You can't ever tell about Austin, but in the rest of Texas, you don't have to even point the gun. I think the term is "threatening manner." If people are trying to stop my car and they are armed, that's enough of a "threatening manner" for me, and I would think most other sensible people would think the same. If you are caught in possession of a gun while trespassing in Texas, I don't care where you are pointing it, the offense automatically becomes a felony.
I’ve wondered about these “surrounded by protesters” moments where they start beating on the car / breaking glass / etc.
Pretty sure you’d be justified (again, Texas) in killing any number of them, until the mob pulled away from your vehicle. Castle doctrine is incredibly powerful.