IfcOpenShell · Moult · Apr 11, 2026 · Apr 11, 2026 · Apr 11, 2026 · Apr 11, 2026
diff --git a/build.sh b/build.sh
@@ -0,0 +1,30 @@
+#!/bin/sh
+set -e
+
+mkdir -p build && cd build
+
+cmake ../cmake \
+  -G Ninja \
+  -DCMAKE_BUILD_TYPE=Release \
+  -DPython_EXECUTABLE=/home/dion/Projects/env/bin/python3.11 \
+  -DPython_INCLUDE_DIR=/usr/include/python3.11 \
+  -DBUILD_IFCPYTHON=ON \
+  -DBUILD_IFCGEOM=ON \
+  -DBUILD_CONVERT=ON \
+  -DBUILD_GEOMSERVER=OFF \
+  -DBUILD_EXAMPLES=OFF \
+  -DWITH_OPENCASCADE=ON \
+  -DWITH_CGAL=ON \
+  -DWITH_MANIFOLD=ON \
+  -DHDF5_SUPPORT=OFF \
+  -DGLTF_SUPPORT=ON \
+  -DIFCXML_SUPPORT=OFF \
+  -DCOLLADA_SUPPORT=OFF \
+  -DSCHEMA_VERSIONS="2x3;4;4x3_add2" \
+  -DOCC_INCLUDE_DIR=/usr/include/opencascade \
+  -DOCC_LIBRARY_DIR=/usr/lib64/opencascade
+
+ninja
+
+cp ifcwrap/_ifcopenshell_wrapper*.so ifcwrap/ifcopenshell_wrapper.py \
+   ../src/ifcopenshell-python/ifcopenshell/
diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
@@ -70,6 +70,7 @@ option(BUILD_EXAMPLES "Build example applications." ON)
 option(BUILD_GEOMSERVER "Build IfcGeomServer executable (Open CASCADE is required)." ON)
 option(BUILD_IFCMAX "Build IfcMax, a 3ds Max plug-in, Windows-only." OFF)
 option(BUILD_QTVIEWER "Build IfcOpenShell Qt GUI Viewer" OFF) # QtViewer requires Qt6
+option(BUILD_IFCVIEWER "Build IfcViewer, a high-performance IFC viewer" OFF) # Requires Qt6 + OpenGL 4.5
 option(BUILD_PACKAGE "" OFF)
 
 option(WITH_OPENCASCADE "Enable geometry interpretation using Open CASCADE" ON)
@@ -332,7 +333,8 @@ if(WASM_BUILD)
 else()
     # @todo review this, shouldn't this be all possible header-only now?
     # ... or rewritten using C++17 features?
-    set(BOOST_COMPONENTS system program_options regex thread date_time iostreams)
+    # set(BOOST_COMPONENTS system program_options regex thread date_time iostreams)
+    set(BOOST_COMPONENTS program_options regex thread date_time iostreams)
 endif()
 
 if(USE_MMAP)
@@ -712,6 +714,9 @@ if(BUILD_IFCGEOM)
 
     install(TARGETS ${IFCGEOM_SCHEMA_LIBRARIES} ${kernel_libraries} IfcGeom)
 endif(BUILD_IFCGEOM)
+if(BUILD_IFCVIEWER)
+    add_subdirectory(../src/ifcviewer ifcviewer)
+endif()
 
 # Cmake uninstall target
 if(NOT TARGET uninstall)

diff --git a/findings.md b/findings.md
@@ -0,0 +1,317 @@
+# Build fix: remove `boost_system` from CMake components
+
+`Boost.System` became header-only in Boost 1.69. Boost 1.90.0 no longer ships a compiled library or CMake config for it, so `find_package(Boost REQUIRED COMPONENTS system ...)` fails.
+
+## Fix
+
+`cmake/CMakeLists.txt`:
+
+```diff
+-    set(BOOST_COMPONENTS system program_options regex thread date_time iostreams)
++    set(BOOST_COMPONENTS program_options regex thread date_time iostreams)
+```
+
+The headers are still available; no linking is needed.
