douady.txt

= Compiling to WebAssembly =

This page loads wasm that draws a set studied by Douady and Hubbard.

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<canvas id="canvas" width="640" height="400"></canvas>
<script>
var e;
var ctx = document.getElementById("canvas").getContext("2d");

function sq(x, y) { ctx.fillRect(x*4, y*4, 4, 4); }

WebAssembly.instantiateStreaming(fetch('douady.wasm'), {
    env:{ plot:sq }
  }).then(obj => {
  e = obj.instance.exports;
  e.rts_init();
  e.draw();
});
</script>
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The Haskell source:

[source,haskell]
------------------------------------------------------------------------
include::wasm/douady.hs[]
------------------------------------------------------------------------

To turn the output of our compiler into wasm, we need minimal implementations
of `malloc` and `memcpy`:

[source,c]
------------------------------------------------------------------------
include::wasm/std.c[]
------------------------------------------------------------------------

Then we supply certain options to Clang:

------------------------------------------------------------------------
$ (cat rts.c && lonely < douady.hs) > douady.c
$ alias wcc=clang -O3 -c --target=wasm32 -Wall
$ alias wld=wasm-ld-8 --export-dynamic --allow-undefined --no-entry
$ wcc douady.c std.c
$ wld --initial-memory=33554432 douady.o std.o -o douady.wasm
------------------------------------------------------------------------