Compile on Windows/ro

Acest articol explică pas cu pas how to compile FreeCAD on Windows.

Premise
Compiling FreeCAD on Windows requires several tools and libraries.

Programe necesare

 * Git Aici sunt câteva dintre alternative ca GitCola, Tortoise Git, și altele.
 * CMake versiunea 2.x.x sau Cmake 3.x.x
 * Python >2.5 (Acest lucru este necesar numai dacă NU utilizați Libpack. Libpack este livrat încpând cu Python(2.7.x) potrivit pentru compilarea și rularea  FreeCAD)


 * A compiler. FreeCAD is tested with Visual Studio (MSVC)—other compilers may work, but instructions for use are not included here. More details in, below.


 * Git (There are also GUI frontends available for Git, see the next section.)


 * CMake version 3.11.x or newer. Hint: Choosing the option Add CMake to the system PATH for all users when installing CMake will make CMake accessible from the Windows command prompt, which can be useful.


 * LibPack (also called FreeCADLibs). This is a single package containing all of the libraries necessary to compile FreeCAD on Windows. Download the version of the LibPack that corresponds to the version of FreeCAD you want to compile. To compile FreeCAD 0.19 or the latest development version 0.20, download the LibPack for 0.19 (64-bit only). Extract the LibPack to a convenient location. (If your computer does not recognize the .7z extension, you should install the program 7-zip.) Note: It is highly recommended to compile FreeCAD with the compiler version the LibPack is designed for. For example, you might run into problems compiling FreeCAD 0.19 using MSVC 15 because the LibPack for 0.19 is designed to be built with MSVC 17.

Optional programs

 * A GUI frontend for Git. There are several frontends available, see this list. The main benefit of a frontend is that you don't have to learn the Git commands to get the source code of FreeCAD or to send patches to the GitHub repository of FreeCAD.

In the following we describe source code handling using the TortoiseGit frontend. This frontend integrates directly into Windows file explorer and has a large user community to get help in case you have problems.


 * NSIS is used to generate the FreeCAD Windows installer (FreeCAD 0.17 and earlier used WiX).

Utilizați Git (de preferință)
Now you can get the source code of FreeCAD:

Using a frontend
When using the Git frontend TortoiseGit:
 * 1) Create a new folder where the source code will be downloaded.
 * 2) Right-click on this folder in the Windows file explorer and select Git Clone in the context menu.
 * 3) A dialog will appear. In it, enter the URL for the FreeCAD Git repository

https://github.com/FreeCAD/FreeCAD.git

and click OK.

The latest source code will be downloaded from the FreeCAD Git repository and the folder will be tracked by Git.

Using the command line
Pentru a crea o ramură de urmărire locală și pentru a descărca codul sursă, trebuie să deschideți un terminal (promp de comandă) și cd(change directory) în directorul pe care doriți să plasați codul sursă, apoi tastați:

Compilator
Sub Windows, compilatorul implicit este MS Visual Studio. CI utilizează versiunea din 2013.

The default (recommended) compiler is MS Visual Studio (MSVC). Though it may be possible to use other compilers, for example gcc via Cygwin or MinGW, it is not tested or covered here.

You can get a free version of MSVC (for individual usage) by downloading the Community edition of MS Visual Studio.

Pentru cei care doresc să evite instalarea imensului Visual Studio pentru simplul scop de a avea un compilator, vezi CompileOnWindows - Reducing Disk Footprint.

Note: Although the Community edition of MSVC is free, to use the IDE for more than a 30-day trial period you must create a Microsoft account. If you will only compile using the command line, you don't need the IDE and thus no Microsoft account.

As a free and OpenSource alternative IDE you can use KDevelop. You can use KDevelop to modify and write C++ code but must use the command line to compile.

