1RTC_GEOMETRY_TYPE_SUBDIVISEImObNr(e3e)Ray Tracing KerRnTeCl_sGE3OMETRY_TYPE_SUBDIVISION(3)
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5   NAME
6              RTC_GEOMETRY_TYPE_SUBDIVISION - subdivision geometry type
7
8   SYNOPSIS
9              #include <embree3/rtcore.h>
10
11              RTCGeometry geometry =
12                rtcNewGeometry(device, RTC_GEOMETRY_TYPE_SUBDIVISION);
13
14   DESCRIPTION
15       Catmull-Clark  subdivision  meshes are supported, including support for
16       edge  creases,  vertex  creases,  holes,  non-manifold  geometry,   and
17       face-varying  interpolation.  The number of vertices per face can be in
18       the range of 3 to 15  vertices  (triangles,  quadrilateral,  pentagons,
19       etc).
20
21       Subdivision meshes are created by passing RTC_GEOMETRY_TYPE_SUBDIVISION
22       to the rtcNewGeometry function.  Various buffers need to be set by  the
23       application  to  set up the subdivision mesh.  See rtcSetGeometryBuffer
24       and rtcSetSharedGeometryBuffer for more details on how to set  buffers.
25       The  face buffer (RTC_BUFFER_TYPE_FACE type and RTC_FORMAT_UINT format)
26       contains the number of edges/indices of each face (3 to  15),  and  the
27       number  of  faces  is inferred from the size of this buffer.  The index
28       buffer (RTC_BUFFER_TYPE_INDEX type) contains multiple (3 to 15)  32-bit
29       vertex  indices  (RTC_FORMAT_UINT format) for each face, and the number
30       of edges is inferred from the size of this buffer.  The  vertex  buffer
31       (RTC_BUFFER_TYPE_VERTEX type) stores an array of single precision x, y,
32       z floating point coordinates (RTC_FORMAT_FLOAT3 format), and the number
33       of vertices is inferred from the size of this buffer.
34
35       Optionally, the application may set additional index buffers using dif‐
36       ferent buffer slots if multiple topologies are required for  face-vary‐
37       ing  interpolation.   The standard vertex buffers (RTC_BUFFER_TYPE_VER‐
38       TEX) are always bound to the geometry topology (topology  0)  thus  use
39       RTC_BUFFER_TYPE_INDEX  with buffer slot 0.  User vertex data interpola‐
40       tion may use different topologies as described later.
41
42       Optionally, the application  can  set  up  the  hole  buffer  (RTC_BUF‐
43       FER_TYPE_HOLE)  which  contains  an  array  of 32-bit indices (RTC_FOR‐
44       MAT_UINT format) of faces that should be considered non-existing in all
45       topologies.  The number of holes is inferred from the size of this buf‐
46       fer.
47
48       Optionally,  the  application  can  fill  the  level  buffer  (RTC_BUF‐
49       FER_TYPE_LEVEL)  with a tessellation rate for each of the edges of each
50       face.  This buffer must have the same size as the  index  buffer.   The
51       tessellation level is a positive floating point value (RTC_FORMAT_FLOAT
52       format) that specifies how many quads along the edge should  be  gener‐
53       ated  during tessellation.  If no level buffer is specified, a level of
54       1 is used.  The maximally supported edge level is 4096, and larger lev‐
55       els  are  clamped to that value.  Note that edges may be shared between
56       (typically 2) faces.  To guarantee a watertight tessellation, the level
57       of these shared edges should be identical.  A uniform tessellation rate
58       for an entire subdivision mesh can be set  by  using  the  rtcSetGeome‐
59       tryTessellationRate  function.   The  existence  of  a level buffer has
60       precedence over the uniform tessellation rate.
61
62       Optionally, the application can fill the sparse edge crease buffers  to
63       make  edges  appear  sharper.   The  edge crease index buffer (RTC_BUF‐
64       FER_TYPE_EDGE_CREASE_INDEX) contains an array of pairs of 32-bit vertex
65       indices  (RTC_FORMAT_UINT2 format) that specify unoriented edges in the
66       geometry  topology.   The   edge   crease   weight   buffer   (RTC_BUF‐
67       FER_TYPE_EDGE_CREASE_WEIGHT)  stores  for  each of these crease edges a
68       positive floating point weight (RTC_FORMAT_FLOAT format).   The  number
69       of  edge  creases is inferred from the size of these buffers, which has
70       to be identical.  The larger a weight, the sharper the edge.   Specify‐
71       ing  a  weight of infinity is supported and marks an edge as infinitely
72       sharp.  Storing an edge multiple times with the same crease  weight  is
73       allowed,  but  has  lower  performance.  Storing an edge multiple times
74       with different crease weights results in  undefined  behavior.   For  a
75       stored  edge (i,j), the reverse direction edges (j,i) do not have to be
76       stored, as both are considered the same unoriented edge.   Edge  crease
77       features are shared between all topologies.
