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%%% Title = "XR Fragments" area = "Internet" workgroup = "Internet Engineering Task Force"
[seriesInfo] name = "XR-Fragments" value = "draft-XRFRAGMENTS-leonvankammen-00" stream = "IETF" status = "informational"
date = 2023-04-12T00:00:00Z
author initials="L.R." surname="van Kammen" fullname="L.R. van Kammen"
%%%
.# Abstract
This draft offers a specification for 4D URLs & navigation, to link 3D scenes and text together with- or without a network-connection.
The specification promotes spatial addressibility, sharing, navigation, query-ing and tagging interactive (text)objects across for (XR) Browsers.
XR Fragments allows us to enrich existing dataformats, by recursive use of existing proven technologies like URI Fragments and BibTags notation.
Almost every idea in this document is demonstrated at https://xrfragment.org
{mainmatter}
Introduction
How can we add more features to existing text & 3D scenes, without introducing new dataformats?
Historically, there's many attempts to create the ultimate markuplanguage or 3D fileformat.
Their lowest common denominator is: (co)authoring using plain text.
XR Fragments allows us to enrich/connect existing dataformats, by recursive use of existing technologies:
- addressibility and navigation of 3D scenes/objects: URI Fragments + src/href spatial metadata
- hasslefree tagging across text and spatial objects using bibs / BibTags appendices (see visual-meta e.g.)
NOTE: The chapters in this document are ordered from highlevel to lowlevel (technical) as much as possible
Core principle
XR Fragments strives to serve (nontechnical/fuzzy) humans first, and machine(implementations) later, by ensuring hasslefree text-vs-thought feedback loops.
This also means that the repair-ability of machine-matters should be human friendly too (not too complex).
"When a car breaks down, the ones without turbosupercharger are easier to fix"
Let's always focus on average humans: our fuzzy symbolical mind must be served first, before serving a greater categorized typesafe RDF hive mind).
Humans first, machines (AI) later.
Thererfore, XR Fragments does not look at XR (or the web) thru the lens of HTML.
XR Fragments itself is HTML-agnostic, though pseudo-XR Fragment browsers can be implemented on top of HTML/Javascript.
Conventions and Definitions
See appendix below in case certain terms are not clear.
List of URI Fragments
| fragment | type | example | info |
|---|---|---|---|
#pos |
vector3 | #pos=0.5,0,0 |
positions camera to xyz-coord 0.5,0,0 |
#rot |
vector3 | #rot=0,90,0 |
rotates camera to xyz-coord 0.5,0,0 |
#t |
vector2 | #t=500,1000 |
sets animation-loop range between frame 500 and 1000 |
#...... |
string | #.cubes #cube |
object(s) of interest (fragment to object name or class mapping) |
xyz coordinates are similar to ones found in SVG Media Fragments
List of metadata for 3D nodes
| key | type | example (JSON) | info |
|---|---|---|---|
name |
string | "name": "cube" |
available in all 3D fileformats & scenes |
class |
string | "class": "cubes" |
available through custom property in 3D fileformats |
href |
string | "href": "b.gltf" |
available through custom property in 3D fileformats |
src |
string | "src": "#q=cube" |
available through custom property in 3D fileformats |
Popular compatible 3D fileformats: .gltf, .obj, .fbx, .usdz, .json (THREE.js), .dae and so on.
NOTE: XR Fragments are file-agnostic, which means that the metadata exist in programmatic 3D scene(nodes) too.
Navigating 3D
Here's an ascii representation of a 3D scene-graph which contains 3D objects ◻ and their metadata:
+--------------------------------------------------------+
| |
| index.gltf |
| │ |
| ├── ◻ buttonA |
| │ └ href: #pos=1,0,1&t=100,200 |
| │ |
| └── ◻ buttonB |
| └ href: other.fbx | <-- file-agnostic (can be .gltf .obj etc)
| |
+--------------------------------------------------------+
An XR Fragment-compatible browser viewing this scene, allows the end-user to interact with the buttonA and buttonB.
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.
