Understanding Shading Rate & PTC (RenderMan)

[noizFACTORY]

I hope this answers your question:

http://www.k-3d.org/wiki/RenderMan_Controls

Also, usually the recommended settings for baking a point cloud are (from whatever I have read on the net and in the docs):

Shading Rate = 1

X/Y Samples = 1

Filter Type set to Box at (1,1) width and height.

-Sachin

[TLobes]

Great resource! I've been looking for something that breaks all those down with descriptions and recommended filter sizes. Thanks.

As for the point cloud, it is the shading rate and resolution along with sample size determining the final size of the ptc file.

[rendermaniac]

Unfortunately it is the camera, shading rate etc that determines your sampling - exactly how is very non obvious.

Ideally sampling should be specified in samples/area (probably world or uv space) - it has been put in as a request for Pixar (multiple times).

Simon

[jeremybirn]

I was wondering what the technical difference is between a 0.1, 0.5 and 1.0 shading rate. Obviously lower is more detailed, but how does that detail relate to micropolygons per pixel?

The general rule is that the number of micropolygons per pixel is 1 / shading rate. So a shading rate of 0.1 would be like asking for 10 micropolygons per pixel, and a 0.5 would be a request for 2 micropolygons per pixel, and a 1.0 would request 1 micropolygon per pixel.

But sometimes you get a different number of micropolygons per pixel than requested by the shading rate. For example, if you had a lot of thin tubes running through an area on the screen, then there could be many micropolygons just to represent all the shapes cutting through the area, and you might get more than the requested number of micropolygons.

-jeremy

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