The actor talked to The Wall Street Journal about this -- explaining that he's simply not taking certain roles that he feels are too dark or psychologically screwy ... because accepting that kind of work will ultimately have an impact at home, with Eva Mendes and their kids.

RG says he considers what sorts of parts/movies will be good for the whole fam -- and he'll dive into stuff that he thinks will help him bond with his partner and their two daughters.

Ryan goes on to say this started when he began working on "La La Land," with him adding ... "It was just sort of like, 'Oh, this will be fun for them, too, because even though they’re not coming to set, we’re practicing piano every day or we’re dancing or we’re singing.'"

Of course, it goes without saying ... the same thinking was applied to his role in "Barbie" -- something he says his daughters were all about, and which brought them closer together.

In other words, if it feels like Ryan is doing more mainstream/popcorn stuff lately -- as opposed to his grittier indie flicks -- then you're 100% spot-on ... it's all on purpose. As it turns out ... the blockbusters go down a little easier, and it keeps him light on his feet.

While fans of his from more serious films might be disappointed to hear this -- because, frankly, he's a damn good actor when he's got something meaty to chew on -- it's too bad!