[x3d-public] [x3dom-users] simple X3D -> JSON -> X3DOM, D3.js
Don Brutzman
brutzman at nps.edu
Fri Feb 20 14:33:48 PST 2015
As before, your insights are much appreciated. Thanks John.
It is looking like there may be some terminology mismatches? That might be an important cause of misunderstanding. Hoping to get clearer.
When talking about "name" values, please clarify. Are your referring to element and attribute names, or DEF/USE ID/IDREF names?
In general, we have been trying to create a JSON representation for X3D that is round-trippable with any other encoding.
Not a goal is to create something incorrect or unusable. This isn't a marketing activity. So no need for a BogusJSON or whatever, there is simply no need for something broken.
The X3dToJson.xslt is trying to take an XML-based .x3d scene and produce a usable JSON representation. If information is lost, and the result can't be written back out as the original scene, then an encoding fails the round-trip test.
Multiple approaches exist for converting XML to JSON. Some were explored and compared on the earlier email threads. First one that pops up on today's search is
http://www.utilities-online.info/xmltojson/
When given the HelloWorld.x3d scene, it replies with
{
"X3D": {
"-profile": "Immersive",
"-version": "3.3",
"-xmlns:xsd": "http://www.w3.org/2001/XMLSchema-instance",
"-xsd:noNamespaceSchemaLocation": " http://www.web3d.org/specifications/x3d-3.3.xsd ",
"head": {
"meta": [
{
"-name": "title",
"-content": "HelloWorld.x3d"
},
{
"-name": "description",
"-content": "Simple X3D scene example: Hello World!"
},
{
"-name": "created",
"-content": "30 October 2000"
},
{
"-name": "modified",
"-content": "23 November 2014"
},
{
"-name": "creator",
"-content": "Don Brutzman"
},
{
"-name": "Image",
"-content": "HelloWorld.tall.png"
},
{
"-name": "reference",
"-content": " http://en.wikipedia.org/wiki/Hello_world "
},
{
"-name": "reference",
"-content": " en.wikipedia.org/wiki/Hello#\"Hello,_World\"_computer_program "
},
{
"-name": "reference",
"-content": " http://en.wikibooks.org/w/index.php?title=Computer_Programming/Hello_world "
},
{
"-name": "reference",
"-content": " http://www.HelloWorldExample.net "
},
{
"-name": "reference",
"-content": " http://www.web3D.org "
},
{
"-name": "reference",
"-content": " http://www.web3d.org/realtime-3d/news/internationalization-x3d "
},
{
"-name": "reference",
"-content": " http://www.web3d.org/x3d/content/examples/HelloWorld.x3d "
},
{
"-name": "reference",
"-content": " http://X3dGraphics.com/examples/X3dForAdvancedModeling/HelloWorldScenes "
},
{
"-name": "identifier",
"-content": " http://X3dGraphics.com/examples/X3dForWebAuthors/Chapter01-TechnicalOverview/HelloWorld.x3d "
},
{
"-name": "license",
"-content": " http://www.web3d.org/x3d/content/examples/license.html "
},
{
"-name": "generator",
"-content": "X3D-Edit 3.3, https://savage.nps.edu/X3D-Edit"
},
{
"-name": "reference",
"-content": "HelloWorld.wrl"
},
{
"-name": "reference",
"-content": "HelloWorld.x3dv"
},
{
"-name": "reference",
"-content": "HelloWorld.x3db"
},
{
"-name": "reference",
"-content": "HelloWorld.xhtml"
},
{
"-name": "reference",
"-content": "HelloWorld.json"
}
]
},
"Scene": {
"Group": {
"Viewpoint": {
"-DEF": "ViewUpClose",
"-centerOfRotation": "0 -1 0",
"-description": "Hello world!",
"-position": "0 -1 7"
},
"Transform": [
{
"-rotation": "0 1 0 3",
"Shape": {
"Appearance": {
"Material": {
"-DEF": "MaterialLightBlue",
"-diffuseColor": "0.1 0.5 1"
},
"ImageTexture": {
"-DEF": "ImageCloudlessEarth",
"-url": " \"earth-topo.png\" \"earth-topo.jpg\" \"earth-topo-small.gif\" \"http://www.web3d.org/x3d/content/examples/Basic/earth-topo.png\" \"http://www.web3d.org/x3d/content/examples/Basic/earth-topo.jpg\" \"http://www.web3d.org/x3d/content/examples/Basic/earth-topo-small.gif\" "
}
}
}
},
{
"-translation": "0 -2 0",
"Shape": {
"Text": {
"-DEF": "TextMessage",
"-string": "\"Hello\" \"world!\"",
"FontStyle": { "-justify": "\"MIDDLE\" \"MIDDLE\"" }
},
"Appearance": {
"Material": { "-USE": "MaterialLightBlue" }
}
}
}
]
}
}
}
}
This varies from the current HelloWorld.json by including X3D/head/meta* tags, using a different attribute prefix (- vice @), and dropping comments and inclusion/exclusion of default attribute values.
http://www.web3d.org/x3d/content/examples/HelloWorld.json
So is the XML -> JSON conversion from http://www.utilities-online.info/xmltojson producing illegal JSON too?
