1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
|
// Copyright 2016 The Draco Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#ifndef DRACO_COMPRESSION_MESH_MESH_EDGEBREAKER_TRAVERSAL_VALENCE_ENCODER_H_
#define DRACO_COMPRESSION_MESH_MESH_EDGEBREAKER_TRAVERSAL_VALENCE_ENCODER_H_
#include "draco/compression/entropy/symbol_encoding.h"
#include "draco/compression/mesh/mesh_edgebreaker_traversal_encoder.h"
#include "draco/core/varint_encoding.h"
namespace draco {
// Predictive encoder for the Edgebreaker symbols based on valences of the
// previously encoded vertices, following the method described in: Szymczak'02,
// "Optimized Edgebreaker Encoding for Large and Regular Triangle Meshes". Each
// valence is used to specify a different entropy context for encoding of the
// symbols.
// Encoder can operate in various predefined modes that can be used to select
// the way in which the entropy contexts are computed (e.g. using different
// clamping for valences, or even using different inputs to compute the
// contexts), see EdgebreakerValenceCodingMode in mesh_edgebreaker_shared.h for
// a list of supported modes.
class MeshEdgebreakerTraversalValenceEncoder
: public MeshEdgebreakerTraversalEncoder {
public:
MeshEdgebreakerTraversalValenceEncoder()
: corner_table_(nullptr),
prev_symbol_(-1),
last_corner_(kInvalidCornerIndex),
num_symbols_(0),
min_valence_(2),
max_valence_(7) {}
bool Init(MeshEdgebreakerEncoderImplInterface *encoder) {
if (!MeshEdgebreakerTraversalEncoder::Init(encoder)) {
return false;
}
min_valence_ = 2;
max_valence_ = 7;
corner_table_ = encoder->GetCornerTable();
// Initialize valences of all vertices.
vertex_valences_.resize(corner_table_->num_vertices());
for (VertexIndex i(0); i < static_cast<uint32_t>(vertex_valences_.size());
++i) {
vertex_valences_[i] = corner_table_->Valence(VertexIndex(i));
}
// Replicate the corner to vertex map from the corner table. We need to do
// this because the map may get updated during encoding because we add new
// vertices when we encounter split symbols.
corner_to_vertex_map_.resize(corner_table_->num_corners());
for (CornerIndex i(0); i < corner_table_->num_corners(); ++i) {
corner_to_vertex_map_[i] = corner_table_->Vertex(i);
}
const int32_t num_unique_valences = max_valence_ - min_valence_ + 1;
context_symbols_.resize(num_unique_valences);
return true;
}
inline void NewCornerReached(CornerIndex corner) { last_corner_ = corner; }
inline void EncodeSymbol(EdgebreakerTopologyBitPattern symbol) {
++num_symbols_;
// Update valences on the mesh and compute the context that is going to be
// used to encode the processed symbol.
// Note that the valences are computed for the so far unencoded part of the
// mesh (i.e. the decoding is reverse). Adding a new symbol either reduces
// valences on the vertices or leaves the valence unchanged.
const CornerIndex next = corner_table_->Next(last_corner_);
const CornerIndex prev = corner_table_->Previous(last_corner_);
// Get valence on the tip corner of the active edge (outgoing edge that is
// going to be used in reverse decoding of the connectivity to predict the
// next symbol).
const int active_valence = vertex_valences_[corner_to_vertex_map_[next]];
switch (symbol) {
case TOPOLOGY_C:
// Compute prediction.
FALLTHROUGH_INTENDED;
case TOPOLOGY_S:
// Update valences.
vertex_valences_[corner_to_vertex_map_[next]] -= 1;
vertex_valences_[corner_to_vertex_map_[prev]] -= 1;
if (symbol == TOPOLOGY_S) {
// Whenever we reach a split symbol, we need to split the vertex into
// two and attach all corners on the left and right sides of the split
// vertex to the respective vertices (see image below). This is
// necessary since the decoder works in the reverse order and it
// merges the two vertices only after the split symbol is processed.
