Building Open CASCADE (OCCT) for EzyCad

EzyCad does not vendor OCCT; builds live outside the tree. Point CMake at an install via OpenCASCADE_DIR (and on Windows desktop, OCCT_3RD_PARTY_DIR).

Official references

Version matrix (EzyCad)

Target

Documented / tested

CMake variables

Windows desktop

OCCT 8.0.0 prebuilt

OpenCASCADE_DIR, OCCT_3RD_PARTY_DIR

WebAssembly

OCCT 8.0.0 via scripts/build-occt-v8-wasm.ps1

OpenCASCADE_DIR only (static install)

After upgrading OCCT, retest sketch dimensions, grid, fillet/chamfer/boolean, and STEP/STL export. OCCT 8.0 changes grid rendering and many modeling paths.

Windows desktop (easiest): prebuilt binaries

No OCCT compile. Use Release builds (EzyCad is tested with Release OCCT).

Download (8.0.0 — current README default)

# Combined (OCCT + 3rd-party, simplest layout for desktop):
https://github.com/Open-Cascade-SAS/OCCT/releases/download/V8_0_0/occt-combined-release-no-pch.zip

Note: The V8 combined release asset is a small wrapper zip containing opencascade-8.0.0-vc14-64-combined.zip. Extracting it yields:

  • opencascade-8.0.0-vc14-64/ (contains cmake/OpenCASCADEConfig.cmake → use for -DOpenCASCADE_DIR=.../opencascade-8.0.0-vc14-64/cmake)

  • 3rdparty-vc14-64/

# Or separate (if you prefer):
https://github.com/Open-Cascade-SAS/OCCT/releases/download/V8_0_0/3rdparty-vc14-64.zip
# + the opencascade-*-vc14-64 combined from the V8_0_0 release page

Configure EzyCad

cmake C:\src\EzyCad -DOpenCASCADE_DIR=C:\bin\OCCT-install\cmake -DOCCT_3RD_PARTY_DIR=C:\bin\3rdparty-vc14-64

  • OpenCASCADE_DIR — directory containing OpenCASCADEConfig.cmake (often ...\cmake or ...\lib\cmake\opencascade depending on package layout; verify on disk).

  • OCCT_3RD_PARTY_DIR — root of 3rdparty-vc14-64 (FreeType, TBB, FFmpeg DLLs copied next to EzyCad.exe per CMakeLists.txt).

Use Visual Studio generator, x64, Release for the app.

Windows desktop: build from source

Only when prebuilts are insufficient (custom flags, Debug OCCT, patches).

  1. Install VS 2022 (C++), CMake 3.16+, Git.

  2. Download 3rdparty-vc14-64.zip matching the OCCT tag.

  3. Clone OCCT, configure with CMake GUI or CLI, BUILD_LIBRARY_TYPE=Shared or Static as needed, enable USE_OPENGL, USE_FREETYPE, etc. per build guide.

  4. Build INSTALL target; set OpenCASCADE_DIR to the install prefix’s cmake package path.

Prefer prebuilt packages unless you need a custom source build.

WebAssembly (Emscripten)

EzyCad’s wasm target links TKOpenGles (not TKOpenGl), static OCCT, and -fexceptions (see CMakeLists.txt Emscripten block).

Automated: scripts/build-occt-v8-wasm.ps1

Builds FreeType 2.13.3 + OCCT V8_0_0 static with GLES2 into a single install prefix.

Prerequisites: Git, CMake 3.16+, Emscripten emsdk 3.0+ with emsdk_env active (emcc, emcmake, emmake on PATH).

Layout created (default RootDir = %USERPROFILE%\occt-wasm-build):

occt-wasm-build/
  src/OCCT/                    git clone V8_0_0
  src/freetype-2.13.3/         from .tar.gz (not .tar.xz on Windows)
  build/freetype/
  build/occt/
  install/                     CMAKE_INSTALL_PREFIX
    lib/cmake/opencascade/     → OpenCASCADE_DIR
    freetype/                  FreeType install (used at OCCT configure time)

PowerShell (repo root, after emsdk_env):

.\scripts\build-occt-v8-wasm.ps1 -RootDir C:\bin\occt-wasm-build

Or use scripts\build-occt-v8-wasm.cmd if PowerShell script execution is restricted.

Script flags: -SkipDownload, -SkipFreeType, -SkipOcct, -ReconfigureOnly, -Jobs 8, -OcctTag V8_0_0, -BuildType Release.

Expect: 1–3+ hours compile, large disk use. Success prints OpenCASCADE_DIR=....

Configure EzyCad wasm (Ninja generator works well with OCCT V8):

mkdir build_em
cd build_em
emcmake cmake C:\src\EzyCad -Wno-dev -G Ninja -DOpenCASCADE_DIR=C:\src\occt-wasm-build\install\lib\cmake\opencascade -DCMAKE_BUILD_TYPE=Release
ninja

Serve: python -m http.server 8000 from the build output directory (the .html + .wasm + .data files).

