During the day, the rules on deadly force are remarkably similar between California and Texas.
The standard on when you can shoot somebody is simple. It's based on a question you ask yourself before shooting somebody: "Is this person criminally putting me in fear of losing my life or suffering great bodily injury?"
This is a yes-or-no question. If answer = "yes", draw and (maybe) shoot. The reason there's a "maybe" in there is that pulling a gun on some goblin often (but NOT always) has the remarkable effect of causing said goblin to run away while making a charming variety of high-pitched vocalizations. Such as:
AAAAHHHHHHHHHHH!
...at which point, the "answer" changes from "yes" to "was".
NOTE: it doesn't always work out that way. So you do NOT bluff. Ya follow? You pull a gun ONLY when somebody needs to die RIGHT NOW, and if that stops being the case, cool. If that is STILL the case when the gun comes out, it's time for Mr. Firing Pin to have relations with Ms. Primer, as facilitated by Rev. Trigger.
All of this applies regardless of weapon. His OR yours. Got that? In California, I haven't been able to score CCW yet, so I carry serious cutlery of my own, Calif knife laws being BETTER (looser!) than Texas.
Now, if somebody has deadly force and are making lethal threats, but they do NOT have a projectile weapon (gun, bow, Trebuchant loaded with gasoline bombs, etc.) but rather have a stabbing/pounding/dicing impliment and they're 100 yards away, they're no immediate threat to you. Recommended solution: leave. If they're at 5ft range, they're gonna geek you any nanosecond...recommended solution: draw and fire in one smooth stroke...they'll remain unshot only if they VERY rapidly stop being a problem before you can activate Rev. Trigger.
Much thought has gone into where the BOUNDARY is between "threat" and "non-threat" of a knife/club/AIDS infected syringe/sword/etc. wielding maniac. The most commonly accepted solution: 21 feet (7 yards, which for you furriners is close enough to 7 meters that you shouldn't sweat the difference).
That's because a loon can cross that difference and geek you in 1.5 seconds (typically), which is also (typically) about how fast you can draw and fire.
Go google the term "Tueller drill" for more info. This concept, that a knifer is dangerous out to about 7 yards, has survived a fair amount of court scrutiny.
NOTE: this does NOT mean you can plug anybody with a knife out to seven yards!!! There's also this thing called "intent"...you need to be able to justify why you thought the guy was a threat. Pulling a pocketknife to cut open a cardboard box is a completely different matter from waving it around and screaming
THE VOICES IN MY HEAD DEMAND A BLOOD SACRAFICE!!!.
(Yes, I'm aware that I've probably mis-spelled "sacrafice". It doesn't matter. People who would actually scream that out probably can't spell either.
BUT, a guy with a knife does need to be very clear about HIS intent too...he has a duty to at least try and put people at ease.
Example: not two days ago, late at night I came across a couple stranded in a car out of gas. The motorcycle I was driving had this weird ability to...well, you unscrew one bolt, twist the petcock control and it'll squirt gasoline out. So I asked 'em if they had any container we would use to transfer a little gas. They came up with an empty antifreeze bottle...great, but the car's gas cap was too far recessed for the bottle to fit. I explained that we'd have to cut away part of the bottle plastic so it'd form a proper funnel, and that I was going to pull a pocketknife to do this, and that I didn't want to freak 'em out...both were perfectly cool with that. They were even cooler with me successfully getting them to a gas station
. In any case, under the circumstances (I am 6'4" 280lbs, biker dressed all in black, it's past midnight, I outweigh the both of 'em put together and I need to pull a
knife) extra care on my part not to cause a heart attack was warranted.
You can't shoot somebody for failing to be as polite, but...well, go google ANOTHER concept that matters:
cooper "color codes"
(Put exactly that line into Google, complete with quotes.)