Add Chromium-only Blender WebEngine parity work

blender-5.2.0/extern/opensubdiv-source/documentation/hbr_overview.rst

@@ -0,0 +1,104 @@
+..
+     Copyright 2013 Pixar
+
+     Licensed under the terms set forth in the LICENSE.txt file available at
+     https://opensubdiv.org/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