78
79       Optionally,  the  application can fill the sparse vertex crease buffers
80       to make vertices  appear  sharper.   The  vertex  crease  index  buffer
81       (RTC_BUFFER_TYPE_VERTEX_CREASE_INDEX), contains an array of 32-bit ver‐
82       tex indices (RTC_FORMAT_UINT format) to specify a set of vertices  from
83       the  geometry  topology.   The  vertex  crease  weight buffer (RTC_BUF‐
84       FER_TYPE_VERTEX_CREASE_WEIGHT) specifies for each of these  vertices  a
85       positive  floating  point weight (RTC_FORMAT_FLOAT format).  The number
86       of vertex creases is inferred from the size of these buffers,  and  has
87       to  be identical.  The larger a weight, the sharper the vertex.  Speci‐
88       fying a weight of infinity is supported and makes the vertex infinitely
89       sharp.   Storing a vertex multiple times with the same crease weight is
90       allowed, but has lower performance.  Storing a  vertex  multiple  times
91       with  different  crease  weights results in undefined behavior.  Vertex
92       crease features are shared between all topologies.
93
94       Subdivision modes can be used to force linear interpolation  for  parts
95       of  the  subdivision  mesh;  see rtcSetGeometrySubdivisionMode for more
96       details.
97
98       For multi-segment motion blur, the number of time steps must  be  first
99       specified  using  the  rtcSetGeometryTimeStepCount call.  Then a vertex
100       buffer for each time step can be set using different buffer slots,  and
101       all these buffers have to have the same stride and size.
102
103       Also  see tutorial [Subdivision Geometry] for an example of how to cre‐
104       ate subdivision surfaces.
105
106   Parametrization
107       The parametrization for subdivision faces is different for quadrilater‐
108       als and non-quadrilateral faces.
109
110       The parametrization of a quadrilateral face uses the first vertex p0 as
111       base point, and the  vector  p1 - p0  as  u-direction  and  p3 - p0  as
112       v-direction.
113
114       The  parametrization  for all other face types (with number of vertices
115       not equal 4), have a special parametrization where the  subpatch  ID  n
116       (of  the n-th quadrilateral that would be obtained by a single subdivi‐
117       sion step) and the local hit location  inside  this  quadrilateral  are
118       encoded  in  the  UV  coordinates.   The  following  code  extracts the
119       sub-patch ID i and local UVs of this subpatch:
120
121              unsigned int l = floorf(0.5f*U);
122              unsigned int h = floorf(0.5f*V);
123              unsigned int i = 4*h+l;
124              float u = 2.0f*fracf(0.5f*U)-0.5f;
125              float v = 2.0f*fracf(0.5f*V)-0.5f;
126
127       This encoding allows local subpatch UVs to be in the  range  [-0.5,1.5[
128       thus  negative  subpatch  UVs can be passed to rtcInterpolate to sample
129       subpatches slightly out of bounds.  This can be useful to calculate de‐
130       rivatives  using  finite differences if required.  The encoding further
131       has the property that one can just move the value u (or v)  on  a  sub‐
132       patch  by  adding  du  (or dv) to the special UV encoding as long as it
133       does not fall out of the [-0.5,1.5[ range.
134
135       To smoothly interpolate vertex attributes over the subdivision  surface
136       we  recommend  using  the rtcInterpolate function, which will apply the
137       standard subdivision rules for interpolation  and  automatically  takes
138       care of the special UV encoding for non-quadrilaterals.
139
140   Face-Varying Data
141       Face-varying interpolation is supported through multiple topologies per
142       subdivision mesh and binding such topologies to vertex  attribute  buf‐
143       fers to interpolate.  This way, texture coordinates may use a different
144       topology with additional boundaries to construct  separate  UV  regions
145       inside one subdivision mesh.
146
147       Each  such  topology  i  has  a  separate index buffer (specified using
148       RTC_BUFFER_TYPE_INDEX with buffer slot i) and separate subdivision mode
149       that   can   be  set  using  rtcSetGeometrySubdivisionMode.   A  vertex
150       attribute buffer RTC_BUFFER_TYPE_VERTEX_ATTRIBUTE  bound  to  a  buffer
151       slot  j  can  be assigned to use a topology for interpolation using the
152       rtcSetGeometryVertexAttributeTopology call.
153
154       The face buffer  (RTC_BUFFER_TYPE_FACE  type)  is  shared  between  all
155       topologies,  which  means  that  the n-th primitive always has the same
156       number of vertices (e.g.  being a triangle or a quad) for  each  topol‐
157       ogy.   However, the indices of the topologies themselves may be differ‐
158       ent.
159
160   EXIT STATUS
161       On failure NULL is returned and an  error  code  is  set  that  can  be
162       queried using rtcDeviceGetError.
163
164   SEE ALSO
165       [rtcNewGeometry]
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169                                              RTC_GEOMETRY_TYPE_SUBDIVISION(3)
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