Linux support

[tmds]

Does SkiaSharp work on Linux?

[migueldeicaza]

SkiaSharp should, but the native supporting code needs to be compiled individually on each Linux distribution.

Sadly, NuGet was not designed to cope with this scenario, so there is not much that we can do to ship precompiled binaries.

What we should do is at least provide a simple Makefile to create the native library support, so third parties can build/install it easily.

[tmds]

@migueldeicaza compilations could be provided for several linux flavors using the runtimes/RID feature: https://dotnet.github.io/docs/core-concepts/rid-catalog.html

[mattleibow]

@tmds An ARM Linux was actually work with this guy: #18
@migueldeicaza not too sure of all the limitations, but as the native dll is the only thing that needs switching... is it possible to do something like this for a few supported (popular) versions of Linux: https://github.com/mono/SkiaSharp/blob/master/binding/SkiaSharp.Desktop/SkiaSharp.dll.config

[migueldeicaza]

The issue is not identifying the library, the issue is that creating a package with the binaries is incredibly cumbersome (you need to create a package with all available systems upfront, build the native bits, and then package all the bits together).

What should ideally happen is that these native binaries should be "addons" to the core package, and could be published independently of the core package.

[KarolKolenda]

@migueldeicaza Any idea when makefiles for popular distros will be available? Is it going to happen this year or are we looking more at 2017? With .Net Core in the wild, lack of server side graphics library in Linux environment all of the sudden seems like a pressing matter.

That being said, you are doing wonderful things with SkiaSharp and in Windows as GDI+ replacement it is just amazing.

[kekekeks]

@migueldeicaza I think if you compile skia using sufficiently old distro (e. g. CentOS 6, Debian 5) it will just work everywhere. In the worst case you can just bundle dependencies (skia don't really need much: libfontconfig, libfreetype, libz, libpng12) and rely only on libc which is guaranteed to be present by LSB.

[jameswalmsley]

I'm looking into the build.cake file and trying to work out how to convert it to build for linux.
Are there any attempts of pointers for me to start updating the build system.

[mattleibow]

@jameswalmsley I would say you probably need to just get the externals building. These are grouped using the Task ("externals-<platform>") steps. For the case of Linux, I would suggest following the Android style: Task ("externals-android") https://github.com/mono/SkiaSharp/blob/v1.53.0/build.cake#L674-L724

It pretty much follows the official docs by google: https://skia.org/user/quick/linux

It follows the pattern of:

1. set global env vars
2. set gyp defines for platform
3. build *.a (using ninja) for platform
4. link all *.a together into a dynamic library of some sort
5. repeat 2-4 for each platform

In the case of Android, I did step 4 using ndk-build, but you could use whatever it is that is used on Linux. @galvesribeiro did it without much trouble, after he built his compilers first ;)

Basically, build all the *.a files and then dynamically link them together. Let me know how this goes as we do want to have support for as many platforms as possible.

The rest of the stuff is pure C#/.NET P/Invoke

[galvesribeiro]

Yes. Build for Android linux is already there on the Gyp files however, if you plan to build it to any other linux, you will either have to hack the .gyp files to point to your dependencies (specially if you are cross compiling to another arch) and the output will be a bunch of .a. After that all compiled, you need to link it to the skiasharp. I had everything statically linked since the ld and glibc on the targed device was too old (pre-C++11).

Basically this is the buld script:

export PATH=/home/guto/x-tools/arm-unknown-linux-gnueabi.485/bin:/home/guto/x-tools/crosstool-ng/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/guto/dev/chromium/depot_tools
export TARGETMACH=arm-arm1176jzs-linux-gnueabi
export BUILDMACH=i686-pc-linux-gnu
export CROSS=arm-arm1176jzs-linux-gnueabi
export CC=${CROSS}-gcc
export LD=${CROSS}-ld
export CXX=${CROSS}-g++
export STRIP=${CROSS}-strip
export LINK=${CROSS}-g++
export AS=${CROSS}-as
export AR=${CROSS}-ar
export RANLIB=${CROSS}-ranlib
export NM=${CROSS}-nm
export CROSS_COMPILE="arm-arm1176jzs-linux-gnueabi"
export PKG_CONFIG_PATH=/home/guto/dev/libs/lib/pkgconfig
export INSTALLPATH=/home/guto/dev/libs/

