BOPAlgo_PaveFiller_6.cxx: protection against creation of thin faces is added
bug29580_1: reverting in original state
dimensions.tcl: correction according to current state of BO algorithm
Implement alternative approach for making the edge seam (closed) on the face. This approach is useful for non-periodic surfaces (e.g. tore-like surface of revolution is periodic in U direction only).
Avoid internal faces in the affected solids of the result of BOP Fuse.
BOPAlgo_PaveFiller::MakeBlocks() - Improve Face/Face post treatment procedure by:
* Adding more existing edge for intersection with section edges to resolve all possible intersections.
* Using tree for edges selection.
* Avoiding intersection of the existing edges among themselves.
IntPatch_ImpImpIntersection::CyCyNoGeometric - add more points to wline to make it more smooth.
Progress indication mechanism is refactored to support incrementing progress within multithreaded algorithms.
The class Message_ProgressIndicator is only an interface to the user application.
It accumulates the progress provided by progress scopes.
The counter is protected by mutex for thread-safety.
The new class Message_ProgressScope replacing Message_ProgressSentry should be used to advance the progress.
The scopes are nested to each other to reflect the nested nature of operations.
The new class Message_ProgressRange should be used to pass the progress to sub-scopes.
All OCCT algorithms involving progress indication have been updated to new API.
Improvements in Draw_ProgressIndicator:
- Separate console mode has been added in order to make possible to put the progress into std::cout instead
or in addition to the draw interpreter, instead of trigger option "-tclOutput".
- Treatment of Ctrl-Break signal has been added.
Now any operation can be aborted by Ctrl-C or Ctrl-Break keystroke.
Added new test case 'perf fclasses progr_par' for testing of parallel work of the progress.
Extrema_ExtCS.cxx: treatment of small line segments is added;
Extrema_GenExtCS.cxx: treatment of particular cases curve-quadric and conic-surface are added
Extrema_GlobOptFuncCQuadric, Extrema_GlobOptFuncConicS: new distance functions for particular cases are added
BOPAlgo_PaveFiller_5.cxx : treatment of large common parts edge-face is improved
ElSLib.cxx : method TorusParameters(...) is modified to avoid divide by zero
math_PSOParticlesPool.cxx : initialization of array is added
Eliminate numerical instability by ensuring that the tolerance of intersection entities is slightly grater than the actual distance to the shapes creating the entity.
Get rid of requirement for the arguments of Boolean operations of type CUT and COMMON to be one-dimensional shape. For FUSE operation this requirement is kept.
When splitting the shell/face with internal faces/edges use the 'internal' criteria of the face to choose the way to create loops.
Side effect changes:
- When performing Boolean operation - move the objects located far from Origin to the Origin to increase the accuracy of intersections.
Modification in static method BoundedArc of IntStart_SearchOnBoundaries:
add exact intersection of canonical curve-surface (when Func is IntPatch_ArcFunction).
The following improvements have been made in Boolean operations algorithm:
1. Added possibility to update FaceInfo structure for many faces at once which helps to avoid nested loops.
2. Improve Point-Face classification procedure by caching the FaceExplorer for a face.
The capabilities of the class BRepOffsetAPI_MakeEvolved have been extended with involving alternate algorithm of resolving the loops in the piped shape. The new option theIsVolume is added for that in the constructor.
New class BRepFill_AdvancedEvolved has been created in order to provide new OCCT-algorithm combining BRepFill_PipeShell and BOPAlgo_MakerVolume.
A change in BOPAlgo_PaveFiller.cxx has been made in order to solve a specific problem of Boolean operation.
The interface of DRAW-command "evolved" has been updated to add the new option. DRAW-command "evolvedsolid" has been deleted. Now it is replaced with DRAW-command "evolved" with the option "-solid".
Testgrid "evolved" has been created.
OSD_Parallel::ToUseOcctThreads() - new flag allowing to use OCCT threads implementation even when compiled with TBB (for testing).
Added new command dparallel for managing default Thread Pool.
OSD_Parallel::For() now avoid creation of universal iterator in simplest case.
BOPTools_Parallel - eliminated redundant typedefs/explicit instantiations of templates.
Added functor using array of per-thread context instead of a map.
Implementation of the new class *BOPAlgo_MakeConnected* for making the group of touching same-dimensional shapes connected.
