Hey guys,
If anyone here is doing 3d stuff with Gambit, you might find my OBJ model loader useful. It'll load vertices, normals, and indices for models from the Wavefront .OBJ format. I'll implement UV coordinates soon. I wrote a blog post about using it and posted the code (it's also in the gambit iphone github project and I'll be improving it there):
http://jlongster.com/blog/2009/08/3/iphone-physics-and-models/
I also studied Gambit's serialization mechanisms using object->u8vector for compressing models and speeding up loading times. It turned out great! You can find examples in my post.
Hope someone finds it useful. Thanks - James
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On 3-Aug-09, at 4:06 PM, James Long wrote:
I also studied Gambit's serialization mechanisms using object->u8vector for compressing models and speeding up loading times. It turned out great! You can find examples in my post.
Nice! I like your binary format where you use a single byte to indicate the length of the binary encoding of the *length* of the binary encoding of the object! I usually write 4 bytes with the 32- bit length, but its much messier. Neat idea!
Marc
2009/8/4 Marc Feeley feeley@iro.umontreal.ca:
On 3-Aug-09, at 4:06 PM, James Long wrote:
I also studied Gambit's serialization mechanisms using object->u8vector for compressing models and speeding up loading times.
Nice! I like your binary format where you use a single byte to indicate the length of the binary encoding of the *length* of the binary encoding of the object!
This sounds like a re-imagining of some of the ASN.1 encoding conventions. IIRC, there were two different length encodings that could be used for a given data field, one applied to any data type and the other (implicit length) only applied to structured types and relied on the components of the structure to all have their lengths completely specified.
The two explicit length methods were a length of length encoding and a string-based length encoding. In the length of length encoding, if the length is less than 128, you just use a single byte, with the high bit set to zero. Otherwise the high bit is set to one, and the low seven bits set to the length of length. The length is then encoded in that many bytes.
The encoding of ASN.1 tags was also interesting because they could potentially be infinitely long. IIRC (again) the first octet reserved 5 bits for the tag ID. If the tag ID was greater than 30, the 5 reserved bits were set to 31 (all ones) and then the low seven bits of the octets following the first tag octet were deemed to be part of the tag value if the high bit of the octet was set to 1. the last tag octet had the high bit set to 0 and the low-order bits were just thrown away.
Just a wee bit of historical context :)
david
On Tue, Aug 4, 2009 at 4:45 AM, David Rushkumoyuki@gmail.com wrote:
2009/8/4 Marc Feeley feeley@iro.umontreal.ca:
On 3-Aug-09, at 4:06 PM, James Long wrote:
I also studied Gambit's serialization mechanisms using object->u8vector for compressing models and speeding up loading times.
Nice! I like your binary format where you use a single byte to indicate the length of the binary encoding of the *length* of the binary encoding of the object!
....
Just a wee bit of historical context :)
david
Thanks David, I'm glad I stumbled upon such interesting methods of encoding! That was a fun problem to think through.
- James
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David Rush -
James Long -
Marc Feeley