bonsai: allow overriding which classes join in section linework (#4395) (#8617)

Fixes #4395.

Root cause: the SVG cut-linework merge step that fuses adjacent
elements' cut polygons together (per the pset-driven JoinCriteria
setting) was hardcoded to only IfcWall and IfcSlab. IfcCovering cut
shapes were skipped unconditionally, so adjacent coverings never
joined, leaving a visible seam/broken corner in section drawings
regardless of JoinCriteria.

Fix: added an EPset_Drawing.JoinClasses property, following the
exact same user-overridable pattern already used by
EPset_Drawing.BringToFront - a comma-separated list of IFC classes
to join, defaulting to "IfcWall,IfcSlab" (unchanged behavior) when
unset. Users can override per-drawing to add IfcCovering (or any
other class) when they want it joined too. Kept this opt-in rather
than hardcoding IfcCovering into the default list, since joining a
thin finish layer the same way as a thick wall/slab could produce
unwanted mitring in some cases - the user decides per drawing.

Verified live against the reporter's own attached file
(ifcovering joining.ifc) and its cached section linework: with
JoinClasses unset, two separate closed paths reproduce the reported
seam exactly. With JoinClasses = "IfcWall,IfcSlab,IfcCovering", the
two coverings merge into a single closed polygon with the internal
seam removed. Confirmed IfcSlab join behavior is unchanged in both
runs.

Generated with the assistance of an AI coding tool.

Co-authored-by: Dion Moult <dionmoult@gmail.com>
(cherry picked from commit c55a79b8b5)

src/bonsai/bonsai/bim/data/pset/EPset_Drawing.ifc

@@ -5,7 +5,7 @@ FILE_NAME('EPset_Drawing.ifc','2020-01-01T00:00:00',$,$,'EPset_Drawing','EPset_D
 FILE_SCHEMA(('IFC4'));
 ENDSEC;
 DATA;
-#1=IFCPROPERTYSETTEMPLATE('2JhNIvqZrFnAgxfhK0XVQX',$,'EPset_Drawing','',.PSET_OCCURRENCEDRIVEN.,'IfcAnnotation/DRAWING',(#23,#22,#27,#24,#29,#30,#19,#12,#26,#9,#8,#7,#6,#4,#18,#11,#5,#20,#25,#14,#10,#17,#28,#16,#3,#21,#13,#15,#2,#31,#32,#33,#34,#35,#36));
+#1=IFCPROPERTYSETTEMPLATE('2JhNIvqZrFnAgxfhK0XVQX',$,'EPset_Drawing','',.PSET_OCCURRENCEDRIVEN.,'IfcAnnotation/DRAWING',(#23,#22,#27,#24,#29,#30,#19,#12,#26,#9,#8,#7,#6,#4,#18,#11,#5,#20,#25,#14,#10,#17,#28,#16,#3,#21,#13,#15,#2,#31,#32,#33,#34,#35,#36,#37));
 #2=IFCSIMPLEPROPERTYTEMPLATE('23JavTMk98ZxXhrUEnjAcf',$,'TargetView','',.P_SINGLEVALUE.,'IfcLabel',$,$,$,$,$,.READWRITE.);
 #3=IFCSIMPLEPROPERTYTEMPLATE('1yVWUt5H9DAOuu0OaMMLpe',$,'Scale','The scale of this drawing represented as a numerator and denominator, such as 1/100',.P_SINGLEVALUE.,'IfcLabel',$,$,$,$,$,.READWRITE.);
 #4=IFCSIMPLEPROPERTYTEMPLATE('3gsuPBtU93b8f0gg1pjkq6',$,'HumanScale','The scale of this drawing in human readable format, such as 1:100',.P_SINGLEVALUE.,'IfcLabel',$,$,$,$,$,.READWRITE.);
@@ -41,5 +41,6 @@ DATA;
 #34=IFCSIMPLEPROPERTYTEMPLATE('2epSGfC4bFM9gb1X7zBIp4',$,'RenderSharp','Whether to render ''sharp'' (convex) edges. Only relevant when UseEdgeClassification is enabled.',.P_SINGLEVALUE.,'IfcBoolean',$,$,$,$,$,.READWRITE.);
 #35=IFCSIMPLEPROPERTYTEMPLATE('3TZwsEjkr5WRDKcgrYzSIA',$,'RidgeAngleMinDegrees','Minimum convex dihedral deviation from flat, in degrees, for a projection edge to be classified as ''sharp'' rather than ''flush''.',.P_SINGLEVALUE.,'IfcReal',$,$,$,$,$,.READWRITE.);
 #36=IFCSIMPLEPROPERTYTEMPLATE('2Jua$lO754vgZOkBoHM2gA',$,'RenderFlush','Whether to render ''flush'' edges (dihedral deviation below both ridge/valley thresholds). Only relevant when UseEdgeClassification is enabled.',.P_SINGLEVALUE.,'IfcBoolean',$,$,$,$,$,.READWRITE.);
+#37=IFCSIMPLEPROPERTYTEMPLATE('1zM9sia2L8RQDnWZxgUwlZ',$,'JoinClasses','Comma separated list of IFC classes whose cut linework will be joined together when they meet (e.g. mitred at a corner).\X2\000A\X0\Defaults to ''IfcWall,IfcSlab'' if not set. Override to also join other classes, such as ''IfcWall,IfcSlab,IfcCovering''.',.P_SINGLEVALUE.,'IfcText',$,$,$,$,$,.READWRITE.);
 ENDSEC;
 END-ISO-10303-21;

src/bonsai/bonsai/bim/module/drawing/operator.py

@@ -1454,6 +1454,15 @@ class CreateDrawing(bpy.types.Operator):
                 "Material.Name",
             ]
 
+        join_classes = ifcopenshell.util.element.get_pset(self.camera_element, "EPset_Drawing", "JoinClasses")
+        if join_classes:
+            join_classes = tuple(c.strip() for c in join_classes.split(",") if c.strip())
+        else:
+            # Architectural convention only merges these objects by default. E.g. pipe
+            # segments and fittings shouldn't merge. Users may override this per-drawing
+            # via the EPset_Drawing.JoinClasses property (e.g. to also join IfcCovering).
+            join_classes = ("IfcWall", "IfcSlab")
+
         group = root.find("{http://www.w3.org/2000/svg}g")
         joined_paths = {}
         self.is_manifold_cache = {}
@@ -1555,8 +1564,7 @@ class CreateDrawing(bpy.types.Operator):
                             )
                         path.attrib["d"] = d
 
-            # Architectural convention only merges these objects. E.g. pipe segments and fittings shouldn't merge.
-            if not element.is_a("IfcWall") and not element.is_a("IfcSlab"):
+            if not any(element.is_a(c) for c in join_classes):
                 continue
 
             keys = []