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jaylib-wasm-demo

A demo of using jaylib in a web browser

Overview

The current approach is to build a small program that embeds janet and is linked to Raylib. The program loads and executes an example game written in Janet that uses Raylib via jaylib.

The program is made executable in a web browser by being compiled by Emscripten.

The goal of this demo is to produce appropriate .wasm, .js, .html, and related files and then to test their functionality via a web browser. Before compilation via Emscripten can take place, some pieces need to be prepared:

  • main.c - the aforementioned small program
  • janet.c + support files - for embedding janet
  • libraylib.a - "HTML5-ready" Raylib static library
  • game.janet - a small game written in Janet / jaylib

Prerequisites

  • Emscripten 3.1.3 (other versions might work)
  • Usual build tools (e.g. to get Emscripten working on Windows Python is needed)
  • Janet

Steps

  • Ensure repository has been cloned recursively:

    git clone --recursive https://github.com/sogaiu/jaylib-wasm-demo

  • For *nixen, with emsdk under ~/src/emsdk:

    source ~/src/emsdk/emsdk_env.sh
janet build-unix.janet

  • For Windows, with emsdk in a sibling directory of this repository (likely need to do via a Native Tools Command Prompt):

    ..\emsdk\emsdk_env.bat
janet build-windows.janet

  • Start a web server to serve the built files:

    For a machine with python3, that might be:

    python3 -m http.server --directory public

  • Try out the results:

    Visit http://localhost:8000 and click on main.html

Notes

The "game loop" currently relies on invoking a modified version of janet_pcall named janet_pcall_keep_env to invoke Janet code. janet_pcall resets passed fibers (or creates completely new ones) which implies that dynamic variables are not preserved between invocations because dynamic variables are associated with specific fibers. If janet_pcall_keep_env is passed a non-NULL fiber, the associated environment (and hence dynamic variables) are reused.

An alternative is to use janet_continue, which allows one to pass a fiber which doesn't get reset. Since the same fiber can be reused without resetting, dynamic variables can be preserved between invocations. However, Emscripten then produces somewhat broken code [1] unless ASYNCIFY is specified when compiling (this was discovered via a DevTools console message). Using ASYNCIFY does yield running code, but the resulting code is likely slower due to added instrumentation. Additionally, at present, audio hasn't been made to work for the janet_continue + ASYNCIFY combination (at least in this demo)...

In summary, current advice is:

  • if audio is desired, either use janet_pcall and don't use dynamic variables, or use janet_pcall_keep_env.
  • if audio is unneeded, one can use janet_continue instead.

[1] Currently, it's not clear why ASYNCIFY is necessary. bakpakin's webrepl.c for janet-lang.org's web REPL also uses janet_continue but ASYNCIFY does not appear to be needed there. One difference that might be relevant is that the demo would be triggering janet_continue via emscripten_set_main_loop, while webrepl.c's janet_continue is user-triggered.

Issues

  • On Windows if janet build-windows.janet fails in the final compilation step, it may be worth trying this workaround.

Thanks

  • bakpakin
  • MikeBeller
  • pyrmont
  • raysan5
  • saikyun
  • yumaikas
  • ZakharValaha