Dump of hello world ifc viewer code

2026-08-28 15:53:00 +00:00 · 2026-04-11 16:30:10 +10:00
parent 543d9f8588
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+# IfcViewer
+
+A high-performance native IFC viewer built on IfcOpenShell's C++ geometry engine with a Qt6 interface and OpenGL 4.5 rendering.
+
+## Architecture
+
+```
+-------------------------------------------+
+|  Qt6 Application (MainWindow)             |
+|  +----------+ +--------------------------+|
+|  | Element  | | 3D Viewport              ||
+|  | Tree     | | (QWindow + OpenGL 4.5)   ||
+|  |          | |                          ||
+|  +----------+ | Single VBO/EBO           ||
+|  | Property | | DrawElementsBaseVertex   ||
+|  | Table    | | GPU pick pass            ||
+|  +----------+ +--------------------------+|
+|  | Status / Progress                      |
+-------------------------------------------+
+        ^                    ^
+        |                    |
+  element metadata     UploadChunks
+        |                    |
+-------------------------------------------+
+|  GeometryStreamer (background QThread)     |
+|  IfcGeom::Iterator with N threads         |
+|  (one per CPU core by default)            |
+-------------------------------------------+
+```
+
+### Key design decisions
+
+- **QWindow viewport** embedded via `QWidget::createWindowContainer()`. This gives us a raw native surface for OpenGL, bypassing `QOpenGLWidget`'s compositor overhead.
+- **One big vertex buffer + index buffer** (64 MB + 32 MB initial). Geometry is appended as it streams in. No per-object VBOs, no rebinding.
+- **Interleaved vertex format**: position (3 floats) + normal (3 floats) + object ID (1 float, bitcast uint32) = 28 bytes per vertex.
+- **GPU object picking**: a second render pass writes object IDs to an R32UI framebuffer. Click reads back one pixel. No CPU-side raycasting.
+- **Multi-threaded tessellation**: `IfcGeom::Iterator` runs on a background thread and internally parallelizes geometry conversion across all CPU cores.
+- **Non-blocking streaming**: the iterator emits `UploadChunk` signals via Qt's queued connection. The main thread uploads to the GPU without blocking iteration.
+- **World coordinates**: geometry is emitted in world space (`use-world-coords=true`) so no per-object transform matrices are needed on the GPU.
+
+### Files
+
+| File | Purpose |
+|------|---------|
+| `main.cpp` | Application entry point, GL 4.5 surface format, CLI argument parsing |
+| `MainWindow.h/cpp` | Qt main window: dockable element tree, property table, status bar, menus |
+| `ViewportWindow.h/cpp` | OpenGL 4.5 Core renderer: shaders, buffer management, camera, picking |
+| `GeometryStreamer.h/cpp` | Background geometry processing: loads IFC, runs iterator, emits chunks |
+| `CMakeLists.txt` | Build configuration |
+
+## Dependencies
+
+- **Qt6** (Core, Gui, Widgets)
+- **OpenGL 4.5** (GL_ARB_direct_state_access) - available on Windows and Linux; macOS will need a Vulkan/MoltenVK backend (not yet implemented)
+- **IfcOpenShell C++ libraries** (IfcParse, IfcGeom, and their dependencies: Open CASCADE, Boost, Eigen3, optionally CGAL)
+
+## Building
+
+IfcViewer is built as part of the IfcOpenShell CMake project. You do not need to build everything - disable the targets you don't need.
+
+### Minimal build (IfcViewer only)
+
+From the repository root:
+
+```sh
+mkdir build && cd build
+
+cmake ../cmake \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DBUILD_IFCVIEWER=ON \
+    -DBUILD_CONVERT=OFF \
+    -DBUILD_IFCPYTHON=OFF \
+    -DBUILD_GEOMSERVER=OFF \
+    -DBUILD_DOCUMENTATION=OFF \
+    -DBUILD_EXAMPLES=OFF \
+    -DCOLLADA_SUPPORT=OFF \
+    -DGLTF_SUPPORT=OFF \
+    -DHDF5_SUPPORT=OFF
+
+make -j$(nproc) IfcViewer
+```
+
+This builds only IfcParse, IfcGeom (with geometry kernels), and IfcViewer itself. All other targets (IfcConvert, Python bindings, serializers, etc.) are skipped.
+
+If Qt6 is not in a standard location, pass `-DQT_DIR=/path/to/qt6`.
+
+### Full build with IfcViewer enabled
+
+```sh
+cmake ../cmake -DBUILD_IFCVIEWER=ON
+make -j$(nproc)
+```
+
+## Usage
+
+```sh
+# Open a file directly
+./IfcViewer model.ifc
+
+# Or use File -> Open from the menu
+./IfcViewer
+```
+
+### Controls
+
+| Input | Action |
+|-------|--------|
+| Middle mouse drag | Orbit camera |
+| Shift + middle mouse drag | Pan camera |
+| Scroll wheel | Zoom |
+| Left click | Select object (highlights in viewport and tree) |
+
+### Keyboard shortcuts
+
+| Key | Action |
+|-----|--------|
+| Ctrl+O | Open file |
+| Ctrl+Q | Quit |
+
+## Roadmap
+
+- [ ] Material color support (currently renders default grey per batch)
+- [ ] Buffer growth (reallocate when 64 MB VBO fills up)
+- [ ] `glMultiDrawElementsIndirect` for fewer draw calls
+- [ ] Vulkan/MoltenVK backend for macOS
+- [ ] Spatial tree (BVH) for frustum culling
+- [ ] LOD: coarse tessellation during streaming, refine in background
+- [ ] Embedded Python scripting console
+- [ ] CJK text input support (Qt6 handles this natively)