REYES is the abbreviation for ‘Renders Everything You Ever Saw’. It is an algorithm developed at Industrial Light and Magic in the early 80’s of the last century. This algorithm, in some form or another, is today used by most RenderMan (RMan) compliant renderers and a few others, for example Side Effect’s VMantra. Speaking of RMan compliant renderers: AIR and Pixie (the latter with some of its hiders) in particular use different approaches.
Basically, REYES dices all geometry into tiny polygons at rendertime. These polygons are so tiny that they are commonly called micropolygons. Under typical circumstances they are about a pixel in size for the resp. image being rendered. This is also the reason why REYES renderers are commonly referred to as “micropolygon renderers”.
The mere details of REYES are beyond the scope of this essay, but a nice description can be found in the SIGGRAPH 2000 RMan course notes. It is called ‘How PhotoRealistic RenderMan Works’. Actually, an exact copy of this text can be found in the book ‘Advanced Renderman — Creating CGI for Motion Pictures’. So essentially, by downloading the above PDF, you get this chapter of the book for free!
‘Primitive’ is the term used for the geometric objects that make up a scene. They are called primitives because there is no geometry more atomic than a primitive in a scene. Let’s talk about primitives in most other renderers a bit first, to see why they are way cooler in a REYES renderer.
Moritz– nice little article.
You may remember me from such productions as ‘Animalia’ (I’m one of the joonya’s that sat next to you).
Question after reading the article– If Subdivision is recalculated frame by frame in order to optimize micropolygon numbers, is it ever likely to encounter artifacts caused by a timestep and resulting mesh change. That is to say if the topology of the surface is changing to incorporate more or less polygons will the change every lead to problems. I wondering both about possible silhouette issues and texture problems. I suppose what I’m really asking is if I was to crank the shading rate to 50 or 100 (assuming it lets me and the control surface is suitably low poly) would the mesh pop in a random fashion either side of the ‘limit surface’ or would the subdivision remain, by some miracle, relatively uniform .
Obviously I would assume such variations would be next to impossible to detect on a moving object with a suitable shading rate but all the same I wonder.
Myles
Yes, it is indeed so that in REYES, the dicing of a mesh will change every frame, if that mesh is deforming/transforming and/or the camera is transforming or changing parameters, relative to the gprim in question.
This can lead to crawling artifacts on very slowly deforming geometry (slowly, as in: little change over many frames and possibly motion blur not being used to worsen things). Particulalrly displacement/bump mapping is prone to expose the problem.
Note, however, that this is all happening in alignement with the primtives’s UV parameterization which (supposedly) is the same, direction wise, over a sequence of frames. This and the fact that motion blur is almost always used in images coming out of REYES renderers, helps hiding the issue, if there is any visible one.
Consider the alternative in a ray tracer: every pixel is sampled (many times). Were a ray hits the primitive (aka: the ray-tracer’s “shading rate”) has nothing to do with the UV parameterization of the surface at all. Even with correct filtering, you can get similar popping of features but it will likely be much more pronounced than in a REYES renderer.
la idea muy buena
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