+
+# Build fix: add `template` keyword for dependent template member calls
+
+Calling a template member function through a dependent expression (e.g. `storage->has_attribute_value<T>(...)` where `storage`'s type depends on a template parameter) requires the `template` keyword to disambiguate from a less-than comparison.
+
+## Error
+
+```
+src/ifcparse/IfcParse.cpp:1856:67: error: expected primary-expression before '>' token
+ 1856 |                     if (storage->has_attribute_value<express::Base>(attr_index)) {
+      |                                                                   ^
+```
+
+Six identical errors at lines 1856, 1865, 1896, 1905, 1934, 1943.
+
+## Fix
+
+`src/ifcparse/IfcParse.cpp`:
+
+```diff
+-storage->has_attribute_value<express::Base>(attr_index)
++storage->template has_attribute_value<express::Base>(attr_index)
+
+-storage->has_attribute_value<Blank>(attr_index)
++storage->template has_attribute_value<Blank>(attr_index)
+```
+
+Applied at all six call sites in `in_memory_file_storage::read_from_stream`.
+
+# Linker fix: missing explicit template instantiations for `InstanceStreamer`
+
+`InstanceStreamer` is a class template with methods defined in `IfcParse.cpp`, not the header. Without explicit instantiations, the linker can't find the symbols when the SWIG wrapper loads.
+
+## Error
+
+```
+ImportError: undefined symbol: _ZN8IfcParse16InstanceStreamerINS_10FileReaderINS_14FullBufferImplEEEEC1EPS3_PNS_7IfcFileE
+  (IfcParse::InstanceStreamer<FileReader<FullBufferImpl>>::InstanceStreamer(FileReader<FullBufferImpl>*, IfcFile*))
+```
+
+## Fix
+
+Cannot use `template class InstanceStreamer<...>` because some constructors have `static_assert` guards that reject certain reader types. Instead, instantiate each member function individually per reader type, only including the constructors valid for that type.
+
+`src/ifcparse/IfcParse.cpp` (after the last `InstanceStreamer` method definition):
+
+```cpp
+// FullBufferImpl
+template IfcParse::InstanceStreamer<FileReader<FullBufferImpl>>::InstanceStreamer(IfcParse::IfcFile*);
+template IfcParse::InstanceStreamer<FileReader<FullBufferImpl>>::InstanceStreamer(const std::string&, bool, IfcParse::IfcFile*);
+template IfcParse::InstanceStreamer<FileReader<FullBufferImpl>>::InstanceStreamer(void*, int, IfcParse::IfcFile*);
+template IfcParse::InstanceStreamer<FileReader<FullBufferImpl>>::InstanceStreamer(FileReader<FullBufferImpl>*, IfcParse::IfcFile*);
+// ... plus ensure_header, initialize_header, hasSemicolon, semicolonCount,
+//     pushPage, bypassTypes, readInstance
+
+// PushedSequentialImpl — same pattern, different valid constructors
+
+// MMapFileReader (ifdef USE_MMAP) — same pattern
+```
+
+# Linker fix: `FullBufferImpl` missing buffer constructor
+
+SWIG's `stream_from_string` calls `InstanceStreamer<FileReader<FullBufferImpl>>(void*, int, IfcFile*)`, but the `(void*, int)` constructor previously hit a `static_assert` for `FullBufferImpl` — it only allowed `PushedSequentialImpl`.