OCCT wasm CMake flags (reference)

Used by build-occt-v8-wasm.ps1 — keep in sync if editing the script:

Variable

Value

Why

BUILD_LIBRARY_TYPE

Static

.a archives linked into EzyCad.wasm

BUILD_MODULE_Draw

OFF

No Tcl/Tk harness

USE_OPENGL

OFF

Desktop GL driver

USE_GLES2

ON

TKOpenGles for WebGL2

USE_VTK

OFF

Default in 8.0; avoids GLES VTK issues

USE_FREETYPE

ON

Dimension / text rendering

USE_TBB, USE_FFMPEG, USE_FREEIMAGE, USE_OPENVR, USE_TK

OFF

Reduce deps and build time

CMAKE_*_FLAGS

-fexceptions

Match EzyCad emscripten link flags

FreeType wasm configure also disables optional zlib/png/harfbuzz finds to simplify the emscripten build.

Wasm troubleshooting

Symptom

Fix

running scripts is disabled

Set-ExecutionPolicy -Scope CurrentUser RemoteSigned or use build-occt-v8-wasm.cmd or powershell -ExecutionPolicy Bypass -File ...

Can't initialize filter; xz

Script uses .tar.gz for FreeType; delete stale *.tar.xz under src/ and re-run

source directory .../build/freetype does not contain CMakeLists.txt

Fixed: do not name a PowerShell function parameter $Args (shadows automatic $Args)

emcc not found

Run emsdk_env.bat / emsdk_env.ps1 in the same shell

EzyCad configure hangs on find_package(OpenCASCADE)

emcmake cmake ... --debug-output; verify OpenCASCADE_DIR path

OCCT 8 + ghosted dimension labels

Retest gui.edge_dim_text_render_mode (Z-layer Topmost); grid compositing changed in 8.0

Note: Older OCCT builds (prior to 8.0) are no longer supported or documented. Use the V8 script above for WebAssembly.

Wrapper scripts and automation

When adding helper scripts under scripts/, follow existing repo conventions.

Windows .cmd (ExecutionPolicy bypass)

scripts/build-occt-v8-wasm.cmd wraps the PowerShell script (same pattern as check-nonascii-src.cmd):

@echo off
powershell -NoProfile -ExecutionPolicy Bypass -File "%~dp0build-occt-v8-wasm.ps1" %*
if errorlevel 1 exit /b 1

Batch + emsdk:

call C:\src\emsdk\emsdk_env.bat
cd /d C:\src\EzyCad
scripts\build-occt-v8-wasm.cmd -RootDir C:\src\occt-wasm-build

Unix .sh

No first-party wasm shell script yet; a scripts/build-occt-v8-wasm.sh may mirror the PowerShell logic:

  • set -euo pipefail

  • Require emcc, git, cmake

  • ROOT="${ROOT:-$HOME/occt-wasm-build}"

  • Download freetype-$VER.tar.gz (gzip portable; avoid .tar.xz if xz missing)

  • emcmake cmake -S ... -B ... with the same -D flags as the .ps1

  • emmake cmake --build ... --target install -j"$(nproc)"

  • Print OpenCASCADE_DIR=$ROOT/install/lib/cmake/opencascade

Use forward slashes in cmake paths on Unix.

PowerShell one-liner (no policy change)

powershell -NoProfile -ExecutionPolicy Bypass -File C:\src\EzyCad\scripts\build-occt-v8-wasm.ps1 -RootDir C:\src\occt-wasm-build

curl downloads (CI)

Windows desktop 8.0 combined:

curl -L -o occt-combined.zip https://github.com/Open-Cascade-SAS/OCCT/releases/download/V8_0_0/occt-combined-release-no-pch.zip

vcpkg (alternative desktop path)

OCCT 8 supports vcpkg (USE_VTK=ON only if needed). EzyCad’s CMakeLists.txt is written for find_package(OpenCASCADE) + manual OCCT_3RD_PARTY_DIR DLL copies — vcpkg integration is not wired in-tree.

Maintaining OCCT version pins

File

What to update

README.md

Pin version, download URLs, example OpenCASCADE_DIR

CMakeLists.txt

OCCT_3RD_PARTY_DIR paths (freetype/tbb/ffmpeg versions in DLLS_COMMON)

.github/workflows/windows-msvc.yml

Prebuilt download URL, cache key, OpenCASCADE_DIR/OCCT_3RD_PARTY_DIR in CI configure

scripts/build-occt-v8-wasm.ps1

$OcctTag, $FreeTypeVersion, cmake flags

docs/building-occt.md

This document

src/ply_io.cpp

Comments if triangulation API changes

Quick reference: EzyCad CMake variables

Variable

Platform

Purpose

OpenCASCADE_DIR

All

Path to OpenCASCADEConfig.cmake directory

OCCT_3RD_PARTY_DIR

Windows desktop

Root of 3rdparty bundle for runtime DLLs

CMAKE_BUILD_TYPE

Native / wasm

Release recommended

EzyCad wasm also sets TKOpenGles in OpenCASCADE_LIBS when CMAKE_CXX_COMPILER_ID is Emscripten.