Configurarea căii de sistem
În interiorul căii dvs. de sistem, asigurați-vă că setați căile corecte la următoarele programe:
 * git (not tortoiseGit, but git.exe) Acest lucru este necesar pentru ca Cmake să actualizeze în mod corespunzător informațiile despre versiunea "Despre FreeCAD".h fișierul care permite FreeCAD să raporteze versiunea corespunzătoare din About FreeCAD din meniul de ajutor.
 * În mod opțional, puteți include Libpack în calea dvs. de sistem. Acest lucru este util dacă intenționați să construiți mai multe configurații / versiuni ale FreeCAD, va trebui să copiați mai puține fișiere după cum este explicat mai târziu în procesul de rulare.

Optionally you can include the paths to some folders to the system PATH variable. This is helpful if you want to access programs in these folders from the command line/powershell or if you want special programs to be found by the compiler or CMake. Besides this, adding folders to the PATH might be necessary if you did not use the corresponding options when installing the program.


 * You can include the folder of your LibPack in your system PATH variable. This is useful if you plan to build multiple configurations/versions of FreeCAD.
 * If you did not use the option to add CMake to the PATH while installing it, add its installation folder

C:\Program Files\CMake\bin to the PATH.
 * If you did not use the option to add TortoiseGit to the PATH while installing it, add its installation folder

C:\Program Files\TortoiseGit\bin to the PATH.

Pentru a adăuga la cale asitemului dvs:

Configurare cu CMake
Once you have all of the necessary tools, libraries, and FreeCAD source code, you are ready to begin the configuration and compilation process. This process will proceed in five steps:
 * 1) Run CMake once to examine your system and begin the configuration progress (this will report that it failed).
 * 2) Adjust necessary CMake settings to set the locations of the LibPack and enable Qt5.
 * 3) Re-run CMake to finalize the configuration (this time it should succeed).
 * 4) Use CMake to generate the Visual Studio build system.
 * 5) Use Visual Studio to build FreeCAD.

CMake
First, configure the build environment using CMake:
 * 1) Open the CMake GUI
 * 2) Specify the source folder of FreeCAD.
 * 3) Specify a build folder (do not use the source folder -- CMake will create this folder if it does not exist).
 * 4) Click Configure.
 * 5) In the dialog that appears specify the generator you want to use: in most cases you will use the defaults in this dialog. For the standard MS Visual Studio use Visual Studio xx 2yyy where xx is the compiler version and 2yyy the year of its release. It is recommended to use the default option Use default native compilers.

Note: It is important to specify the correct bit variant. If you have the 64-bit variant of the LibPack you must also use the x64 compiler.

Aceasta va începe configurarea și ar trebui să eșueze deoarece locația FREECAD_LIBPACK_DIR is unset.
 * Expand the FREECAD category and set FREECAD_LIBPACK_DIR to the correct location
 * Check FREECAD_USE_EXTERNAL_PIVY
 * Optionally Check FREECAD_USE_FREETYPE this is required to use the Draft WB's Shape String functionality
 * Click Configure again
 * There should be no errors
 * Click Generate
 * Close CMake
 * Copy libpack\bin folder into the new build folder CMake created

If it fails with the message that Visual Studio could not be found, the CMake support in MSVC is not yet installed. To do this:
 * 1)  Open the MSVC IDE
 * 2)  Use the menu Tools → Get Tools and Features
 * 3)  In the Workloads tab enable Desktop development with C++
 * 4) On the right side you should now see that the component Visual C++ tools for CMake will be installed.
 * 5) Install it.

If it fails with a message about the wrong Python version or missing Python, then:
 * 1)  Use the "Search:" box in CMake to search for the string "Python"
 * 2)  If you see there a path like C:/Program Files/Python38/python.exe, CMake recognized the Python that is already installed on your PC, but that version is not compatible with the LibPack. Since the LibPack includes a compatible version of Python, modify the following Python settings in CMake to its paths (assuming the LibPack is in the folder D:\FreeCAD-build\FreeCADLibs_12.4.2_x64_VC17):

If there is no error about Visual Studio or Python, everything is fine, but CMake does not yet know all necessary settings. Therefore now:
 * 1) Search in CMake for the variable FREECAD_LIBPACK_DIR and specify the location of the LibPack folder you downloaded earlier.
 * 2) Only if building FreeCAD 0.19, search for the variable BUILD_QT5 and enable this option.
 * 3) Click Configure again.

