Examples on asm.js

[bullno1]

Due to the use of while(true), none of the examples work on asm.js.

To suport emscripten_set_main_loop, all examples will have to be rewritten. The lack of a stack makes it quite troublesome. Local variables will have to become static or instance variables.

[bkaradzic]

Yup, that's why it's not supported yet... 17-drawstress work.

[RichardGale]

+1 vote for statics.

[bkaradzic]

@RichardGale Another problem is that resources have to be downloaded since there is no file system. Most of examples require some assets to be loaded.

[RichardGale]

Latest emscripten could make this problem easier to solve than other platforms.

If you add --preload-file [directory of resources] to emcc during finalization that entire directory is packed into a virtual file system that is automatically mounted by the Javascript. Then fopen() and other calls "just work".

Any other known issues?

[bkaradzic]

That's cool, nope. I just need to create init/update/shutdown for all examples, instead main with while loop.

[bkaradzic]

Do you know did they fix setjmp/longjmp?

Also if they add pthreads, that would also fix examples.

[RichardGale]

I don't know the state of setjmp/longjmp as I stopped using them. pthreads are experimental (emscripten-core/emscripten-fastcomp#67).

I took a look at drawstress and the transformation seemed:

1. move process events while loop contents into a separate function
2. mainloop calls loop.
3. set loop for emscripten, while(1) for all other platforms
4. resolve variables due to 1)
   and am thinking of looking at the other examples too.

[bkaradzic]

If setjmp/longjmp works no change to will be necessary... It could be faked with it.

[bkaradzic]

I had this before, but it didn't work:
https://searchcode.com/codesearch/view/26623312/

extern int _main_(int _argc, char** _argv);

static jmp_buf s_main;
static jmp_buf s_loop;

void emscripten_yield()
{
    if (!setjmp(s_main) )
    {
        longjmp(s_loop, 1);
    }
}

void loop()
{
    if (!setjmp(s_loop) )
    {
        longjmp(s_main, 1);
    }
}

int main(int _argc, char** _argv)
{
    if (!setjmp(s_loop) )
    {
        alloca(16<<10);
        _main_(_argc, _argv);
    }

    emscripten_set_main_loop(loop, 10, true);
}

Then in while loop just call (and it should work with any example):

emscripten_yield();

If this works, then I'll bury that emscripten_yield() somewhere in entry.cpp.

[RichardGale]

State of play:

Code that uses low-level features of the native environment, for example native stack manipulation in conjunction with setjmp/longjmp (we support normal setjmp/longjmp, but not with stack replacing, etc.)

https://kripken.github.io/emscriptem-site/docs/porting/guidelines/portability_guidelines.html

I'll try your code in my app.

[RichardGale]

Integrated with example-00-helloworld and got:

uncaught exception: longjmp

[bkaradzic]

I'm trying this now: https://github.com/kripken/emscripten/wiki/Emterpreter#emterpreter-async-run-synchronous-code

[bkaradzic]

This works, you just need to uncomment and rebuild:
bkaradzic/bx@a611d0b
f9e63f1

It's slow, but it can get you to other examples until I change them to have init/update/shutdown.

[bkaradzic]

I fixed a few examples to work with emscripten.