Embedding 3D content
Here's an ascii representation of a 3D scene-graph with 3D objects ◻ which embeds remote & local 3D objects ◻ with/out using queries:
+--------------------------------------------------------+ +-------------------------+
| | | |
| index.gltf | | ocean.com/aquarium.fbx |
| │ | | │ |
| ├── ◻ canvas | | └── ◻ fishbowl |
| │ └ src: painting.png | | ├─ ◻ bass |
| │ | | └─ ◻ tuna |
| ├── ◻ aquariumcube | | |
| │ └ src: ://rescue.com/fish.gltf#q=bass%20tuna | +-------------------------+
| │ |
| ├── ◻ bedroom |
| │ └ src: #q=canvas |
| │ |
| └── ◻ livingroom |
| └ src: #q=canvas |
| |
+--------------------------------------------------------+
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).
Also, after lazy-loading ocean.com/aquarium.gltf, only the queried objects bass and tuna will be instanced inside aquariumcube.
Resizing will be happen accordingly to its placeholder object aquariumcube, see chapter Scaling.
XR Fragment queries
Include, exclude, hide/shows objects using space-separated strings:
#q=cube#q=cube -ball_inside_cube#q=* -sky#q=-.language .english#q=cube&rot=0,90,0#q=price:>2 price:<5
It's simple but powerful syntax which allows css-like class/id-selectors with a searchengine prompt-style feeling:
- queries are showing/hiding objects only when defined as
srcvalue (prevents sharing of scene-tampered URL's). - queries are highlighting objects when defined in the top-Level (browser) URL (bar).
- search words like
cubeandfooin#q=cube fooare matched against 3D object names or custom metadata-key(values) - search words like
cubeandfooin#q=cube fooare matched against tags (BibTeX) inside plaintextsrcvalues like@cube{redcube, ...e.g. #equals#q=*- words starting with
.like.germanmatch class-metadata of 3D objects like"class":"german" - words starting with
.like.germanmatch class-metadata of (BibTeX) tags in XR Text objects like@german{KarlHeinz, ...e.g.
For example:
#q=.foois a shorthand for#q=class:foo, which will select objects with custom propertyclass:foo. Just a simple#q=cubewill simply select an object namedcube.
including/excluding
| operator | info |
|---|---|
* |
select all objects (only useful in src custom property) |
- |
removes/hides object(s) |
: |
indicates an object-embedded custom property key/value |
. |
alias for "class" :".foo" equals class:foo |
> < |
compare float or int number |
/ |
reference to root-scene. Useful in case of (preventing) showing/hiding objects in nested scenes (instanced by src) (*) |
* =
#q=-/cubehides objectcubeonly in the root-scene (not nestedcubeobjects)
#q=-cubehides both objectcubein the root-scene AND nestedskyboxobjects |
» example implementation » example 3D asset » discussion
Query Parser
Here's how to write a query parser:
- create an associative array/object to store query-arguments as objects
- detect object id's & properties
foo:1andfoo(reference regex:/^.*:[><=!]?/) - detect excluders like
-foo,-foo:1,-.foo,-/foo(reference regex:/^-/) - detect root selectors like
/foo(reference regex:/^[-]?\//) - detect class selectors like
.foo(reference regex:/^[-]?class$/) - detect number values like
foo:1(reference regex:/^[0-9\.]+$/) - expand aliases like
.foointoclass:foo - for every query token split string on
: - create an empty array
rules - then strip key-operator: convert "-foo" into "foo"
- add operator and value to rule-array
- therefore we we set
idtotrueorfalse(false=excluder-) - and we set
roottotrueorfalse(true=/root selector is present) - we convert key '/foo' into 'foo'
- finally we add the key/value to the store like
store.foo = {id:false,root:true}e.g.
An example query-parser (which compiles to many languages) can be found here
XR Fragment URI Grammar
reserved = gen-delims / sub-delims
gen-delims = "#" / "&"
sub-delims = "," / "="
Example:
://foo.com/my3d.gltf#pos=1,0,0&prio=-5&t=0,100
| Demo | Explanation |
|---|---|
pos=1,2,3 |
vector/coordinate argument e.g. |
pos=1,2,3&rot=0,90,0&q=.foo |
combinators |
Text in XR (tagging,linking to spatial objects)
We still think and speak in simple text, not in HTML or RDF.
The most advanced human will probably not shout <h1>FIRE!</h1> in case of emergency.
Given the new dawn of (non-keyboard) XR interfaces, keeping text as is (not obscuring with markup) is preferred.