There should now be no errors. If you continue to encounter errors that you cannot diagnose, visit the Install/Compile forum on the FreeCAD forum website. If CMake proceeded correctly, click on Generate. After this is done you can close CMake and start the compilation of FreeCAD using Visual Studio. However, for the first compilation keep it open in case you want or need to change some options for the build process.

Opțiuni pentru compilarea Proceselor
Sistemul de compilare CMake ne oferă o mult mai mare flexibilitate în procesul de compilare. Asta înseamnă că putem porni și dezactiva câteva funcționalități sau module. Este într-un fel ca compilarea kernel-ului Linux. Aveți o mulțime de comutatoare pentru a determina procesul de compilare.

Iată descrierea unora dintre aceste switch-uri. Probabil că se vor schimba mult în viitor pentru că vrem să creștem flexibilitatea compilării mult mai mult.

Note: Some components are required for other components. If you for example uncheck BUILD_ROBOT CMake will inform you that then the component Path cannot be compiled correctly. Therefore check the CMake output after you changed a BUILD_XXX option! || depends
 * CMAKE_INSTALL_PREFIX  || The output folder when building the target INSTALL, see also section Running and installing FreeCAD || Windows' default program installation folder
 * FREECAD_COPY_DEPEND_DIRS_TO_BUILD || Copies depending libraries needed to execute the FreeCAD.exe to the build folder. See also section Running and installing FreeCAD. Note: the options FREECAD_COPY_XXX only appear if the libraries were not already copied. So when you change to another LibPack version, it is important to delete all folders in your build folder, except of the LibPack folder. In CMake delete the cache and start as if you compile for the first time and you will get the FREECAD_COPY_XXX options. || OFF
 * FREECAD_COPY_LIBPACK_BIN_TO_BUILD || Copies the LibPack binaries needed to execute the FreeCAD.exe to the build folder. See also section Running and installing FreeCAD. || OFF
 * FREECAD_COPY_PLUGINS_BIN_TO_BUILD|| Copies Qt's plugin files needed to execute the FreeCAD.exe to the build folder. See also section Running and installing FreeCAD. || OFF
 * FREECAD_LIBPACK_USE || Switch the usage of the FreeCAD LibPack on or off || ON
 * FREECAD_LIBPACK_DIR || Directory where the LibPack is || FreeCAD's source code folder
 * FREECAD_RELEASE_PDB || Create debug libraries also for release builds || ON
 * }
 * FREECAD_LIBPACK_USE || Switch the usage of the FreeCAD LibPack on or off || ON
 * FREECAD_LIBPACK_DIR || Directory where the LibPack is || FreeCAD's source code folder
 * FREECAD_RELEASE_PDB || Create debug libraries also for release builds || ON
 * }
 * FREECAD_RELEASE_PDB || Create debug libraries also for release builds || ON
 * }
 * }

Compilarea FreeCAD
În funcție de configurația actuală, procesul de construire a FreeCAD va fi ușor diferit. Acest lucru se datorează diferențelor dintre versiunile de software disponibile pentru fiecare sistem de operare.

Depending on your compiler, the process for building FreeCAD will be slightly different. In the following sections you known workflows are described. If you are building with Qt Creator, jump to Building with Qt Creator, otherwise proceed directly:

Release Build
This will now take quite a long time.
 * 1) Start the Visual Studio IDE. This can either be done by pressing the button Open Project in the CMake GUI or by double-clicking on the file FreeCAD.sln that you find in your build folder.
 * 2) In the toolbar of the MSVC IDE assure that you use for the first compilation Release.
 * 3) There is a window called Solution Explorer. It lists all possible compilation targets. To start a full compilation, right-click on the target ALL_BUILD and then choose Build.

