And Audiard’s texts exist as islands unto themselves, devoid of the unifying aesthetic found in the oeuvres of, say, Wes Anderson or Spike Lee. His films are only ever provisional, taking shape through the editing process and sometimes even on set, where he is famous for rewriting — or adding new — scenes during the shooting. “He’s constantly seeking authenticity,” Marion Cotillard told me, “and more than authenticity, he’s searching for the accident that will create passion.”

“Jacques reshoots the same scene in different settings just to see how it feels,” the screenwriter Noé Debré, who co-wrote “Dheepan,” explained. “I think that’s his greatest strength. If you have a conversation, you have it in the staircase, and then you have the same scene in a car. And so it feels very different. I’ve not seen other directors do that to such extent. They all say they do it. That’s a thing directors say: ‘I make a movie on the set.’ But Jacques really does it, and he knows how to do it.” Schoenaerts told me that Audiard “directs like Jackson Pollock would paint.”

Measuring the quality of a film strictly in terms of the strength of its images is one of the principal reasons Audiard is willing, without apparent reservation, to direct American actors in French or an entire film in Tamil. It is a signature of his practice along with, paradoxically, his distinctive ability to work collaboratively, accepting and often incorporating feedback from all manner of sources. This is no doubt bolstered by a further attribute, what Reilly described to me as “one of the most sensitive [expletive] detectors I have ever worked with.” This detector is so sensitive, in fact, that when I relayed some of Reilly’s and Phoenix’s exuberant praise to Audiard, he rolled his eyes and said not to believe whatever an actor tells me.

One smoldering morning in Spain, after reviewing the viscosity of four different kinds of fake blood, Audiard, wearing the same clothes as he had the day before but with a new neck scarf, made his rounds of the set. He was driven around in an elaborately souped-up Cadillac Escalade the color of freshly beaten mayonnaise, with an elevated thronelike command bench in the back that would be the envy of any rapper or oligarch but seemed to mortify him. We stopped by a stable where Reilly and Phoenix were to rehearse one of the trickier scenes in the film, a shootout with loud bursts and jumpy animals in a confined space. Audiard began by going through the motions, demonstrating for the actors how to lead the horses, which he did with the elegance of a matador.

As soon as he began directing, whatever aloofness or fatigue I’d noticed dissipated as the magic of moviemaking ensorcelled him. He looked younger, or perhaps whole is more like it. “Don’t overthink it,” he screamed in English. “It’s a murder, that’s all.” As the actors began going through the scene again, Audiard switched to French, with Pouilloux and Lugan translating. “The people who are coming for you are rednecks,” he explained to Reilly and Phoenix, “but they aspire to noblesse. They’re cretins, and you look down on them.” Phoenix improvised a line about cretins wanting prestige, which pleased Audiard so much he wrote it into the script.

Whether or not a text really is a universe unto itself, it is safe to say that it can only ever be as rich as its most sensitive interpreter. I was reminded of this exchange in the stables much later, while speaking to Phoenix about the expansiveness of Audiard’s direction. He described another scene in which his character needed to bury stolen jewelry. “We were rehearsing, and I was digging quickly, you know, pretending to dig so I could get in, and Audiard said: ‘Look around you. You seem like you’re running from the cops. The most dangerous thing around you is a squirrel!’ And I just — it was so [expletive] brilliant that I just laughed so hard. It was amazing.” He added: “He brings you into the whole world.”

Fort Bravo and the other spaghetti-western sets are open to the public, and enthusiasts often visit. After rehearsing in the stables, we walked through the dusty streets, and a man timidly approached Audiard and introduced himself. “I’m a tourist and a fan,” he told him. Audiard smiled at the man and said, “Me too,” before excusing himself to return to his whirlwind schedule. Later in the day, after a table reading and fittings, when we climbed back into the Escalade, he brought up the fact that Gyllenhaal had independently hired the world’s pre-eminent accent coach and arrived on set with a magnificent 19th-century Oregon talking style ready to go. For a man who has spent his entire life around the film industry, he seemed genuinely impressed and even taken aback by the enormous discrepancy in resources between Hollywood and the French system this detail seemed to encapsulate.

Then he said that he had never even previously thought about doing a western. On the surface at least, he conceded, gesturing around the S.U.V., he would appear an odd choice to helm a $40-million endeavor. “It’s a big film with lots of special effects and things that I’m not necessarily comfortable with,” he told me. “It’s difficult to be in a system that calls for foresight.” Outside the tinted window I could see the pit where the actors learned to ride their horses, and the tepee encampment and so many vaguely familiar facades of movies past mingling in the distance — and it would all soon exist as nothing more than an image, which, to Audiard, would be more than enough. “Everything needs to be planned,” he said. “And yet, in the end, there needs to be a kind of innocence.”