gistfile1.c

    steer = 0;
    gas   = 0;

    /* Input */

    // Xbox 360 Controller
    steer = steer - SDL_JoystickGetAxis(joystick, 0) / 32768.0;
    gas   = gas   + ( SDL_JoystickGetAxis(joystick, 4) / 32768.0 + 1 ) / 2.0;

    // Keyboard
    steer = steer + keystate[SDLK_LEFT];
    steer = steer - keystate[SDLK_RIGHT];
    gas   = gas   + keystate[SDLK_UP];

    /* Normalization */

    if (steer < -1) { steer = -1; }
    if (steer >  1) { steer =  1; }
    if (gas   >  1) { gas   =  1; }

    /* Physics */

    tvel = tvel + steer * taccel*2*M_PI / fps;

    vel[0] = vel[0] + gas * accel * -sin(t) / fps;
    vel[1] = vel[1] + gas * accel *  cos(t) / fps;

    t = t + tvel / fps;
    pos[0] = pos[0] + vel[0] / fps;
    pos[1] = pos[1] + vel[1] / fps;
    tvel = tvel * pow(1.0 - tdrag, 1.0/fps);
    vel[0] = vel[0] * pow(1.0 - drag, 1.0/fps);
    vel[1] = vel[1] * pow(1.0 - drag, 1.0/fps);