To compile a ready-to use FreeCAD, compile the target INSTALL, see section Running and installing FreeCAD.

If you don't get any errors you are done. Congratulations! You can exit MSVC or keep it open.

Debug Build
For a debug build it is necessary that the Python is used that is included in the LibPack. To assure this:
 * 1)  Search in the CMake GUI for "Python"
 * 2)  If you see there a path like C:/Program Files/Python38/python.exe, CMake recognized the Python that is installed on your PC and not the one of the LibPack. In this case adapt these different Python settings in CMake to this (assuming the LibPack is in the folder D:\FreeCAD-build\FreeCADLibs_12.4.2_x64_VC17):

Now This will now take quite a long time. If there were no compilation errors, you can start the debug build:
 * 1) Start the Visual Studio IDE. This can either be done by pressing the button Open Project in the CMake GUI or by double-clicking on the file FreeCAD.sln that you find in your build folder.
 * 2) In the toolbar of the MSVC IDE assure that you use for the first compilation Debug.
 * 3) There is a window called Solution Explorer. It lists all possible compilation targets. To start a full compilation, right-click on the target ALL_BUILD and then choose Build in the context menu.
 * 1) Right-click on the target FreeCADMain and then choose Set as Startup Project in the context menu.
 * 2) Finally click in the toolbar on the button with the green triangle named Local Windows Debugger.

This will start the debug build of FreeCAD and you can use the MSVC IDE to debug it.

Video Resource
An English language tutorial that begins with configuration in CMake Gui and continues to the `Build` command in Visual Studio 16 2019 is available unlisted on YouTube at Tutorial: Build FreeCAD from source on Windows 10.

Building with Visual Studio 12 2013
Make sure to specify Visual Studio 12 x64(or the alternate C-Compiler you are using) as the generator in CMake before you continue.

Make sure to specify Visual Studio 12 x64(or the alternate C-Compiler you are using) as the generator in CMake before you continue.


 * Start Visual Studio 12 2013 by clicking on the desktop icon created at installation.

File -> Open -> Project/Solution
 * Open the project by:


 * Open FreeCAD_Trunk.sln from the build folder CMake created

This may take a while depending on your sytem
 * Switch the Solutions Configuration drop down at the top to Release X64


 * Build -> Build Solution


 * This will take a long time...

If you don't get any errors you are done. Exit Visual Studio and start FreeCAD by double clicking the FreeCAD icon in the bin folder of the build directory.

Installation and configuration of Qt Creator

 * Download and install Qt Creator
 * Tools -> Options -> Text Editor -> Behavior tab:
 * File Encodings -> Default Encodings:
 * Set to: ISO-8859-1 /...csISOLatin1 (Certain characters create errors/warnings with Qt Creator if left set to UTF-8. This seems to fix it.)
 * Tools -> Options -> Build & Run:
 * CMake tab
 * Fill Executable box with path to cmake.exe
 * Kits tab
 * Name: MSVC 2008
 * Compiler: Microsoft Visual C++ Compiler 9.0 (x86)
 * Debugger: Auto detected...
 * Qt version: None
 * General tab
 * Uncheck: Always build project before deploying it
 * Uncheck: Always deploy project before running it


 * Download and install Qt Creator
 * Tools → Options → Text Editor → Behavior tab:
 * File Encodings → Default Encodings:
 * Set to: ISO-8859-1 /...csISOLatin1 (Certain characters create errors/warnings with Qt Creator if left set to UTF-8. This seems to fix it.)
 * Tools → Options → Build & Run:
 * CMake tab
 * Fill Executable box with path to cmake.exe
 * Kits tab
 * Name: MSVC 2008
 * Compiler: Microsoft Visual C++ Compiler 9.0 (x86)
 * Debugger: Auto detected...
 * Qt version: None
 * General tab
 * Uncheck: Always build project before deploying it
 * Uncheck: Always deploy project before running it

Import project and Build

 * File -> Open File or Project
 * Open CMakeLists.txt which is in the top level of the source
 * This will start CMake
 * Choose build directory and click next
 * Set generator to NMake Generator (MSVC 2008)
 * Click Run CMake. Follow the instructions depicted above to configure CMake to your liking.


