Create libpack.md with starting instructions

Note that this is currently incomplete, and the library combination is currently untested.

Author: chennes

technical/libpack.md

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+---
+layout: default
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+
+# Maintaining the FreeCAD LibPack for Windows
+
+To create a new LibPack for Windows, begin by creating an empty directory. The suggested naming scheme
+is to name it "LibPack-XX-YY-ARCH" where XX is the release of FreeCAD the pack is intented to work with,
+YY is a version number of the LibPack itself, and ARCH is the architecture the LibPack was build for
+(e.g. x86_64 or arm64). The rest of this document will refer to that directory as *LIBPACK*.
+
+Note that in several places below you are instructed to load a developer's power shell: you may use
+whichever shell you'd like, but ensure that you are loading the shell configured with the x64 native
+compilation tools if you are compiling on an Intel processor. ARM compilation is untested.
+
+For the most part, the libraries below are self-compiled in order to reduce dependency on third-party
+packagers. In some cases it is feasible to download precompiled binaries of the individual items. Major
+exceptions here are that both Python and Qt are used in their precompiled forms since the packages are
+provided for Windows by the first parties in each case.
+
+WORK IN PROGRESS!!
+
+Perform the following in this order (the order does not *always* matter, but sometimes does):
+* **[Python](https://python.org)** -- Install in a newly-created *LIBPACK\bin* subdirectory using the basic Python installer. Only install
+  Python itself: the Idle IDE, debug symbols, etc. are not included in the LibPack.
+* **[Qt](https://qt.io)** -- The Open Source installer is found at https://www.qt.io/download-open-source
+* Most of the optional components of Qt can be omitted, except for:
+  - Qt WebEngine
+  - Qt PDF
+  - Qt Image Formats
+* Qt should be installed into an arbitrary location outside of the LibPack you are creating: the Qt installer
+  will create a subdirectory structure that is based on the version number and architecture of the installation.
+  Within that subdirectory are many directories: `bin`,`doc`,`include`, etc. These should all be copied into
+  the top level of the LibPack
+* **[Boost](https://boost.org)** -- this is split into its headers and libraries:
+  - Many Boost libraries are header-only, but FreeCAD does require several compiled libraries
+  - Follow the Boost instructions for compiling: the easiest is to run `bootstrap` from a developer's command prompt
+  - Copy the libraries from *BOOST_ROOT\stage\lib* into *LIBPACK\lib*
+  - Copy the entire *BOOST_ROOT\boost* directory into *LIBPACK\include*
+* **[Coin](https://www.coin3d.org)** -- obtained by cloning and compiling https://github.com/coin3d/coin
+  - Make sure you compile against the Boost libraries downloaded above by setting BOOST_ROOT to the top of the *LIBPACK*
+  - Set CMAKE_INSTALL_PATH to the top of the *LIBPACK*
+  - Add include directory to find the Boost include files by editing CXXFLAGS and adding "/I C:\path\to\libpack\include" to it
+  - Do not build the Tests or Documentation
+  - In Visual Studio, run the ALL_BUILD and then INSTALL targets in Release mode.
+* **[Quarter](https://www.coin3d.org)** -- obtained by cloning and compiling https://github.com/coin3d/quarter
+  - Set Coin_DIR to *LIBPACK/lib/cmake/Coin-4.0.1* (or the current version, if it is not 4.0.1)
+  - Set Qt6_DIR to *LIBPACK/lib/cmake/Qt6*
+  - Set CMAKE_INSTALL_PREFIX to *LIBPACK*
+  - In some cases even with Qt6_DIR specified, Quarter will fail to find all necessary Qt library cmake files. In
+    those cases you will need to manually set the path to the cmake files as *LIBPACK/lib/cmake/Qt6XXX*.
+  - Do not build the examples, tests, or documentation
+  - At this time this guide was written, Quarter did not correctly support Qt 6.4: the file QuarterWidgetP.cpp had to
+    be modified to add `#include <QOpenGLContext>` in the Qt includes section at the top of the file.
+  - Build the ALL_BUILD and INSTALL targets in Release mode
+* **[SWIG](https://www.swig.org)** -- obtained from https://www.swig.org, prebuilt binaries are available for Windows
+  - Copy the downloaded folder to *LIBPACK\bin\swig* (e.g. change its name to remove the version number)
+* **[Pivy](https://www.coin3d.org)** -- obtained by cloning and compiling https://github.com/coin3d/pivy
+  - Set Python_ROOT_DIR to *LIBPACK/bin*
+  - Set SWIG_EXECUTABLE to *LIBPACK/bin/swig/swig.exe*
+  - Set SWIG_DIR to *LIBPACK/bin/swig/Lib* (note the "Lib" at the end of the path!)
