[ODE] XML ODE Data Interchange Format (revision 5)

[Chris Gregan]

Another nice aspect of being able to specify the format is if you are 
porting data from one application to another where the world has been 
set up differently. For instance if the data you have is defined with 
the z axis as up, whereas yours has the y axis as up.
We get this all the time when importing stuff from 3DSMAX. Instead of 
having to reformat the whole file, you could just change the format to 
"x,z,y". Similarly if you wanted to convert row major to column major 
matrices or vice-versa you could just change the format attribute. It 
may also open up the format to graphics as you could add color, alpha, 
texture co-ords, etc.. You could also make the format attribute 
optional, so that <vertices> assumes a format "x,y,z" unless you specify 
otherwise - or would this confuse things?

Chris Gregan

Jon Watte wrote:

>I would recommend that you allow the addition of more components. Thus, I'd suggest that you add a format="x,y,z" attribute to the "vertices" element, which is a comma-separated list of components, where the components x, y and z are currently well-defined, and others should be ignored. This means that a loader has to have slightly more smarts, in that it has to count how many numbers there are per vertex (>= 3) and remember which index corresponds to each of x, y and z for a vertex. However, it buys lots of flexibility.
>
>This is very useful for people who attach other things to their vertices, such as normals, friction, surface Id, etc.
>
>Cheers,
>
>			/ h+
>
>
>-----Original Message-----
>From: William Denniss [mailto:lists at omegadelta.net]
>Sent: Saturday, March 13, 2004 3:41 PM
>To: Jon Watte
>Cc: Chris Gregan; ode at q12.org
>Subject: RE: [ODE] XML ODE Data Interchange Format (revision 5)
>
>
>Lets go with the first option, the <v> tags are hardly necessary - and
>it is the smallest size of the three.
>
>I agree that not everything must be represented in XML.  In some cases
>it makes life easier, but for a simple array of numbers, it's hardly
>necessary.
>
>
>How's this for the spec:
>
>Vertices are represented as a one dimensional array of floats whose
>length is three times the vertex count (i.e. there are three floats for
>each vertex).  The data is delimited by commas and new lines, spaces are
>ignored.
>
>Thus:
>
><vertices>
>0,1,2,1,2,3
></vertices>
>
><vertices>
>0,1,2
>1,2,3
></vertices>
>
>and
>
><vertices>
>0  , 1.0, 2
>1.0, 2.1, 3
></vertices>
>
>are all valid.
>
>I guess whatever method we adopt for the vertices, we should adopt for
>the matrix representation, ie.
>
><matrix>
>0,1,2,3
>4,5,6,3
>4,2,1,2
>3,4,5,6
></matrix>
>
>
>Do you think the format attribute is really needed when we know exactly
>ahead of time what the data should be?  I don't want to make the job of
>writing a parser any harder than it need be.
>
>Thanks for your feedback.
>
>Will.
>
>On Sun, 2004-03-14 at 03:07, Jon Watte wrote:
>  
>
>>Another approach is to use the CDATA for vertices:
>>
>><vertices format="x,y,z">
>>0,1,2
>>1,2,3
>></vertices>
>>
>>Also, putting the x, y and z as attributes of the "v" tag seems a poor
>>choice if file size is what you want. If you don't like using
>>linefeeds or other separators in your CDATA for some reason, try this:
>>
>><vertices format="x,y,z">
>><v>1,2,3</v>
>><v>2,3,4</v>
>></vertex>
>>
>>Which may be a happy medium. Anyway, on previous work, I've found that
>>putting the template/format of vertex/array data in the description is
>>a Really Good Thing, because you WILL want to add more attributes that
>>are only valid in certain arrays.
>>
>>Just because XML is structured doesn't mean that all data should be
>>accessible using the XML structure (attributes and elements). CDATA is
>>there for a reason, you know :-)
>>
>>
>>Cheers,
>>
>>			/ h+
>>
>>
>>-----Original Message-----
>>From: ode-bounces at q12.org [mailto:ode-bounces at q12.org]On Behalf Of Chris
>>Gregan
>>Sent: Saturday, March 13, 2004 7:05 AM
>>Cc: ode at q12.org
>>Subject: Re: [ODE] XML ODE Data Interchange Format (revision 5)
>>
>>
>>I am using my own XML format to represent physical geometry in an FPS. 
>>For large tri-mesh style meshes I found it to be a good idea to use a 
>>"v" tag instead of the full "vertex" to keep the file size down. 
>>Similarly for indices. I think it is still clear what is intended. I 
>>haven't followed this discussion too closely so apologies if this has 
>>been mentioned already.
>>
>><vertices>
>>    <v x="0" y="1" z="1" />
>>    <v x="1" y="2" z="2" />
>>    <v x="2" y="0" z="1" />
>></vertices>
>>
>>Cheers,
>>
>>Chris Gregan
>>    
>>