 * File → Open File or Project
 * Open CMakeLists.txt which is in the top level of the source
 * This will start CMake
 * Choose build directory and click next
 * Set generator to NMake Generator (MSVC 2008)
 * Click Run CMake. Follow the instructions depicted above to configure CMake to your liking.

Now FreeCAD can be built
 * Build -> Build All
 * This will take a long time...

Once complete, it can be run: There are 2 green triangles at the bottom left. One is debug. The other is run. Pick whichever you want.

Command line build
Here an example how to build FreeCAD from the Command line:

The steps how to compile from the command line depends on the compiler. For MSVC 2017 the steps are:
 * 1) In Windows' start menu go to  and choose Developer Command Prompt for VS 2017
 * 2) Change to your build folder.
 * 3) Execute the command

or

These steps can also be automaized. Here is for example a solution for MSVC 2017:
 * 1) Download the script compile-FC.txt.
 * 2) Rename it to compile-FC.bat
 * 3) In Winddows' file explorer Shift+Right-click on your build folder and use from the context menu Command prompt here.
 * 4) Execute the command

Instead of calling compile-FC with the option install you can also use debug or release:

debug  - compile FreeCAD in debug configuration

release - compile FreeCAD in release configuration

install   - compile FreeCAD in release configuration and create an install setup

Running and installing FreeCAD
There are 2 methods to run the compiled FreeCAD:

Method 1: You execute the FreeCAD.exe that you find in your build folder in the subfolder bin

Method 2: You build the target INSTALL

Method 2 is the simpler one because it automatically assures that all libraries needed to run the FreeCAD.exe are in the correct folder. The FreeCAD.exe and the libraries will be output in the folder you specified in the CMake variable CMAKE_INSTALL_PREFIX.

For Method 1 you need to put the libraries into the bin folder of your build folder (where the FreeCAD.exe is). This can easily be done:
 * 1) Open the CMake GUI.
 * 2) Search there for the variable option FREECAD_COPY_DEPEND_DIRS_TO_BUILD and check it. If there is no such option, the libraries were already copied, see the description of the options.
 * 3) Search there for the variable option FREECAD_COPY_LIBPACK_BIN_TO_BUILD and check it.
 * 4) Search there for the variable option FREECAD_COPY_PLUGINS_BIN_TO_BUILD and check it.
 * 5) Click on Configure. At the end of the configuration CMake will automatically copy the necessary libraries from the LibPack folder.

For FreeCAD 0.19 using LibPack 12.1.4 and older, there is one issue that requires manual action:
 * 1) Download the file qwindowsvistastyle.zip from the FreeCAD forum.
 * 2) Create a new subfolder named styles in the bin folder (where the FreeCAD.exe is).
 * 3) Extract the ZIP-file to this folder.

This adds the necessary style to make FreeCAD look like a normal Win 10 program. Otherwise it looks like in Windows 98.

Updating the build
FreeCAD is very actively developed. Therefore its source code changes almost daily. New features are added and bugs are fixed. To benefit from these source code changes, you must rebuild your FreeCAD. This is done in two steps:
 * 1) Updating the source code
 * 2) Recompilation

Using a frontend
When using the Git frontend TortoiseGit:
 * 1) Right-click on your FreeCAD source code folder in the Windows file explorer and select in the context menu Pull.
 * 2) A dialog will appear. Select there what development branch you want to get. master is the main branch. Therefore use this unless you want to compile a special new feature from a branch that has not yet been merged to master. (For more about Git branches, see Git development process.)

