This is a Standard ML implementation of the Pong Wars animation that became somewhat popular this year, in 2024.
It uses GLFW and OpenGL 3/3.0 ES, although it may work with older versions too.
This is the first program I made on my journey of learning OpenGL as I decided it would be a small and fun project.
This project uses the "functional core, imperative shell" architecture, which is my preferred way to structure programs when possible. I wrote a blog post about it here.
There are some C files in this repository, only two of which (gles3-export.c and glfw-export.c) I wrote myself, declaring the FFI functions used.
The file export.h is generated by MLton and defines types used for FFI. THe other C files (glad.c, glad.h and khrplatform.h) are just there for the sake of using and initialising OpenGL.
The following must be installed in order to build:
- The MLton compiler for Standard ML
- The pkg-config utility to find system libraries
- The GLFW library for window management
Unix (BSD, Linux)
Clone the repository and run ./build-unix.sh.
A file called shell will be generated and you can enter ./shell to run the program.
OSX
Clone the repository and run ./build-osx.sh.
Afterwards, run ./shell to run the generated shell file.
Note: Untested (don't have a Mac I can run on) but I assume the build-osx.sh file works.
Windows
I don't have a Windows computer with me, but MLton (either via Cygwin or MinGW) and GLFW both run on Windows. There should be a way to run this program on Windows too.
Since I don't know and can't test, I would suggest anyone interested uses the Windows Subsystem for Linux and follows the instructions there.
There are some reasons a minimal amount of code will need to be written in order to run using a different Standard ML compiler.
FFI
First, there are FFI bindings to a very small subset of GLFW (in glfw-import.sml) and OpenGL 3 (in gles3-import.sml).
As there's no standardised FFI across Standard ML compilers, that will need to be rewritten.
Syntax extensions
Secondly, game-init.sml and game-draw.sml both use a syntax extension supported at least by MLton and SML/NJ.
That syntax extension is for vector (immutable array) literals, which can be written using #[my, vector, elements].
There are only two uses of this syntax extension across the whole project.
These uses can be rewritten using the Vector.fromList function (Vector.fromList [my, vector, elements]) but I didn't see a reason to avoid it.
MLton-exclusive types
There is a third reason that limits the portability of the code here, which is the use of the Real32.real type (the 32-bit float type in C).
This just specifies the number of bits used by the type. OpenGL typically uses 32-bit floats, but MLton's real type defaults to 64-bit (the double type in C).
The exact C type represented by a real might vary by the Standard ML compiler used, but I wasn't planning on using a different compiler anyway.