//
// * -----
// / \--------
// / \--------
// / \-------
// *-------v-------*
// \ /c\ /
// \ / \ /
// \ /n S p\ /
// *.......*
//
// Count the number of faces on the left side of the split vertex and
// update the valence on the "left vertex".
int num_left_faces = 0;
CornerIndex act_c = corner_table_->Opposite(prev);
while (act_c != kInvalidCornerIndex) {
if (encoder_impl()->IsFaceEncoded(corner_table_->Face(act_c))) {
break; // Stop when we reach the first visited face.
}
++num_left_faces;
act_c = corner_table_->Opposite(corner_table_->Next(act_c));
}
vertex_valences_[corner_to_vertex_map_[last_corner_]] =
num_left_faces + 1;
// Create a new vertex for the right side and count the number of
// faces that should be attached to this vertex.
const int new_vert_id = static_cast<int>(vertex_valences_.size());
int num_right_faces = 0;
act_c = corner_table_->Opposite(next);
while (act_c != kInvalidCornerIndex) {
if (encoder_impl()->IsFaceEncoded(corner_table_->Face(act_c))) {
break; // Stop when we reach the first visited face.
}
++num_right_faces;
// Map corners on the right side to the newly created vertex.
corner_to_vertex_map_[corner_table_->Next(act_c)] = new_vert_id;
act_c = corner_table_->Opposite(corner_table_->Previous(act_c));
}
vertex_valences_.push_back(num_right_faces + 1);
}
break;
case TOPOLOGY_R:
// Update valences.
vertex_valences_[corner_to_vertex_map_[last_corner_]] -= 1;
vertex_valences_[corner_to_vertex_map_[next]] -= 1;
vertex_valences_[corner_to_vertex_map_[prev]] -= 2;
break;
case TOPOLOGY_L:
vertex_valences_[corner_to_vertex_map_[last_corner_]] -= 1;
vertex_valences_[corner_to_vertex_map_[next]] -= 2;
vertex_valences_[corner_to_vertex_map_[prev]] -= 1;
break;
case TOPOLOGY_E:
vertex_valences_[corner_to_vertex_map_[last_corner_]] -= 2;
vertex_valences_[corner_to_vertex_map_[next]] -= 2;
vertex_valences_[corner_to_vertex_map_[prev]] -= 2;
break;
default:
break;
}
if (prev_symbol_ != -1) {
int clamped_valence;
if (active_valence < min_valence_) {
clamped_valence = min_valence_;
} else if (active_valence > max_valence_) {
clamped_valence = max_valence_;
} else {
clamped_valence = active_valence;
}
const int context = clamped_valence - min_valence_;
context_symbols_[context].push_back(
edge_breaker_topology_to_symbol_id[prev_symbol_]);
}
prev_symbol_ = symbol;
}
void Done() {
// Store the init face configurations and attribute seam data
MeshEdgebreakerTraversalEncoder::EncodeStartFaces();
MeshEdgebreakerTraversalEncoder::EncodeAttributeSeams();
// Store the contexts.
for (int i = 0; i < context_symbols_.size(); ++i) {
EncodeVarint<uint32_t>(static_cast<uint32_t>(context_symbols_[i].size()),
GetOutputBuffer());
if (context_symbols_[i].size() > 0) {
EncodeSymbols(context_symbols_[i].data(),
static_cast<int>(context_symbols_[i].size()), 1, nullptr,
GetOutputBuffer());
}
}
}
int NumEncodedSymbols() const { return num_symbols_; }
private:
const CornerTable *corner_table_;
// Explicit map between corners and vertices. We cannot use the one stored
// in the |corner_table_| because we may need to add additional vertices to
// handle split symbols.
IndexTypeVector<CornerIndex, VertexIndex> corner_to_vertex_map_;
IndexTypeVector<VertexIndex, int> vertex_valences_;
// Previously encoded symbol.
int32_t prev_symbol_;
CornerIndex last_corner_;
// Explicitly count the number of encoded symbols.
int num_symbols_;
int min_valence_;
int max_valence_;
std::vector<std::vector<uint32_t>> context_symbols_;
};
} // namespace draco
#endif // DRACO_COMPRESSION_MESH_MESH_EDGEBREAKER_TRAVERSAL_VALENCE_ENCODER_H_
|
