T-Pain's a serious gamer, but totally bows down to Lil Wayne and Birdman, who used to turn gaming into hardcore gambling ... according to the singer.

T-Pain was live streaming his own game of 'Doom' on Twitch ... when he spilled some tea about Weezy and Birdman's days playing 'Madden' when they were all in the studio.

He claims they'd wager $10,000 per game -- and that wasn't even the bizarre part. Check out his description of HOW they played the games. It's good to be rich.

Ironic that they used to throw around that kinda cash -- on a video game -- considering the current state of their financial relationship.