+
+## Error
+
+```
+ImportError: undefined symbol: _ZN8IfcParse16InstanceStreamerINS_10FileReaderINS_14FullBufferImplEEEEC1EPviPNS_7IfcFileE
+  (InstanceStreamer<FileReader<FullBufferImpl>>::InstanceStreamer(void*, int, IfcFile*))
+```
+
+## Fix
+
+Three changes to make `FullBufferImpl` support buffer-based and default construction:
+
+`src/ifcparse/FileReader.h` — add buffer constructor to `FullBufferImpl`:
+
+```diff
+ class IFC_PARSE_API FullBufferImpl {
+ public:
+     explicit FullBufferImpl(const std::string& fn);
++    FullBufferImpl(void* data, size_t length);
+```
+
+`src/ifcparse/FileReader.h` — add `FileReader(void*, size_t)` forwarding constructor:
+
+```diff
++    FileReader(void* data, size_t length)
++        : cursor_(0) {
++        if constexpr (std::is_same_v<Impl, FullBufferImpl>) {
++            impl_ = std::make_shared<Impl>(data, length);
++        } else {
++            static_assert(...);
++        }
++    }
+```
+
+`src/ifcparse/FileReader.cpp` — implement the constructor:
+
+```cpp
+FullBufferImpl::FullBufferImpl(void* data, size_t length)
+    : buf_(static_cast<char*>(data), static_cast<char*>(data) + length)
+    , size_(length) {
+}
+```
+
+`src/ifcparse/IfcParse.cpp` — extend the two `InstanceStreamer` constructors to accept `FullBufferImpl`:
+
+```diff
+ // InstanceStreamer(IfcFile*):
++    } else if constexpr (std::is_same_v<Reader, FileReader<FullBufferImpl>>) {
++        owned_stream_ = std::make_unique<Reader>(nullptr, (size_t)0);
+
+ // InstanceStreamer(void*, int, IfcFile*):
++    } else if constexpr (std::is_same_v<Reader, FileReader<FullBufferImpl>>) {
++        owned_stream_ = std::make_unique<Reader>(data, (size_t)length);
+```
+
+# Runtime fix: segfault in `parse_context::push()` due to vector reallocation
+
+`parse_context_pool` stores nodes in a `std::vector<parse_context>`. During parsing, `load()` takes a `parse_context&` parameter and calls `context.push()`, which calls `pool_->make()`. If the pool's vector reallocates (via `emplace_back`), all existing references into the vector — including the `context` reference held by the caller — become dangling. Subsequent access through the dangling reference causes a segfault.
+
+Triggered by larger IFC files (e.g. `ISSUE_159_kleine_Wohnung_R22.ifc`, 9.5 MB) that cause enough pool growth to trigger reallocation.
+
+## Error
+
+```
+Thread 1 received signal SIGSEGV, Segmentation fault.
+0x... in IfcParse::parse_context::push()
+  #1  in_memory_file_storage::load(...)   // context& is dangling after reallocation
+  #2  in_memory_file_storage::load(...)   // parent call
+  #3  InstanceStreamer::readInstance()
+```
+
+## Fix
+
+`src/ifcparse/storage.h` — change the pool container from `std::vector` to `std::deque`, which does not invalidate references on `push_back`/`emplace_back`:
+
+```diff
++#include <deque>
+
+ struct parse_context_pool {
+-    std::vector<parse_context> nodes_;
++    std::deque<parse_context> nodes_;
+```
+
+# Runtime fix: `express::Base` comparison operators throw on null/expired instances
+
+`express::Base::operator<` and `operator==` called `data()`, which throws `std::runtime_error("Trying to access deleted instance reference")` when the internal `weak_ptr` is expired. A default-constructed `express::Base` (the value-type equivalent of a null pointer) always has an expired `weak_ptr`.
+
+## Why this model triggers it
+
+The bug requires two conditions to coincide:
+
+1. A representation is shared by **more than one product** (via `IfcRepresentationMap` / `IfcMappedItem`).
+2. At least one of those products has **no material association**, so `get_single_material_association()` returns `express::Base{}` (the null equivalent).
+
+In `advanced_model.ifc`, Body representations like `#449` (Body/Brep) have a single `IfcRepresentationMap` (`#453`) with 13 `IfcMappedItem` usages, meaning 13 products share the geometry. Some of those products (e.g. `IfcFlowTerminal` instances) have no `IfcRelAssociatesMaterial`, so `get_single_material_association` returns `express::Base{}`.
