Cross-compiling ScummVM on for Raspberry Pi
Installing the official Raspberry Pi cross-compiler on PC
We will clone the Raspberry Pi tools repository which includes the cross-compiler we need:
git clone https://github.com/raspberrypi/tools.git
It will get cloned to a directory called tools at your current location.
Add it to the PATH environment variable so that we have the cross-compiler binaries available from our scummvm building directory. For example, if my Raspberry Pi tools repository ended cloned in tools under my home directory, I would do:
After adding the cross-compiler executables directory to PATH, we should be able to run arm-linux-gnueabihf-gcc, arm-linux-gnueabihf-g++, etc... just try. They should yield an error because you pass them no input files, but that's expected. It's just a test so we know we have the cross-compiler installed and accessible.
Installing the needed Raspberry Pi headers and libraries on PC
We need to copy over the /usr, /lib and /opt directories from your Raspbian SD Card to your host PC (the computer where you will do the cross-compilation) for the needed headers and libraries to be available.
Of course, first you'll have to install any additional libraries from Raspbian running on the Pi before expecting them to be available so, if you want compile ScummVM with FLAC support, you should have installed the libflac development libraries on the Pi beforehand.
As an example, on the Raspberry Pi running Raspbian (Buster) OS 3.2 (January 2020) we can execute the following to install third party libraries that ScummVM needs for its features and various game engines:
sudo apt-get update sudo apt-get upgrade sudo apt-get install -y --no-install-recommends \ libsdl2-dev \ liba52-0.7.4-dev \ libjpeg62-turbo-dev \ libmpeg2-4-dev \ libogg-dev \ libvorbis-dev \ libflac-dev \ libmad0-dev \ libpng-dev \ libtheora-dev \ libfaad-dev \ libfluidsynth-dev \ libfreetype6-dev \ libcurl4-openssl-dev \ libsdl2-net-dev \ libspeechd-dev \ zlib1g-dev
On the host PC we first export the path where we will copy these into, and then we manually copy them. I choose to copy the Raspberry Pi headers and libraries to /opt/rpi_root, but any other path with the right permissions for your user (within common sense) should be ok:
mkdir -p /opt/rpi_root export RPI_ROOT=/opt/rpi_root cd <Raspbian_SD_card_mountpoint_directory> cp -R usr lib opt $RPI_ROOT
The above copying of files has the unfortunate side-effect that many symbolic links that were copied over are now invalid, particularly those linking to absolute paths. Fortunately, we can remedy this situation by downloading and running a python script that will fix those links:
wget https://raw.githubusercontent.com/riscv/riscv-poky/master/scripts/sysroot-relativelinks.py chmod +x sysroot-relativelinks.py ./sysroot-relativelinks.py $RPI_ROOT
Finally, update the PATH variable to be preceded by the RPI_ROOT path, since this is required for proper detection of libcurl related files by ScummVM's configure script.
First, you should make sure have the latest version of the ScummVM code locally (using git clone or git pull appropriately).
Then, navigate inside your local scummvm source code folder.
Now we can configure ScummVM buildsystem so it knows what backend we target and where our Raspberry Pi local sysroot is located, containing the Raspberry Pi headers and libraries the cross-compiler and linker will need. In this example configuration, we disable debug symbols since it's intended for final users.
PKG_CONFIG_SYSROOT_DIR=$RPI_ROOT PKG_CONFIG_LIBDIR=$RPI_ROOT/usr/lib/arm-linux-gnueabihf/pkgconfig ./configure --host=raspberrypi --with-sdl-prefix=$RPI_ROOT/usr --with-png-prefix=$RPI_ROOT/usr --disable-debug --enable-release
Remember you should have exported the RPI_ROOT environment variable previously and updated the PATH environment variable to be preceded by the RPI_ROOT path and succeeded by the path to the Raspberry Pi toolchain bin folder (as shown in the previous steps).
On the Raspberry Pi, SDL2 will always be used, since it provides graphics acceleration.
Unfortunately, the official toolchain for cross-compiling for Pi is, as of yet, using an old gcc version (4.3.9) and hence, the configure script may fail to detect the FluidSynth library specifically. FluidSynth and MT-32 emulation are features that are very demanding on CPU processing power so it should be ok to skip them entirely. Alternatively, you could seek out a more up-to-date armhf toolchain for the cross-compilation, such as this Raspberry Pi toolchain by Stefan Profanter (Pro) which, in its 1.0.1 version, uses gcc version 8.3.0 and reportedly "supports all new Raspberry PIs (ARMv7), and the older ones, including Zero, A, B, B+ (ARMv6) with newer GCCs."
Note 1: If you use the Raspberry Pi toolchain by Stefan Profanter (Pro), then make sure you read the instructions from the README file (also available from the main page of the repository). Specifically, this toolchain needs to be installed in /opt/cross-pi-gcc since it's not location independent.
Note 2: If you are building ScummVM directly on your Raspberry Pi itself, you might run out of memory during the final linking process of the build. If you use GNU ld for compiling, you could execute the following before running configure:
This tells GNU ld to optimize for memory usage.
Run the following commands:
make clean make -j$(nproc)
Installing ScummVM on the Raspberry Pi
Simply copy over the resulting scummvm executable to your Raspberry Pi (Raspbian OS) SD Card. A good idea is to create a scummvm folder in your /home/pi directory on the Raspian OS SD Card, and put the executable there along with any games you want to use with it.
In order to have the text-to-speech feature available for ScummVM you should also install the speech-dispatcher package and a text-to-speech engine (as per the instructions in this pertinent Pull Request)
For example you'd need to execute the following on your Raspbian OS on the Pi in order to use the espeak-ng text-to-speech engine:
sudo apt-get install --no-install-recommends speech-dispatcher speech-dispatcher-espeak-ng