[build][cmake] Added emscripten build options

[brccabral]

Missing options for compiling as Web.

[raysan5]

@brccabral Thanks for the review and clarifications!

[Peter0x44]

Are you sure this is a good idea? -sASYNCIFY is not needed if you use emscripten_set_main_loop and apparently makes perf worse.

[Peter0x44]

IMO this should be reverted.

[raysan5]

@Peter0x44 thanks for the review and the comments! As per mi understanding, this CMake is intended only for raylib examples collection, that requires -sASYNCIFY... or I missunderstood it? @brccabral please, can you confirm?

And yeah, -sASYNCIFY affects performance, it must not be used if using emscripten_set_main_loop().

[Peter0x44]

If I'm reading this correctly, it will make sure any time you link with raylib through cmake, -sASYNCIFY gets passed. When you might not want it.
It's not specific to the examples.

[Peter0x44]

If the intention is that it only passes this to the examples, then IMO, it should be the examples CMakeLists.txt providing the link options, not raylib.

[brccabral]

Well, the option -sUSE_GLFW=3 was already there, I saw the others in the examples/build_example_web.bat and thought this was the way Raylib uses Emscripten.
I am fine with having link options in the examples (SDL does it).
It would be nice having a specific example, but I am not sure how emscripten_set_main_loop() works.
SDL examples sets only -sALLOW_MEMORY_GROWTH=1, no -sASYNCIFY ...

[Peter0x44]

-sUSE_GLFW=3 is fine because it is required 100% of the time. The other two flags are not, and ASYNCIFY has negative consequences!

It's unacceptable to require those flags for everyone consuming raylib through cmake.

core_basic_window_web.c demonstrates how to use emscripten_set_main_loop.
I'll submit a PR reverting this tomorrow if no one else gets to it first.

[brccabral]

This line is in examples/CMakeLists.txt

set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -s WASM=1 -s ASYNCIFY -s ALLOW_MEMORY_GROWTH=1 --shell-file ${CMAKE_SOURCE_DIR}/src/shell.html")

[brccabral]

Where is core_basic_window_web.c? https://github.com/raysan5/raylib/tree/master/examples/core ?

[Peter0x44]

Ray deleted it in this commit.
c17f82a

[brccabral]

Found something, the browser error was caused by emscripten_sleep(12); in src/platforms/rcore_web.c.
There is no Javascript error if I comment this line.
Edit: after reading the comment, looks like WindowShouldClose() should not be used on web...

bool WindowShouldClose(void)
{
    // Emscripten Asyncify is required to run synchronous code in asynchronous JS
    // REF: https://emscripten.org/docs/porting/asyncify.html

    // WindowShouldClose() is not called on a web-ready raylib application if using emscripten_set_main_loop()
    // and encapsulating one frame execution on a UpdateDrawFrame() function,
    // allowing the browser to manage execution asynchronously

    // Optionally we can manage the time we give-control-back-to-browser if required,
    // but it seems below line could generate stuttering on some browsers
    emscripten_sleep(12);

    return false;
}

[brccabral]

This file contains a PLATFORM_WEB example projects/CMake/core_basic_window.c, but its projects/CMake/CMakeLists.txt uses -s ASYNCIFY

[raysan5]

Ray deleted it in this commit. c17f82a

Yeah, I'm reorganizing examples at the moment and I just deleted it temporally to place it somewhere else. It was just a few days ago, sorry for the confusion.

@brccabral When building for web, it's recommended to use the emscripten_set_main_loop() mechanism provided by emscriptem but that's not always possible so ASYNCIFY alternative is available, with some performance hit. Examples structure is common for all platforms so using that ASYNCIFY approach but users creating code from scratch with web in mind (specially if it is a big project) should use the emscripten_set_main_loop() approach.

When using ASYNCIFY, emscripten must be notified when it has time to manage the loop, so emscripten_sleep() is required... but never when using emscripten_set_main_loop().