Emscripten version of http://schellcode.github.io/webassembly-without-emscripten

comparison.markdown

Sizes

(html+js+wasm)

Non-emscripten: 19,964 bytes
Emscripten:     11,086 bytes

The biggest factor here is that the emscripten version uses emscripten's standard minification features (like closure compiler, --low-memory-unused, etc.) which the other one doesn't (it was minified using Uglify3 as mentioned in that post).

Please let me know if I missed something or got anything wrong!

Building

• Non-emscripten: See details in http://schellcode.github.io/webassembly-without-emscripten and in particular the Makefile.
• Emscripten: emcc -Os main_ems.cpp -o main_ems.html -s MINIMAL_RUNTIME -lwebgl.js --closure 1 -s JS_MATH

Notes:

• The non-emscripten version uses JS to do Math.asin etc., which is smaller than emscripten's default behavior which is to use compiled musl code, which is faster. For a more apples-to-apples comparison, the emscripten version sets JS_MATH which does something similar. This makes both versions about 25% smaller, but also both suffer a speed penalty because of this, so it's not recommended in general.

Summary

Emscripten aims to provide a simple interface for users (at the cost of internal complexity inside the tool), and to integrate the most powerful minification and optimization tools. So there are tradeoffs to using it versus a more barebones approach like in that post.

It's good we have options! And that post does a good job of explaining the technical details of one type of approach. We just need to be aware of the tradeoffs.

In this case, it's less work to set up the emscripten version (everything in a single compile command on one line; no need for the 100+ line Makefile), and it's smaller (and likely faster, see the note above on musl vs JS). On the other hand, the barebones approach gives you more control, and if you put in enough work, you can get interesting results for specific use cases.

main_ems.cpp

/*
This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to <http://unlicense.org/>
*/

#include <emscripten/emscripten.h>
#include <emscripten/html5.h>

#define GL_GLEXT_PROTOTYPES
#define EGL_EGLEXT_PROTOTYPES
#include <GL/gl.h>
#include <GLES2/gl2.h>
#include <math.h>

static const char* vertex_shader_text =
	"precision lowp float;"
	"uniform mat4 uMVP;"
	"attribute vec4 aPos;"
	"attribute vec3 aCol;"
	"varying vec3 vCol;"
	"void main()"
	"{"
		"vCol = aCol;"
		"gl_Position = uMVP * aPos;"
	"}";

static const char* fragment_shader_text =
	"precision lowp float;"
	"varying vec3 vCol;"
	"void main()"
	"{"
		"gl_FragColor = vec4(vCol, 1.0);"
	"}";

typedef struct Vertex { float x, y, r, g, b; } Vertex;
static GLuint program, vertex_buffer;
static GLint uMVP_location, aPos_location, aCol_location;

int WAFNDraw(double f, void*);

// This function is called at startup
int main(int argc, char *argv[])
{
  emscripten_set_canvas_element_size("canvas", 640, 480);

  EmscriptenWebGLContextAttributes attrs;
  emscripten_webgl_init_context_attributes(&attrs);
  attrs.alpha = 0;
  auto glContext = emscripten_webgl_create_context("canvas", &attrs);
  emscripten_webgl_make_context_current(glContext);

	glViewport(0, 0, 640, 480);

	GLuint vertex_shader = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vertex_shader, 1, &vertex_shader_text, NULL);
	glCompileShader(vertex_shader);

	GLuint fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragment_shader, 1, &fragment_shader_text, NULL);
	glCompileShader(fragment_shader);

	program = glCreateProgram();
	glAttachShader(program, vertex_shader);
	glAttachShader(program, fragment_shader);
	glLinkProgram(program);

	uMVP_location = glGetUniformLocation(program, "uMVP");
	aPos_location = glGetAttribLocation(program, "aPos");
	aCol_location = glGetAttribLocation(program, "aCol");

	glGenBuffers(1, &vertex_buffer);
	glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);

	glEnableVertexAttribArray(aPos_location);
	glVertexAttribPointer(aPos_location, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)0);
	glEnableVertexAttribArray(aCol_location);
	glVertexAttribPointer(aCol_location, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)(sizeof(float) * 2));

  emscripten_request_animation_frame_loop(&WAFNDraw, 0);

	return 0;
}

// This function is called by loader.js every frame
int WAFNDraw(double f, void*)
{
	f /= 1000.0;

	glClear(GL_COLOR_BUFFER_BIT);