GYP_DEFINES='skia_gpu=0 skia_pdf= skia_os=linux skia_arch_type=arm' SK_SUPPORT_PDF=0  CC='arm-unknown-linux-gnueabi-gcc' CXX='arm-unknown-linux-gnueabi-g++' PKG_CONFIG_PATH=/home/guto/dev/libs/lib/pkgconfig LDFLAGS=-L/home/guto/dev/libs/lib  python bin/sync-and-gyp

ninja -C out/Release skia_lib

//Compiling source to object files
$CXX -MMD /home/guto/dev/SkiaSharp/native-builds/src/SkiaKeeper.c /home/guto/dev/SkiaSharp/native-builds/src/SkManagedStream.cpp /home/guto/dev/SkiaSharp/native-builds/src/sk_managedstream.cpp /home/guto/dev/SkiaSharp/native-builds/src/sk_xamarin.cpp -g -fPIC -O3 -DSKIA_DLL -DSKIA_IMPLEMENTATION=1 -DSK_INTERNAL -DSK_BUILD_FOR_UNIX -I/home/guto/dev/SkiaSharp/skia/include -I/home/guto/dev/SkiaSharp/skia/include/c -I/home/guto/dev/SkiaSharp/skia/include/config -I/home/guto/dev/SkiaSharp/skia/include/core -I/home/guto/dev/SkiaSharp/skia/include/pathops -I/home/guto/dev/SkiaSharp/skia/include/pipe -I/home/guto/dev/SkiaSharp/skia/include/ports -I/home/guto/dev/SkiaSharp/skia/include/private -I/home/guto/dev/SkiaSharp/skia/include/utils -I/home/guto/dev/SkiaSharp/skia/include/images -I/home/guto/dev/SkiaSharp/skia/src/c -I/home/guto/dev/SkiaSharp/skia/src/core -I/home/guto/dev/SkiaSharp/skia/src/sfnt -I/home/guto/dev/SkiaSharp/skia/src/image -I/home/guto/dev/SkiaSharp/skia/src/opts -I/home/guto/dev/SkiaSharp/skia/src/utils -I/home/guto/dev/SkiaSharp/skia/include/gpu -I/home/guto/dev/SkiaSharp/skia/src/gpu -I/home/guto/SSBuild/SkiaSharp/SkiaSharp/obj/Debug/prec/Debug -L/home/guto/dev/libs/lib -lfontconfig -c -std=c++11

//Generating shared object "libSkiaSharp.so" from object files
$CXX -shared -o Release/libSkiaSharp.so SkiaKeeper.o sk_managedstream.o SkManagedStream.o sk_xamarin.o -L/home/guto/dev/SkiaSharp/skia/out/Release/lib -Wl,--start-group /home/guto/dev/SkiaSharp/skia/out/Release/libskia_core.a /home/guto/dev/SkiaSharp/skia/out/Release/libskia_ports.a /home/guto/dev/SkiaSharp/skia/out/Release/libskia_images.a /home/guto/dev/SkiaSharp/skia/out/Release/libskia_sfnt.a /home/guto/dev/SkiaSharp/skia/out/Release/libskia_opts.a /home/guto/dev/SkiaSharp/skia/out/Release/libskia_codec.a /home/guto/dev/SkiaSharp/skia/out/Release/libskia_effects.a /home/guto/dev/SkiaSharp/skia/out/Release/libskia_utils.a -Wl,--end-group /home/guto/dev/SkiaSharp/skia/out/Release/libpng_static.a /home/guto/dev/libs/lib/libfreetype.a /home/guto/dev/libs/lib/libfontconfig.so /home/guto/dev/libs/lib/libz.a /home/guto/dev/libs/lib/libturbojpeg.a /home/guto/dev/libs/lib/libjpeg.a /home/guto/dev/libs/lib/libexpat.a /home/guto/dev/libs/lib/libwebp.a /home/guto/dev/libs/lib/libwebpdecoder.a /home/guto/dev/libs/lib/libwebpdemux.a /home/guto/dev/libs/lib/libwebpextras.a /home/guto/dev/libs/lib/libwebpmux.a  /home/guto/x-tools/arm-unknown-linux-gnueabi.485/arm-unknown-linux-gnueabi/lib/libstdc++.a -L/home/guto/dev/libs/lib -lfontconfig

One can create a makefile and make things easier but this native linux "macumba" is not something we are good here. So thanks to @mattleibow we got it to work.

