ENH: Add script to install python packages locally

INSTALLATION.md

@@ -20,6 +20,25 @@ For RTK developpers, it may be useful to compile RTK independently from ITK. Thi
 * Manually download RTK's source repository from [GitHub](https://github.com/RTKConsortium/RTK) with `git` (recommended) or as a [zip package](https://codeload.github.com/RTKConsortium/RTK/zip/main).
 * Configure the project with CMake pointing to RTK's source directory and setting the CMake option `ITK_DIR` to ITK's compilation directory. All CMake options above can be set except `Module_RTK`.
 
+#### Installing the Python wrapping into a Python environment
+Configure and build RTK pointing `-DITK_DIR` to an ITK build tree with Python wrapping enabled (`ITK_WRAP_PYTHON=ON`) and, when using CUDA, `-DRTK_USE_CUDA=ON`. RTK's Python files are installed as plain copies by default. For local development, the optional `-DRTK_EDITABLE_PYTHON_PACKAGES=ON` (off by default) installs those files as symbolic links back to the RTK source tree instead, so edits to the Python scripts are picked up without reinstalling.
+
+The `itk` Python package is installed into the directory given by `-DPY_SITE_PACKAGES_PATH`; this destination is fixed at configure time. If left unset, ITK detects it automatically from the Python executable it finds. Set it explicitly to install into a self-contained folder as an alternative to a `site-packages` directory, then add that folder to `PYTHONPATH`.
+
+Then install RTK with `cmake --install build-dir --component RuntimeLibraries`.
+
+**Note**: unlike a wheel installed with `pip install itk-rtk`, this CMake install does not put the `rtk*` command-line applications (e.g. `rtkfdk`) on the `PATH`. Run them with `python -m itk.rtkfdk` instead.
+
+[utilities/rtk_install_bindings.sh](https://github.com/RTKConsortium/RTK/blob/main/utilities/rtk_install_bindings.sh) builds ITK from source with RTK as a local remote module and installs the bindings into a self-contained folder; edit the configuration variables at the top of the script, then run it. After it finishes, add the install folder to your `PYTHONPATH` for the current session, or permanently in your shell profile:
+```
+export PYTHONPATH=/path/to/bindings:$PYTHONPATH
+```
+Then run the RTK applications as Python modules, e.g.:
+```
+python3 -m itk.rtkfdk -g geometry.xml --path . --regexp '*.mha' -o output.mha
+```
+
+
 ## Python pre-compiled binaries
 We only provide pre-compiled binaries for the Python package which depends on ITK. Use the following commands to install the RTK module with `pip`.
 ```

utilities/rtk_install_bindings.sh

@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+
+# Build ITK with RTK as a remote module and install the Python bindings into a
+# self-contained folder usable via PYTHONPATH.
+# Edit the configuration variables below, then run it.
+
+exec > >(tee "$(basename "$0" .sh).log")
+exec 2> >(tee "$(basename "$0" .sh).err" >&2)
+
+set -e
+set -x
+
+# ==================== Config (edit these) ====================
+ITK_SRC=/path/to/ITK
+RTK_SRC=/path/to/RTK
+DEST_DIR=/path/to/bindings
+NTHREADS=${NTHREADS:-24}
+RTK_USE_CUDA=OFF
+EDITABLE=OFF       # symlink the RTK Python files back to $RTK_SRC