Ideally metadata must come with text, but not obfuscate the text, or spawning another request to fetch it.
Spectrum of speak/scan/write/listen/keyboard-friendly 'tagging' notations:
(just # and @) (string only) (obuscated text) (type-aware text)
<---- Bibs ---------- BibTeX ---------- XML / HTML --------- JSON / YAML / RDF -------->
Hence:
- XR Fragments promotes the importance of hasslefree plain text and string-based patternmatching
- XR Fragments allows hasslefree spatial tagging, by detecting metadata at the end of content of text (see default mimetype & Data URI)
- XR Fragments allows hasslefree spatial tagging, by treating 3D object name/class-pairs as BibTeX tags.
- XR Fragments allows hasslefree textual tagging, spatial tagging, and supra tagging, by mapping 3D/text object (class)names using BibTeX 'tags'
- Appending plain text with requestless metadata (microformats) is the first class citizen for XR text (HTML/RDF/JSON is great, but fits better in the application-layer)
- string-only, typeless (polyglot) microformats are first-class citizen metadata, since they are easy to edit/add by humans
- BibTex and hashtagbibs are first-class citizens for adding/describing relationships spatially.
- Opening tags for metadata (
#,@,{, or<) should always start at the beginning of the line. This allows recursive connections between text itself, as well as 3D objects and vice versa.
Here's an example by expanding polyglot metadata to BibTeX associations:
http://y.io/z.fbx | Derived BibTex / 'wires' & tags
----------------------------------------------------------------------------+--------------------------------------
| @house{castle,
+-[src: data:.....]----------------------+ +-[3D mesh]-+ | url = {https://y.io/z.fbx#castle}
| Chapter one | | / \ | | }
| | | / \ | | @baroque{castle,
| John built houses in baroque style. | | / \ | | url = {https://y.io/z.fbx#castle}
| | | |_____| | | }
| #john@baroque | +-----│-----+ | @baroque{john}
| | │ |
| | ├─ name: castle |
| | └─ class: house baroque |
+----------------------------------------+ |
[3D mesh ] |
+-[remotestorage.io / localstorage]------+ | O + name: john |
| #contactjohn@todo@house | | /|\ | |
| ... | | / \ | |
+----------------------------------------+ +--------+ |
A (rare) example of polyglot tags:
http://y.io/z.fbx | Derived BibTex / 'wires' & tags
----------------------------------------------------------------------------+--------------------------------------
| @house{castle,
+-[src: data:.....]----------------------+ +-[3D mesh]-+ | url = {https://y.io/z.fbx#castle}
| Chapter one | | / \ | | }
| | | / \ | | @baroque{castle,
| John built houses in baroque style. | | / \ | | url = {https://y.io/z.fbx#castle}
| | | |_____| | | }
| #john@baroque | +-----│-----+ | @baroque{john}
| @house{baroque, info = {classic}, } | │ | @house{baroque,
| { "tag":"john", "match":"john"} | ├─ name: castle | info = {classic}
| <tag name="john" match="john"/> | └─ class: house baroque | }
+----------------------------------------+ | @house{contactjohn}
[3D mesh ] |
+-[remotestorage.io / localstorage]------+ | O + name: john | @todo{contactjohn}
| #contactjohn@todo@house | | /|\ | |
| ... | | / \ | | john{john}
+----------------------------------------+ +--------+ |
As seen above, we can extract tags/associations between text & 3D objects, by converting all scene metadata to (in this case) BibTeX, by expanding hashtagbibs and interpreting its polyglot tag-notation.
One huge advantage of polyglot tags is authoring and copy-paste by humans, which will be discussed later in this spec.
hashtagbibs also allows 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@todoe.g.
The Evaluated BiBTeX allows XR Browsers to show/hide relationships in realtime at various levels:
| scope | tag-matching algo |
|---|---|
| textual | text containing 'baroque' is now automatically tagged with 'house' (incl. plaintext src child nodes) |
| spatial | spatial object(s) with name baroque or "class":"house" are now automatically tagged with 'house' (incl. child nodes) |
| supra | text- or spatial-object(s) (non-descendant nodes) elsewhere, (class)named 'baroque' or 'house', are automatically tagged with 'house' (current node to root nodes) |
| omni | text- or spatial-object(s) (non-descendant nodes) elsewhere, (class)named 'baroque' or 'house', are automatically tagged with 'house' (root node to all nodes) |
| infinite | text- or spatial-object(s) (non-descendant nodes) elsewhere, (class)named 'baroque' or 'house', are automatically tagged with 'house' (root node to all nodes ) |
This allows the enduser to adjust different levels of associations (see the core principle): spatial wires can be rendered, words/objects can be highlighted/scaled etc.
