From dbf5c6273002ddd96ebadb8c0168c8292355db53 Mon Sep 17 00:00:00 2001
From: artemyev <a.e.artemyev.work@yandex.ru>
Date: Fri, 4 Jul 2025 14:18:58 +0700
Subject: [PATCH 1/2] feat: add new function mesh/sharp_halfedges.m

This function is based on sharp_edges function.
---
 mesh/sharp_halfedges.m | 58 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 mesh/sharp_halfedges.m

diff --git a/mesh/sharp_halfedges.m b/mesh/sharp_halfedges.m
new file mode 100644
index 00000000..f0ab7756
--- /dev/null
+++ b/mesh/sharp_halfedges.m
@@ -0,0 +1,58 @@
+function SHE = sharp_halfedges(V, F, angle, varargin)
+% SHARP_HALFEDGES Compute sharp halfedges for a mesh based on dihedral angles.
+%
+% SHE = sharp_halfedges(V, F, angle)
+% SHE = sharp_halfedges(V, F, angle, 'CornerIndexing')
+% SHE = sharp_halfedges(V, F, angle, 'CyclicIndexing')
+%
+% This function marks "sharp" edges in a triangular mesh based on a given dihedral
+% angle threshold. An edge is considered sharp if its dihedral angle exceeds the
+% specified angle (in radians).
+%
+% Input:
+%   V  #V by 3 matrix of vertex positions.
+%   F  #F by 3 matrix of triangle vertex indices.
+%   angle  Scalar threshold angle (in radians). An edge with a larger dihedral
+%          angle is marked as sharp.
+%
+% Optional argument (mode):
+%   'CornerIndexing' (default) - Uses corner-based indexing convention: edge j
+%     is defined as the edge opposite vertex j in F(i,:).
+%   'CyclicIndexing' - Uses edge-based cyclic indexing convention: local edge
+%     indices follow the order of edges (1→2, 2→3, 3→1) in each triangle.
+%
+% Output:
+%   SHE  #F by 3 matrix, where SHE(i,j) = 1 if the j-th edge of face i is sharp
+%        (dihedral angle > angle), and 0 otherwise. Indexing depends on the mode.
+%
+% Example:
+%   SHE = sharp_halfedges(V, F, pi/6, 'CyclicIndexing');
+
+  % Default mode
+  mode = 'CornerIndexing';
+
+  % Parse optional argument
+  if ~isempty(varargin)
+    if ischar(varargin{1}) || isstring(varargin{1})
+      mode = varargin{1};
+    else
+      error('Optional argument must be a string: ''CornerIndexing'' or ''CyclicIndexing''.');
+    end
+  end
+
+  [A,C] = adjacency_dihedral_angle_matrix(V,F);
+  [AI,AJ,AV] = find(A);
+  keep = abs(AV-pi)>(angle) & ~isnan(AV);
+  A = sparse(AI(keep),AJ(keep),1,size(A,1),size(A,2));
+  [CI,~,CV] = find(C.*A);
+  idx = sub2ind(size(C), CI, CV);
+  SHE = zeros(size(F));
+  SHE(idx)=1;
+
+  % Apply cyclic reordering if requested
+  if strcmpi(mode, 'CyclicIndexing')
+    SHE = [SHE(:,3), SHE(:,1), SHE(:,2)];
+  elseif ~strcmpi(mode, 'CornerIndexing')
+    error('Unknown indexing mode. Use ''CornerIndexing'' or ''CyclicIndexing''.');
+  end
+end
\ No newline at end of file

From 8497f576f2bfb925814dbac617ed23c4984f7594 Mon Sep 17 00:00:00 2001
From: artemyev <a.e.artemyev.work@yandex.ru>
Date: Fri, 4 Jul 2025 15:01:15 +0700
Subject: [PATCH 2/2] feat(sharp_edges): improve example

---
 mesh/sharp_halfedges.m | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mesh/sharp_halfedges.m b/mesh/sharp_halfedges.m
index f0ab7756..19920bdf 100644
--- a/mesh/sharp_halfedges.m
+++ b/mesh/sharp_halfedges.m
@@ -26,7 +26,11 @@
 %        (dihedral angle > angle), and 0 otherwise. Indexing depends on the mode.
 %
 % Example:
-%   SHE = sharp_halfedges(V, F, pi/6, 'CyclicIndexing');
+%   SHE = sharp_halfedges(V, F, pi/2-0.0001);
+%   [EF, EI, uE, EMAP] = edge_flaps(F);
+%   % isSharpEdge - mask of undirected sharp edges in uE.
+%   isSharpEdge = zeros(size(uE,1),1);
+%   isSharpEdge(EMAP(SHE==1)) = 1;
 
   % Default mode
   mode = 'CornerIndexing';