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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 interactive text across for (XR) Browsers. XR Fragments allows us to enrich existing dataformats, by recursive use of existing technologies like URI Fragments & visual-meta.

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. However, thru the lens of authoring their lowest common denominator is still: plain text. XR Fragments allows us to enrich existing dataformats, by recursive use of existing technologies:

addressibility & navigation of 3D objects: URI Fragments + (src/href) metadata
bi-directional links between text and spatial objects: visual-meta

Conventions and Definitions

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 defined in 3D Scene or Object(nodes)
XR fragment: URI Fragment with spatial hints (#pos=0,0,0&t=1,100 e.g.)
src: a (HTML-piggybacked) metadata-attribute of a 3D object which instances content
href: a (HTML-piggybacked) metadata-attribute of a 3D object which links to content
query: an URI Fragment-operator which queries object(s) from a scene (#q=cube)
visual-meta: metadata appended to text which is only indirectly visible/editable in XR.

{::boilerplate bcp14-tagged}

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

List of metadata for 3D nodes

key	type	example	info
name	string	name: "cube"	already available in all 3D fileformats & scenes
class	string	class: "cubes"	supported through custom property in 3D fileformats
href	string	href: "b.gltf"	supported through custom property in 3D fileformats
src	string	src: "#q=cube"	supported through custom property in 3D fileformats

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                            |
  |                                                        |
  +--------------------------------------------------------+

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 (other.fbx).

Embedding 3D content

Here's an ascii representation of a 3D scene-graph with 3D objects (◻) which embeds remote & local 3D objects (◻) (without) 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.

Embedding text

Text in XR has to be unobtrusive, for readers as well as authors. We think and speak in simple text, and given the new paradigm of XR interfaces, logically (spoken) text must be enriched afterwards (lazy metadata). Therefore, yet-another-markuplanguage is not going to get us very far. What will get us far, is when XR interfaces always guarantee direct feedbackloops between plainttext and humans. Humans need to be always served first, and machines later.

In the next chapter you can see how XR Fragments enjoys hasslefree rich text, by adding visual-meta(data) support to plain text.

Default Data URI mimetype

The XR Fragment specification bumps the traditional default browser-mimetype

text/plain;charset=US-ASCII

to:

text/plain;charset=utf-8;visual-meta=1

This means that visual-meta(data) can be appended to plain text without being displayed.

URL and Data URI

  +--------------------------------------------------------------+  +------------------------+
  |                                                              |  | author.com/article.txt |
  |  index.gltf                                                  |  +------------------------+
  |    │                                                         |  |                        |
  |    ├── ◻ article_canvas                                      |  | Hello friends.         |
  |    │    └ src: ://author.com/article.txt                     |  |                        |
  |    │                                                         |  | @{visual-meta-start}   |
  |    └── ◻ note_canvas                                         |  | ...                    |
  |           └ src:`data:welcome human @{visual-meta-start}...` |  +------------------------+ 
  |                                                              | 
  |                                                              |
  +--------------------------------------------------------------+

The enduser will only see welcome human rendered spatially. The beauty is that text (AND visual-meta) in Data URI is saved into the scene, which also promotes rich copy-paste. In both cases will the text get 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.).

NOTE: this is not to say that XR Browsers should not load HTML/PDF/etc-URLs thru src, it is just that text/plain;charset=utf-8;visual-meta=1 is the default.

The mapping between 3D objects and text (src-data) is simple:

Example:

  +------------------------------------------------------------------------------------+ 
  |                                                                                    | 
  |  index.gltf                                                                        | 
  |    │                                                                               | 
  |    ├── ◻ AI                                                                        | 
  |    │    └ class: tech                                                              | 
  |    │                                                                               | 
  |    └ src:`data:@{visual-meta-start}                                                | 
  |                @{glossary-start}                                                   |
  |                @entry{                                                             |
  |                    name="AI",                                                      |
  |                    alt-name1 = "Artificial Intelligence",                          |
  |                    description="Artificial intelligence",                          |
  |                    url = "https://en.wikipedia.org/wiki/Artificial_intelligence",  |
  |                }                                                                   |
  |                @entry{                                                             |
  |                    name="tech"                                                     |
  |                    alt-name1="technology"                                          |
  |                    description="when monkeys start to play with things"            |
  |                }`                                                                  |
  +------------------------------------------------------------------------------------+

Attaching visualmeta as src metadata to the (root) scene-node hints the XR Fragment browser. 3D object names and classes map to name of visual-meta glossary-entries. This allows rich interaction and interlinking between text and 3D objects:

When the user surfs to https://.../index.gltf#AI the XR Fragments-parser points the enduser to the AI object, and can show contextual info about it.
When (partial) remote content is embedded thru XR Fragment queries (see XR Fragment queries), its related visual-meta can be embedded along.

HYPER copy/paste

The previous example, offers something exciting compared to simple copy/paste of 3D objects or text. XR Fragment 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 visual-meta if any)
interlinked: Collected objects by visual-meta tag

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 only executed when embedded in the asset/scene (thru src). This is to prevent sharing of scene-tampered URL's.
search words are matched against 3D object names or metadata-key(values)
# equals #q=*
words starting with . (.language) indicate class-properties

(For example: #q=.foo is a shorthand for #q=class:foo, which will select objects with custom property class:foo. Just a simple #q=cube will simply select an object named cube.

see an example video here

including/excluding

|''operator'' | ''info'' | |* | select all objects (only allowed in src custom property) in the current scene (after the default predefined_view # was executed)| |- | 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=-/cube hides object cube only in the root-scene (not nested cube objects)
#q=-cube hides both object cube in the root-scene AND nested skybox objects |

» 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:1 and foo (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 .foo into class: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 id to true or false (false=excluder -)
and we set root to true or false (true=/ root selector is present)
we convert key '/foo' into 'foo'
finally we add the key/value to the store (store.foo = {id:false,root:true} e.g.)

An example query-parser (which compiles to many languages) can be found here

List of XR URI Fragments

Security Considerations

TODO Security

IANA Considerations

This document has no IANA actions.

Acknowledgments

TODO acknowledge.

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