NOTE: infinite matches both 'baroque' and 'house'-occurences in text, as well as spatial objects with
"class":"house"or name "baroque". This multiplexing of id/category is deliberate, in order to support the core principle.
- When moving/copying/pasting metadata, always prefer converting to string-only microformats (BibTex/Bibs)
- respect multi-line metadata because of the core principle
- Default font (unless specified otherwise) is a modern monospace font, for maximized tabular expressiveness (see the core principle).
- anti-pattern: hardcoupling a mandatory obtrusive markup/scripting-language or with an XR browser (HTML/VRML/Javascript) (see the core principle)
- anti-pattern: limiting human introspection, by abandoning plain text as first class citizen.
- 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)
- 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.
The simplicity of appending metadata (and leveling the metadata-playfield between humans and machines) is also demonstrated by visual-meta in greater detail.
Default Data URI mimetype
The src-values work as expected (respecting mime-types), however:
The XR Fragment specification bumps the traditional default browser-mimetype
text/plain;charset=US-ASCII
to a hashtagbib(tex)-friendly one:
text/plain;charset=utf-8;meta=<#@{
This indicates that:
- utf-8 is supported by default
- lines beginning with
<,#,@or{(regex:^(<|#|@|{)) will not be rendered verbatim by default (=Bibs/BibTex/JSON/XML)
By doing so, the XR Browser (applications-layer) can interpret microformats (visual-meta to connect text further with its environment ( setup links between textual/spatial objects automatically e.g.).
for more info on this mimetype see bibs
Advantages:
- auto-expanding of hashtagbibs associations
- out-of-the-box (de)multiplex human text and metadata in one go (see the core principle)
- no network-overhead for metadata (see the core principle)
- ensuring high FPS: HTML/RDF historically is too 'requesty'/'parsy' for game studios
- rich send/receive/copy-paste everywhere by default, metadata being retained (see the core principle)
- netto result: less webservices, therefore less servers, and overall better FPS in XR
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.).
For all other purposes, regular mimetypes can be used (but are not required by the spec).
URL and Data URI
+--------------------------------------------------------------+ +------------------------+
| | | author.com/article.txt |
| index.gltf | +------------------------+
| │ | | |
| ├── ◻ article_canvas | | Hello friends. |
| │ └ src: ://author.com/article.txt | | |
| │ | | { |
| └── ◻ note_canvas | | ... |
| └ src:`data:welcome human\n{...` | | } |
| | +------------------------+
| |
+--------------------------------------------------------------+
The enduser will only see welcome human and Hello friends rendered spatially (see mimetype).
The beauty is that text in Data URI automatically promotes rich copy-paste (retaining metadata).
In both cases, the text gets rendered immediately (onto a plane geometry, hence the name '_canvas').
The XR Fragment-compatible browser can let the enduser access visual-meta(data)-fields after interacting with the object (contextmenu e.g.).
