` with 'todo', the enduser can type or speak `#note_canvas@todo`
To prime the XRWG with text from plain text `src`-values, here's an example XR Text (de)multiplexer in javascript (which supports inline bibs & bibtex):
> when an XR browser updates the human text, a quick scan for nonmatching tags (`@book{nonmatchingbook` e.g.) should be performed and prompt the enduser for deleting them.
> due to the popularity, maturity and extensiveness of HTTP codes for client/server communication, non-HTTP protocols easily map to HTTP codes (ipfs ERR_NOT_FOUND maps to 404 e.g.)
> This would hide all object tagged with `topic`, `courses` or `theme` (including math) so that later only objects tagged with `math` will be visible
This makes spatial content multi-purpose, without the need to separate content into separate files, or show/hide things using a complex logiclayer like javascript.
The only dynamic parts are [W3C Media Fragments](https://www.w3.org/TR/media-frags/) and [URI Templates (RFC6570)](https://www.rfc-editor.org/rfc/rfc6570).<br>
The use of URI Templates is limited to pre-defined variables and Level0 fragments-expansion only, which makes it quite safe.<br>
In fact, it is much safer than relying on a scripting language (javascript) which can change URN too.
**Q:** Why is everything HTTP GET-based, what about POST/PUT/DELETE HATEOS<br>
**A:** Because it's out of scope: XR Fragment specifies a read-only way to surf XR documents. These things belong in the application layer (for example, an XR Hypermedia browser can decide to support POST/PUT/DELETE requests for embedded HTML thru `src` values)
**Q:** Why isn't there support for scripting, URI Template Fragments are so limited compared to WASM & javascript
**A:** This is out of scope as it unhyperifies hypermedia, and this is up to XR hypermedia browser-extensions.<br> Historically scripting/Javascript seems to been able to turn webpages from hypermedia documents into its opposite (hyperscripted nonhypermedia documents).<br>In order to prevent this backward-movement (hypermedia tends to liberate people from finnicky scripting) XR Fragment uses [W3C Media Fragments](https://www.w3.org/TR/media-frags/) and [URI Templates (RFC6570)](https://www.rfc-editor.org/rfc/rfc6570), to prevent unhyperifying itself by hardcoupling to a particular markup or scripting language. <br>
XR Fragments supports filtering objects in a scene only, because in the history of the javascript-powered web, showing/hiding document-entities seems to be one of the most popular basic usecases.<br>
Doing advanced scripting & networkrequests under the hood are obviously interesting endavours, but this is something which should not be hardcoupled with XR Fragments or hypermedia.<br>This perhaps belongs more to browser extensions.<br>
Non-HTML Hypermedia browsers should make browser extensions the right place, to 'extend' experiences, in contrast to code/javascript inside hypermedia documents (this turned out as a hypermedia antipattern).
|URI | some resource at something somewhere via someprotocol (`http://me.com/foo.glb#foo` or `e76f8efec8efce98e6f` [see interpeer.io](https://interpeer.io))|
|URL | something somewhere via someprotocol (`http://me.com/foo.glb`) |
|visual-meta | [visual-meta](https://visual.meta.info) data appended to text/books/papers which is indirectly visible/editable in XR. |
|requestless metadata | metadata which never spawns new requests (unlike RDF/HTML, which can cause framerate-dropping, hence not used a lot in games) |
|FPS | frames per second in spatial experiences (games,VR,AR e.g.), should be as high as possible |
|introspective | inward sensemaking ("I feel this belongs to that") |
|extrospective | outward sensemaking ("I'm fairly sure John is a person who lives in oklahoma") |
|`◻` | ascii representation of an 3D object/mesh |
|(un)obtrusive | obtrusive: wrapping human text/thought in XML/HTML/JSON obfuscates human text into a salad of machine-symbols and words |
|BibTeX | simple tagging/citing/referencing standard for plaintext |
|BibTag | a BibTeX tag |
|(hashtag)bibs | an easy to speak/type/scan tagging SDL ([see here](https://github.com/coderofsalvation/hashtagbibs) which expands to BibTex/JSON/XML |
