[Development] ERROR: Feature 'webengine-system-libwebp' was enabled, but the pre-condition 'libs.webengine-webp' failed.

[Michal Klocek]

Hi

With 'system-webengine-webp' option you are trying to force qwebenigne
to use system webp. WebEngine uses pkg-config for webp, there is no
separate test, you can check it yourself with:

pkg-config --libs libwebp libwebpmux libwebpdemux

Br

Michal

On 03/12/2018 11:07 AM, YuGiOhJCJ Mailing-List via Development wrote:
> Hello,
> 
> I am trying to build Qt 5.10.1 on Slackware64 14.2 with the "-system-webengine-webp" option and libwebp 0.6.1:
> ---
> $ ./configure -v \
> [...]
> 	-system-assimp \
> 	-system-doubleconversion \
> 	-system-freetype \
> 	-system-harfbuzz \
> 	-system-libjpeg \
> 	-system-libpng \
> 	-system-pcre \
> 	-system-sqlite \
> 	-system-xcb \
> 	-system-webengine-icu \
> 	-system-webengine-ffmpeg \
> 	-system-webengine-opus \
> 	-system-webengine-webp \
> 	-system-zlib \
> [...]
> 	-pulseaudio
> [...]
> Note: Also available for Linux: linux-clang linux-icc
> 
> Note: -headerdir is not a subdirectory of -prefix.
> Note: -libdir is not a subdirectory of -prefix.
> Note: -docdir is not a subdirectory of -prefix.
> 
> Note: -optimized-tools is not useful in -release mode.
> 
> Note: Dropped compiler flags '-pthread' when detecting library 'glib'.
> 
> Note: Dropped compiler flags '-pthread' when detecting library 'gtk3'.
> 
> Note: No wayland-egl support detected. Cross-toolkit compatibility disabled.
> 
> Note: Dropped compiler flags '-pthread' when detecting library 'gstreamer'.
> 
> Note: Dropped compiler flags '-pthread' when detecting library 'gstreamer_app'.
> 
> Note: Dropped compiler flags '-pthread' when detecting library 'webengine-protobuf'.
> 
> ERROR: Feature 'webengine-system-libwebp' was enabled, but the pre-condition 'libs.webengine-webp' failed.
> 
> ERROR: Feature 'webengine-system-ffmpeg' was enabled, but the pre-condition 'libs.webengine-ffmpeg && features.webengine-system-opus && features.webengine-system-libwebp' failed.
> ---
> 
> As you can see in the output above, the error is about the libwebp library that is not found (or at least that is not working correctly).
> 
> However, I found the test file that is checking the libwebp library and I tried it manually:
> ---
> $ cd qtimageformats/config.tests/libwebp
> $ qmake libwebp.pro
> $ make
> g++ -c -pipe -O2 -Wall -W  -I/usr/lib64/qt/mkspecs/linux-g++ -I. -o libwebp.o libwebp.cpp
> libwebp.cpp: In function ‘int main(int, char**)’:
> libwebp.cpp:40:20: warning: unused variable ‘output_buffer’ [-Wunused-variable]
>      WebPDecBuffer *output_buffer = &config.output;
>                     ^~~~~~~~~~~~~
> libwebp.cpp:41:28: warning: unused variable ‘bitstream’ [-Wunused-variable]
>      WebPBitstreamFeatures *bitstream = &config.input;
>                             ^~~~~~~~~
> libwebp.cpp:42:17: warning: variable ‘picture’ set but not used [-Wunused-but-set-variable]
>      WebPPicture picture;
>                  ^~~~~~~
> libwebp.cpp:44:16: warning: variable ‘config2’ set but not used [-Wunused-but-set-variable]
>      WebPConfig config2;
>                 ^~~~~~~
> libwebp.cpp:47:18: warning: unused variable ‘demuxer’ [-Wunused-variable]
>      WebPDemuxer *demuxer = WebPDemux(&data);
>                   ^~~~~~~
> libwebp.cpp:48:18: warning: variable ‘iter’ set but not used [-Wunused-but-set-variable]
>      WebPIterator iter;
>                   ^~~~
> ---
> 
> So, the test file is working.
> I am able to build it manually.
> 
> Why the Qt build system is complaining about this library installed on my system please?
> 
> Thank you.
> Best regards.
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