The first truly striking detail in writer-director Jake Paltrow’s sci-fi-western whatsit — after the obligatory opening shot of a scorching sun, and the equally obligatory voice-over narration — is a big gun being wielded by Michael Shannon. It’s some sort of rifle-shotgun hybrid, a “dualie” in the local lingo, and if you’re a 14-year-old boy, you’re going to want one. Later, along similar lines, there’s a robot with walking legs in front and tractor wheels in the back. It becomes clear that the whole movie will be like one of these contraptions — silly, yet sort of cool, and evidently the result of a hurried spare-parts binge in some genre-movie scrapyard. Yes, it’s another goddamned near-future dystopia, with all the dusty tough-guy stoicism of yore, plus gadgets. In a nearly waterless world — and Paltrow’s style is nothing if not sufficiently parched — Shannon plays a weary, bandit-rebuffing farmer. Kodi Smit-McPhee, who knows his way around a dystopia from playing the kid in The Road, plays his kid. Nicholas Hoult plays the pretty boy-slash-bad boy who’s after his daughter, played by Elle Fanning, and his land. The robots, or “simulants,” in the local lingo, play themselves. One of them records incriminating evidence of a certain plot turn, prompting some fine acting from Smit-McPhee. And eventually, if not quite soon enough, the machine stops.