Finally click OK.

Using the command line
Open a terminal (command prompt) and switch there to your source directory. Then type:

where master the the name of the main development branch. If you want to get code from another branch, use its name instead of master.

Recompilation

 * 1) Open the MSVC IDE by double-clicking either on the file FreeCAD.sln or on the file ALL_BUILD.vcxproj in your build folder.
 * 2) Continue with step 2 from section Building with Visual Studio 15 2017.

Tools
In order to join the FreeCAD development you should compile and install the following tools:

Qt Designer plugin
FreeCAD uses Qt as toolkit for its user interface. All dialogs are setup in UI-files that can be edited using the program Qt Designer that is part of any Qt installation and also included in the LibPack. FreeCAD has its own set of Qt widgets to provide special features like adding a unit to input fields and to set preferences properties.

Installation
To make Qt Designer aware of the FreeCAD widgets, you must


 * 1) Download this ZIP file. (Compiled using Qt 5.12, see below.)
 * 2) Extract the DLL file in the ZIP and copy it
 * If you use the LibPack: to the folder ~\FreeCADLibs_12.1.4_x64_VC15\bin\designer Since there will only be a bin folder and you must first create the designer subfolder.
 * If you have a full Qt installation: you can choose between the folder C:\Qt\Qt5.12.5\5.12.5\msvc2017_64\plugins\designer or C:\Qt\Qt5.12.5\5.12.5\msvc2017_64\bin\designer (adapt the paths to your installation!).

(Re)Start Qt Designer and check its menu. If the plugin FreeCAD_widgets.dll is listed as being loaded, you can now design and change FreeCAD's .ui files. If not, you must compile the DLL by yourself.

If you prefer using Qt Creator instead of Qt Designer, the DLL must be placed in this folder: C:\Qt\Qt5.12.5\Tools\QtCreator\bin\plugins\designer (Re)Start Qt Creator, switch to the mode Design and then check the menu. If the plugin FreeCAD_widgets.dll is listed as being loaded, you can now design and change FreeCAD's .ui files. If not, you must compile the DLL by yourself.

Compilation
The DLL cannot be loaded as plugin if it was compiled using another Qt version than the one your Qt Designer/Qt Creator is based on. In this case you must compile the DLL by yourself. This is done the following way:


 * 1) Change to the FreeCAD source folder ~\src\Tools\plugins\widget
 * 2) Open a MSVC x64 command prompt using the Windows Start menu and change within it to the above folder. It is important that it is the x64 version of the MSVC command prompt!
 * 3) Execute this command If qmake could not be found, use the full path to it, e.g. for the LibPack it should be this one (adapt it to your installation): D:\FreeCAD-build\FreeCADLibs_12.1.4_x64_VC15\bin\qmake -t vclib plugin.pro for a full Qt installation it is C:\Qt\Qt5.12.5\5.12.5\msvc2017_64\bin\qmake -t vclib plugin.pro (adapt the paths to your installation!)
 * 4) The call of qmake created the file FreeCAD_widgets.vcxproj in the folder ~\src\Tools\plugins\widget. Double-click on it and the MSVC IDE will open.
 * 5) In the toolbar of the MSVC IDE assure that you use the compilation target Release.
 * 6) There is a window called Solution Explorer. Right-click there on FreeCAD_widgets and then choose Build.
 * 7) As result you should now have a FreeCAD_widgets.dll in the folder ~\src\Tools\plugins\widget\release that you can install as plugin as described above.

Thumbnail Provider
FreeCAD has the feature to provide preview thumbnails for *.FCStd files. That means that in the Windows file explorer *.FCStd files are shown with a screenshot of the model it contains. To provide this feature, FreeCAD needs to have the file FCStdThumbnail.dll installed to Windows.

