kkrotchbulge - SDL2+GL capture on Linux & BSD

kkrotchbulge.c

// kkrotchbulge: a cheap nasty hack to capture 60fps vids on Linux & BSD systems / GreaseMonkey, 2015 - Public Domain
// note, only does video right now, and only handles SDL2 + GL.
// compile+render: cc -fPIC -shared -o libkkrotchbulge.so kkrotchbulge.c -I/usr/local/include `sdl2-config --cflags` -L/usr/local/lib -lGL && env LD_PRELOAD=./libkkrotchbulge.so ./tfiy
// transcode (in another terminal): ffmpeg -s 1280x720 -r 60 -pix_fmt rgba -f rawvideo -i kkrotchbulge-out-vid tfiy-vid.mkv
// combine audio: ffmpeg -i tfiy-vid.mkv -i dat/ds15rel-gm.ogg -acodec copy -vcodec copy tfiy-60fps.mkv
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <errno.h>

#include <assert.h>

#include <epoxy/gl.h>
#include <SDL.h>

#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>

#include <dlfcn.h>

// bypass epoxy shim
#undef glReadPixels
GLAPI void GLAPIENTRY glReadPixels( GLint x, GLint y,
                                    GLsizei width, GLsizei height,
                                    GLenum format, GLenum type,
                                    GLvoid *pixels );

#undef glFinish
GLAPI void GLAPIENTRY glFinish( void );

#undef glFlush
GLAPI void GLAPIENTRY glFlush( void );
//

static uint64_t frame_counter = 0;
static int outfp_vid = -1;
static int outfp_aud = -1;

DECLSPEC void SDLCALL SDL_GL_SwapWindow(SDL_Window *window)
{
	static void (*f_next)(SDL_Window *) = NULL;
	static uint8_t *pbuf = NULL;
	static int old_wnd_w = -1;
	static int old_wnd_h = -1;

	if(f_next == NULL)
		f_next = dlsym(RTLD_NEXT, "SDL_GL_SwapWindow");
	
	if(outfp_vid == -1)
	{
		mkfifo("kkrotchbulge-out-vid", 0660);
		outfp_vid = open("kkrotchbulge-out-vid", O_WRONLY);
		assert(outfp_vid >= 3);
	}
	
	frame_counter++;

	glFlush();

	int wnd_w, wnd_h;
	SDL_GetWindowSize(window, &wnd_w, &wnd_h);
	assert(wnd_w > 0);
	assert(wnd_h > 0);
	assert(wnd_w < 32000);
	assert(wnd_h < 32000);

	if(wnd_w != old_wnd_w || wnd_h != old_wnd_h)
	{
		if(pbuf != NULL)
			free(pbuf);

		pbuf = malloc(((uint64_t)wnd_w)*((uint64_t)wnd_h)*(uint64_t)4);
		old_wnd_w = wnd_w;
		old_wnd_h = wnd_h;
	}

	glFinish();
	glReadPixels(0, 0, wnd_w, wnd_h, GL_RGBA, GL_UNSIGNED_BYTE, pbuf);
	glFinish();

	// Y-flip
	int y;
	for(y = 0; y < wnd_h; y++)
		write(outfp_vid, pbuf + wnd_w*4*(wnd_h-1-y), wnd_w*4);

	fsync(outfp_vid);

	f_next(window);

}

extern DECLSPEC Uint32 SDLCALL SDL_GetTicks(void)
{
	return (Uint32)((frame_counter * (uint64_t)1000) / (uint64_t)60);
}