The C# side of SkiaSharp is just PInvokes with a .Net like APIs, so just point it to the right lib name and you are set.

I hope it help.

[mattleibow]

Thanks for this @galvesribeiro!

[kekekeks]

Hello guys, I have some tips for you here. When I was messing with skia on linux half a year ago, I've run into an issue with really huge library file (50MB+). I've managed to strip it down to 2MB.

• Linker has a wonderful flag --gc-sections which allows it to remove parts that aren't needed by the final so binary. The issue is it doesn't work properly for shared libs unless you specify -ffunction-sections -fdata-sections compiler flags for each source file
• Disabling RTTI also saves a great deal of space

You can find a patch to skia.gyp here: https://github.com/AvaloniaUI/libperspesk/blob/master/linux/skia.patch

Another issue with linking it was the fact that for some reason linker doesn't work properly with static library dependencies when you compile your shared library. --whole-archive just bloats your binary size and even then doesn't always work. So the trick is to unpack object files from static libs using ar utility and then combine them into one. The script for that is here: https://github.com/AvaloniaUI/libperspesk/blob/master/linux/mergelibs.sh

I also recommend you to specify --no-undefined linker flag so you won't run into weird undefined symbol errors at runtime, and could figure out dependencies properly.

My old makefile is here:

https://github.com/AvaloniaUI/libperspesk/blob/master/linux/Makefile#L32

[kekekeks]

Oh, forgot to add the script that downloads and actually builds skia itself: https://github.com/AvaloniaUI/libperspesk/blob/master/linux/getskia.sh

[galvesribeiro]

I wish I had that! Hehehe btw, after strip, my release build was 3mb with everything statically linked.

[jameswalmsley]

@mattleibow Did you see this? https://github.com/phusion/holy-build-box

[kekekeks]

If anyone is interested, I've managed to run Cake in that docker container.

First, you need to acquire mono-opt package for CentOS 5. For some reason I wasn't able to use the repo, so I've downloaded it manually from https://copr-be.cloud.fedoraproject.org/results/tpokorra/mono-opt/epel-5-x86_64/00496651-mono-opt/mono-opt-4.6.2-1.x86_64.rpm . In case it gets deleted, here is mega link: https://mega.nz/#!cswD2Jza!EqE-Q_rwmTK0vwYeNDaWSGm0aHK6y5roF1BHZdPGtz8

You need to install this package with --no-gpg-check option. You also need to install curl and unzip packages. Synchronizing certs is also mandatory.

yum install -y --nogpgcheck ./mono-opt-4.6.2-1.x86_64.rpm
yum install -y curl unzip
source /opt/mono/env.sh

After that you should be able to run bootstrapper.sh. Of course it would need more steps to produce an actual build.

BTW, last time when I was messing with Skia, my library was depending on:

        linux-vdso.so.1 =>  (0x00007ffd7adf3000)
        libfreetype.so.6 => /usr/lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007f1cabc08000)
        libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f1cab9ee000)
        libfontconfig.so.1 => /usr/lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007f1cab7af000)
        libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f1cab591000)
        libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f1cab20f000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f1caaf06000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f1caab3c000)
        libpng12.so.0 => /lib/x86_64-linux-gnu/libpng12.so.0 (0x00007f1caa916000)
        libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007f1caa6ec000)
        /lib64/ld-linux-x86-64.so.2 (0x000055b85c884000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f1caa4d5000)

So it probably should be possible to provide a build of Skia that works everywhere