README.md: Update according to new build system features

README.md

@@ -5,7 +5,8 @@ a fork of the [TORCS](https://torcs.sourceforge.net/) project,
 it has evolved into a higher level of maturity, featuring realistic physics
 with tens of high-quality cars and tracks to choose from.
 
-> **This repository only contains the engine source code.**
+> **This repository contains the engine source code,**
+> **and the base assets [as a submodule](/data/).**
 > **End users are expected to download the pre-built packages listed below.**
 >
 > The assets repository is located on
@@ -22,35 +23,121 @@ Speed Dreams binaries are available for the following platforms:
 
 ## Building from source
 
+In-tree builds (i.e., including both code and data on the same build)
+are recommended for simplicity. To achieve this, update the [`data/`](/data/)
+submodule with:
+
+```
+git submodule update --init --recursive
+```
+
+Otherwise, CMake will search the `speed-dreams-data` package on a
+well-known location, or rely on the
+[`CMAKE_PREFIX_PATH`](https://cmake.org/cmake/help/latest/variable/CMAKE_PREFIX_PATH.html)
+variable to search for an **installed** version of the `speed-dreams-data`
+package, which must then be indicated when configuring the project:
+
+```
+cmake -DCMAKE_PREFIX_PATH=<path-to-speed-dreams-data> # other args...
+```
+
+> **The steps below will assume in-tree builds unless noted otherwise.**
+
+Once configured as described below, the project can be built with:
+
+```
+cmake --build build/ # Optionally, add -j8 or any other number for faster builds
+```
+
+Optionally, the project can be installed via:
+
+```
+cmake --install build/
+```
+
+### BSDs, Linux
+
 Speed Dreams can be built from source using the conventional build process
 in CMake projects:
 
 ```
 cmake -B build
-cmake --build build/ # Optionally, add -j8 or any other number for faster builds
 ```
 
-This assumes the
+### Windows
-[`speed-dreams-data`](https://forge.a-lec.org/speed-dreams/speed-dreams-data/)
+
-package is already installed on a well-known location. If not, use the
+- [CMake](https://cmake.org/download/#latest) `3.12.0` or newer
+- [Git](https://git-scm.com/download/win)
+- [OpenJDK](https://jdk.java.net/) `8` or newer (for the track editor)
+- [MinGW](https://winlibs.com/), with support for C++11.
+
+> Please ensure these tools are added to the `%PATH%` environment variable.
+
+On Windows, dependencies cannot be fetched from a package manager as in
+conventional Linux distributions. To solve this, Speed Dreams defines
+[a separate build system for third-party dependencies](/packaging/3rdParty-devel/).
+This would build all dependencies from source, so they can be later found
+by CMake.
+
+> **Both methods described below will require the path to the pre-built**
+> **dependencies**.
+> Please read [the instructions](/packaging/3rdParty-devel/README.md)
+> for further reference.
+
+#### Native builds
+
+If building from Windows, append the path to the pre-built dependencies to
+the
 [`CMAKE_PREFIX_PATH`](https://cmake.org/cmake/help/latest/variable/CMAKE_PREFIX_PATH.html)
-variable to indicate CMake where to locate an **installed** version of the
+variable:
-`speed-dreams-data` package:
 
 ```
-cmake -B build -DCMAKE_PREFIX_PATH=<path-to-speed-dreams-data>
+cmake -B build -DCMAKE_PREFIX_PATH=<path-to-dependencies>
 ```
 
-And then build the project as usual.
+If using MinGW, then the `MinGW Makefiles` CMake generator might have to be
+manually selected:
 
-> If the `speed-dreams-data` package is not found, the game should still be
+```
-> able to build, but it would not be able to run.
+cmake -B build -G "MinGW Makefiles" -DCMAKE_PREFIX_PATH=<path-to-dependencies>
+```
+
+#### Cross-compiling from Linux
+
+Speed Dreams can not only be compiled natively from Windows, but can be also
+cross-compiled for Windows from a fully free (as in freedom) operating
+system like GNU/Linux. The
+[`w64-mingw32`](https://git.code.sf.net/p/mingw-w64/mingw-w64)
+toolchain can be used for the cross-compilation, with dedicated
+toolchain files for
+[`i686-w64-mingw32`](/packaging/3rdParty-devel/i686-w64-mingw32.cmake)
+and
+[`x86_64-w64-mingw32`](/packaging/3rdParty-devel/x86_64-w64-mingw32.cmake),
+referred to by the
+[`CMAKE_TOOLCHAIN_FILE`](https://cmake.org/cmake/help/latest/variable/CMAKE_TOOLCHAIN_FILE.html)
+variable. Third-party dependencies are then referred to by the
+[`CMAKE_FIND_ROOT_PATH`](https://cmake.org/cmake/help/latest/variable/CMAKE_FIND_ROOT_PATH.html)
+variable, as intended for cross-builds.
+
+> **`CMAKE_FIND_ROOT_PATH` must be an absolute path.**
+
+##### `x86_64`
+
+```
+cmake -B build -DCMAKE_TOOLCHAIN_FILE=packaging/3rdParty-devel/x86_64-w64-mingw32.cmake -DCMAKE_FIND_ROOT_PATH=<path-to-dependencies>
+```
+
+#### `i686`
+
+```
+cmake -B build -DCMAKE_TOOLCHAIN_FILE=packaging/3rdParty-devel/i686-w64-mingw32.cmake -DCMAKE_FIND_ROOT_PATH=<path-to-dependencies>
+```
 
 ### Dependencies
 
 #### Debian/Ubuntu
 
-```
+```sh
 sudo apt install git cmake build-essential libopenscenegraph-dev libcurl4-gnutls-dev libsdl2-dev libsdl2-mixer-dev librhash-dev libenet-dev libpng-dev libjpeg-dev zlib1g-dev libminizip-dev libopenal-dev libplib-dev libexpat1-dev libcjson-dev openjdk-17-jdk openjdk-17-jre
 ```
 
@@ -71,3 +158,5 @@ located in their respective directories for further reference.
 Windows is a registered trademark of Microsoft Corporation.
 
 Ubuntu is a registered trademark of Canonical Ltd.
+
+Linux is a registered trademark of Linus Torvalds.