[Bf-committers] Final Design of Basics (render api)
j.merritt at pgrad.unimelb.edu.au
Sat Jun 30 02:27:53 CEST 2007
Aaron Moore wrote:
> I just completed my final design of:
> 1) The basic Render API.
> 2) The Render API plugin system.
I think this document looks very good, and you've come to grips with the
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.
- 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.
2. Deformation Motion Blur
In the RenderMan world, there are really two different kinds of motion
blur: transformation motion blur and deformation motion blur (I'm
considering camera motion blur as a kind of transformation motion blur
here; some people choose to separate it too). Transformation motion
blur deals with the "bulk" motion blur of an object, expressed purely
through its transformation; eg:
MotionBegin 0 1
Whereas deformation motion blur deals with the motion blur of
deformations *within* the geometry and shading of the object itself; eg:
MotionBegin 0 1
I can see how transformation motion blur is likely to work with the API,
but I'm not sure that quite enough infrastructure is there yet for
deformation motion blur. There are some important restrictions on
deformation motion blur that the render API must ensure before it can be
used. Even Section 6 of the RiSpec is a little incomplete on this (the
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
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
2. The render API should provide a guarantee of identical topology
and identical order of elements if an object is iterated more than once
within the current frame.
Anyway, enough for now. I'll let you know if I have any other ideas.
:-) Again, it looks like great work so far. I can't wait to see this
running, since it will open up an enormous range of possibilities! :-)
PS: Typo; GEOMETRY_PARTICAL_SYSTEM -> GEOMETRY_PARTICLE_SYSTEM
More information about the Bf-committers