Installation
The DLL is installed this way:
 * 1) Download this ZIP file and extract it.
 * 2) Open a Windows command prompt with administrator privileges (these privileges are a requirement).
 * 3) Change to the folder where the DLL is.
 * 4) Execute this command

So check if it works, assure that in FreeCAD the preferences option Save thumbnail into project file when saving document is enabled and save a model. Then view in Windows Explorer the folder of the saved model using a symbol view. You should now see a screenshot of the model in the folder view.

Compilation
To compile the FCStdThumbnail.dll
 * 1) Change to the FreeCAD source folder ~\src\Tools\thumbs\ThumbnailProvider
 * 2) Open the CMake GUI
 * 3) Specify there as source folder the one you are currently in.
 * 4) Use the same folder as build folder.
 * 5) Click Configure
 * 6) In the appearing dialog, specify the generator according to the one you want to use. For the standard MS Visual Studio use Visual Studio xx 2yyy where xx is the compiler version and 2yyy the year of its release. It is recommended to use the default option Use default native compilers. Note: It is important to specify the correct bit variant. If you have the 64bit variant of LibPack you must also use the x64 compiler.
 * 7) Click on Generate.
 * 8) You should now have the file ALL_BUILD.vcxproj in the folder ~\src\Tools\thumbs\ThumbnailProvider. Double-click on it and the MSVC IDE will open.
 * 9) In the toolbar of the MSVC IDE assure that you use the compilation target Release.
 * 10) There is a window called Solution Explorer. Right-click there on ALL_BUILD and then choose Build.
 * 11) As result you should now have a FCStdThumbnail.dll in the folder ~\src\Tools\thumbs\ThumbnailProvider\release that you can install as described above.

Compiling OpenCASCADE
The standard Libpack comes with a version of OpenCASCADE that is suitable for general use. However, under some circumstances you may wish to compile against an alternate version of OpenCASCADE, such as one of their official releases, or a patched fork. Note that there is no guarantee that FreeCAD will work with all versions of OpenCASCADE, and using a non-Libpack version is for advanced users only. Note also that if you are using the Netgen library, it uses OpenCASCADE for some of its functionality and must be compiled against the same version of OpenCASCADE that you use when compiling FreeCAD.

The process for building a custom version of OpenCASCADE is similar to that for FreeCAD, and can make use of the FreeCAD Libpack that you have already downloaded to provide the third-party dependencies it needs (Freetype and Tcl/Tk).

First obtain the OpenCASCADE source code, either directly from the release page at OpenCASCADE.org, via git, or by cloning someone else's fork, such as the "blobfish" fork maintained by FreeCAD forum member tanderson69.

Next, use CMake to configure the build system in a similar manner to building FreeCAD. Notable CMake options for OpenCASCADE are:
 * 3RDPARTY_DIR - The location of your thrid-party libraries, typically set to your FreeCAD Libpack directory
 * INSTALL_DIR - Where to install the finished libraries. A good practice is to use an isolated directory on your system, rather than installing globally, or overwriting the Libpack's version.

Finally, open the project in Visual Studio and build the ALL_BUILD and then INSTALL targets.

Once you have generated the appropriate DLLs for OpenCASCADE (there are many of them), you will need to rebuild FreeCAD. Open CMake and set up the source and build directories of a FreeCAD build as directed above. It is generally a good idea to use a new build directory for this alternate version of OpenCASCADE so that it is easy to switch back to your old version of FreeCAD if something goes wrong, and to set up an install directory so you can ensure the correct libraries are in place. In addition to the CMake variables discussed above, set the OpenCASCADE_DIR variable to the location of the cmake folder containing your OpenCASCADE build information. For example: CMAKE_INSTALL_PREFIX   C:/Users/JaneDoe/Work/FreeCAD_occt751-install/ OpenCASCADE_DIR        C:/Users/JaneDoe/Work/opencascade-7.5.1-install/cmake/

Once you have used CMake to generate the build files for FreeCAD, open it in Visual Studio, build it, and then run build on the INSTALL target.