Improve README and reduce the pypatch required

Author: will-v-pi

README.md

@@ -1,4 +1,29 @@
-Starting from fresh Raspberry Pi OS 32bit
+# Pylibcamera
+This package is for the libcamera python bindings only. It requires you to already have installed a version of libcamera onto your system.
 
-Required apt packages for pylibcamera build:
-- libcamera-dev
+## Installation Instructions
+These instructions are designed for use in a python virtual environment. If you are using the system python then it is much simpler to install the system apt package for the libcamera python bindings (eg `sudo apt install python3-libcamera`), as these will match the version of libcamera correctly.
+
+The default installation instructions (which work on Raspberry Pi OS) are:
+```
+sudo apt install -y libcamera-dev
+pip install libcamera
+```
+If you have an older release of libcamera on your system then you may need to use `libcamera==version` to install the correct release.
+
+### If that doesn't work...
+
+If you have built your own version of libcamera, or your system has a version which is not compatible with a release version, then you may need to pass the repository and revision to meson. The arguments to do this are `-C setup-args="-Drepository=https://my.repository.git"` for the repository and `-C setup-args="-Drevision=branch"` for the revision. These are passed directly into `git clone` and `git checkout` respectively, so and strings that work with those will work here. The `-C, --config-settings` argument require an up to date version of `pip>=23.1` so you may first need to run `pip install --upgrade pip`
+
+For example, the if you have built the master version of libcamera on your system, then you would run:
+```
+pip install libcamera -C setup-args="-Drevision=master"
+```
+
+If you have built the main version from the Raspberry Pi repository then you would use:
+```
+pip install libcamera -C setup-args="-Drepository=https://github.com/raspberrypi/libcamera.git" -C setup-args="-Drevision=main"
+```
+
+## How it works
+This package works by building just the libcamera python bindings against your existing version of libcamera. It does this by cloning the libcamera repository and checking out the specified revision. A patch (pypatch.patch) is then applied to modify the src/py/libcamera/meson.build file to prevent building of the existing python bindings and allow for the building of custom ones using the meson-python build system. Finally, the build includes the subdirectory libcamera/src/py to only include the files required for the python bindings, rather than building the whole of libcamera.

meson.build

@@ -15,12 +15,17 @@ message('Cloning from: @0@, revision @1@'.format(get_option('repository'), get_o
 r = run_command('clone-libcamera.sh', get_option('repository'), get_option('revision'), get_option('patch'), check : true)
 
 libcamera_includes = include_directories('libcamera/include')
-libcamera_private = dependency('libcamera', required : true)
+libcamera_private = dependency(
+    'libcamera', required : true,
+    not_found_message : 'Requires libcamera-dev package to be installed - apt install libcamera-dev'
+)
 
 py = import('python').find_installation()
 
 subdir('libcamera/src/py')
 
+pycamera_args += '-DLIBCAMERA_BASE_PRIVATE'
+
 message('Using python version @0@ from @1@'.format(py.version(), py.path()))
 
 py.install_sources(

pypatch.patch

@@ -1,5 +1,5 @@
 diff --git a/src/py/libcamera/meson.build b/src/py/libcamera/meson.build
-index f58c719..071e6f6 100644
+index f58c7198..c65fc044 100644
 --- a/src/py/libcamera/meson.build
 +++ b/src/py/libcamera/meson.build
 @@ -1,13 +1,13 @@
@@ -18,11 +18,9 @@ index f58c719..071e6f6 100644
 
  if not pybind11_dep.found()
      pycamera_enabled = false
-@@ -76,31 +76,5 @@ pycamera_args = [
-     '-fvisibility=hidden',
+@@ -77,30 +77,3 @@ pycamera_args = [
      '-Wno-shadow',
      '-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT',
-+    '-DLIBCAMERA_BASE_PRIVATE',
  ]
 -
 -destdir = get_option('libdir') / ('python' + py3_dep.version()) / 'site-packages' / 'libcamera'

pyproject.toml

@@ -4,8 +4,13 @@ requires = ['meson-python', 'pyyaml', 'pybind11']
 
 [project]
 name = 'libcamera'
-version = '0.1.0'
-description = 'Libcamera python bindings'
+version = '0.1.0a1'
+description = 'libcamera python bindings'
+readme = 'README.md'
+
+[project.urls]
+Source = "https://github.com/will-v-pi/pylibcamera"
+libcamera = "https://git.libcamera.org/libcamera/libcamera.git"
 
 [tool.meson-python.args]
 setup = [