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Add possibility for disabling inlining wasm in opencv.js #23344

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merged 1 commit into from Mar 21, 2023
Merged

Add possibility for disabling inlining wasm in opencv.js #23344

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3 changes: 3 additions & 0 deletions doc/js_tutorials/js_setup/js_setup/js_setup.markdown
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Expand Up @@ -83,6 +83,9 @@ Building OpenCV.js from Source
It requires `python` and `cmake` installed in your development environment.

-# The build script builds asm.js version by default. To build WebAssembly version, append `--build_wasm` switch.
By default everything is bundled into one JavaScript file by `base64` encoding the WebAssembly code. For production
builds you can add `--disable_single_file` which will reduce total size by writing the WebAssembly code
to a dedicated `.wasm` file which the generated JavaScript file will automatically load.
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Can this approach fix this issue as well? #21431. Which size reduction do you observe?

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  • Single file: 8.74 MB .js
  • Separate .wasm file: 170 kB .js + 6.43 MB .wasm

I.e. bundling the generated webassembly code with base64 is ~32-33 % larger in total compared with separate .wasm file (consistent with typical base64 encoding size increases).


For example, to build wasm version in `build_wasm` directory:
@code{.bash}
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2 changes: 1 addition & 1 deletion modules/js/CMakeLists.txt
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Expand Up @@ -70,7 +70,7 @@ if(COMPILE_FLAGS)
endif()

set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} --memory-init-file 0 -s TOTAL_MEMORY=128MB -s WASM_MEM_MAX=1GB -s ALLOW_MEMORY_GROWTH=1")
set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} -s MODULARIZE=1 -s SINGLE_FILE=1")
set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} -s MODULARIZE=1")
set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} -s EXPORT_NAME=\"'cv'\" -s DEMANGLE_SUPPORT=1")
set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} -s FORCE_FILESYSTEM=1 --use-preload-plugins --bind --post-js ${JS_HELPER} ${COMPILE_FLAGS}")
set_target_properties(${the_module} PROPERTIES LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS}")
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3 changes: 3 additions & 0 deletions platforms/js/build_js.py
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Expand Up @@ -180,6 +180,8 @@ def get_build_flags(self):
flags += "-s WASM=1 "
elif self.options.disable_wasm:
flags += "-s WASM=0 "
if not self.options.disable_single_file:
flags += "-s SINGLE_FILE=1 "
if self.options.threads:
flags += "-s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=4 "
else:
Expand Down Expand Up @@ -233,6 +235,7 @@ def build_loader(self):
parser.add_argument('--emscripten_dir', default=emscripten_dir, help="Path to Emscripten to use for build (deprecated in favor of 'emcmake' launcher)")
parser.add_argument('--build_wasm', action="store_true", help="Build OpenCV.js in WebAssembly format")
parser.add_argument('--disable_wasm', action="store_true", help="Build OpenCV.js in Asm.js format")
parser.add_argument('--disable_single_file', action="store_true", help="Do not merge JavaScript and WebAssembly into one single file")
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I think it make sense highlight wasm in the flag naming. Something like --disable_wasm_merge or --build_standalone_wasm.

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However, origin option is SINGLE_FILE so it's also logical to keep --disable_single_file 🤔

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Agree, pros and cons, no strong opinion from my side on argument name 🙂 If we are to move away from single_file in the argument name I think I personally like your second suggestion the best, i.e. --build_standalone_wasm (we then avoid the word disable, which maybe makes the argument name slightly easier to interpret by removing a negation).

Happy to modify the PR if you decide on some other name instead of --disable_single_file.

parser.add_argument('--threads', action="store_true", help="Build OpenCV.js with threads optimization")
parser.add_argument('--simd', action="store_true", help="Build OpenCV.js with SIMD optimization")
parser.add_argument('--build_test', action="store_true", help="Build tests")
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