The plymouth label plugin pulls in too many dependencies

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Just a note, pango is indispensable for any dynamic strings in languages such as Thai or Lao that require character composition; or for languages that mix RTL and LTR text (such as Arabic or Hebrew with embedded Latin filenames). This may save us some space now in Ubuntu Core, but are we going to find ourselves right back where we started in 2 years when we need support for such languages?

Font rendering should, in theory, have zero dependencies on graphics libraries. If you disable GPU-accelerated paths, which are probably rare, then you're only left with the need to write bytes into a simple pixel buffer.

No well-designed font rendering library should have any dependencies on graphics libraries to achieve that. If they do then I would hope it's just a matter of changing build flags.

libharzbuff would allow drawing glyphs for most languages with much less requirements than libpango. But that requires some work. So it is an alternative if in the future we need something more powerful but want to avoid pango. The change itself is easy to revert thanks to plymouth plugin base architecture - label-ft and label have the same ABI, it is just that label-ft has a subset of label's capabilities.

Regarding dependencies, this is what pangocairo pulls:

$ ldd /lib/x86_64-linux-gnu/libpangocairo-1.0.so.0
 linux-vdso.so.1 (0x00007fff72bfa000)
 libpango-1.0.so.0 => /lib/x86_64-linux-gnu/libpango-1.0.so.0 (0x00007f3840a6d000)
 libpangoft2-1.0.so.0 => /lib/x86_64-linux-gnu/libpangoft2-1.0.so.0 (0x00007f3840a52000)
 libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f384096b000)
 libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007f3840831000)
 libgobject-2.0.so.0 => /lib/x86_64-linux-gnu/libgobject-2.0.so.0 (0x00007f38407d1000)
 libharfbuzz.so.0 => /lib/x86_64-linux-gnu/libharfbuzz.so.0 (0x00007f3840700000)
 libfontconfig.so.1 => /lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007f38406b6000)
 libcairo.so.2 => /lib/x86_64-linux-gnu/libcairo.so.2 (0x00007f384058e000)
 libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f3840366000)
 libgio-2.0.so.0 => /lib/x86_64-linux-gnu/libgio-2.0.so.0 (0x00007f384018e000)
 libfribidi.so.0 => /lib/x86_64-linux-gnu/libfribidi.so.0 (0x00007f3840172000)
 libthai.so.0 => /lib/x86_64-linux-gnu/libthai.so.0 (0x00007f3840167000)
 libfreetype.so.6 => /lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007f384009d000)
 /lib64/ld-linux-x86-64.so.2 (0x00007f3840b02000)
 libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f3840027000)
 libffi.so.8 => /lib/x86_64-linux-gnu/libffi.so.8 (0x00007f384001a000)
 libgraphite2.so.3 => /lib/x86_64-linux-gnu/libgraphite2.so.3 (0x00007f383fff3000)
 libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007f383ffc2000)
 libuuid.so.1 => /lib/x86_64-linux-gnu/libuuid.so.1 (0x00007f383ffb7000)
 libpixman-1.so.0 => /lib/x86_64-linux-gnu/libpixman-1.so.0 (0x00007f383ff0c000)
 libpng16.so.16 => /lib/x86_64-linux-gnu/libpng16.so.16 (0x00007f383fed1000)
 libxcb-shm.so.0 => /lib/x86_64-linux-gnu/libxcb-shm.so.0 (0x00007f383fecc000)
 libxcb.so.1 => /lib/x86_64-linux-gnu/libxcb.so.1 (0x00007f383fea2000)
 libxcb-render.so.0 => /lib/x86_64-linux-gnu/libxcb-render.so.0 (0x00007f383fe93000)
 libXrender.so.1 => /lib/x86_64-linux-gnu/libXrender.so.1 (0x00007f383fe84000)
 libX11.so.6 => /lib/x86_64-linux-gnu/libX11.so.6 (0x00007f383fd44000)
 libXext.so.6 => /lib/x86_64-linux-gnu/libXext.so.6 (0x00007f383fd2f000)
 libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f383fd13000)
 libgmodule-2.0.so.0 => /lib/x86_64-linux-gnu/libgmodule-2.0.so.0 (0x00007f383fd0c000)
 libmount.so.1 => /lib/x86_64-linux-gnu/libmount.so.1 (0x00007f383fcc8000)
 libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007f383fc9a000)
 libdatrie.so.1 => /lib/x86_64-linux-gnu/libdatrie.so.1 (0x00007f383fc91000)
 libbrotlidec.so.1 => /lib/x86_64-linux-gnu/libbrotlidec.so.1 (0x00007f383fc83000)
 libXau.so.6 => /lib/x86_64-linux-gnu/libXau.so.6 (0x00007f383fc7d000)
 libXdmcp.so.6 => /lib/x86_64-linux-...

Confirmed libpangocairo (or cairo itself) is the problem here. Plain libpango has much more sane dependencies. Can we just use libpango?

cairo is used to provide the drawing surface [1]. Not sure what would be the best replacement.

[1] https://gitlab.freedesktop.org/plymouth/plymouth/-/blob/main/src/plugins/controls/label/plugin.c#L227

Sounds like a weak excuse. Cairo is implemented on top of software buffers that plymouth/pango/any-font-renderers should be writing to directly. Hence Cairo should not be involved, ideally.

I would say Cairo is what needs to be removed from Plymouth to remove most dependencies.

Sure, but what should be proposed to upstream?

> Sure, but what should be proposed to upstream?

A minor rewrite of the label plugin that perhaps none of us have time to do right now. :)

Although if Steve's concern becomes a blocker then one of us will need to.

This bug was fixed in the package plymouth - 0.9.5+git20211018-1ubuntu4

---------------
plymouth (0.9.5+git20211018-1ubuntu4) kinetic; urgency=medium

  * Add patches to build the label-ft plugin, an alternative to the label
    plugin that has less dependencies (LP: #1976352).
  * Apply labelft-0004-label-ft-fix-alignment.patch to fix alignment
    issue with the label-ft control plugin.

 -- Alfonso Sanchez-Beato <email address hidden> Mon, 11 Jul 2022 11:07:22 +0100

Hi, could please somebody sponsor to jammy-proposed plymouth package from kinetic (0.9.5+git20211018-1ubuntu4)?

FYI this binary package has just been demoted to universe in kinetic because it has no reverse-dependencies in main. If it's to be used in images, please make sure it ends up in the appropriate seed.