json and c++ collada reader

I’m working on a simple engine for webgl in javascript.
I have a c++ collada reader that builds a scenegraph of the scene with nodes, meshes , trasformations and materials.
The shaders are already in js.
Now i would create a json from the read classes and send they to javascript for the deserialization.
My question is :
json is only an interchange format that must be parsed after the eval or can be a deserializable format that with eval creates ex novo the instances of the javascript classes and fills it with properties?

I use c++ for reading from collada, which json c++ library you advice to me?

I use ‘fprintf’.

If there is one thing I’ve learned about web-based game development, it’s to put as much flexibility as possible into these kinds of process. I’ve spent a LOT of effort getting model exporters and converters working as smoothly and painlessly as possible.

The first step is that we export models from either ‘blender’ or Maya into our own XML format (which is used in projects other than WebGL - Windows and Linux-based games, stuff I’ve been playing with on Nintendo-DS, etc). I wrote plugins for those two tools to do that. I’d like to get a working exporter for 3DStudio as well…but I don’t have the time/need right now.

(I dislike Collada because its importers and exporters don’t hold up to it’s original promise as a universal 3D format…it’s full of junk that I don’t need - and it’s missing robust exporters for stuff like skeletal mesh animation and shader parameterization.)

For WebGL I wrote a C++ program that uses TinyXML to load the XML file. We don’t mess with JSON - it’s just as easy to write JavaScript data structures directly and for this kind of data (98% of which is dense arrays of floating point vertex data), any ASCII format is as good as any other…so why bother with JSON? It’s just more stuff to go wrong.

This tool knows what kind of model it is (furniture, a human, a vehicle, etc) - and which of our games it’s going to be use in. I use this opportunity to aggressively trim the precision of the numbers in a way that depends on “game knowledge”. (eg, in “BarFight” where we’re talking about a ‘human-scale’ world no more than 40 meters across, positions are stored accurately to 1mm, normals to 1%, texture coordinates to the resolution of the texture maps, etc. In our upcoming “Ships of Oak” sailing ship combat game, precisions for things like islands are only accurate to the nearest meter, for ships, accurate to a centimeter, etc). I also trim leading and trailing zeroes and decimal points from the numbers and use exponential notation (eg 1e3 instead of 1000.0) whenever it’s more compact. This dramatically reduces the file size and the load times compared to JSON.

This XML-to-JS tool has a command-line option to emit nicely laid out JavaScript with neatly aligned columns of numbers, indentation and comments - so I can more easily debug art problems if I have to. I can also convert our XML format to JavaScript on-the-fly using a PHP program on the server that runs the XML-to-JS program and writes the results to HTTP. This allows the artist to simply dump his exported blender files onto the server and use his browser to start either the game, our model viewer, our animation viewer or our “DNA viewer” and get instant results - albeit with slightly slower download times.

We have two websites - one “live” site (tubagames.net) and one development site which is heavily password-protected and kept strictly “private” - we don’t even let the search engines “spider” it! The live site has only compressed JS files on it - the dev site lets you choose the uncompressed form from a preferences panel. The client code that runs in the browser can’t tell the difference. To “release” a game, we just run a batch file to bulk-convert all of the models - then copy all of the files on the dev site over to the live site. This is also automated to eliminate human error.

Since we use the “Unison” program to synchronize data between our computers and the dev site server (and also between the dev site and the live site) - it takes about 10 seconds (three mouse-clicks!) to sync the artists machine to the dev site - which sends .xml, .glsl and .png files from PC to server. When he hits “reload” on the model viewer, PHP converts models to JS as necessary and sends them back into his browser. That painless/rapid turnaround REALLY helps when you’re in the heat of art development.

As our games get more complex, with more art assets, I plan to have the PHP model “loader” check the timestamps on the .xml and .js files and only convert the ones that are outdated…but right now, for the two games we have in progress, the process is fast enough to be bearable.

very thanks for your precious tips.
but i have to clarify in my mind how works with js and php.
I thinking to creates a data text file , like you said.
How i can send the text file from server to client for parse it with js and fill the vertexbuffer in opengles 2.0 and js?

I have two possibility:
1)open the data file on the server(after the user click on the model that would view) and write all the data in the php page that is send to the client.
2)use of ajax.

and for the textures?
There are some tips for save time and space?

How about using webSocket? I don’t look in deep but it seems like a good solution for duplex communicating between server and browser in HTML5.

By the way,
Steve, can you give me some resource about developing exporter plugin for Maya & Blender? such as demos, tutorials or specs.
Thank u very much!

Blender uses Python plugins - there are dozens of them in the public domain - I just found one that was kinda similar to what I wanted and just started modifying it. At some point I tossed it out and started again - but that’s another story. The worst part was learning Python. (I confess: The only python code I’ve ever written is my blender exporter!)

Blender’s python API documentation is poor - and perpetually out of date. Using other exporters as examples is really the only way forward.

Maya uses Mel-Script - which is a specialized scripting language. If you have a copy of Maya, you’ll have access to a bunch of Mel tutorials…the API is well documented - and it works.

– Steve

Thank you very much!

I thought WebSockets were deprecated right now…some kind of horrible security issue. Both Firefox and Opera have disabled them pending specification revisions.

I export my models in Blender to an x3d file.
I upload that x3d file to the server and open it using javascript.
I parse through the XML and convert it to json and then evaluate that json into a variable.

The solution is not perfect, but its a good start.
Writing the parser was fiddly but it really got down to traversing through the shapes, setting global colour variables and when a shape "USE"d a colour, i just called upon that global variable.

You can do the same with COLLADA files, but I didn’t get how they laid their data out.

This whole process allows me to have beautiful models in my webgl with just an upload of a file, and a direction to that file.

If you want any more info on my method, please ask!