WebAssembly (wasm) target support, faster/smaller than asm.js

[satoshinm]

Build for wasm in addition to asm.js, expected faster but less compatible (requires prerelease browsers at the time of this writing). Build for both and let the user choose, or fallback automatically.

Add -s WASM=1 to emcc, and BINARYEN_METHOD native-wasm and/or asmjs, refer to: https://github.com/kripken/emscripten/wiki/WebAssembly

[satoshinm]

Adding -s WASM to CMakeFiles.txt LINK_FLAGS, it builds but cannot test locally due to promise fetch API:

craft.js:1806 Fetch API cannot load file:////NetCraft/build/craft.wasm. URL scheme must be "http" or "https" for CORS request.
Uncaught (in promise) TypeError: Failed to fetch
at getBinaryPromise (craft.js:1806)
at doNativeWasm (craft.js:1877)
at Object.Module.asm (craft.js:2027)
at craft.js:9827

run from a local server:

python -m SimpleHTTPServer

then http://localhost:8000/craft.html - this works in Chrome 57.0.2987.133, and seems snappier. The wasm build output with emscripten is a lot smaller:

build $ ls -lh craft*
-rw-r--r--  1 admin  staff   100K Apr  4 22:24 craft.html
-rw-r--r--  1 admin  staff   1.1M Apr  4 22:24 craft.js
-rw-r--r--  1 admin  staff   2.6M Apr  4 22:24 craft.wasm

than the asm.js emscripten output:

build $ ls -lh craft*
-rw-r--r--  1 admin  staff   100K Apr  4 22:32 craft.html
-rw-r--r--  1 admin  staff    14M Apr  4 22:32 craft.js

1.1M + 2.6M = 3.7M for wasm vs 14M for asm.js. But the downside is less browser compatibility, just hangs in Safari Technical Preview. So the asm.js-based emscripten build would still be needed.

Question now is how to integrate this variant into the build system. Make it a cmake option (to add to the arguments of cmake -DCMAKE_TOOLCHAIN_FILE=$EMSCRIPTEN/cmake/Modules/Platform/Emscripten.cmake ..)? Or maybe better, always build both asm.js and wasm (run build twice?), then load either with a fallback?

[satoshinm]

Added for GH-45 and this a wasm build type:

mkdir wasm-build
cmake -DWASM=1 -DCMAKE_BUILD_TYPE=Release -DCMAKE_TOOLCHAIN_FILE=$EMSCRIPTEN/cmake/Modules/Platform/Emscripten.cmake ..
make

However, wasm used to work, when I first tried it -- but now, get an out-of-memory access?!

craft.html:1251 exception thrown: RuntimeError: memory access out of bounds,RuntimeError: memory access out of bounds
at ([273]+70)
at ([279]+40)
at Object.Module._main (http://localhost:8000/craft.js:1:827350)
at Object.callMain (http://localhost:8000/craft.js:1:836819)
at doRun (http://localhost:8000/craft.js:1:837562)
at http://localhost:8000/craft.js:1:837712

What changed? Need to regress to 4/4, isolate

---

cp CMakeLists.txt /tmp

git checkout CMakeLists.txt
git checkout X
cp /tmp/CMakeLists.txt .

cd wasm-build
rm craft* ; make ; ls -l craft.wasm && python -m SimpleHTTPServer

works:

• 4/4 350ed47
• 4/5 7c2b666
• 4/8 13b538d before glfw 3.2.1 update
• 4/8 f658c51 Update to glfw 3.2.1

fails to compile (missing conditional compilation for web):

• aa99147 Add fullscreen/windowed toggle with F11 using glfwSetWindowMonitor()

broken (memory access out of bounds error):

• 4/8 999ac5e Add HTML5 fullscreen, on key callback (user action required)
• 4/8 a6774a2
• 4/8 93ae334

so it's something from aa99147 or 999ac5e? Wouldn't have expected it...

---

Starting with aa99147 and commenting out native calls so it compiles:

--- a/src/main.c
+++ b/src/main.c
@@ -2430,13 +2430,13 @@ void get_fullscreen_monitor_dimensions() {
 }
 
 void fullscreen_exit() {
-    glfwSetWindowMonitor(g->window, NULL, g->window_xpos, g->window_ypos, g->window_width, g->window_height, GLFW_DONT_CARE);
+    //glfwSetWindowMonitor(g->window, NULL, g->window_xpos, g->window_ypos, g->window_width, g->window_height, GLFW_DONT_CARE);
 }
 
 void fullscreen_enter() {
     glfwGetWindowPos(g->window, &g->window_xpos, &g->window_ypos);
     glfwGetWindowSize(g->window, &g->window_width, &g->window_height);
-    glfwSetWindowMonitor(g->window, g->fullscreen_monitor, 0, 0, g->fullscreen_width, g->fullscreen_height, GLFW_DONT_CARE);
+    //glfwSetWindowMonitor(g->window, g->fullscreen_monitor, 0, 0, g->fullscreen_width, g->fullscreen_height, GLFW_DONT_CARE);
 }
 
 void create_window() {

wasm does crash with RuntimeError: memory access out of bounds,RuntimeError: memory access out of bounds, so, it is something added in this commit

---

Found it: get_fullscreen_monitor_dimensions(). This calls glfwGetPrimaryMonitor() and indexes the video modes array, certainly not needed for the web. The variables it sets weren't being used on the web (native only, where there are monitors) so execution was harmless except for the out-of-bounds memory accesses it caused.

[satoshinm]