Cut a hole tangent inside a stepped boss (zero-thickness curved wall) (#986)

Touching sews now split 4-use straight edges on extruded walls (along their rulings), not only on planes. Faces round such an edge are ordered by the way they leave it and, where they leave it tangent, by their curvature. Sheets bound the material wedges as before, except where that would make a face touch itself (a hole touching the outline from inside); edges ending there pair the empty wedges instead, so each loop gets its own vertex. Coincident faces are still refused, plain sew still refuses vertex contact, and shell_groups is unchanged.

A Ø10 hole tangent inside a stepped Ø40/Ø20 boss now cuts exactly instead of failing with "wire is not simple". Robustness seeds 42 and 51 are recorded: their touching hole patterns in stepped bodies now cut exactly instead of by a tool nudge.

Co-authored-by: froglemonade2 <[email protected]>

tests/robustness/goldens.json

@@ -43,7 +43,7 @@
   "39": {"area":1892.050815,"bodies":1,"edges":27,"error":null,"faces":11,"outcome":"ok","rejected":0,"shells":1,"steps":["extruded profile","chamfer","cut sphere","rectangular pattern"],"unsupported":1,"volume":4040.62787},
   "40": {"area":15548.516294,"bodies":1,"edges":49,"error":"offset: a corner whose faces don't meet the same way after t","faces":22,"outcome":"failed","rejected":0,"shells":1,"steps":["extruded profile","cut cylinder","shell","cut cylinder","join cylinder","shell"],"unsupported":0,"volume":16543.777532},
   "41": {"area":7611.393446,"bodies":1,"edges":99,"error":null,"faces":35,"outcome":"ok","rejected":1,"shells":1,"steps":["box","cut sphere","shell","fillet","cut cylinder","rectangular pattern","cut sphere","join cylinder"],"unsupported":1,"volume":5973.93328},
-  "42": {"area":5486.881252,"bodies":1,"edges":45,"error":null,"faces":17,"outcome":"ok","rejected":0,"shells":1,"steps":["extruded profile","cut box","cut cylinder","rectangular pattern"],"unsupported":0,"volume":19095.110963},
+  "42": {"area":5486.877622,"bodies":1,"edges":63,"error":null,"faces":20,"outcome":"ok","rejected":0,"shells":1,"steps":["extruded profile","cut box","cut cylinder","rectangular pattern"],"unsupported":0,"volume":19095.106157},
   "43": {"area":3492.988343,"bodies":1,"edges":72,"error":null,"faces":26,"outcome":"ok","rejected":2,"shells":1,"steps":["extruded profile","cut cylinder","rectangular pattern","fillet","hole","rectangular pattern","join cylinder"],"unsupported":1,"volume":7528.548742},
   "44": {"area":7972.435565,"bodies":1,"edges":36,"error":null,"faces":15,"outcome":"ok","rejected":0,"shells":1,"steps":["extruded profile","shell","cut sphere"],"unsupported":0,"volume":7622.184369},
   "45": {"area":14416.876392,"bodies":2,"edges":62,"error":"boolean Union: implausible result volume ","faces":29,"outcome":"failed","rejected":0,"shells":3,"steps":["revolved section","join cylinder","fillet","shell","cut box","join box"],"unsupported":1,"volume":14286.791174},
@@ -52,7 +52,7 @@
   "48": {"area":9651.031297,"bodies":1,"edges":66,"error":null,"faces":28,"outcome":"ok","rejected":0,"shells":1,"steps":["extruded profile","hole","circular pattern","join box","shell","cut box"],"unsupported":2,"volume":7044.773463},
   "49": {"area":7512.5,"bodies":1,"edges":24,"error":null,"faces":11,"outcome":"ok","rejected":0,"shells":1,"steps":["box","join box"],"unsupported":0,"volume":40546.875},
   "50": {"area":9387.513708,"bodies":2,"edges":48,"error":null,"faces":20,"outcome":"ok","rejected":1,"shells":2,"steps":["extruded profile","fillet","join cylinder","join cylinder","fillet","cut box","cut cylinder"],"unsupported":1,"volume":40128.140215},
-  "51": {"area":3316.022299,"bodies":1,"edges":51,"error":null,"faces":21,"outcome":"ok","rejected":0,"shells":1,"steps":["box","cut box","hole","rectangular pattern","chamfer","chamfer"],"unsupported":1,"volume":6812.582331},
+  "51": {"area":4230.232922,"bodies":1,"edges":66,"error":null,"faces":26,"outcome":"ok","rejected":1,"shells":2,"steps":["box","cut box","hole","rectangular pattern","chamfer","join box"],"unsupported":1,"volume":8742.066663},
   "52": {"area":7851.282527,"bodies":1,"edges":32,"error":null,"faces":14,"outcome":"ok","rejected":0,"shells":1,"steps":["box","shell","cut cylinder","chamfer","fillet"],"unsupported":0,"volume":5741.788461},
   "53": {"area":17168.464938,"bodies":1,"edges":110,"error":null,"faces":46,"outcome":"ok","rejected":1,"shells":4,"steps":["extruded profile","cut cylinder","shell","join cylinder","circular pattern","fillet"],"unsupported":0,"volume":16607.030819},
   "54": {"area":7080.555724,"bodies":4,"edges":90,"error":null,"faces":38,"outcome":"ok","rejected":0,"shells":4,"steps":["extruded profile","join box","circular pattern","cut cylinder","cut box","join cylinder","cut cylinder"],"unsupported":3,"volume":15737.224446},
@@ -110,6 +110,7 @@
   {"reason":"#921 with its grid lines kept to display and export meshes (Booleans mesh as before #921): measured volume and area move by about 1e-6 (seed 94 also as in #936)","seeds":[22,78,94]},
   {"reason":"a hole placed on a face without a direction drills into that face (it took the direction from any face whose plane passed through the point, the last one found, such as a side of a patterned box standing on the point's plane): the holes on these seeds now go straight in (#950)","seeds":[7,21,85]},
   {"reason":"the last-resort tool nudge is tried the other way when it fails or leaves sliver faces the operands didn't have: seed 43's join builds and the design runs to the end, 31 and 78 come out with fewer faces (#827, #897)","seeds":[31,43,78]},
-  {"reason":"main's fillet changes since the last record (#926, #949) move seeds 33 and 91: a fillet step builds differently or is picked differently","seeds":[33,91]}
+  {"reason":"main's fillet changes since the last record (#926, #949) move seeds 33 and 91: a fillet step builds differently or is picked differently","seeds":[33,91]},
+  {"reason":"hole tangent inside a stepped boss: touching sews split zero-thickness curved walls, so a pattern of holes spaced by their diameter (touching) in a stepped body cuts exactly instead of by a tool nudge: 42 builds more faces (the walls split where the holes touch), 51 picks other edges afterwards","seeds":[42,51]}
  ]
 }