[Bf-committers] Final Design of Basics (render api)

Aaron Moore two.a.ron at gmail.com
Sat Jun 30 03:13:26 CEST 2007

Hi Jonathan,

> I think this document looks very good, and you've come to grips with the
> requirements quickly.

Good to hear. Having few people to discuss it with at home, being the
only geek around, I can sometimes get tunnel vision, I'm glad to hear
this makes sense to people.

> I have a couple of initial thoughts:
> 1. Object Names
> I think it's useful to include these simply for debugging / editing
> purposes.  In the RenderMan world, it's common to mark objects with
> something like this (RIB chunk):
>     Attribute "identifier" "name" ["MyWonderfulMesh"]
> This has multiple uses:
>     - The renderer can name the object if something goes wrong (eg.
> eyesplits exceeded).
>     - You can find the object later (eg. if you need to tweak something
> like a shader).
> Without this information, identifying objects - troublesome or otherwise
> - can be difficult.

You make an excellent case, consider it done.

> 2. Deformation Motion Blur
> Advanced RenderMan book is a more thorough reference), but for meshes,
> parametric and subdiv surfaces those conditions are:
>     - Topology must be identical for all motion samples (no changes in
> number of vertices or connectivity)
>     - Elements must be presented in the same order for all motion
> samples (eg. you can't change the order in which polygons or vertices
> are listed).

Right, I had assumed this was the case, I might as well write it down
in the document that the API will ensure these conditions.

> For best efficiency, I think the following requirements should be met:
>     1. There should be a way to query whether the geometry of an object
> has deformed within the current frame.  Many objects don't deform, and
> IMHO it's not "premature optimization" to flag this if possible.
> Naturally, you could simply indicate that all objects deform as a
> starting point.

This sounds like a good idea, I'll put it in.

Thanks for the feedback!


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