Tag Archives: hints

Building a project with dependencies for Emscripten

In this note I will describe the assembly of a project consisting of several libraries using Emscripten.
At the moment Emscripten does not support building shared libraries, so the first thing we do is convert all libraries from Shared to Static. Emscripten works with its own include files, so we need to solve the issue with the visibility of header files, I solved this by forwarding a symlink from the system directory to the Emscripten toolchain:

ln -s /usr/local/include/FlameSteelFramework $EMSDK/fastcomp/emscripten/system/include/FlameSteelFramework

If you use CMake, you need to change SHARED->STATIC in the CMakeLists.txt file of the add_library method. You can build a library/application for further static linking using the commands:

emcmake cmake .
emmake make

Next, you will need to build the main application specifying *.a library files at the linking stage. I was unable to specify a relative path, the build completed correctly only after specifying the full paths in the CMakeLists.txt file:

elseif(EMSCRIPTEN)
target_link_libraries(${FSEGT_PROJECT_NAME} GL GLEW 
/home/demensdeum/Sources/cube-art-project-bootstrap/cube-art-project/sharedLib/libCubeArtProject.a 
/home/demensdeum/Sources/cube-art-project-bootstrap/FlameSteelFramework/FlameSteelEngineGameToolkitFSGL/libFlameSteelEngineGameToolkitFSGL.a 
/home/demensdeum/Sources/cube-art-project-bootstrap/FlameSteelFramework/FlameSteelEngineGameToolkit/libFlameSteelEngineGameToolkit.a 
/home/demensdeum/Sources/cube-art-project-bootstrap/FlameSteelFramework/FlameSteelCore/libFlameSteelCore.a 
/home/demensdeum/Sources/cube-art-project-bootstrap/FlameSteelFramework/FlameSteelBattleHorn/libFlameSteelBattleHorn.a 
/home/demensdeum/Sources/cube-art-project-bootstrap/FlameSteelFramework/FSGL/libFSGL.a 
/home/demensdeum/Sources/cube-art-project-bootstrap/FlameSteelFramework/FlameSteelCommonTraits/libFlameSteelCommonTraits.a)
else()

Sources

https://emscripten.org/ docs/compiling/Building-Projects.html#using-libraries

Emscripten’s Lost Exceptions and Regex Issues

Lost exception

An interesting feature of Emscripten is that when starting a game loop via emscripten_set_main_loop, you should remember that exception handling must be re-added via try catch directly in the loop method, since the runtime loses the try catch block from the outside.
The easiest way to display the error text is through the browser, using javascript alert:

            catch (const std::exception &exc)
            {
                const char *errorText = exc.what();
                cout << "Exception: " << errorText << "; Stop execution" << endl;

                EM_ASM_(
                {
                    var errorText = UTF8ToString($0);
                    alert(errorText);

                }, errorText);

                abort();

Too complex regexp

The std implementation of regex may throw an error_complexity exception if it finds the regular expression too complex. This happens in the current emscripten implementation, so I suggest you implement tests for parsing via regular expressions, or use third-party regex implementations.