Looking forward to continued scrutiny and improved understanding.
On 2/20/2015 11:15 AM, John Carlson wrote:
>
>>> On Feb 19, 2015 12:21 AM, "John Carlson" <yottzumm at gmail.com <mailto:yottzumm at gmail.com> <mailto:yottzumm at gmail.com <mailto:yottzumm at gmail.com>>> wrote:
>>>
>>> How does the X3D JSON encoding handle two Shapes or Transforms or Groups of the same type at the same depth in the tree with the same parent? Do you modify the tree structure significantly? I'm not that familiar with the schema. I just know you're going to have to do something else in JavaScript, even if your JSON parses and works. You can't use the JSON directly as Javascript. JSON != JavaScript. We desire a *JavaScript* and JSON encoding.
>>
>>
>> This is a crucial point and I'm really glad you are raising it.
>
> You're right it's a crucial point. It's so crucial I brought it up with Douglas Crockford. He said the standard did not need to be changed. What's important is how the standard is *used*. Say I'm in Java, and I'm reading in a A JSON object. What happens if I see a name in and object twice? What do I do? Do I instantly change my attribute to a list? How? Must I use a list for every single attribute because that's what is allowed by JSON? No, is the answer. JSON doesn't specify a set of name/list pairs, it specifies name/value pairs. JSON objects are meant to be associative arrays or struct or record as is mentioned in the standard. I asked Douglas to change the standard so names appeared only once in an object. He demurred. The thing is, it's the *use* that matters, and you're going to pull a lot of programmer's hair out and stick their fingers in electrical sockets if you continue to use names more than once in a JSON object. It violates the spirit of the
> standard if not the letter.
>
>> If we think about use cases for Javascript applications loading X3D models, I think they are most interested in reusing geometry for their own nefarious/magnificent purposes. Javascript programmers are likely less interested in X3D event models, Scripts, protos and whatnot. Library loaders might convert such things to match their paradigm, or might also ignore non-geometry nodes completely.
>
> I guess what matters ultimately is that JSON parsers must reject names appearing in objects more that once. Also, please do not call your encoding JSON because it
> just *isn't*. If we must, programmers will move away from your JSON encoding, and use their own, as I have already done. All I'm actually doing is to asking you to make an X3D JSON standard which makes good sense, and if not, don't call it JSON. FJSON or Fake JSON might be more appropriate.
>>
>> Rephrase, Let JSON be JSON (a subset that is good for data objects) and Javascript be Javascript (a full-blown programming language).
>>
>> Not trying to downplay or avoid anything, just looking at what the most common uses of an X3D scene encoded as JSON might be.
>>
>> Such an idea actually brings us full circle to the design premise of all the scene encodings (XML .x3d, Classic VRML .x3dv, binary .x3db) which is to completely/compatibly represent an X3D scene, period.
>>
>> If we achieve that with JSON, making common geometry constructs easy for programmers to access, then great they will do so. If we also try to tell them "For Advanced Graphics Using X3D JSON You Must Program Your Javascript Application This Way" they will laugh.
>>
>> Viva la difference, programming styles and practices will always vary and evolve. Whatever works.
>
> Yes, whatever works. Names or field slots appearing in an object more than once in a struct or record don't work in programmers' minds. You will force every value to be a list in their minds. Which may be what you intend. If so, then explicitly do that in your JSON output (my restructuring in my previous message). Don't force the programmer into cognitive overload. Please only have names appearing once in your objects, I beg you desperately, if you want your X3D JSON standard to be relevant. If not, then call it X3DON not *JS*ON
>
all the best, Don
--
Don Brutzman Naval Postgraduate School, Code USW/Br brutzman at nps.edu
Watkins 270, MOVES Institute, Monterey CA 93943-5000 USA +1.831.656.2149
X3D graphics, virtual worlds, navy robotics http://faculty.nps.edu/brutzman
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