wip

@@ -250,3 +251,3 @@
 
         for (const int inner_edge :
-             poly_edges.slice(poly_loop_index, poly_edges.size() - poly_loop_index)) {
+             poly_edges.slice(poly_loop_index, poly_edges.size() - poly_loop_index))

@@ -348,6 +350,196 @@ void paintface_select_linked(bContext *C, Object *ob, const int mval[2], const b
   paintface_flush_flags(C, ob, true, false);
 }
 
+static int get_closest_edge_index(ARegion *region,

@@ -351,0 +353,4 @@
+static int get_closest_edge_index(ARegion *region,
+                                  blender::Span<blender::int2> edges,
+                                  blender::Span<int> poly_edges,
+                                  blender::Span<blender::float3> verts,

@@ -351,0 +359,4 @@
+  using namespace blender;
+  int closest_edge_index;
+
+  const float mval_f[2] = {float(mval[0]), float(mval[1])};

@@ -351,0 +366,4 @@
+    const int2 edge = edges[i];
+    const float3 v1 = verts[edge[0]];
+    const float3 v2 = verts[edge[1]];
+    float3 edge_vert_average;

@@ -351,0 +383,4 @@
+  return closest_edge_index;
+}
+
+static int get_opposing_edge_index(blender::IndexRange &poly,

@@ -351,0 +387,4 @@
+                                   const blender::Span<int> corner_edges,
+                                   const int current_edge_index)
+{
+  for (int i = 0; i < poly.size(); i++) {

@@ -351,0 +396,4 @@
+    if (i - 2 >= 0) {
+      return corner_edges[poly[i - 2]];
+    }
+    else {

@@ -351,0 +403,4 @@
+  return -1;
+}
+
+/* Follow quads around the mesh by finding opposing edges. Bool return value indicates if the whole

@@ -351,0 +407,4 @@
+ * loop has been traced. */
+static bool follow_face_loop(const int poly_start_index,
+                             const int edge_start_index,
+                             const blender::offset_indices::OffsetIndices<int> polys,

@@ -351,0 +408,4 @@
+static bool follow_face_loop(const int poly_start_index,
+                             const int edge_start_index,
+                             const blender::offset_indices::OffsetIndices<int> polys,
+                             const blender::VArray<bool> hide_poly,

@@ -351,0 +410,4 @@
+                             const blender::offset_indices::OffsetIndices<int> polys,
+                             const blender::VArray<bool> hide_poly,
+                             const blender::Span<int> corner_edges,
+                             blender::Vector<int> &r_loop_polys,

@@ -351,0 +411,4 @@
+                             const blender::VArray<bool> hide_poly,
+                             const blender::Span<int> corner_edges,
+                             blender::Vector<int> &r_loop_polys,
+                             const blender::Array<blender::Vector<int, 2>> edge_to_poly_map)

@@ -351,0 +419,4 @@
+
+  while (current_edge_index > 0) {
+    int next_poly_index;
+    bool found_poly = false;

@@ -351,0 +440,4 @@
+    }
+
+    /* Happens if we looped around the mesh. */
+    if (r_loop_polys.contains(next_poly_index)) {

@@ -351,0 +473,4 @@
+
+  /* Need to use the evaluated mesh for projection to region space. */
+  Scene *scene_eval = DEG_get_evaluated_scene(vc.depsgraph);
+  Mesh *mesh_eval = mesh_get_eval_final(vc.depsgraph, scene_eval, ob_eval, &CD_MASK_BAREMESH);

@@ -351,0 +493,4 @@
+  const OffsetIndices polys = mesh->polys();
+  const Span<int2> edges = mesh->edges();
+
+  IndexRange poly = polys[poly_pick_index];

@@ -351,0 +509,4 @@
+  const VArray<bool> hide_poly = *attributes.lookup_or_default<bool>(
+      ".hide_poly", ATTR_DOMAIN_FACE, false);
+
+  Vector<int, 2> polys_to_closest_edge = edge_to_poly_map[closest_edge_index];

@@ -368,6 +368,7 @@ void PAINT_OT_face_select_all(wmOperatorType *ot);
 void PAINT_OT_face_select_more(wmOperatorType *ot);
 void PAINT_OT_face_select_less(wmOperatorType *ot);
 void PAINT_OT_face_select_hide(wmOperatorType *ot);
+void PAINT_OT_face_select_loop(struct wmOperatorType *ot);

@@ -4481,2 +4481,4 @@
         ("paint.face_select_more", {"type": 'NUMPAD_PLUS', "value": 'PRESS', "ctrl": True}, None),
         ("paint.face_select_less", {"type": 'NUMPAD_MINUS', "value": 'PRESS', "ctrl": True}, None),
+        ("paint.face_select_loop", {"type": "LEFTMOUSE", "value": 'PRESS', "alt": True}, None),
+        ("paint.face_select_loop", {"type": "LEFTMOUSE", "value": 'PRESS', "alt": True, "shift": True},

@@ -250,3 +252,3 @@
 
         for (const int inner_edge :
-             poly_edges.slice(poly_loop_index, poly_edges.size() - poly_loop_index)) {
+             poly_edges.slice(poly_loop_index, poly_edges.size() - poly_loop_index))

@@ -351,0 +385,4 @@
+                                   const blender::Span<int> corner_edges,
+                                   const int current_edge_index)
+{
+  for (int i = 0; i < poly.size(); i++) {

@@ -351,0 +449,4 @@
+
+    r_loop_polys.append(next_poly_index);
+
+    IndexRange next_poly = polys[next_poly_index];

@@ -351,0 +471,4 @@
+  }
+
+  uint poly_pick_index = uint(-1);
+  if (!ED_mesh_pick_face(C, ob_eval, mval, ED_MESH_PICK_DEFAULT_FACE_DIST, &poly_pick_index)) {

@@ -351,0 +496,4 @@
+
+  Array<int> edge_to_loop_offsets;
+  Array<int> edge_to_loop_indices;
+  const GroupedSpan<int> edge_to_loop_map = bke::mesh::build_edge_to_loop_map(

@@ -351,0 +528,4 @@
+  bke::SpanAttributeWriter<bool> select_poly = attributes.lookup_or_add_for_write_span<bool>(
+      ".select_poly", ATTR_DOMAIN_FACE);
+
+  for (const int poly_index : polys_to_select) {

@@ -351,0 +381,4 @@
+  return closest_edge_index;
+}
+
+static int get_opposing_edge_index(blender::IndexRange poly,

@@ -351,0 +385,4 @@
+                                   const blender::Span<int> corner_edges,
+                                   const int current_edge_index)
+{
+  const int poly_index = corner_edges.slice(poly).first_index(current_edge_index);

@@ -351,0 +410,4 @@
+  int current_poly_index = poly_start_index;
+  int current_edge_index = edge_start_index;
+
+  VectorSet<int> vector_set;