	Vertex vertices[3] =
	{
		{ -0.6f, -0.4f, 1.f, 0.f, 0.f },
		{  0.6f, -0.4f, 0.f, 0.f, 1.f },
		{   0.f,  0.6f, 1.f, 1.f, 1.f },
	};
	vertices[0].r = 0.5f + sinf(f * 3.14159f * 2.0f) * 0.5f;
	vertices[1].b = 0.5f + cosf(f * 3.14159f * 2.0f) * 0.5f;
	glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

	GLfloat mvp[4*4] = { 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, -1, 0, 0, 0, 0, 1 };
	glUseProgram(program);
	glUniformMatrix4fv(uMVP_location, 1, GL_FALSE, mvp);
	glDrawArrays(GL_TRIANGLES, 0, 3);

  return EM_TRUE;
}

main_ems.html

<!doctypehtml><html lang=en-us><head><meta charset=utf-8></head><body><canvas style=display:block;margin:auto></canvas><script>var Module={};function binary(e){return new Promise((n,r)=>{var a=new XMLHttpRequest;a.open("GET",e,!0),a.responseType="arraybuffer",a.onload=()=>{n(a.response)},a.send(null)})}function script(e){return new Promise((n,r)=>{var a=document.createElement("script");a.src=e,a.onload=()=>{n()},document.body.appendChild(a)})}Promise.all([binary("main_ems.js"),binary("main_ems.wasm")]).then(e=>{Module.wasm=e[1];var n=URL.createObjectURL(new Blob([e[0]],{type:"application/javascript"}));script(n).then(()=>{URL.revokeObjectURL(n)})})</script></body></html>