Provide the material association for the first sub-elements of the input shapes.
Provide possibility to make the connected shape periodic.
Draw commands for new algorithm:
* makeconnected - make the input shapes connected or glued, performs material associations;
* cmaterialson - returns the materials located on the requested side of a shape;
* cmakeperiodic - makes the connected shape periodic in requested directions;
* crepeatshape - repeats the periodic connected shape in requested directions requested number of times;
* cperiodictwins - returns all periodic twins for the shape;
* cclearrepetitions - clears all previous repetitions of the periodic shape, keeping the shape periodic.
Documentation & test cases for the new algorithm.
Implementation of the new class *BOPAlgo_MakePeriodic* for making the shape periodic in 3D space.
Periodicity of the shape means that the shape can be repeated in any periodic direction any number of times without creation of the new geometry or splits.
The idea of this algorithm is to make the shape look similarly on the opposite sides or on the period bounds of periodic directions.
It does not mean that the opposite sides of the shape will be mirrored. It just means the the opposite sides of the shape should be split by each other and obtain the same geometry on opposite sides.
Such approach will allow repeating the shape, i.e. translating the copy of a shape on the period, without creation of new geometry because there will be no coinciding parts of different dimension.
Draw commands for the new algorithm:
* makeperiodic - makes the shape periodic in required directions;
* repeatshape - repeats the periodic shape in requested periodic direction;
* periodictwins - returns the periodic twins for the shape;
* clearrepetitions - clears all previous repetitions of the periodic shape.
Documentation & test cases for the algorithm.
Boolean Operations - Force the face with internal edges to be treated by the BuilderFace algorithm. It is needed for the cases when internal edges of the face go from side to side and should really split the face.
Test case for the issue.
Provide possibility to perform Boolean operations on open solids.
Implementation of the new method *BOPAlgo_Builder::BuildBOP* performing the construction of the result shape for the given type of Boolean operation.
This approach does not rely on the splits of solid to be correct and looks for the faces with necessary state relatively opposite solids to build the result solid.
The call to this method is performed from BOP algorithm in case there were open solids in the arguments.
Implementation of the draw command *buildbop* performing a call to the method above.
The following improvements have been made in Boolean operations algorithm in order to fix the problem:
1. Initialization of the pave blocks which vertices have acquired the SD ones.
2. Removing from Data Structure the small edges having the same vertices on both ends (either initially or acquired).
3. Avoid adding empty SD connections when one vertex points to itself.
Test case for the issue.
The following improvements have been introduced in Boolean Operations algorithm s:
1. UBTree is replaced with EBTree in Boolean operations to be able to add/remove elements into the tree of bounding boxes.
2. Repeated (nested) intersection of sub-shapes is performed with argument vertices whose tolerances increased during the operation.
3. The algorithms of Edge/Edge and Edge/Face intersection have been improved for the cases when the intersection point is located close to the edge boundaries .
4. New procedure has been implemented to ensure forced creation of Edge/Face common blocks in cases when the edge is really close to the face.
5. Post-processing of Face/Face intersection results has been improved.
6. Extension of the planar faces for Plane/Plane intersection is avoided.
7. Builder Face now better classifies potentially internal edges relatively to new faces with filtering by bounding boxes.
Side effect changes:
1. IntTools_ShrunkRange now keeps the length of the valid range of the edge.
2. The method BOPDS_DS::UpdateEdgeTolerance() has been removed as unused (replaced by the BOPAlgo_PaveFiller::UpdateEdgeTolerance()).
Test case for the issue 0029900.
Test case for the issue 0029711.
Adjustments of the existing test cases.
Avoid using uninitialized variables.
Fast rebuilding of the face is now avoided if its edges have been unified during the intersection.
Full rebuilding of the face is required in this case (using BuilderFace algorithm).
TopoDS_Shape::NbChildren() - new method has been introduced.
TopoDS_Shape.lxx, TopoDS_TShape.lxx - inline methods have been moved to hxx.
TopoDS_TShape_Flags has been redeclared as enumeration instead of preprocessor macros.
Cyclic dependency between headers TopoDS_Shape.hxx and TopoDS_TShape.hxx eliminated.
Places where TopoDS_Iterator is used only for calculation of number of sub-shapes are updated to use NbChildren() instead
Modified method: Approx_ComputeLine::Compute
Check of multicurve is now always unconditional, the procedure of check is modified to avoid infinite loops.
