Robin Williams' Son -- Smiling and Mingling With Friends

Robin Williams' son Cody put on a brave face ... mingling with friends Tuesday in San Francisco to celebrate his dad's life.

Cody was dressed casually as he arrived at an invitation-only event at Marsha Garces' home ... she's Cody's mom and Robin's second wife. The outside of the house was strewn with candles and bouquets from well-wishers.

The 22-year-old Cody is not seen in the pic with his sister, Zelda, or half-brother, Zac.