# Building VTK-9 with Emscripten+GLES for rendering
**URL:** https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038
**Category:** Development
**Created:** [April 13, 2020, 5:28pm UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038 "2020-04-13T17:28:50Z")
**Posts on this page:** 11
**Page:** 1
### Author:  [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [April 13, 2020, 5:28pm UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/1 "2020-04-13T17:28:51Z")
I’m trying to port the excellent work that was done [here](https://github.com/dicehub/VTK/commit/e7029bce36a9d51b5bdfae215fe280d7d86ba365) on an old version of VTK to todays VTK while hoping it could make it to VTK 9.
### Steps to reproduce
#### Getting the sources
Create and go into a working directory for that project
```auto
mkdir webassembly-work
cd webassembly-work
```
Clone VTK and fetch the proper WIP branch
```auto
git clone https://gitlab.kitware.com/vtk/vtk.git VTK
cd VTK
git submodule update --init --recursive
git fetch "git@gitlab.kitware.com:sebastien.jourdain/vtk.git" "web-assembly-rendering"
git checkout -b "sebastien.jourdain/vtk-web-assembly-rendering" FETCH_HEAD
git submodule update
```
#### Building inside emscripten docker image
Starting docker while mounting your working directory
```auto
cd /.../webassembly-work
docker run --rm --entrypoint /bin/bash -v $PWD:/work -it dockcross/web-wasm:20200119-1c10fb2
```
At that point your shell is running inside the docker image.
```auto
mkdir -p /work/VTK-build
cd /work/VTK-build
cmake -G Ninja \
\
-DCMAKE_CXX_FLAGS="-s USE_FREETYPE=1" \
-DCMAKE_BUILD_TYPE:STRING=Release \
-DBUILD_SHARED_LIBS:BOOL=OFF \
-DCMAKE_TOOLCHAIN_FILE=${CMAKE_TOOLCHAIN_FILE} \
\
-DVTK_OPENGL_HAS_EGL=ON \
-DVTK_OPENGL_USE_GLES=ON \
-DVTK_BUILD_TESTING=OFF \
-DVTK_GROUP_ENABLE_Qt=DONT_WANT \
\
-DVTK_USE_SYSTEM_FREETYPE:BOOL=ON \
-DFREETYPE_INCLUDE_DIRS:PATH=include \
-DFREETYPE_LIBRARY:STRING=freetype \
-DH5_HAVE_GETPWUID:BOOL=OFF \
-DVTK_NO_PLATFORM_SOCKETS:BOOL=ON \
\
-DVTK_ENABLE_LOGGING=OFF \
-DVTK_ENABLE_WRAPPING=OFF \
-DVTK_IOS_BUILD=OFF \
\
-DVTK_MODULE_ENABLE_VTK_ChartsCore=DONT_WANT \
-DVTK_MODULE_ENABLE_VTK_FiltersParallel=DONT_WANT \
-DVTK_MODULE_ENABLE_VTK_IOH5part=DONT_WANT \
-DVTK_MODULE_ENABLE_VTK_RenderingContext2D=DONT_WANT \
-DVTK_MODULE_ENABLE_VTK_RenderingFreeType=DONT_WANT \
-DVTK_MODULE_ENABLE_VTK_RenderingGL2PSOpenGL2=DONT_WANT \
-DVTK_MODULE_ENABLE_VTK_RenderingOpenVR=DONT_WANT \
-DVTK_MODULE_ENABLE_VTK_RenderingParallel=DONT_WANT \
-DVTK_MODULE_ENABLE_VTK_ViewsContext2D=DONT_WANT \
-DVTK_MODULE_ENABLE_VTK_hdf5=DONT_WANT \
\
-DVTK_MODULE_USE_EXTERNAL_VTK_freetype=ON \
\
-DOPENGL_egl_LIBRARY=/emsdk_portable/emscripten/tag-1.38.48/system/lib/pkgconfig/egl.pc \
-DOPENGL_gles2_LIBRARY=/emsdk_portable/emscripten/tag-1.38.48/system/lib/pkgconfig/glesv2.pc \
-DOPENGL_gles3_LIBRARY=/emsdk_portable/emscripten/tag-1.38.48/system/lib/pkgconfig/glesv2.pc \
\
../VTK
```
This attempt was inspired from the example available [here](https://github.com/dicehub/EmVTK).
### Error
While running the cmake command, I’m getting the following error and my guess is that we may need custom handling in VTK/CMake/FindOpenGL to handle the WebAssembly target. As we are getting the following error output.
```auto
[...]
-- Could NOT find OpenGL (missing: OpenGL)
CMake Error at CMake/vtkModule.cmake:4134 (message):
Could not find the OpenGL external dependency.
Call Stack (most recent call first):
CMake/vtkModule.cmake:4657 (vtk_module_find_package)
Utilities/OpenGL/CMakeLists.txt:36 (vtk_module_third_party_external)
```
Any advice or suggestion would be great.