+
+Smaller or simpler models don't hit this because either:
+- Every representation maps to only 1 product → `reuse_ok_` short-circuits at `products.size() == 1` before reaching the material check.
+- Every product has a material association → no null `express::Base` is ever inserted into the set.
+
+## Exact call sequence
+
+```
+Iterator::initialize()
+  try {
+    mapping::get_representations(reps, filters_)
+      addRepresentationsFromDefaultContexts(representations)
+        → collects reps from subcontexts in order:
+          Axis (#115): 143 reps
+          Body (#117): 7550 reps
+          FootPrint (#119): 12 reps
+
+      for (auto representation : representations):
+
+        ── Axis reps (indices 0–142) ──────────────────────────
+        products_represented_by(rep, rmap)
+          → OfProductRepresentation: 1 product each
+        filter_products(products, filters)   → 1 product
+        reuse_ok_(ifcproducts)
+          → products.size() == 1 → return true  ← SHORT-CIRCUIT, no material check
+        representation_mapped_to(rep)        → null (no MappedItem)
+        → task created.  143 tasks accumulated.
+
+        ── First Body rep #449 (Body/Brep) ────────────────────
+        products_represented_by(#449, rmap)
+          → OfProductRepresentation: empty
+          → RepresentationMap: 1 map (#453)
+          → MapUsage: 13 MappedItems → traces through to 13 IfcProducts
+        filter_products(products, filters)   → 13 products
+        reuse_ok_(ifcproducts)               ← CRASH HERE
+          → products.size() == 1?  NO (13 products)
+          → for each product:
+              find_openings(product)          → OK
+              get_single_material_association(product)
+                → some products have no IfcRelAssociatesMaterial
+                → returns express::Base{}     (expired weak_ptr)
+              associated_single_materials.insert(result)
+                → std::set::insert calls operator<
+                → operator< calls data()
+                → data() calls data_.lock() → expired → THROWS
+                  "Trying to access deleted instance reference"
+
+  } catch (const std::exception& e) {
+    Logger::Error(e)       ← exception caught here, get_representations aborted
+  }
+
+  → reps contains only the 143 Axis tasks created before the throw
+  → all 143 Axis reps have Curve2D geometry → map(representation) returns null
+  → no valid elements produced → initialize() returns false
+```
+
+In the old pointer-based code, `reuse_ok_` used `std::set<const IfcUtil::IfcBaseEntity*>` and `get_single_material_association` returned `nullptr`. Inserting `nullptr` into a `std::set<T*>` is a plain pointer comparison — no dereference, no throw. The refactoring to `std::set<express::Base>` changed the comparison from pointer comparison to `express::Base::operator<`, which unconditionally dereferences through `data()`.
+
+## Error
+
+```
+[Error] Trying to access deleted instance reference
+[Notice] Created 143 tasks for 143 products    ← only Axis reps; all Body reps lost
+initialize() returned: False
+```
+
+## Fix
+
+`src/ifcparse/express.h` — use `weak_ptr::lock().get()` instead of `data()` so that expired pointers compare as `nullptr` (matching old raw-pointer semantics):
+
+```diff
+     bool operator<(const Base& other) const {
+-        return data() < other.data();
++        auto a = data_.lock();
++        auto b = other.data_.lock();
++        return a.get() < b.get();
+     }
+
+     bool operator==(const Base& other) const {
+-        return data() == other.data();
++        auto a = data_.lock();
++        auto b = other.data_.lock();
++        return a.get() == b.get();
+     }
+```
+
+# Runtime fix: `entity_instance` missing `get_inverse` due to SWIG `%rename` collision
+
+Accessing inverse attributes (e.g. `element.IsDecomposedBy`) on any entity raises `AttributeError: entity instance of type 'IFC2X3.IfcProject' has no attribute 'get_inverse'`.
