exclude MESH without vertices or faces from DXF export #1219

MESH entities without vertices or faces create an invalid
DXF file for AutoCAD and BricsCAD.

And Mesh.audit() now also destroys such entities.

notes/pages/CHANGELOG.md

@@ -1,4 +1,8 @@
-## Version 1.3.5 - 2024-12-15
+## Version 1.3.6 - dev
+	- NEW: `Mesh.audit()` removes `MESH` entities without vertices or faces
+	- BUGFIX: Exported `MESH` entities  without vertices or faces create invalid DXF files
+		- {{issue 1219}}
+- ## Version 1.3.5 - 2024-12-15
 	- ((65ed4f6c-edc8-4390-880c-c604a3fa5ec0))
 	- NEW: `ezdxf.blkrefs.find_unreferenced_blocks()` function returns the names of unused block definitions
 	- NEW: `Auditor` checks if modelspace and active paperspace exists

src/ezdxf/audit.py

@@ -94,6 +94,7 @@ class AuditError(IntEnum):
     INVALID_ELLIPSE_RATIO = 225
     INVALID_HATCH_BOUNDARY_PATH = 226
     TAG_ATTRIBUTE_MISSING = 227
+    INVALID_MESH_DATA = 228
 
 
 REQUIRED_ROOT_DICT_ENTRIES = ("ACAD_GROUP", "ACAD_PLOTSTYLENAME")

src/ezdxf/entities/mesh.py

@@ -292,6 +292,20 @@ def process_creases():
         self._edges = process_edges()
         self._creases = process_creases()
 
+    def preprocess_export(self, tagwriter: AbstractTagWriter) -> bool:
+        """Pre requirement check and pre-processing for export.
+
+        Returns ``False``  if entity should not be exported at all.
+
+            - MESH without vertices creates an invalid DXF file for AutoCAD and BricsCAD.
+            - MESH without faces creates an invalid DXF file for AutoCAD and BricsCAD.
+
+        (internal API)
+        """
+        if len(self.vertices) == 0 or len(self.faces) == 0:
+            return False
+        return True
+
     def export_entity(self, tagwriter: AbstractTagWriter) -> None:
         """Export entity specific data as DXF tags."""
         super().export_entity(tagwriter)
@@ -410,6 +424,14 @@ def audit(self, auditor: Auditor) -> None:
                 message=f"fixed invalid count of crease values in {str(self)}",
                 dxf_entity=self,
             )
+        if len(self.vertices) == 0 or len(self.faces) == 0:
+            # A MESH without vertices or vertices creates an invalid DXF file for
+            # AutoCAD and BricsCAD
+            auditor.fixed_error(
+                code=AuditError.INVALID_VERTEX_COUNT,
+                message=f"removed {str(self)} without vertices or faces",
+            )
+            auditor.trash(self)
 
 
 class MeshData:

src/ezdxf/version.py

@@ -24,5 +24,5 @@
 #   1. bug fix release beta0: VERSION = "0.9.1b0"; version = (0, 9, 1, 'b0')
 #   2. bug fix release: VERSION = "0.9.2"; version = (0, 9, 2, 'release')
 
-version = (1, 3, 5, "release")
-__version__ = "1.3.5"
+version = (1, 3, 6, "b0")
+__version__ = "1.3.6b0"

tests/test_02_dxf_graphics/test_228_mesh.py

@@ -83,11 +83,12 @@ def test_load_from_text(entity):
     assert entity.dxf.subdivision_levels == 0
 
 
-def test_write_dxf():
+def test_export_without_vertices_or_faces():
+    # MESH without vertices creates an invalid DXF file for AutoCAD and BricsCAD.
+    # MESH without faces creates an invalid DXF file for AutoCAD and BricsCAD.
     entity = Mesh.from_text(MESH)
     result = TagCollector.dxftags(entity)
-    expected = basic_tags_from_text(MESH)
-    assert result == expected
+    assert len(result) == 0
 
 
 @pytest.fixture(scope="module")
@@ -200,6 +201,18 @@ def test_auditor_fixes_invalid_crease_count(msp: Modelspace):
     assert list(mesh.creases) == [0.0]
 
 
+def test_auditor_destroys_invalid_meshes_without_vertices_or_faces():
+    # new document required
+    doc = ezdxf.new()
+    msp = doc.modelspace()
+    # add a mesh without vertices or faces
+    mesh = msp.add_mesh()
+
+    auditor = msp.doc.audit()
+    assert len(auditor.fixes) == 1
+    assert mesh.is_alive is False
+
+
 def test_vertex_format(msp: Modelspace):
     mesh = msp.add_mesh()
     with mesh.edit_data() as mesh_data: