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181 lines
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Copyright 2013 Pixar
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License
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and the following modification to it: Section 6 Trademarks.
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deleted and replaced with:
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6. Trademarks. This License does not grant permission to use the
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trade names, trademarks, service marks, or product names of the
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Licensor and its affiliates, except as required for reproducing
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the content of the NOTICE file.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
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either express or implied. See the License for the specific
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language governing permissions and limitations under the
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License.
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Introduction
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------------
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.. contents::
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:local:
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:backlinks: none
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.. image:: images/geri.jpg
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:width: 600px
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:align: center
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----
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Introduction
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============
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OpenSubdiv is a set of open source libraries that implement high performance
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subdivision surface (subdiv) evaluation on massively parallel CPU and GPU
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architectures. This codepath is optimized for drawing deforming surfaces with
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static topology at interactive framerates. The resulting limit surfaces are a match
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for Pixar's Renderman specification within numerical precision limits.
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OpenSubdiv is a code API which we hope to integrate into 3rd. party digital
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content creation tools. It is **not** an application, nor a tool that can be used
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directly to create digital assets.
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----
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Why Fast Subdivision ?
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======================
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Subdivision surfaces are commonly used for final rendering of character shapes
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for a smooth and controllable limit surfaces. However, subdivision surfaces in
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interactive apps are typically drawn as their polygonal control hulls because of
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performance. The polygonal control hull is an approximation that is offset from
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the true limit surface. Looking at an approximation in the interactive app makes
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it difficult to see exact contact, like fingers touching a potion bottle or hands
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touching a cheek. It also makes it difficult to see poke-throughs in cloth simulation
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if the skin and cloth are both approximations. This problem is particularly bad when
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one character is much larger than another and unequal subdiv face sizes cause
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approximation errors to be magnified.
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Maya and Pixar's proprietary Presto animation system can take 100ms to subdivide
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a character of 30,000 polygons to the second level of subdivision (500,000 polygons).
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Being able to perform the same operation in less than 3ms allows the user to interact
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with the smooth, accurate limit surface at all times.
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.. image:: images/efficient_subdivision.png
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:height: 400px
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:align: center
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:target: images/efficient_subdivision.png
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----
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Research
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========
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The new GPU technology behind OpenSubdiv is the result of a joint research effort
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between Pixar and Microsoft.
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| *Feature Adaptive GPU Rendering of Catmull-Clark Subdivision Surfaces*
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| Matthias Niessner, Charles Loop, Mark Meyer, and Tony DeRose
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| ACM Transactions on Graphics, Vol. 31 No. 1 Article 6 January 2012
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| `<http://research.microsoft.com/en-us/um/people/cloop/tog2012.pdf>`_
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| *Efficient Evaluation of Semi-Smooth Creases in Catmull-Clark Subdivision Surfaces*
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| Matthias Niessner, Charles Loop, and Guenter Greiner.
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| Eurographics Proceedings, Cagliari, 2012
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| `<http://research.microsoft.com/en-us/um/people/cloop/EG2012.pdf>`_
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| *Analytic Displacement Mapping using Hardware Tessellation*
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| Matthias Niessner, Charles Loop
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| ACM Transactions on Graphics, To appear 2013
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| `<http://research.microsoft.com/en-us/um/people/cloop/TOG2013.pdf>`_
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----
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Heritage
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========
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This is the fifth-generation subdiv library in use by Pixar's proprietary animation
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system in a lineage that started with code written by Tony DeRose and Tien Truong
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for Geri\u2019s Game in 1996. Each generation has been a from-scratch rewrite that
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has built upon our experience using subdivision surfaces to make animated films.
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This code is live, so Pixar's changes to OpenSubdiv for current and future films
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will be released as open source at the same time they are rolled out to Pixar
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animation production.
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| *Subdivision for Modeling and Animation*
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| Denis Zorin, Peter Schroder
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| Course Notes of SIGGRAPH 1999
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| `<http://www.multires.caltech.edu/pubs/sig99notes.pdf>`_
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| *Subdivision Surfaces in Character Animation*
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| Tony DeRose, Michael Kass, Tien Truong
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| Proceedings of SIGGRAPH 1998
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| `<http://graphics.pixar.com/library/Geri/paper.pdf>`_
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| *Recursively generated B-spline surfaces on arbitrary topological meshes*
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| Catmull, E.; Clark, J. Computer-Aided Design 10 (6) (1978)
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----
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Licensing
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=========
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OpenSubdiv is covered by the Apache License, and is free to use for commercial or
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non-commercial use. This is the same code that Pixar uses internally for animated
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film production. Our intent is to encourage a geometry standard for subdivision
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surfaces, by providing consistent (i.e. yielding the same limit surface), high
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performance implementations on a variety of platforms.
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Why Apache? We were looking for a commercial-friendly license that would convey
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our patents to the end users. This quickly narrowed the field to Microsoft Public
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License or Apache. Initially we chose MSPL because it handled trademarks better.
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But at the request of several companies we gave Apache another look, and decided
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to go with Apache with a very slight modification that simply says you cannot use
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any contributors' trademarks. In other words, you can use OpenSubdiv to make a
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product, but you cannot use a Luxo Lamp (or other character, etc.) when marketing
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your product.
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----
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Contributing
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============
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In order for us to accept code submissions (merge git pull-requests), contributors
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need to sign the Contributor License Agreement (CLA). There are two CLAs, one for
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individuals and one for corporations. As for the end-user license, both are based
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on Apache. They are found in the code repository (`individual form
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<https://github.com/PixarAnimationStudios/OpenSubdiv/blob/master/OpenSubdivCLA_individual.pdf>`__,
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`corporate form <https://github.com/PixarAnimationStudios/OpenSubdiv/blob/master/OpenSubdivCLA_corporate.pdf>`__).
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Please email the signed CLA to opensubdiv-cla@pixar.com.
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For more details about OpenSubdiv, see `Pixar Graphics Technologies <http: graphics.pixar.com>`__.
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----
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External Resources
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==================
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Microsoft Research:
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`Charles Loop <http://research.microsoft.com/en-us/um/people/cloop/>`__
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`Matthias Niessner <http://lgdv.cs.fau.de/people/card/matthias/niessner/>`__
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Pixar Research:
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`Pixar R&D Portal <http://graphics.pixar.com/research/>`__
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