Accumulating relative mouse motion

SDL3-accumulate-relative-motion.c

while (SDL_PollEvent(&event) > 0) {
    if (event.type == SDL_EVENT_MOUSE_MOTION)  {
        static float dx_frac, dy_frac;
        float dx, dy;

        /* Accumulate new motion with previous sub-pixel motion */
        dx = event.motion.xrel + dx_frac;
        dy = event.motion.yrel + dy_frac;

        /* Split the integral and fractional motion, dx and dy will contain whole pixel deltas */
        dx_frac = SDL_modff(dx, &dx);
        dy_frac = SDL_modff(dy, &dy);
        if (dx != 0.0f || dy != 0.0f) {
            SDL_Log("Relative motion: %g,%g\n", dx, dy);
        }
    }
}