How to build OpenCascade with Emscripten

[Anyicheng2015]

Hi,
I tried to build OpenCascade with Emscripten by myself, but failed.

1. Download a tagged commit from the OpenCascade git server.
2. Compile the OpenCascade library using the Emscripten compiler.

The root cause is that I don't know how to build FreeType with Emscripten.
Or is there any way to skip Freetype?

My practice is:

1. Download source code, use cmake and Emscripten tool chain to generate code.
2. Enter the result folder and tried to build, get error. "fatal error: 'ft2build.h' file not found
   
3. I tried to take two solution, skip freetype or build freetype with Emscripten
   Remove lines below, opencascade-7.5.0\CMakeLists.txt, but not work:

if (USE_FREETYPE)
message (STATUS "Info: Freetype is used by OCCT")
OCCT_INCLUDE_CMAKE_FILE ("adm/cmake/freetype")
else()
OCCT_CHECK_AND_UNSET_GROUP ("3RDPARTY_FREETYPE")
OCCT_CHECK_AND_UNSET ("3RDPARTY_FREETYPE_INCLUDE_DIR_freetype2")
OCCT_CHECK_AND_UNSET ("3RDPARTY_FREETYPE_INCLUDE_DIR_ft2build")
OCCT_CHECK_AND_UNSET ("INSTALL_FREETYPE")
endif()

Tried to build freetype, but get errors:
BROTLIDEC_INCLUDE_DIRS-NOTFOUND
BROTLIDEC_LIBRARIES-NOTFOUND
BZIP2_INCLUDE_DIR-NOTFOUND
BZIP2_LIBRARY_RELEASE-NOTFOUND
Search the internet, I didn't find what is BROTLIDEC, maybe due to that I'm not familiar with FreeType.

Could you help me?
Do you have any suggestions?

Thanks,
Andy

[donalffons]

Hey there,

try to add -sUSE_FREETYPE=1 in your Emscripten build settings. Alternatively, you could try to exclude everything that depends on Freetype from the build (if you don't need it). I think that's mostly the Font package.

Also, OpenCascade has a WebGL example, which you can follow.

[Anyicheng2015]

Thank you!
I tried to add -sUSE_FREETYPE=1 into Cmake settings. Seems not work.
Is this the right way? I'm quite new with CMake.

[donalffons]

Hmm, no, that's not correct, I think.
I haven't used the CMake GUI before, but the values in that list are not passed on to Emscripten.

As a starting point, you might be able to go ahead and edit OpenCascade's CMakeLists.txt and manually add set_target_properties there. Inside that call, you can add COMPILE_FLAGS and LINK_FLAGS. -sUSE_FREETYPE=1 is a link flag.

i.e.

set_target_properties(sometarget PROPERTIES LINK_FLAGS "-sUSE_FREETYPE=1")

Have a look at this SO issue.

EDIT: However, you might be able to change OCCT's CMake flag USE_FREETYPE (that's just named identical to Emscripten's flag) to false from that list, maybe?! In that case, OCCT should skip all packages depending on Freetype?! I'm just guessing...

[Anyicheng2015]

Hi Sebastian,
I tried to turn off the option freetype in occt-1f3c505\CMakeLists.txt:

But there still some error, seems freetype cannot be skipped:

Could you tell me the way you build opencasecade to webassembly?
My OS is windows.

Thanks,
Andy

[donalffons]

In the current version of OpenCascade.js, I don't use the CMake based build system any more. Instead I use a custom build system...

If you want to use CMake (which is certainly recommended in most cases), you might want to have a look at OpenCascade.js v0.1.19, which did use OpenCascade's CMake based build system.
The most relevant bits are

• this Dockerfile, which installs Emscripten and some additional tools.
• make.py, which contains all the relevant build steps

The build happens in this order

1. Download OCCT
2. Extract OCCT and apply some patches (patches are probably not neccesary in your case)
3. Download and extract regal (maybe also not necessary)
4. Download and extract freetype
5. Download and extract fontconfig
6. Generate and build the JS bindings (you don't need this step or might want to use a simplified approach - depending on what you want to do)
7. Configure OpenCascade via CMake
8. Build OpenCascade via make

Hope that helps!

[mengxyokok]

Thank you, it's helpful for me!