Thanks!
cc: @brad.king @ben.boeckel @thewtex
---
### Author:  [@thewtex](https://discourse.vtk.org/u/thewtex)
#### Post date: [April 13, 2020, 5:41pm UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/2 "2020-04-13T17:41:07Z")
@Sebastien_Jourdain the DiceHub EGL rendering was built on additional patches for [itk.js](https://insightsoftwareconsortium.github.io/itk-js/docs/index.html):
- [https://github.com/dicehub/VTK/commits/emscripten](https://github.com/dicehub/VTK/commits/emscripten)
These also need to be ported to the latest VTK.
---
### Author:  [@brad.king](https://discourse.vtk.org/u/brad.king)
#### Post date: [April 13, 2020, 7:58pm UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/3 "2020-04-13T19:58:36Z")
The error in `CMake/vtkModule.cmake` is occurring after a call it makes of this form:
```auto
find_package(OpenGL COMPONENTS OpenGL GLES3 EGL)
```
The CMake command line was given `-DOPENGL_egl_LIBRARY=...` and `-DOPENGL_gles3_LIBRARY=...` options that cover the `EGL` and `GLES3` components, though the latter specifies `glesv2.pc` for GLES3. Nothing provides the `OpenGL` component. The `/emsdk_portable/emscripten/tag-1.38.48/system/lib/pkgconfig/` directory does not contain any `.pc` file for the GLVND “OpenGL” component (or `glesv3.pc`).
Under emscripten what is supposed to provide the GLVND `OpenGL` component? Or, if it doesn’t exist, what is VTK supposed to do instead?
---
### Author:  [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [April 14, 2020, 11:33am UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/4 "2020-04-14T11:33:07Z")
That’s why we use [my branch](https://gitlab.kitware.com/sebastien.jourdain/vtk/-/commit/c8fc56307bafc062e4a4e72eefea4ce29d240689) that try to bring their contribution to the level of VTK/release.
Also EGL is not really used or working for them. I just filled that property to see if I could by-pass the OpenGL requirement.
---
### Author:  [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [April 14, 2020, 11:53am UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/5 "2020-04-14T11:53:29Z")
Hey Brad,
My understanding (which might be wrong) is that as soon as I provide a GLES library, I don’t necessary need the OpenGL one (probably only true for iOS and Emscripten builds). It means that OpenGL is given to me by the GLES one while having a more limited API (The GL code should have some ifdef with GLES so slightly different path could be taken inside the GL code).
@ken-martin might be able to provide more context on that aspect.
Thanks Brad for looking into that,
Seb
---
### Author:  [@ken-martin](https://discourse.vtk.org/u/ken-martin)
#### Post date: [April 16, 2020, 2:21pm UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/6 "2020-04-16T14:21:23Z")
gles is basically an opengl implementation. If we are using gles then that becomes our OpenGL if that helps
---
### Author:  [@ben.boeckel](https://discourse.vtk.org/u/ben.boeckel)
#### Post date: [April 16, 2020, 3:00pm UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/7 "2020-04-16T15:00:07Z")
@Sebastien_Jourdain Please try [https://gitlab.kitware.com/vtk/vtk/-/merge\_requests/6751](https://gitlab.kitware.com/vtk/vtk/-/merge_requests/6751).
Let’s also open an issue to add Emscripten builds to CI.
---
### Author:  [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [April 16, 2020, 7:00pm UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/8 "2020-04-16T19:00:55Z")
The issue for adding an emscripten builder is here: [https://gitlab.kitware.com/vtk/vtk/-/issues/17856](https://gitlab.kitware.com/vtk/vtk/-/issues/17856)
---
### Author:  [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [April 24, 2020, 11:50am UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/9 "2020-04-24T11:50:16Z")
Things are moving forward and we start having working examples inside FireFox.
If you want to learn more on how to build VTK for Emscripten and write some C++ application with rendering for Web client usage, please follow the VTK/Emscripten examples and [README](https://gitlab.kitware.com/vtk/vtk/-/tree/master/Examples%2FEmscripten%2FCxx).
---
### Author:  [@sheonny](https://discourse.vtk.org/u/sheonny)
#### Post date: [February 16, 2023, 1:22am UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/10 "2023-02-16T01:22:35Z")
There is no InteractionImage module in the VTK built with emscripten, so vtkimageViewer2 cannot be used. Why?
---
### Author:  [@ben.boeckel](https://discourse.vtk.org/u/ben.boeckel)
#### Post date: [February 16, 2023, 6:27am UTC](https://discourse.vtk.org/t/building-vtk-9-with-emscripten-gles-for-rendering/3038/11 "2023-02-16T06:27:53Z")
A new thread would be best. However, you can pass `-DVTK_DEBUG_MODULE=ON -DVTK_DEBUG_MODULE_ALL=ON` to see why it is disabled (these flags tell the module system to log what it finds, why they’re on/off, etc.).