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## Copyright (C) 2024 David Legland
## All rights reserved.
##
## Redistribution and use in source and binary forms, with or without
## modification, are permitted provided that the following conditions are met:
##
## 1 Redistributions of source code must retain the above copyright notice,
## this list of conditions and the following disclaimer.
## 2 Redistributions in binary form must reproduce the above copyright
## notice, this list of conditions and the following disclaimer in the
## documentation and/or other materials provided with the distribution.
##
## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ''AS IS''
## AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
## IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
## ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
## ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
## DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
## SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
## CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
## OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
## OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
##
## The views and conclusions contained in the software and documentation are
## those of the authors and should not be interpreted as representing official
## policies, either expressed or implied, of the copyright holders.
function BE = meshBoundaryEdges(varargin)
%MESHBOUNDARYEDGES Determine the boundary edges of a mesh.
%
% BE = meshBoundaryEdges(V, F)
% Determine for each edge of the mesh if it is a boundary edge of the
% mesh.
%
% Example
% run createTrefoilKnot.m
% f2 = triangulateFaces(f2);
% % clip the mesh with a plane
% plane = createPlane([0 0 0], [-1 -2 3]);
% [v2, f2] = clipMeshVertices(v2, f2, plane, 'shape', 'plane');
% % draw the mesh
% figure('color','w'); drawMesh(v2, f2); axis equal; view(3);
% % calculate the boundary edges
% be2 = meshBoundaryEdges(v2, f2);
% % draw boundary edges
% drawEdge3d([v2(be2(:,1),:) v2(be2(:,2),:)], 'LineWidth',4,'Color','g')
%
% See also
% meshes3d, meshBoundary, meshBoundaryVertexIndices, meshEdgeFaces,
% meshBoundaryEdgeIndices
%
% Source:
% is_boundary_facet.m by Alec Jacobson:
% https://github.com/alecjacobson/gptoolbox
% ------
% Author: oqilipo
% E-mail: N/A
% Created: 2023-05-15, using Matlab 9.13.0.2080170 (R2022b) Update 1
% Copyright 2023
[V, E, F] = parseMeshData(varargin{:});
% Compute edge-vertex map if not specified
if isempty(E)
E = meshEdges(V, F);
end
switch size(F,2)
case 3
allE = [F(:,[2 3]);F(:,[3 1]);F(:,[1 2])];
case 4
allE = [ ...
F(:,2) F(:,4) F(:,3); ...
F(:,1) F(:,3) F(:,4); ...
F(:,1) F(:,4) F(:,2); ...
F(:,1) F(:,2) F(:,3); ...
];
end
[~,~,EMAP] = unique(sort([E;allE],2),'rows');
N = accumarray(EMAP,1);
% Look of occurances of 2: one for original and another for boundary
B = N(EMAP(1:size(E,1)))==2;
BE = E(B,:);
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