if(strcmp(argv[i], "-opengl") == 0) {
api = GFX_GL;
printf("Backend: OpenGL.\n");
if(strcmp(argv[i], "-opengl") == 0) {
api = GFX_GL;
printf("Backend: OpenGL.\n");
glfwSetKeyCallback(win, clbk_key);
glfwSetCursorPosCallback(win, clbk_motion);
glfwSetMouseButtonCallback(win, clbk_mouse);
glfwSetKeyCallback(win, clbk_key);
glfwSetCursorPosCallback(win, clbk_motion);
glfwSetMouseButtonCallback(win, clbk_mouse);