+# =============================================================
+
+BUILD_DIR=PythonWrapping
+INSTALL_PATH=${BUILD_DIR}-install
+
+echo "ITK source:    $ITK_SRC"
+echo "RTK source:    $RTK_SRC"
+echo "Install folder: $DEST_DIR"
+echo "Editable:      $EDITABLE"
+echo "RTK_USE_CUDA:  $RTK_USE_CUDA"
+
+mkdir -p "$ITK_SRC/Modules/Remote"
+ln -sfn "$RTK_SRC" "$ITK_SRC/Modules/Remote/RTK"
+
+CMAKE_EXTRA=
+if [ "$RTK_USE_CUDA" = "ON" ]; then
+  CMAKE_EXTRA=-DModule_CudaCommon:BOOL=ON
+fi
+
+mkdir -p "$BUILD_DIR" "$DEST_DIR"
+
+cmake "$ITK_SRC" \
+  -B"$BUILD_DIR" \
+  -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+  -DBUILD_EXAMPLES=OFF \
+  -DBUILD_SHARED_LIBS=OFF \
+  -DBUILD_TESTING=OFF \
+  -DITK_BUILD_DEFAULT_MODULES=ON \
+  -DITK_WRAP_PYTHON=ON \
+  -DCMAKE_INSTALL_PREFIX="$INSTALL_PATH" \
+  -DPY_SITE_PACKAGES_PATH:STRING="$DEST_DIR" \
+  -DITK_WRAP_unsigned_short:BOOL=ON \
+  -DITK_WRAP_double:BOOL=ON \
+  -DITK_WRAP_complex_double:BOOL=ON \
+  -DITK_WRAP_IMAGE_DIMS:STRING="2;3;4" \
+  -DModule_RTK:BOOL=ON \
+  -DModule_RTK_GIT_TAG:STRING="" \
+  -DRTK_USE_CUDA:BOOL="$RTK_USE_CUDA" \
+  -DRTK_BUILD_APPLICATIONS:BOOL=OFF \
+  -DRTK_EDITABLE_PYTHON_PACKAGES:BOOL="$EDITABLE" \
+  $CMAKE_EXTRA
+
+cmake --build "$BUILD_DIR" --parallel "$NTHREADS" -- -k
+cmake --install "$BUILD_DIR"
+
+echo "Done. Export $DEST_DIR for this session, or add it permanently to your shell profile:"
+echo "  export PYTHONPATH=$DEST_DIR:\$PYTHONPATH"
+echo "Then run the RTK applications as Python modules, e.g.:"
+echo "  python3 -m itk.rtkfdk -g geometry.xml --path . --regexp *.mha -o output.mha"

wrapping/CMakeLists.txt

@@ -48,11 +48,45 @@ file(
   "${RTK_SOURCE_DIR}/applications/rtk*/rtk*.py"
 )
 
-wrap_itk_python_bindings_install(/itk "RTK"
-  __init_rtk__.py
+set(
+  RTK_PYTHON_FILES
+  "${RTK_SOURCE_DIR}/wrapping/__init_rtk__.py"
   ${RTK_GROUP_SCRIPTS}
   ${RTK_APP_SCRIPTS}
-  ${RTK_BINARY_DIR}/Wrapping/Generators/Python/rtkConfig.py
-  ${RTK_SOURCE_DIR}/wrapping/rtkExtras.py
-  ${RTK_SOURCE_DIR}/applications/rtkargumentparser.py
+  "${RTK_BINARY_DIR}/Wrapping/Generators/Python/rtkConfig.py"
+  "${RTK_SOURCE_DIR}/wrapping/rtkExtras.py"
+  "${RTK_SOURCE_DIR}/applications/rtkargumentparser.py"
 )
+
+# Editable dev mode: install the Python files above as symbolic links back to
+# the source tree instead of copies, so edits are picked up without
+# reinstalling. Off by default: keep plain copies.
+option(
+  RTK_EDITABLE_PYTHON_PACKAGES
+  "Install RTK Python scripts into the itk package as symbolic links (editable dev mode)."
+  OFF
+)
+
+if(RTK_EDITABLE_PYTHON_PACKAGES)
+  set(_rtk_editable_dir "${RTK_BINARY_DIR}/rtk_editable_python")
+  file(REMOVE_RECURSE "${_rtk_editable_dir}")
+  file(MAKE_DIRECTORY "${_rtk_editable_dir}")
+  foreach(_rtk_src IN LISTS RTK_PYTHON_FILES)
+    get_filename_component(_rtk_name "${_rtk_src}" NAME)
+    file(
+      CREATE_LINK
+        "${_rtk_src}"
+        "${_rtk_editable_dir}/${_rtk_name}"
+      SYMBOLIC
+      COPY_ON_ERROR
+    )
+  endforeach()
+  install(
+    DIRECTORY
+      "${_rtk_editable_dir}/"
+    DESTINATION "${PY_SITE_PACKAGES_PATH}/itk"
+    COMPONENT RuntimeLibraries
+  )
+else()
+  wrap_itk_python_bindings_install(/itk "RTK" ${RTK_PYTHON_FILES})
+endif()