SDL-like API on top of an inversion of control API.

inverted_sdl.c

#include <stdbool.h>
#include <math.h>
#include <stdio.h>

#include <GL/gl.h>

// A vaguely SDL-like API
void iSDL_init(void);
bool iSDL_should_exit;
void iSDL_swap_buffers(void);
void iSDL_quit(void);

// A simple main-loop style SDL program.
int main(int argc, const char* argv[]){
	iSDL_init();
	
	int tick = 0;
	while(!iSDL_should_exit){
		glClearColor(fmod(tick/100.0f, 1), 0, 0, 1);
		glClear(GL_COLOR_BUFFER_BIT);
		tick++;
		
		iSDL_swap_buffers();
	}
	
	iSDL_quit();
	printf("exiting main()\n");
}

// The SDL-like API yields to another fiber where Sokol runs. (Sokol is an inverted control style API)
// This still allows everything to share the main thread, but Sokol can only hijak the fiber it's confined to.

#define TINA_IMPLEMENTATION
#include "tina.h"

tina* sokol_fiber;
void* sokol_fiber_body(tina* fiber, void* value);

void iSDL_init(){
	// Create a coroutine/fiber to run sokol on and start it
	sokol_fiber = tina_init(NULL, 256*1024, sokol_fiber_body, NULL);
	tina_resume(sokol_fiber, iSDL_init);
}

bool iSDL_should_exit;

// There would probably be more stuff here, but in this simple example they just need to switch to the Sokol fiber.
void iSDL_swap_buffers(void){tina_resume(sokol_fiber, iSDL_swap_buffers);}
void iSDL_quit(){tina_resume(sokol_fiber, iSDL_quit);}

// === Now for the Sokol implementation...

#include <assert.h>

#define SOKOL_APP_IMPL
#define SOKOL_GLCORE33
#define SOKOL_NO_ENTRY
#include "sokol_app.h"

void frame(void){
	// Yields back to the main loop and exits the iSDL_swap_buffers() call.
	void* reason = tina_yield(sokol_fiber, NULL);
	assert(reason == iSDL_swap_buffers);
}

void cleanup(void){
	// Set the quit flag.
	iSDL_should_exit = true;
	// Now wait for iSDL_quit() to be called in the main loop before exiting cleanup().
	void* reason = tina_yield(sokol_fiber, NULL);
	assert(reason == iSDL_quit);
}

void* sokol_fiber_body(tina* fiber, void* value){
	// This fiber function runs on a separate fiber from the main loop
	assert(value == iSDL_init);
	
	// This is a blocking call that implement's Sokol App's main loop.
	sapp_run(&(sapp_desc){
		.frame_cb = frame,
		.cleanup_cb = cleanup,
		.width = 400,
		.height = 300,
		.window_title = "Inside Out",
		.icon.sokol_default = true,
	});
	
	puts("sapp_run has exited");
}