additional tagging using bibs: to tag spatial object
note_canvaswith 'todo', the enduser can type or speak@note_canvas@todo
XR Text example parser
Here's an example XR Text (de)multiplexer in javascript, which supports inline bibs & bibtex:
xrtext = {
expandBibs: (text) => {
let bibs = { regex: /(#[a-zA-Z0-9_+@\-]+(#)?)/g, tags: {}}
text.replace( bibs.regex , (m,k,v) => {
tok = m.substr(1).split("@")
match = tok.shift()
if( tok.length ) tok.map( (t) => bibs.tags[t] = `@${t}{${match},\n}` )
else if( match.substr(-1) == '#' )
bibs.tags[match] = `@{${match.replace(/#/,'')}}`
else bibs.tags[match] = `@${match}{${match},\n}`
})
return text.replace( bibs.regex, '') + Object.values(bibs.tags).join('\n')
},
decode: (str) => {
// bibtex: ↓@ ↓<tag|tag{phrase,|{ruler}> ↓property ↓end
let pat = [ /@/, /^\S+[,{}]/, /},/, /}/ ]
let tags = [], text='', i=0, prop=''
let lines = xrtext.expandBibs(str).replace(/\r?\n/g,'\n').split(/\n/)
for( let i = 0; i < lines.length && !String(lines[i]).match( /^@/ ); i++ )
text += lines[i]+'\n'
bibtex = lines.join('\n').substr( text.length )
bibtex.split( pat[0] ).map( (t) => {
try{
let v = {}
if( !(t = t.trim()) ) return
if( tag = t.match( pat[1] ) ) tag = tag[0]
if( tag.match( /^{.*}$/ ) ) return tags.push({ruler:tag})
if( tag.match( /}$/ ) ) return tags.push({k: tag.replace(/}$/,''), v: {}})
t = t.substr( tag.length )
t.split( pat[2] )
.map( kv => {
if( !(kv = kv.trim()) || kv == "}" ) return
v[ kv.match(/\s?(\S+)\s?=/)[1] ] = kv.substr( kv.indexOf("{")+1 )
})
tags.push( { k:tag, v } )
}catch(e){ console.error(e) }
})
return {text, tags}
},
encode: (text,tags) => {
let str = text+"\n"
for( let i in tags ){
let item = tags[i]
if( item.ruler ){
str += `@${item.ruler}\n`
continue;
}
str += `@${item.k}\n`
for( let j in item.v ) str += ` ${j} = {${item.v[j]}}\n`
str += `}\n`
}
return str
}
}
The above functions (de)multiplexe text/metadata, expands bibs, (de)serialize bibtex (and all fits more or less on one A4 paper)
above can be used as a startingpoint for LLVM's to translate/steelman to a more formal form/language.
str = `
hello world
here are some hashtagbibs followed by bibtex:
#world
#hello@greeting
#another-section#
@{some-section}
@flap{
asdf = {23423}
}`
var {tags,text} = xrtext.decode(str) // demultiplex text & bibtex
tags.find( (t) => t.k == 'flap{' ).v.asdf = 1 // edit tag
tags.push({ k:'bar{', v:{abc:123} }) // add tag
console.log( xrtext.encode(text,tags) ) // multiplex text & bibtex back together
This expands to the following (hidden by default) BibTex appendix:
hello world
here are some hashtagbibs followed by bibtex:
@{some-section}
@flap{
asdf = {1}
}
@world{world,
}
@greeting{hello,
}
@{another-section}
@bar{
abc = {123}
}
when an XR browser updates the human text, a quick scan for nonmatching tags (
@book{nonmatchingbooke.g.) should be performed and prompt the enduser for deleting them.
HYPER copy/paste
The previous example, offers something exciting compared to simple copy/paste of 3D objects or text. XR Text according to the XR Fragment spec, allows HYPER-copy/paste: time, space and text interlinked. Therefore, the enduser in an XR Fragment-compatible browser can copy/paste/share data in these ways:
- time/space: 3D object (current animation-loop)
- text: TeXt object (including BibTeX/visual-meta if any)
- interlinked: Collected objects by visual-meta tag
Security Considerations
Since XR Text contains metadata too, the user should be able to set up tagging-rules, so the copy-paste feature can :
- filter out sensitive data when copy/pasting (XR text with
class:secrete.g.)
IANA Considerations
This document has no IANA actions.
Acknowledgments
Appendix: Definitions
| definition | explanation |
|---|---|
| human | a sentient being who thinks fuzzy, absorbs, and shares thought (by plain text, not markuplanguage) |
| scene | a (local/remote) 3D scene or 3D file (index.gltf e.g.) |
| 3D object | an object inside a scene characterized by vertex-, face- and customproperty data. |
| metadata | custom properties of text, 3D Scene or Object(nodes), relevant to machines and a human minority (academics/developers) |
| XR fragment | URI Fragment with spatial hints like #pos=0,0,0&t=1,100 e.g. |
| src | (HTML-piggybacked) metadata of a 3D object which instances content |
| href | (HTML-piggybacked) metadata of a 3D object which links to content |
| query | an URI Fragment-operator which queries object(s) from a scene like #q=cube |
| visual-meta | visual-meta 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 |