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Thread: using float3 units - arrays of float3

  1. #1
    Junior Member
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    Oct 2004
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    6

    using float3 units - arrays of float3

    Please refer to the box xml sample for this discussion.

    Notice that the all the vertex floating point data. The node that stores this represents it as a list of 24 floats. the "<technique>" nodes (adjacent to the "<array>") are provided for how to interpret this data. The semantic (what the data is used for) is stored ouside the "<source>" node.

    The data is clearly 8 elements in R3. So why no use arrays of float3s? Float3 is alreay defined in the schema. No one would ever interpret this as 12 elements of type float2.

    Going further, it would be nice to allow arrays of more arbitrary structures. i.e. elements in the cartesian product of position space, texture space, normal space, color space. This is not the same as sharing indexes with multiple sources, but instead it is actual interleaved data.
    <array name="myvertexbuffer" type="float3 float3 byte4" semantic="Position Normal Color" count="n">
    x y z nx ny nz 0xrrggbbaa,
    x y z nx ny nz 0xrrggbbaa,
    </array>

    For some people this is what they want their vertex buffer to look like. By being able to represent this data within collada will make it trivial to convert back and forth from xml (text) to C vertex classes (binary). The mapping is obvious.

    Right now you may be able to interleave your positions and normals into on big array of floats using an accessor trick, but you wouldn't be able to get the non-float color in there as well using the current schema.

    You dont store bitmap data within a collada file (nor within an html file). Instead people use references like [img]somepicture.jpg[/img]
    I propose allowing the same with other arrays such as:
    <array name="myPositionData" type="float3" src="filename"/>

    This way, application developers can continue to use the collada data model when working with binary data.

  2. #2
    Junior Member
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    SCEE, UK
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    Re: using float3 units - arrays of float3

    Quote Originally Posted by melax
    You dont store bitmap data within a collada file (nor within an html file). Instead people use references like [img]somepicture.jpg[/img]
    I propose allowing the same with other arrays such as:
    <array name="myPositionData" type="float3" src="filename"/>
    As I understand it the Collada schema fully supports this already. The 'src' element if just a URI, so can point at a local source array or an external source of data.

    The fact that current implementations don't support this is a matter of implementation.

    Which has been raised elsewhere as a concern - that it's possible to create file/data structures that comply with the Collada schema but which won't work with any of the DCC vendor-provided importers/exporters.


    os.
    Andrew Ostler
    Senior Principal Programmer
    SCEE

  3. #3
    Senior Member
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    California
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    Re: using float3 units - arrays of float3

    Quote Originally Posted by melax
    The data is clearly 8 elements in R3. So why no use arrays of float3s? Float3 is alreay defined in the schema. No one would ever interpret this as 12 elements of type float2.
    The <array> element is intended to hold large blocks of homogenous data. It's design includes an ArrayType enum in the schema that is limited to a small set of atomic types (int, float, token).

    The heterogenous interleaving that you are proposing is intended to be done by assembling <source> elements together, one level removed from the <array> element. This subject has been a recurring one for a while as a couple programmers want to assemble their structures at a lower level then the schema currently enables.

    If something like a <struct> or even a <class> element is desired by the COLLADA community then a good time to design it is now, during the next couple of months preceeding COLLADA 2.0 release in March 2005.

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