+
+## Why
+
+`entity_instance_mixin.__getattr__` (line 106 of `entity_instance.py`) calls `self.get_inverse(name)` when it detects an inverse attribute. Since the mixin inherits into the SWIG-generated `entity_instance` class (via the `object = custom_base` hack in `IfcParseWrapper.i:936`), `self.get_inverse` must resolve to a method on the SWIG class.
+
+However, `IfcParseWrapper.i:70` has a global rename:
+
+```
+%rename("get_inverses_by_declaration") get_inverse;
+```
+
+This was intended for `ifcopenshell::file::get_inverse` (which takes an entity + declaration and returns instances by reference), but SWIG `%rename` is global — it also renames the `%extend express::Base` method `get_inverse(const std::string& a)` at line 551. So the Python-side `entity_instance` class exposes the method as `get_inverses_by_declaration`, not `get_inverse`.
+
+The old code (`v0.8.0`) didn't hit this because `__getattr__` called `self.wrapped_data.get_inverse(name)` on an inner `ifcopenshell_wrapper.entity_instance` object — but in that old layout, the inner object was constructed differently and the rename didn't apply the same way (or the method had a different path). In the new mixin approach, `self` **is** the SWIG object, so the rename is directly visible.
+
+## Fix
+
+`src/ifcwrap/IfcParseWrapper.i` — override the global rename specifically for `express::Base::get_inverse`, restoring the original name on entity instances:
+
+```diff
++%rename("get_inverse") express::Base::get_inverse;
+ %rename("get_inverses_by_declaration") get_inverse;
+```
+
+Add this line **before** the global rename (or anywhere before the `%extend express::Base` block). This scoped rename takes precedence for `express::Base`, so:
+- `entity_instance.get_inverse(name)` works as the mixin expects
+- `file.get_inverses_by_declaration(...)` keeps its intended name
+
+## Python-side workaround
+
+`entity_instance.py:106` — call the method by its SWIG-renamed name:
+
+```diff
+-            vs = self.get_inverse(name)
++            vs = self.get_inverses_by_declaration(name)
+```
+
+# Runtime fix: `entity_instance` class no longer importable from `entity_instance` module
+
+The class rename from `entity_instance` to `entity_instance_mixin` broke external code that does `from ifcopenshell.entity_instance import entity_instance`.
+
+## Error
+
+```
+ImportError: cannot import name 'entity_instance' from 'ifcopenshell.entity_instance'
+```
+
+Triggered at import time via `ifcopenshell.util.pset` (and likely other modules).
+
+## Fix
+
+`src/ifcopenshell-python/ifcopenshell/entity_instance.py` — add a backwards-compatible alias at the bottom of the module:
+
+```python
+entity_instance = entity_instance_mixin
+```
diff --git a/src/ifcgeom/mapping/IfcOffsetCurveByDistance.cpp b/src/ifcgeom/mapping/IfcOffsetCurveByDistance.cpp
@@ -158,7 +158,7 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcOffsetCurveByDistances& inst
 
 	 // at this point, next == end and prev == end-1
     #if defined SCHEMA_HAS_IfcDistanceExpression
-    double last_distance = (*prev)->DistanceAlong() * length_unit_;
+    double last_distance = (*prev).DistanceAlong() * length_unit_;
     #else
     double last_distance = (double) prev->DistanceAlong().as<IfcSchema::IfcLengthMeasure>() * length_unit_;
     #endif

diff --git a/src/ifcopenshell-python/ifcopenshell/__init__.py b/src/ifcopenshell-python/ifcopenshell/__init__.py
@@ -94,6 +94,9 @@
 from .file import rocksdb_lazy_instance
 from . import guid
 from .ifcopenshell_wrapper import entity_instance
+from .entity_instance import _patch_swig_comparisons
+_patch_swig_comparisons()
+del _patch_swig_comparisons
 from .sql import sqlite, sqlite_entity
 
 # explicitly specify available imported symbols