Someday, when your grandkids breathlessly ask, “Were you alive when 3-D cinema begin?” you can say; “Yup, I saw ‘Avatar,’ ‘Alice in Wonderland’ and ‘How to Train Your Dragon ,’” technology’s next generation, Hollywood’s new big three .

“Avatar” and “Alice” are still playing in theaters, and six months from now, when some of us are returning for the umpteenth time to revisit “Dragon,” we may actually begin to forget how we used to watch moving pictures.

Hiccup (voiced by Jay Baruchel) is a young, un-Viking-like Viking who lives in a remote village under constant siege by firebreathing dragons, lethal enemies for generations. Hiccup discovers he has no stomach for dragonslaying, and when he chances upon an injured Night Fury—the most rare and feared of all dragons—Hiccup and the beast form an uneasy alliance.

If anyone remembers the folk tale “Androcles and the Lion”— well, yeah, it’s kinda like that. But kind of new and different and altogether terrific as well.

Directors Chris Sanders and Dean DeBlois have crafted a nearly perfect empathetic fable of growing up different, of selfworth and redemption, and of thinking outside the box because, well—kids love to do that , too.

The last crop of tykes had “Finding Nemo” at their disposal. Now we have “How to Train Your Dragon,” a film comparable in significance and craftsmanship. This beautifully rendered, wonderfully scripted treat should indeed be a family experience (although children under 5 or 6 may be overwhelmed by some of the film’s fire-snorting exuberance. Vikings tend to be an unruly bunch, after all).

The student-becomes-theteacher theme isn’t new (“Happy Feet,” “WALL-E”) nor is the dragon-as-man’s-best-friend scenario. But sometimes a second look isn’t necessarily repetitive or boring. I found “How to Train Your Dragon” astounding.

And in the end—heroically— Hiccup and his friend find they need each other (in a new, surprisingly astute way). “Dragon” is a rallying cry for kids—and probably adults—everywhere. See it now, then buy it later. For my money, “Dragon” is already a classic, a keeper.

Remember “The Hangover”? That bawdy, slyly mischievous, unabashedly funny film brought back the concept of “date night” for adults. A year later comes along “Hot Tub Time Machine ” —unabashedly goofy, slyly mischievous and unashamed to be exactly what it is—politically incorrect, 21st century vaudeville.

But leave the kids at home.

I suspect many of us, while perusing the theater listings, will come upon a film named “Hot Tub Time Machine” and immediately know we’ve (a) just gotta see it or (b) stay the heck away. There are time machine movies and there are hot tub movies, and usually the same sort of audience will gravitate toward both. But a hot tub and a time machine?

This, my fellow frolicky filmgoers, is exactly that type of movie.

Four friends (or rather three friends and a tagalong relative)— and we are talking “Hot Tub” here, not “Hangover”— decide to rekindle the passion of their former lives by revisiting their old ski haunt. One’s just been dumped, one’s in a deadend job, the third’s in a dead-end life and the last is the obligatory geeky kid (John Cusack, Craig Robinson, Rob Corddry and Clark Duke, respectively.)

So off they go for a boozy weekend at Kodiak Valley, to relive “Winterfest ’86,” celebrated before their young lives were corrupted by actual living.

But Kodiak Valley’s little more than a broken-down ghost town, a reflection of their own current state, and instead of a raucous night on the town, the four find themselves drinking morosely in their room’s dilapidated hot tub.

And then the strangest thing happens. . . .

Miss the ’80s? You’re going to love this one. Miss the music? Ditto. Miss the hot pink, bright blue, Izod skiware? Ski bums named Chaz? Miss laughing aloud at movies so stupid you’re not afraid to laugh aloud? Ditto, ditto and ditto.

I do appreciate serious drama. I love “The Last Station” and “Rachel Getting Married” and “The Shipping News.” But there’s room in my heavy soul for “Hot Tub Time Machine” as well. Man does not live on pathos alone.

A final word (and studio execs sit up, take note): It’s the writing. It’s always been the writing. A film like “HTTM” could have gone horribly, horribly wrong in so many ways... but it’s the writing (from “Avatar” to “Precious” to this one) that ultimately makes a film watch-worthy.

Director and co-writer Steve Pink, who co-wrote—with Cusack and others—the insanely brilliant “Grosse Pointe Blank” keeps the humor sharp and challenging.

Stupid comedy doesn’t have to be stupidly written comedy. “Hot Tub Time Machine” is a delightfully ribald, robust treat.