mirror of
https://github.com/PixarAnimationStudios/OpenSubdiv
synced 2024-11-29 23:01:05 +00:00
fe7f840048
- reverted section header titles to match existing external links
- modified internal explicit targets to match existing external links
- changed internal links to match restored section titles and targets
122 lines
4.3 KiB
ReStructuredText
122 lines
4.3 KiB
ReStructuredText
..
|
|
Copyright 2013 Pixar
|
|
|
|
Licensed under the Apache License, Version 2.0 (the "Apache License")
|
|
with the following modification; you may not use this file except in
|
|
compliance with the Apache License and the following modification to it:
|
|
Section 6. Trademarks. is deleted and replaced with:
|
|
|
|
6. Trademarks. This License does not grant permission to use the trade
|
|
names, trademarks, service marks, or product names of the Licensor
|
|
and its affiliates, except as required to comply with Section 4(c) of
|
|
the License and to reproduce the content of the NOTICE file.
|
|
|
|
You may obtain a copy of the Apache License at
|
|
|
|
http://www.apache.org/licenses/LICENSE-2.0
|
|
|
|
Unless required by applicable law or agreed to in writing, software
|
|
distributed under the Apache License with the above modification is
|
|
distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
|
|
KIND, either express or implied. See the Apache License for the specific
|
|
language governing permissions and limitations under the Apache License.
|
|
|
|
|
|
HBR Overview
|
|
------------
|
|
|
|
.. contents::
|
|
:local:
|
|
:backlinks: none
|
|
|
|
|
|
Hierarchical Boundary Representation (Hbr)
|
|
==========================================
|
|
|
|
Hbr is an interconnected topological data representation. The high level of vertex
|
|
connectivity information makes this representation well suited for creation and
|
|
editing purposes. It is however inefficient for interactive refinement operations:
|
|
Separate objects are allocated for each vertex and edge with pointers to neighboring
|
|
vertices and edges.
|
|
|
|
Hbr is also the lowest-level subdivision library in Pixar's `Photorealistic RenderMan`.
|
|
|
|
.. container:: notebox
|
|
|
|
**Note**
|
|
|
|
As of OpenSubdiv 3.0, all **Hbr** dependencies have been removed from the
|
|
core APIs (**Sdc**, **Vtr**, **Far**, **Osd**). The legacy source code of
|
|
**Hbr** is provided purely for regression and legacy purposes. If your code
|
|
is currently depending on Hbr functionality, we recommend migrating to the
|
|
newer APIs as we cannot guarantee that this code will be maintained in
|
|
future releases.
|
|
For more information see the `3.0 release notes <release_notes.html>`_
|
|
|
|
|
|
----
|
|
|
|
Half-edge Data Structure
|
|
========================
|
|
|
|
The current implementation is based on a half-edge data structure.
|
|
|
|
.. image:: images/half_edge.png
|
|
:align: center
|
|
|
|
----
|
|
|
|
Half-edge cycles and Manifold Topology
|
|
======================================
|
|
|
|
Because half-edges only carry a reference to their opposite half-edge, a given
|
|
edge can only access a single neighboring edge cycle.
|
|
|
|
.. image:: images/half_edge_cycle.png
|
|
:align: center
|
|
|
|
This is a fundamental limitation of the half-edge data structure, in that it
|
|
cannot represent non-manifold geometry, in particular fan-type topologies. A
|
|
different approach to topology will probably be necessary in order to accommodate
|
|
non-manifold geometry.
|
|
|
|
----
|
|
|
|
Templated Vertex Class
|
|
======================
|
|
|
|
The vertex class has been abstracted into a set of templated function accesses.
|
|
Providing Hbr with a template vertex class that does not implement these functions
|
|
allows client-code to use Hbr as a pure topological analysis tool without having
|
|
to pay any costs for data interpolation. It also allows client-code to remain in
|
|
complete control of the layout of the vertex data : interleaved or non-interleaved.
|
|
|
|
----
|
|
|
|
Boundary Interpolation Rules
|
|
============================
|
|
|
|
**Hbr** recognizes 4 rule-sets of boundary interpolation:
|
|
|
|
+------------------------------------+
|
|
| Interpolation Rule-Sets |
|
|
+====================================+
|
|
| k_InterpolateBoundaryNone |
|
|
+------------------------------------+
|
|
| k_InterpolateBoundaryEdgeOnly |
|
|
+------------------------------------+
|
|
| k_InterpolateBoundaryEdgeAndCorner |
|
|
+------------------------------------+
|
|
| k_InterpolateBoundaryAlwaysSharp |
|
|
+------------------------------------+
|
|
|
|
This enum is shared for both vertex and face-varying interpolation,
|
|
with the following distinctions:
|
|
|
|
- vertex boundaries:
|
|
- the *BoundaryNone* rule skips all boundary vertices (results are ''undefined'')
|
|
- the *AlwaysSharp* rule does not apply
|
|
|
|
- face-varying boundaries:
|
|
- the *BoundaryNone* rule selects bilinear face-varying interpolation
|