How to configure an emscripten target to be built with the default html wrapper?

Question

My question is regarding using a CMakeLists.txt with Emscriptem and specifying the output type along with a command line option.

I want to take a simple Emscripten command such as: emcc file.cpp -o file.html --preload-file asset_dir/ and change it to something that I can specify within my CMake system. I tried the naive approach of renaming the executable to have an extension of html but that didn't work. I also tried using -D--preload-file:PATH=asset_dir and that did not work either.

My CMakeLists.txt file is small and is contained below. I use the command emcmake cmake -G"Unix Makefiles" -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_COMPILER=em++ .. && emmake make to build it.

CMAKE_MINIMUM_REQUIRED(VERSION 3.2.0 FATAL_ERROR)
PROJECT(ProjJS)

# Set typical CMAKE settings
SET(CMAKE_BUILD_TYPE_INIT "Release")
SET(CMAKE_VERBOSE_MAKEFILE OFF CACHE BOOL "Turn on Verbose Makefiles" FORCE)
set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake/modules")

SET(CMAKE_CXX_STANDARD 11)
SET(CMAKE_CXX_STANDARD_REQUIRED ON)

SET(PROJ_SOURCES
    hello.cpp
    ....
)

set(NAME_OF_EXE "ProjJS")

set(BOOST_LIB "boost")
set(BOOST_INCLUDE_PATH "${CMAKE_SOURCE_DIR}/extlibs/")
set(BOOST_LIB_PATH "${CMAKE_SOURCE_DIR}/extlibs/boost/libs/")

add_subdirectory(extlibs/boost)


SET(BOOST_PROGRAM_OPTIONS_SOURCES
    ${BOOST_LIB_PATH}/program_options/cmdline.cpp
    ${BOOST_LIB_PATH}/program_options/config_file.cpp
    ....
)

SET(BOOST_SYSTEM_SOURCES
    ${BOOST_LIB_PATH}/system/error_code.cpp
)

ADD_EXECUTABLE(${NAME_OF_EXE} ${PROJ_SOURCES})
add_library(${BOOST_LIB} STATIC ${BOOST_PROGRAM_OPTIONS_SOURCES} ${BOOST_SYSTEM_SOURCES})
TARGET_INCLUDE_DIRECTORIES(${BOOST_LIB} PUBLIC "${BOOST_INCLUDE_PATH}")

TARGET_LINK_LIBRARIES(${NAME_OF_EXE} PUBLIC ${BOOST_LIB})
TARGET_INCLUDE_DIRECTORIES(${NAME_OF_EXE} BEFORE PRIVATE "${CMAKE_SOURCE_DIR}/include")
TARGET_INCLUDE_DIRECTORIES(${NAME_OF_EXE} BEFORE PRIVATE "${BOOST_INCLUDE_PATH}" ${PROJ_SOURCES})

I am not familiar with emscripten, but it seems that it differs a lot from "normal" compilers. So, it is not sufficient to just change a compiler executable, and expect CMake to do other work. Aside from the compiler itself you need to adjust many other compiler-related things. The best way for doing this is toolchain file. You may prepare your own toolchain file, or google for existed one. E.g., you may try this toolchain. — Tsyvarev
– Tsyvarev, Commented Feb 22, 2017 at 7:39
Did you figure it out? Im stuck with the same (just made a ticket stackoverflow.com/questions/45260216/…) — DutchKevv
– DutchKevv, Commented Jul 22, 2017 at 23:42
I don't think you need to explicitly specify CMAKE_CXX_COMPILER when you're already wrapping with emcmake. emcmake adds the emscripten toolchain file argument, which should cover that for you. — starball
– starball ♦, Commented Nov 27, 2022 at 20:45

Alon Zakai · Accepted Answer · 2020-05-14 17:18:01Z

3

For the output suffix this should work:

set(CMAKE_EXECUTABLE_SUFFIX ".html")

Complete example:

cmake_minimum_required(VERSION 2.6 FATAL_ERROR)
project(demo)

set(CMAKE_EXECUTABLE_SUFFIX ".html")

add_executable(hello tests/hello_world.cpp)

That will emit hello.html etc.

For other flags, the best option I've found is to use target_link_libraries which CMake just appends to the link line, and can contain anything. For example:

target_link_libraries(binaryen_js "-s MODULARIZE")
target_link_libraries(binaryen_js "-s INITIAL_MEMORY=512MB")

That turns on modularize and sets the initial memory to 512MB (example from the Binaryen CMake script).

answered May 14, 2020 at 17:18

Alon Zakai

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2 Comments

starball Over a year ago

Why (ab)use target_link_libraries for linker flags when there is target_link_options dedicated for the purpose of setting linker flags?

Alon Zakai Over a year ago

Good point, target_link_options is probably better. It was added later to CMake I think, so target_link_libraries was needed in the past but probably isn't today.

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