__ __ ____ ____ ____ __ ____ / \\/ \ _ \ _ \ _ \ (__)/ __\ \ / __/ _ \ __/ _) \_ \ \__\__/_____/____/_/ /____/____/ Description: ============ This file describes the compilation of libwebp into a JavaScript decoder using Emscripten and CMake. - install the Emscripten SDK following the procedure described at: After installation, you should have some global variable positioned to the location of the SDK. In particular, $EMSCRIPTEN should point to the top-level directory containing Emscripten tools. - make sure the file $EMSCRIPTEN/cmake/Modules/Platform/Emscripten.cmake is accessible. This is the toolchain file used by CMake to invoke Emscripten. - configure the project 'WEBP_JS' with CMake using: cd webp_js && \ cmake -DWEBP_BUILD_WEBP_JS=ON \ -DEMSCRIPTEN_GENERATE_BITCODE_STATIC_LIBRARIES=1 \ -DCMAKE_TOOLCHAIN_FILE=$EMSCRIPTEN/cmake/Modules/Platform/Emscripten.cmake \ ../ - compile webp.js using 'make'. - that's it! Upon completion, you should have the webp.js and webp.js.mem files generated. The callable JavaScript function is WebPToSDL(), which decodes a raw WebP bitstream into a canvas. See webp_js/index.html for a simple usage sample (see below for instructions). Demo HTML page: =============== The HTML page webp_js/index.html requires an HTTP server to serve the WebP image example. It's easy to just use Python for that. cd webp_js && python -m SimpleHTTPServer 8080 and then navigate to http://localhost:8080 in your favorite browser. Web-Assembly (WASM) version: ============================ CMakeLists.txt is configured to build the WASM version when using the option WEBP_BUILD_WEBP_JS=ON. The compilation step will assemble the files 'webp_wasm.js', 'webp_wasm.wasm' in the webp_js/ directory. See webp_js/index_wasm.html for a simple demo page using the WASM version of the library. You will need a fairly recent version of Emscripten (at least 1.37.8) and of your WASM-enabled browser to run this version. Consider it very experimental! Caveat: ======= - First decoding using the library is usually slower, due to just-in-time compilation. - Some versions of llvm produce the following compile error when SSE2 is enabled. "Unsupported: %516 = bitcast <8 x i16> %481 to i128 LLVM ERROR: BitCast Instruction not yet supported for integer types larger than 64 bits" The corresponding Emscripten bug is at: Therefore, SSE2 optimization is currently disabled in CMakeLists.txt.