Consortium A JSON encoding for X3D Roy Walmsley roy.walmsley@ntlworld.com Don Brutzman brutzman@nps.edu John Carlson john@carlsonsolutiondesign.com Web3D 2016, Anaheim, California 23 rd July 2016 1
Consortium Contents • ISO/IEC standards • Requirements • JSON structure • Methodology • Encoding of nodes • Encoding of fields • Validation • Implementations Web3D 2016, Anaheim, California 23 rd July 2016 2
Consortium ISO/IEC standards Series Series Title Title Part Part Content Content 1 1 Architecture Architecture 19775 19775 X3D X3D 2 2 Scene access interface (SAI) Scene access interface (SAI) 1 1 XML (.x3d) XML (.x3d) 19776 File encodings 2 2 Classic VRML (.x3dv) Classic VRML (.x3dv) 19776 File encodings 3 3 Compressed Binary (.x3db) Compressed Binary (.x3db) 5 1 JSON (.x3dj or .json) ECMAScript 19777 Language bindings 2 1 Java ECMAScript 19777 Language bindings 2 Java Web3D 2016, Anaheim, California 23 rd July 2016 3
Consortium Requirements • Must fully specify everything defined in the X3D abstract specification. – Nodes and fields – Statements and other constructs – Comments – Scripts and Shader code • "Round trippable" with no loss of X3D content for any of the file encodings. Web3D 2016, Anaheim, California 23 rd July 2016 4
Consortium JSON structure • Two primary data structures – Objects: An unordered collection of name/value pairs – Arrays: An ordered collection of values • JSON value – Object, array, number, string, true, false, null • Structural tokens – { } [ ] : , – Strings delimited by " • JSON doesn't have specific comments structures Web3D 2016, Anaheim, California 23 rd July 2016 5
Consortium Methodology • Examples archive – stylesheet conversion • JSON validation • Specific issues: – Handling of ROUTEs and Comments – Character escaping – No hexadecimal number representation • X3D JSON Validation • Implementation Web3D 2016, Anaheim, California 23 rd July 2016 6
Consortium Encoding of nodes • Nodes encoded: – In XML as elements, e.g. <Group/> – In JSON as objects, e.g. "Group":{} • Node type is name in name/value pair • Empty object means all attributes have default values Web3D 2016, Anaheim, California 23 rd July 2016 7
Consortium Encoding of fields • Usefully categorized as follows: – 'value field', holds numbers, strings, or boolean true/false – 'node field', holds references to other nodes • Field names are strings, so to distinguish them from other strings a name is prepended with: – '@' for value fields – '-' for node fields Web3D 2016, Anaheim, California 23 rd July 2016 8
Consortium Encoding of value fields • In XML fields are attributes of elements (nodes), e.g.: <Group bboxSize='-1 -1 -1'/> • In JSON fields are properties of objects (nodes), e.g.: "Group": { "@bboxSize":[-1,-1,-1] } Web3D 2016, Anaheim, California 23 rd July 2016 9
Consortium Encoding on node fields • In XML referenced nodes are child elements, e.g. <Group bboxSize='-1 -1 -1'> <Viewpoint containerField='children'/> <Group/> • In JSON the field is a property of the containing node, and the referenced node is an object, e.g. "Group": { "@bboxSize":[-1,-1,-1], "-children": [ { "Viewpoint": {} } ] Web3D 2016, Anaheim, California 23 rd July 2016 10
Consortium Comments / ROUTEs, etc. • In XML: <!–- This is a comment --> • In JSON: "#comment":"This is a comment" "Group":{ <Group bboxSize='-1 -1 -1'> "Group":{ "@bboxSIze":[-1,-1,-1], "@bboxSIze":[-1,-1,-1], <!–- Before Viewpoint --> "-children":[ "#comment":"Before Viewpoint", <Viewpoint containerField='children'/> {"#comment":"Before Viewpoint"}, "-children":[ <!-- After Viewpoint --> {"Viewpoint":{}}, {"Viewpoint":{}} <Group/> {"#comment":"After Viewpoint"} ], ] "#comment":"After Viewpoint" } } Web3D 2016, Anaheim, California 23 rd July 2016 11
Consortium Validation • Like XML, use a Schema – Covers all X3D nodes, statements, etc. – Available online at: http://www.web3d.org/specifications/x3d-3.3-JSONSchema.json • JSON schema has improved validation capabilities: – Validates child node content of individual node fields – Validates individual array elements Web3D 2016, Anaheim, California 23 rd July 2016 12
Consortium Implementations • For web browsers: – X3DOM and Cobweb use XML encoded files – JSON loader developed. Either: • Loads directly into DOM, or • Via XML to X3DOM or Cobweb • A standalone C++ application – Uses XML encoded files – JSON loader / validator developed Web3D 2016, Anaheim, California 23 rd July 2016 13
Consortium Questions Web3D 2016, Anaheim, California 23 rd July 2016 14
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