Modified classes: GeomLib_CheckBSplineCurve and GeomLib_Check2dBSplineCurve
Correction of poles at the ends of curve is modified to fit the direction of tangent defined by two first points or two last points of walking line.
Also modified:
BOPAlgo_PaveFiller: modified methods PostTreatFF, RemoveUsedVertices - now unused vertices are included in the list of vertices to be absorbed by other ones.
Implementation of the method for simplification of the result of Boolean Operation on the API level.
The method BRepAlgoAPI_BuilderAlgo::SimplifyResult has been added, so the derived classes such as BooleanOpeation and Splitter can also use this method.
The result shape simplification should be called after the operation is done. The simplification is performed by the means of ShapeUpgrade_UnifySameDomain algorithm.
Draw command "bsimplify" has been added to control the simplification options.
Documentation for new functionality and draw commands controlling the options of Boolean operations.
Test cases for the new functionality.
Side-effect change:
The algorithms in Boolean component have been changed to use the BRepTools_History as a History tool.
Now it became possible to disable the collection of shapes modifications during Boolean Operations, which may be useful for performance sake (in draw the option is controlled by *setfillhistory* command).
Draw command "unifysamedom" has been changed to accept the angular tolerance in degrees instead of radians.
When checking if the split edge is oriented as the original one (BOPTools_AlgoTools::IsSplitToReverse()) the tangent vectors should be computed for both edges at the same point. This point is taken on the split edge and projected on the original edge.
The fix is intended to ensuring that the reference point will be taken inside the valid range of the split edge (i.e. not covered by the tolerance spheres of its bounding vertices) and the projection of this point on the original edge will be successful. Moreover, several sampling points are now taken on the split edge and processed until first valid point is found.
If requested (by a not null pointer) all *BOPTools_AlgoTools::IsSplitToReverse()* methods are now return the error status of the check. Before using the returned flag, the calling program should check this error status. For successful check the error status should be equal to zero.
New warning *BOPAlgo_AlertUnableToOrientTheShape* is now returned in the algorithms in Boolean component in case the check for correct shape orientation failed.
Test case for the issue.
Implementation of the mechanism for unification of the history commands for all OCCT algorithms.
The following Draw commands should be used to track the history of shapes modifications of any operation:
- modified - to find the shapes modified from the given shape in the given history.
- generated - to find the shapes generated from the given shape in the given history.
- isdeleted - to check if the given shape has been deleted during operation.
The mechanism allows fast & easy enabling of the DRAW history support for the algorithms supporting the history on the API level (i.e. the algorithm should have the methods Modified(), Generated() and IsDeleted()).
To enable the draw history support it is necessary to store the history of the algorithm into the session. For instance:
TopTools_ListOfShape Objects = ...; // Objects
TopTools_ListOfShape Tools = ...; // Tools
BRepAlgoAPI_Cut aCut(Objects, Tools); // Boolean cut operation
BRepTest_Objects::SetHistory(Objects, aCut); // Store the history for the Objects (overwrites the history in the session)
BRepTest_Objects::AddHistory(Tools, aCut); // Add the history for the Tools
To get the stored history in draw the command "savehistory" should be used. It saves the history kept in session into a Drawable object with the given name:
# perform cut
bcut r s1 s2
# save history of cut
savehistory cut_history
explode s1 f
modified m cut_history s1_1
The Draw History commands of the following algorithms have been removed:
- Boolean Operations;
- Defeaturing;
- Unify same domain;
- Sweep;
- Thrusections;
All these algorithms have been switched to support the new Draw history mechanism.
The Fillet and Blend algorithms have been also enabled to support history commands.
Boolean Operations - when splitting the face by the intersections with other arguments check if the face (e.g. really thin one) can be split by a vertex. In this case avoid simple face reconstruction and use the BuilderFace algorithm to split the face.
Test case for the issue.
Boolean operations - Allow repeated intersection of edges to find the coinciding pairs.
Previously, only the edges rejected by bounding boxes classification has been additionally checked on coincidence. The current patch removes this filter allowing all edges with coinciding vertices to be checked on coincidence.
