I understand when Vin is +V , the slope of Vout is straight line .

But I don't understand when Vin is 0 V why V out is not 0 V because when Vin is 0 and there are virtual ground it mean there are voltage drop across Rin 0 V

therefore I in = IF = 0 A

And in equation IF = -C(dVout/dt)

The slope of Vout should be 0 when Vin is 0 V but in picture it's slope . What's wrong in my analysis ?

Thank you.