Add meson as a secondary build system

This will bring back a first-party buildsystem for MSVC
after the previous solution https://github.com/libass/libass-msvc
was retired and make it easier to use libass as a subproject
in other meson projects.

It does not currently support all of our utilities nor testing
and fuzzing infrastructure and x86_32 assembly is always built in
PIC mode.
Due to meson deficiencies shared libraries lack symbol export control
and it is not possible to build x32 assembly.

However, for packaging and downstream use it is feature complete on
Windows and static-only builds are sufficient for subproject use on any
platform, so it brings a net positive and keeping this level of support
up alongside autotools is expected to be barely any effort.
And ofc future meson versions and patches
to this build setup might improve it further.

The port was initially brought up by Ryan Lucia (CoffeeFlux)
and later further adapted and polished for merge
by arch1t3cht and torque, but several more people
contributed bits and pieces. They are listed in the following.

Reviewed-by: Eli Schwartz <eschwartz93@gmail.com>
Reviewed-by: Oneric <oneric@oneric.stub>

Co-authored-by: arch1t3cht <arch1t3cht@gmail.com>
Co-authored-by: torque <torque@users.noreply.github.com>
Co-authored-by: Luni-4 <luni-4@hotmail.it>
Co-authored-by: Funami580 <Funami580@users.noreply.github.com>
Co-authored-by: woclass <5158738+inkydragon@users.noreply.github.com>
Co-authored-by: line0 <line0@inbox.lv>
Co-authored-by: Myaamori <myaamori1993@gmail.com>
Co-authored-by: Xavier Claessens <xavier.claessens@collabora.com>

2 files changed, 147 insertions, 0 deletions

diff --git a/libass/ass/meson.build b/libass/ass/meson.build
new file mode 100644
index 0000000..6b4de1f
--- /dev/null
+++ b/libass/ass/meson.build
@@ -0,0 +1,13 @@
+# See: https://github.com/mesonbuild/meson/issues/2546
+# This hack is needed because the install directory of the libass public headers
+# ('ass') is different than the name of the directory ('libass') that they live under
+# in the source tree. In the scenario where the libass meson build system is being used
+# as a subproject of some parent project, that parent project will need the libass
+# headers to be copied into the appropriate 'ass' directory either before or during the
+# build process so that they are in an appropriate include path prior to the time that
+# the build system starts trying to build the parent project that needs to include
+# them.
+fs = import('fs')
+foreach header : libass_headers
+    fake_installed_headers += fs.copyfile(header, fs.name(header))
+endforeach
diff --git a/libass/meson.build b/libass/meson.build
new file mode 100644
index 0000000..55a04fc
--- /dev/null
+++ b/libass/meson.build
@@ -0,0 +1,134 @@
+libass_lt_current = 11
+libass_lt_revision = 1
+libass_lt_age = 2
+
+libass_so_version = '@0@.@1@.@2@'.format(
+    libass_lt_current - libass_lt_age,
+    libass_lt_age,
+    libass_lt_revision,
+)
+
+src_x86 = files(
+    'x86/be_blur.asm',
+    'x86/blend_bitmaps.asm',
+    'x86/blur.asm',
+    'x86/cpuid.asm',
+    'x86/rasterizer.asm',
+)
+src_aarch64 = files(
+    'aarch64/asm.S',
+    'aarch64/be_blur.S',
+    'aarch64/blend_bitmaps.S',
+    'aarch64/blur.S',
+    'aarch64/rasterizer.S',
+)
+src_fontconfig = files('ass_fontconfig.c')
+src_directwrite = files('ass_directwrite.c')
+src_coretext = files('ass_coretext.c')
+
+libass_src = files(
+    'c/c_be_blur.c',
+    'c/c_blend_bitmaps.c',
+    'c/c_blur.c',
+    'c/c_rasterizer.c',
+    'ass.c',
+    'ass_bitmap.c',
+    'ass_bitmap_engine.c',
+    'ass_blur.c',
+    'ass_cache.c',
+    'ass_drawing.c',
+    'ass_filesystem.c',
+    'ass_font.c',
+    'ass_fontselect.c',
+    'ass_library.c',
+    'ass_outline.c',
+    'ass_parse.c',
+    'ass_rasterizer.c',
+    'ass_render.c',
+    'ass_render_api.c',
+    'ass_shaper.c',
+    'ass_string.c',
+    'ass_strtod.c',
+    'ass_utils.c',
+)
+
+libass_link_with = []
+
+libass_headers = files('ass.h', 'ass_types.h')
+
+if fontconfig
+    libass_src += src_fontconfig
+endif
+if directwrite
+    libass_src += src_directwrite
+endif
+if coretext
+    libass_src += src_coretext
+endif
+
+if enable_asm
+    asm_sources = []
+    if cpu_family == 'x86'
+        asm_sources = src_x86
+    elif cpu_subfamily == 'aarch64'
+        asm_sources = src_aarch64
+    endif
+
+    if asm_is_nasm
+        libass_src += asm_sources
+    else
+        asm_lib = static_library(
+            'libass_asm',
+            config_h,
+            sources: asm_sources,
+            c_args: asm_args,
+            include_directories: incs,
+        )
+        libass_link_with += asm_lib
+    endif
+endif
+
+if host_system == 'windows'
+    gen_defs = find_program('../gen_defs.py')
+    libass_def = custom_target(
+        'libass.def',
+        input: ['libass.sym'],
+        output: ['libass.def'],
+        command: [gen_defs, '@INPUT@', '@OUTPUT@'],
+    )
+    kwargs = {'vs_module_defs': libass_def}
+else
+    kwargs = {}
+endif
+
+# this is a list of custom targets for copying the libass public headers into the build
+# directory. These targets are passed as part of the libass library build step in order
+# to enforce the desired build sequence.
+fake_installed_headers = []
+subdir('ass')
+
+libass = library(
+    'ass',
+    libass_src,
+    config_h,
+    link_with: libass_link_with,
+    version: libass_so_version,
+    # This emulates the GNU libtool compat/current versioning computation
+    darwin_versions: [
+        '@0@'.format(libass_lt_current + 1),
+        '@0@.@1@'.format(libass_lt_current + 1, libass_lt_revision),
+    ],
+    install: true,
+    include_directories: incs,
+    dependencies: deps,
+    kwargs: kwargs,
+)
+
+libass_dep = declare_dependency(
+    link_with: libass,
+    include_directories: incs,
+    dependencies: deps,
+    sources: fake_installed_headers,
+)
+
+install_headers(libass_headers, subdir: 'ass')