2017-02-07 10:25:41 +01:00
|
|
|
__ __ ____ ____ ____ __ ____
|
|
|
|
|
/ \\/ \ _ \ _ \ _ \ (__)/ __\
|
|
|
|
|
\ / __/ _ \ __/ _) \_ \
|
|
|
|
|
\__\__/_____/____/_/ /____/____/
|
|
|
|
|
|
|
|
|
|
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:
|
2021-05-21 20:47:01 +02:00
|
|
|
https://emscripten.org/docs/getting_started/downloads.html#installation-instructions-using-the-emsdk-recommended
|
2017-02-07 10:25:41 +01:00
|
|
|
After installation, you should have some global variable positioned to the
|
2021-05-21 20:47:01 +02:00
|
|
|
location of the SDK. In particular, $EMSDK should point to the
|
2017-02-07 10:25:41 +01:00
|
|
|
top-level directory containing Emscripten tools.
|
|
|
|
|
|
|
|
|
|
- configure the project 'WEBP_JS' with CMake using:
|
|
|
|
|
|
|
|
|
|
cd webp_js && \
|
2021-05-21 20:47:01 +02:00
|
|
|
emcmake cmake -DWEBP_BUILD_WEBP_JS=ON \
|
2017-02-07 10:25:41 +01:00
|
|
|
../
|
|
|
|
|
|
2021-05-21 20:47:01 +02:00
|
|
|
- compile webp.js using 'emmake make'.
|
2017-02-07 10:25:41 +01:00
|
|
|
|
|
|
|
|
- that's it! Upon completion, you should have the webp.js and
|
2020-04-16 04:53:12 +02:00
|
|
|
webp.wasm files generated.
|
2017-02-07 10:25:41 +01:00
|
|
|
|
|
|
|
|
The callable JavaScript function is WebPToSDL(), which decodes a raw WebP
|
2018-04-03 13:55:33 +02:00
|
|
|
bitstream into a canvas. See webp_js/index.html for a simple usage sample
|
|
|
|
|
(see below for instructions).
|
2017-02-07 10:25:41 +01:00
|
|
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
|
|
|
|
2017-03-20 14:03:57 +01:00
|
|
|
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.
|
|
|
|
|
|
2021-05-24 19:35:36 +02:00
|
|
|
You will need a fairly recent version of Emscripten (at least 2.0.18,
|
2020-04-17 02:58:26 +02:00
|
|
|
latest-upstream is recommended) and of your WASM-enabled browser to run this
|
|
|
|
|
version.
|
2017-03-20 14:03:57 +01:00
|
|
|
|
2017-02-07 10:25:41 +01:00
|
|
|
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:
|
|
|
|
|
https://github.com/kripken/emscripten/issues/3788
|
|
|
|
|
|
|
|
|
|
Therefore, SSE2 optimization is currently disabled in CMakeLists.txt.
|
2020-11-24 03:47:05 +01:00
|
|
|
|
|
|
|
|
- If WEBP_ENABLE_SIMD is set to 1 the JavaScript version (webp.js) will be
|
|
|
|
|
disabled as wasm2js does not support SIMD.
|