Adjustment of the test cases for current behavior:
1. The following cases are improvements:
boolean volumemaker A8
bugs modalg_1 buc60703_1
bugs modalg_1 buc60703_2
bugs modalg_1 buc60703_4
bugs modalg_6 bug26789_1
bugs modalg_6 bug26789_2
bugs modalg_7 bug26883_4
bugs modalg_7 bug27948
2. bugs modalg_7 bug29580_1 is modified to extend the validity checks.
All occurrences of Standard_EXPORT attached to inline methods in OCCT code are eliminated.
Some unused classes and C++ files producing no code are deleted.
Boolean Operation - avoid creation of INTERNAL solid from unclassified faces in Solid Builder algorithm.
Instead warn the user that some of the faces have been unclassified and not used for solids creation.
Adjustment of the test cases.
Test cases for the issue.
Implementation of the 3D model De-featuring algorithm intended for the removal of the unwanted parts (or features) from the model consisting of solids. The features can be the holes, protrusions, gaps, chamfers, fillets etc.
The algorithm removes all possible requested features from the shape and builds the new shape as a result. The input model is not modified.
On the API level the algorithm is implemented in the class *BRepAlgoAPI_Defeaturing*. The actual features removal is performed by the low-level algorithm *BOPAlgo_RemoveFeatures*.
Documentation of the new classes.
Implementation of the DRAW commands for working with new algorithm.
Test cases for the new functionality.
Changes in other algorithms used by De-featuring algorithm:
- Provide history support for the solids in *ShapeUpgrade_UnifySameDomain* algorithm;
- Implementation of the mechanism to merge History of any Algorithm with standard history methods such as IsDeleted(), Modified() and Generated() into *BRepTools_History*.
The usage of *BRepAlgo_Section* has been replaced with the usage of *BRepAlgoAPI_Section* in *BRepProj_Projection* algorithm.
The TODO statements have been removed from the failing test case in the "prj" grid as they are working correctly now.
The following changes have been made to improve the performance *BRepAlgoAPI_Section*:
1. Revision of the *IntPolyh_Intersection* class to avoid repeated calculation of the deflection of the same triangulation.
2. Small revision of the Edge/Face intersection algorithm to perform Extrema computation on the whole intersection range of the edge instead of discrete ranges.
3. Implementation of the extrema computation for the Circle and Sphere.
4. Correct computation of the parameter of the point on the Circle.
In the algorithm math_FunctionRoots, improve the case when it is needed to find the extremum of the function. Earlier, to solve this task the method of gold section was used. With the patch, firstly the algorithm tries to find zero value of the derivative function. In most cases it gives precise result. Secondly, the algorithm tries to find zero value of the function using the old approach. The algorithm chooses the best solution among two computed by different methods.
In the method PutStickPavesOnCurve of BOPAlgo_PaveFiller, forbid putting a vertex to the end of the curve if this end already has a vertex assigned to it. This allows getting rid of unwanted colliding of vertices.
In the method UpdatePaveBlocks of BOPAlgo_PaveFiller, make the check for micro edges more precise.
New category of tests "lowalgos" has been added. Tests for low level algorithms are to be put there. "2dinter" is a new group of tests in this category.
Introduction of the new key for "2dintersect" command, allowing printing the intersection state for each point.
It has the following syntax now:
"2dintersect curve1 [curve2] [-tol tol] [-state]"
Options:
-tol - allows changing the intersection tolerance (default value is 1.e-3);
-state - allows printing the intersection state for each point.
Correct the test case bugs/modalg_7/bug28274 to make proper checks of the result.
1. Implementation of the *Generated* method for the algorithms in Boolean Component.
In terms of these algorithms the shape from the arguments can have Generated shapes only if these new shapes have been obtained as a result of pure intersection (not overlapping) of this shape with any other shapes from arguments.
Thus, the Generated shapes are always:
* VERTICES created from the intersection points and may be Generated from edges and faces only;
* EDGES created from the intersection edges and may be Generated from faces only.
So, only EDGES and FACES could have information about Generated shapes. For all other types of shapes the list of Generated shapes will be empty.
2. Optimization and simplification of the Modified and IsDeleted methods based on the correct filling of the BOPAlgo_BuilderShape::myImagesResult map.
3. Provide history of unification of the solids in the CellsBuilder algorithm.
4. Update of the documentation of Boolean Operations User guide with new chapter "History Information" describing rules for filling history for operations in Boolean Component.
