calculating pot odds

Hi everyone...I have a vague understanding of pot odds, but still have a few questions about just how you figure them out.

Assume after the flop for instance there is 100 in the pot and a player in front of you bets another 100. Obviously, this makes your pot odds 2 to 1. Assuming you raise another 100, that makes your pot odds 2 to 2 (am i right so far?). Now let's say a person behind you re-raises another 100 dollars, and the first player who bet in front of you folds. Now are your pot odds for a call 4 to 3, in which case the 4 is coming from what was in the pot plus the players bet and the other players raise (100 + 100 +200) and the 3 is coming from my raise and my call (200 + 1)? Or are they 6 to 1, in which case I'm incorporating my initial raise into the size of the pot I'm playing for. What I mean to say is should I no longer consider my intial raise MY money and instead treat it as money that's already in the pot that I'm trying to win. Thanks for your help, hope I made this clear.

Every poker decision is a new decision. Once your money is in the pot, it belongs to the pot. You need to count all the money from everyone's bets and whatever is in the middle already then compare that to how much you need to call.

Examples:
Blinds are 100/200
You are sitting on the button.
Everyone folds to you.
The pot is 300 and it costs you 200 to play your pot odds are 300/200 or 1.5:1

You call, SB calls, BB raises it to 400.
The pot is now at 800 (200 from you, 200 from SB, 400 from BB) and it will cost you 200 to call.
You pot odds are now 800/200 or 4:1 (slightly more if you believe the SB will call as well)