cosmo-sokol

Sample sokol+dearimgui application compiled with cosmopolitan toolchain.

Build instruction

Download cosmocc at: https://github.com/jart/cosmopolitan/releases. At least v3.9.5 is required. With cosmocc in your PATH, run ./build.

Then run bin/cosmo-sokol.

Checkout the github workflow for all the required dependencies.

How it works

Linux

Platform header directories are symlinked into the shims/linux. This is done instead of adding -I/usr/include so that we can restrict what is exposed to the compiler.

Using dlopen, all required dynamic libraries can be dynamically loaded. Instead of linking directly to those libraries (e.g: libgl, libx11...), we can link to a stub implementation. When called, it will load the actual library and forward the call to the actual implementation. e.g: the stub XPending dynamically loads libX11.so and then forward the call to the actual XPending retrieved through dlsym.

gen-x11 is a Python script that generates x11.c. All undefined references have to be manually added to the list of generated functions. Take note that a nullary function such as XInitThreads have to be declared as: Status XInitThreads().

For OpenGL, the exhaustive list of functions can be found at: https://github.com/KhronosGroup/OpenGL-Registry/blob/main/xml/gl.xml. gen-gl simply requires a minimum version number to generate gl.c.

Windows

cosmopolitan's own headers lack a lot of Windows function prototype so we have to ignore implicit-function-declaration. However, it has a simple way to import required win32 functions: https://github.com/jart/cosmopolitan/blob/master/libc/nt/master.sh. Simply list the name, dll and arity in that file. This requires making upstream changes to cosmopolitan. As of this writing, the required changes are merged and sokol_app + sokol_gfx can run on Windows.

windows.h (and its transitive headers) includes a lot of struct definitions and macros. Unfortunately, including the official windows.h directly or its MinGW counterpart often results in a lot of duplicated and conflicting definitions when compiling using cosmocc. Therefore, all relevant definitions are instead replicated inside sokol_windows.c.

Multi-platform runtime

sokol makes use of platform ifdef to selectively compile platform-dependent code. In cosmopolitan, we want to compile all platform-dependent code paths and select the right implementation at runtime instead.

In order to do that with the same library, we can use the following preprocessor trick:

1. For each platform, prefix every sokol public function with its platform name. e.g: sapp_show_keyboard becomes linux_sapp_show_keyboard and windows_sapp_show_keyboard.

   This can simply be done by #define sapp_show_keyboard linux_sapp_show_keyboard right before including sokol_app.h.

2. Create a multi-platform shim (sokol_cosmo.c) that selects the right implementation at runtime.

gen-sokol takes in a list of sokol public functions and generate the required #define-s and the cosmo shim.