5. Test cases for the issue. New grid "history" has been added into "boolean" category.
Usage of Bnd_Box-filtering is eliminated while putting a (definitely) common vertex between two faces on the intersection curve.
Algorithm of putting not-common (ON/IN) vertices has not been changed.
1. Implementation of the user-defined option for usage of Oriented Bounding Boxes (OBB) in Boolean Operations for additional filtering (rejection) of selected for intersection pairs of sub-shapes.
By default the usage of OBB is turned off.
To enable/disable its usage the method SetUseOBB(flag) should be used. This method is available for all operations in Boolean Component.
To enable/disable it in draw the command "buseobb 0/1" should be used. Note, that this will affect all subsequent operations.
The OBB for the shapes are built by first necessity and stored into operation context (IntTools_Context).
2. Usage of the OBB in some test cases.
Prevent modification of the input shapes in destructive mode in case their sub-shapes have not been modified:
1. Prevent edge splitting for the pave blocks with old vertices if it is possible to use the existing edge (*BOPAlgo_PaveFiller::MakeSplitEdges*);
2. Prevent creation of the new containers (WIRES/SHELLS/COMPSOLIDS) if non of its parts have been modified (*BOPAlgo_Builder::FillImagesContainer*);
3. Prevent creation of the new face if non of its wires have been modified (*BOPAlgo_Builder::FillImagesFaces*);
4. If possible, use the original face to be the representative for the group of SD faces (*BOPAlgo_Builder::FillSameDomainFaces*).
Cosmetic changes:
1. Documentation of the *BOPAlgo_Builder* class.
2. Making simple methods of the *BOPAlgo_Builder* class inline.
3. Getting rid of the *BOPAlgo_Builder::mySplits* field as it is excessive. *BOPAlgo_Builder::myImages* can be used instead.
3. Moving the Check Inverted option from *BOPAlgo_Options* to *BOPAlgo_Builder*.
Test cases for the issue.
Adjustment of the test case to their current behavior.
Test case *blend/complex/H2* has been deleted as duplicate of the test case *blend/simple/Z1*.
1. The package BOPCol has been fully removed:
- *BOPCol_BaseAllocator* is replaced with *Handle(NCollection_BaseAllocator)*;
- *BOPCol_BoxBndTree* is replaced with *BOPTools_BoxBndTree*;
- *BOPCol_Box2DBndTree* is removed as unused;
- *BOPCol_DataMapOfIntegerInteger* is replaced with *TColStd_DataMapOfIntegerInteger*;
- *BOPCol_DataMapOfIntegerListOfInteger* is replaced with *TColStd_DataMapOfIntegerListOfInteger*;
- *BOPCol_DataMapOfIntegerListOfShape* is replaced with *TopTools_DataMapOfIntegerListOfShape*;
- *BOPCol_DataMapOfIntegerMapOfInteger.hxx* is removed as unused;
- *BOPCol_DataMapOfIntegerReal* is replaced with *TColStd_DataMapOfIntegerReal*;
- *BOPCol_DataMapOfIntegerShape* is replaced with *TopTools_DataMapOfIntegerShape*;
- *BOPCol_DataMapOfShapeBox* is replaced with *TopTools_DataMapOfShapeBox*;
- *BOPCol_DataMapOfShapeInteger* is replaced with *TopTools_DataMapOfShapeInteger*;
- *BOPCol_DataMapOfShapeListOfShape* is replaced with *TopTools_DataMapOfShapeListOfShape*;
- *BOPCol_DataMapOfShapeReal* is replaced with *TopTools_DataMapOfShapeReal*;
- *BOPCol_DataMapOfShapeShape* is replaced with *TopTools_DataMapOfShapeShape*;
- *BOPCol_DataMapOfTransientAddress* is removed as unused;
- *BOPCol_IndexedDataMapOfIntegerListOfInteger* is removed as unused;
- *BOPCol_IndexedDataMapOfShapeBox* is removed as unused;
- *BOPCol_IndexedDataMapOfShapeInteger* is removed as unused;
- *BOPCol_IndexedDataMapOfShapeListOfShape* is replaced with *TopTools_IndexedDataMapOfShapeListOfShape*;
- *BOPCol_IndexedDataMapOfShapeReal* is removed as unused;
- *BOPCol_IndexedDataMapOfShapeShape* is replaced with *TopTools_IndexedDataMapOfShapeShape*;
- *BOPCol_IndexedMapOfInteger* is replaced with *TColStd_IndexedMapOfInteger*;