+  - Set Coin_DIR to *LIBPACK/lib/cmake/Coin-4.0.1* (or the current version, if it is not 4.0.1)
+  - NOTE: Do *not* install SoQt -- doing so will trigger a dependency on Qt5
+  - Set Qt6_DIR to *LIBPACK/lib/cmake/Qt6*
+  - In some cases even with Qt6_DIR specified, Quarter will fail to find all necessary Qt library cmake files. In
+    those cases you will need to manually set the path to the cmake files as *LIBPACK/lib/cmake/Qt6XXX*.
+  - Set CMAKE_INSTALL_PREFIX to *LIBPACK*
+  - Build the ALL_BUILD and INSTALL targets in Release mode
+* **[libclang](https://clang.llvm.org)** -- Needed by pyside6, and provided prebuilt by Qt
+  - Download from https://download.qt.io/development_releases/prebuilt/libclang/
+  - Decompress and move the contents to the *LIBPACK* directory
+* **[Pyside](https://pypi.org/project/PySide6)** -- now part of the Qt project, installed as a Python package with pip
+  - E.g. `LIBPACK/bin/python.exe -m pip install pyside6==6.5.2`
+  - Note that this will also install Shiboken, in the same location
+* **[VTK](https://vtk.org)** -- installed with pip
+  - E.g. `LIBPACK/bin/python.exe -m pip install vtk==9.2.4`
+* **[HarfBuzz](https://harfbuzz.github.io)** -- Required by FreeType (and thus by OCCT)
+  - Clone https://github.com/harfbuzz/harfbuzz
+  - Switch to the latest release branch
+  - Set PYTHON_EXECUTABLE to *LIBPACK/bin/python.exe*
+  - Set CMAKE_INSTALL_PREFIX to *LIBPACK*
+  - Build the ALL_BUILD and INSTALL targets in Release mode
+* **[ZLIB](http://zlib.net)** -- Required by FreeType (and thus by OCCT)
+  - Download and unpack the latest source code
+  - Set CMAKE_INSTALL_PREFIX to *LIBPACK* (note: must be done prior to running Configure if using the GUI)
+  - Build the ALL_BUILD and INSTALL targets in Release mode
+* **[libpng](http://www.libpng.org)** -- Required by FreeType (and thus by OCCT)
+  - Download the zipfile of the source code and extract it
+  - Set ZLIB_INCLUDE_DIR to *LIBPACK/include*
+  - Set ZLIB_LIBRARY_RELEASE to *LIBPACK/lib/zlib.lib*
+  - Set CMAKE_INSTALL_PREFIX to *LIBPACK*
+  - Build the ALL_BUILD and INSTALL targets in Release mode
+* **[bzip2](https://sourceware.org.bzip2)** -- Required by FreeType (and this by OCCT)
+  - Download the source from https://sourceware.org/bzip2/downloads.html
+  - Extract it to a directory with no spaces or non-ASCII characters in it
+  - Open a Developer's PowerShell
+  - `cd X:\path\to\extracted\files`
+  - `nmake -f .\makefile.msc`
+  - Copy libbz2.lib into *LIBPACK\lib*
+  - Copy all header files into *LIBPACK\include*
+* **[FreeType](https://freetype.org)** -- Required by OCCT
+  - Download the latest version from https://sourceforge.net/projects/freetype/files/freetype2/ (a Windows .zip file is available)
+  - Extract the files and run cMake
+  - Set HarfBuzz_INCLUDE_DIR to *LIBPACK/include*
+  - Set HarfBuzz_LIBRARY to *LIBPACK/lib/harfbuzz.lib*
+  - Set ZLIB_INCLUDE_DIR to *LIBPACK/include*
+  - Set ZLIB_LIBRARY_RELEASE to *LIBPACK/lib/zlib.lib*
+  - Set PNG_INCLUDE_DIR to *LIBPACK/include*
+  - Set PNG_LIBRARY_RELEASE to *LIBPACK/lib/libpng16.lib*
+  - Set BZIP2_INCLUDE_DIR to *LIBPACK/include*
+  - Set BZIP2_LIBRARY_RELEASE to *LIBPACK/lib/libbz2.lib*
+  - Set CMAKE_INSTALL_PREFIX to *LIBPACK*
+  - Add BUILD_SHARED_LIBS as a boolean value, set to true
+  - Add BUILD_STATIC_LIBS as a boolean value, set to true
+* **[Tcl/Tk](https://www.tcl.tk)**
+  - Download the latest source code for Tcl and Tk
+  - Unpack each, and for each
+    - Open a Developer's Powershell window and change to the *win* subdirectory in the source download
+    - Run `nmake -f makefile.vc release`
+    - Run `nmake -f makefile.vc install INSTALLDIR=C:\path\to\libpack`
+* **[OpenCASCADE](https://www.opencascade.org)** -- Also known as OCCT, the core CAD kernel used by FreeCAD is fetched from a gitlab mirror that
+  provides additional improvements over the upstream version
+  - Clone https://gitlab.com/blobfish/occt
+  - Run cMake
+  - Enable USE_VTK
+  - For each of TCL, TK, VTK, and FreeType (represented below by XXX):
+    - Set 3RDPARTY_XXX_DIR to *LIBPACK*
+    - Set 3RDPARTY_XXX_DLL_DIR to *LIBPACK/bin/*
+    - Set 3RDPARTY_XXX_LIBRARY_DIR to *LIBPACK/lib/*
+    - Set 3RDPARTY_XXX_LIBRARY to *LIBPACK/lib/xxxYYY.lib* (the name of the library varies, use whatever is present)
+  - Set INSTALL_DIR to *LIBPACK*
+  - Configure, Generate, and open the project in Visual Studio
+  - Switch to Release and build the ALL_BUILD target
+* **[Netgen](https://ngsolve.org)**
+  - Clone https://github.com/NGSolve/netgen
+  - Switch to the tag you wish to compile (e.g. `git checkout v6.2.2304`)
+  - Run cMake
+* **[GMSH](https://gmsh.info)**