main_ems.js

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function z(a){return x[a]||("undefined"!==typeof document?document.querySelector(w(a)):void 0)}function A(a){var b=a.getExtension("ANGLE_instanced_arrays");b&&(a.vertexAttribDivisor=function(c,d){b.vertexAttribDivisorANGLE(c,d)},a.drawArraysInstanced=function(c,d,e,f){b.drawArraysInstancedANGLE(c,d,e,f)},a.drawElementsInstanced=function(c,d,e,f,g){b.drawElementsInstancedANGLE(c,d,e,f,g)})}
function B(a){var b=a.getExtension("OES_vertex_array_object");b&&(a.createVertexArray=function(){return b.createVertexArrayOES()},a.deleteVertexArray=function(c){b.deleteVertexArrayOES(c)},a.bindVertexArray=function(c){b.bindVertexArrayOES(c)},a.isVertexArray=function(c){return b.isVertexArrayOES(c)})}function D(a){var b=a.getExtension("WEBGL_draw_buffers");b&&(a.drawBuffers=function(c,d){b.drawBuffersWEBGL(c,d)})}var E=1,F=0,G=[],H=[],I=[],J=[],K=[],L=null,M={};
function N(a){for(var b=E++,c=a.length;c<b;c++)a[c]=null;return b}var O=[0];
function P(a){a||(a=L);if(!a.H){a.H=!0;var b=a.B;2>a.version&&(A(b),B(b),D(b));b.L=b.getExtension("EXT_disjoint_timer_query");var c="OES_texture_float OES_texture_half_float OES_standard_derivatives OES_vertex_array_object WEBGL_compressed_texture_s3tc WEBGL_depth_texture OES_element_index_uint EXT_texture_filter_anisotropic EXT_frag_depth WEBGL_draw_buffers ANGLE_instanced_arrays OES_texture_float_linear OES_texture_half_float_linear EXT_blend_minmax EXT_shader_texture_lod EXT_texture_norm16 WEBGL_compressed_texture_pvrtc EXT_color_buffer_half_float WEBGL_color_buffer_float EXT_sRGB WEBGL_compressed_texture_etc1 EXT_disjoint_timer_query WEBGL_compressed_texture_etc WEBGL_compressed_texture_astc EXT_color_buffer_float WEBGL_compressed_texture_s3tc_srgb EXT_disjoint_timer_query_webgl2 WEBKIT_WEBGL_compressed_texture_pvrtc".split(" ");(b.getSupportedExtensions()||
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WebAssembly.instantiate(h.wasm,{a:{m:function(a){return Math.cos(a)},l:function(a){return Math.sin(a)},t:function(a,b){function c(d){V(a,d,b)&&requestAnimationFrame(c)}return requestAnimationFrame(c)},y:function(a,b,c){a=z(a);if(!a)return-4;a.width=b;a.height=c;return 0},q:function(a,b){var c={};b>>=2;c.alpha=!!u[b];c.depth=!!u[b+1];c.stencil=!!u[b+2];c.antialias=!!u[b+3];c.premultipliedAlpha=!!u[b+4];c.preserveDrawingBuffer=!!u[b+5];c.powerPreference=Q[u[b+6]];c.failIfMajorPerformanceCaveat=!!u[b+
7];c.I=u[b+8];c.P=u[b+9];c.C=u[b+10];c.G=u[b+11];c.R=u[b+12];c.S=u[b+13];a=z(a);if(!a||c.G)c=0;else if(a=a.getContext("webgl",c)){b=N(K);var d={M:b,attributes:c,version:c.I,B:a};a.canvas&&(a.canvas.J=d);K[b]=d;("undefined"===typeof c.C||c.C)&&P(d);c=b}else c=0;return c},x:function(a){a>>=2;for(var b=0;14>b;++b)u[a+b]=0;u[a]=u[a+1]=u[a+3]=u[a+4]=u[a+8]=u[a+10]=1},k:function(a){L=K[a];h.K=R=L&&L.B;return!a||R?0:-5},a:function(a,b){R.attachShader(H[a],J[b])},g:function(a,b){R.bindBuffer(a,G[b])},r:function(a,
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main_ems.wasm

But there are valid scenarios where not depending on the emscripten SDK makes a lot of sense.

I definitely agree!

Specifically, if you need little Web API integration, then emscripten is probably not necessary - but may still be useful as it gives good default optimizations, otherwise you need to integrate with lld and binaryen manually, and it's easy to miss important optimizations (like --low-memory-unused). But if you do need significant JS or Web API stuff, or you need stuff like files, pthreads, exceptions, asyncify, etc. etc., then that's what emscripten is for.

The one small critique I have with the current emscripten SDK is that it is such a "hodge podge" of tooling technologies. There's python, node.js, Java and native tools. Thankfully that's all hidden under "emcc", but I wonder how much overhead is required to keep it all running. It "feels" a bit brittle :)

I would prefer to have fewer as well. However, it doesn't take much overhead, and isn't brittle (at least I see no signs of that? the one annoyance I can think of is python issues with certificates, but not sure another language would avoid those...). The one thing we could in theory remove is the python code, and rewrite that for node or for native code. But I'm not sure that would be worth it as the benefit would mainly be just that things feel simpler. If someone is interested though, it's worth talking about.

Java, btw, is no longer necessary. The one thing we used Java for was the closure compiler. As we use that from node now, Java isn't normally needed (on most platforms the closure package will install a native executable, which I believe is AOT compiled Java).

Otherwise, we need those things:

• Node.js is necessary for JS parsing and optimization. We use acorn and other things. It would be very hard to do JS integration without those!
• Native tools are necessary since without LLVM, clang, lld, and binaryen we would be completely lost!

Java, btw, is no longer necessary.

That is most excellent news :)