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// Copyright 2017 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.
//
#include "draco/mesh/mesh_stripifier.h"
namespace draco {
void MeshStripifier::GenerateStripsFromCorner(int local_strip_id,
CornerIndex ci) {
// Clear the storage for strip faces.
strip_faces_[local_strip_id].clear();
// Start corner of the strip (where the strip starts).
CornerIndex start_ci = ci;
FaceIndex fi = corner_table_->Face(ci);
// We need to grow the strip both forward and backward (2 passes).
// Note that the backward pass can change the start corner of the strip (the
// start corner is going to be moved to the end of the backward strip).
for (int pass = 0; pass < 2; ++pass) {
if (pass == 1) {
// Backward pass.
// Start the traversal from the B that is the left sibling of the next
// corner to the start corner C = |start_ci|.
//
// *-------*-------*-------*
// / \ / \C / \ /
// / \ / \ / \ /
// / \ / B\ / \ /
// *-------*-------*-------*
//
// Perform the backward pass only when there is no attribute seam between
// the initial face and the first face of the backward traversal.
if (GetOppositeCorner(corner_table_->Previous(start_ci)) ==
kInvalidCornerIndex)
break; // Attribute seam or a boundary.
ci = corner_table_->Next(start_ci);
ci = corner_table_->SwingLeft(ci);
if (ci == kInvalidCornerIndex)
break;
fi = corner_table_->Face(ci);
}
int num_added_faces = 0;
while (!is_face_visited_[fi]) {
is_face_visited_[fi] = true;
strip_faces_[local_strip_id].push_back(fi);
++num_added_faces;
if (num_added_faces > 1) {
// Move to the correct source corner to traverse to the next face.
if (num_added_faces & 1) {
// Odd number of faces added.
ci = corner_table_->Next(ci);
} else {
// Even number of faces added.
if (pass == 1) {
// If we are processing the backward pass, update the start corner
// of the strip on every even face reached (we cannot use odd faces
// for start of the strip as the strips would start in a wrong
// direction).
start_ci = ci;
}
ci = corner_table_->Previous(ci);
}
}
ci = GetOppositeCorner(ci);
if (ci == kInvalidCornerIndex)
break;
fi = corner_table_->Face(ci);
}
// Strip end reached.
if (pass == 1 && (num_added_faces & 1)) {
// If we processed the backward strip and we add an odd number of faces to
// the strip, we need to remove the last one as it cannot be used to start
// the strip (the strip would start in a wrong direction from that face).
is_face_visited_[strip_faces_[local_strip_id].back()] = false;
strip_faces_[local_strip_id].pop_back();
}
}
strip_start_corners_[local_strip_id] = start_ci;
// Reset all visited flags for all faces (we need to process other strips from
// the given face before we choose the final strip that we are going to use).
for (int i = 0; i < strip_faces_[local_strip_id].size(); ++i) {
is_face_visited_[strip_faces_[local_strip_id][i]] = false;
}
}
} // namespace draco
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