- *BOPCol_IndexedMapOfOrientedShape* is replaced with *TopTools_IndexedMapOfOrientedShape*;
- *BOPCol_IndexedMapOfShape* is replaced with *TopTools_IndexedMapOfShape*;
- *BOPCol_ListOfInteger* is replaced with *TColStd_ListOfInteger*;
- *BOPCol_ListOfListOfShape* is replaced with *TopTools_ListOfListOfShape*;
- *BOPCol_ListOfShape* is replaced with *TopTools_ListOfShape*;
- *BOPCol_MapOfInteger* is replaced with *TColStd_MapOfInteger*;
- *BOPCol_MapOfOrientedShape* is replaced with *TopTools_MapOfOrientedShape*;
- *BOPCol_MapOfShape* is replaced with *TopTools_MapOfShape*;
- *BOPCol_PListOfInteger* is removed as unused;
- *BOPCol_PInteger* is removed as unused
- *BOPCol_SequenceOfPnt2d* is replaced with *TColgp_SequenceOfPnt2d*;
- *BOPCol_SequenceOfReal* is replaced with *TColStd_SequenceOfReal*;
- *BOPCol_SequenceOfShape* is replaced with *TopTools_SequenceOfShape*;
- *BOPCol_Parallel* is replaced with *BOPTools_Parallel*;
- *BOPCol_NCVector* is replaced with *NCollection_Vector*;
2. The class *BOPDS_PassKey* and containers for it have been removed as unused;
3. The unused containers from *IntTools* package have been removed:
- *IntTools_DataMapOfShapeAddress* is removed as unused;
- *IntTools_IndexedDataMapOfTransientAddress* is removed as unused;
4. The container *BiTgte_DataMapOfShapeBox* is replaced with *TopTools_DataMapOfShapeBox*;
5. The class *BOPTools* has been removed as duplicate of the class *TopExp*;
1. Unify the faces classification procedure of the methods BOPAlgo_BuilderSolid::PerformInternalShapes() and BOPAlgo_Builder::FillIn3DParts() using the latter as a base.
The new method BOPAlgo_Tools::ClassifyFaces() has been created for that. Both methods mentioned above have been updated to use the new one.
2. Forced intersection of the edges after enlarge of the tolerance values of their vertices during the operation has been added into BOP's intersection algorithm (BOPAlgo_PaveFiller).
BOPAlgo_Tools::PerformCommonBlocks() method has been updated to avoid loosing faces of the already created Common blocks.
As a result the case "boolean gdml_private ZF6" became more stable, because the intermediate result is no longer invalid.
Additional test cases have been added to verify this improvement (bugs modalg_7 bug29322_*)
3. When building PCurves for edges on faces, check the existing PCurves on its validity for periodic surfaces and adjust PCurves if necessary.
The improvement helps to produce the valid result in the test case "bugs moddata_1 bug152".
4. Avoid creation of empty Edge-Edge interference if the intersection point is lying close to a shared vertex.
The improvement helps obtain the valid result of the "bopcheck" operation in the test case "bugs modalg_7 bug27683".
Adjustment of the test case to current behavior:
- Avoid usage of the self-intersecting torus in the test case "boolean gdml_public A9".
- Fix the input shape in the test case "boolean bopfuse_complex H1" to provide valid result.
- Test cases "bugs moddata_1 bug152_1 bug152_2" have been unified into single test case "bugs moddata_1 bug152". Now, the case rebuilds invalid input data and performs all types of Boolean operations.
- Change the test case "bugs modalg_7 bug22750" to produce valid intermediate results used in subsequent operations as arguments.
- The following test cases are improvements:
- "boolean volumemaker D8"
- "boolean volumemaker G1"
- "bugs modalg_7 bug27683"
Make the algorithm BRepOffsetAPI_NormalProjection use section operation instead of common to get the edge-result of projection to be in face restrictions.
Correct Boolean operation algorithm to produce correctly oriented result in the case of common between face and edge.
The algorithm ShapeUpgrade_UnifySameDomain has been patched to correctly gather same domain faces in a compound.
The TCL script snowflake.tcl has been corrected to get rid of dependence on the order of edges in the result of Boolean operation.
