WHEN SCOTT SNYDER learned that frequent collaborator and longtime friend “Jock” would be filling in on art duties for Greg Capullo on Issue No. 44 of Batman (which hits shelves physical and virtual tomorrow), the acclaimed writer seized the move as an opportunity to revisit Gotham City with the artist who helped teach him a valuable lesson about writing comic books.

Snyder considers Jock (who also works with Snyder on the hit Image Comics series Wytches) to be the first superstar artist to take a chance on him, and still applies what he learned from working together with Jock (and artist Francesco Francavilla) on their under-the-radar hit run on Detective Comics to his current works.

“As a writer, the joy of comics is the collaborative aspect of it. What you realize pretty quickly is that trying to do a one-size-fits-all type scripting process doesn’t work, and it’s just not fun,” Snyder told The Post’s Comic Riffs. “When you learn how exciting it is to write to [someone’s] strengths, for me, for [Batman No. 44] and working with Jock in general, a lot of the joy comes from knowing not just the things that he excels at, but more what kind of emotional material we both respond to as friends.”

Batman No. 44 serves as a key issue in Snyder’s “Superheavy” storyline — an arc that deals with [thar be spoilers ahead] the aftermath of Bruce Wayne’s having survived an epic showdown with the Joker and coming back with little desire to be Batman. Rising to take the place of Gotham’s irreplaceable hero is a buzzcut-wearing, non-mustachioed, smok-free and very much in shape Jim Gordon, who takes on the tall task of being Batman with a new suit and a giant, Voltron-esque Batman robot that he can control from inside.

Jock doesn’t get to test his pencils on the new Bat-Gordon, though, as this issue is a backstory set during moments shortly after Snyder’s Zero Year storyline, and therefore features a young Bruce Wayne as Batman. For some fans who might be eager to see Bruce Wayne back in the mantle of the Bat, issue No. 44 could be a welcome break from Gordon under the cowl. Although Snyder does like to be humorous about the situation at times.

“As much as I like to joke that Bruce Wayne is never going to be Batman ever again and it will only be Jim Gordon [as Batman] forever, we all know that Bruce eventually will come back and be Batman,” Snyder said. “For me, I think the joy of a story like this is being able to go on the journey and see how all of it happens and what new angles we get to explore and the mythos. The idea of getting to write Bruce is a real joy, but it’s more [about] writing Bruce from an angle I’ve never written him before, because it’s organic to this particular arc.”

The key villain in the Superheavy arc is the mysterious Mr. Bloom, a shadowy figure who takes on Gordon’s Batman, but (as issue 44 will show) who also played a key role in the cases of Batman’s early years. Snyder said that Bloom “exploits all of the entrenched and systemic problems in a place like Gotham,” and that this issue will reveal the effects Bloom has had on both a young Batman of the past and how they relate to what Gordon’s Batman is going through in the present. “This [issue] is almost the beating heart of the arc,” Snyder said. “It’s an issue that both introduces the villain and shows what he is about, but for me it cuts to the core of what’s scary about Bloom and what’s hopeful about Gordon — even though it’s a Bruce story.”

Bloom’s presence supplies the pulse of this issue, but Snyder’s decision to take a slightly more sociological approach ends up being the issue’s heartbeat.

Jock became all the more eager to draw the book after reading the script and seeing some of the tough issues Snyder was trying to tackle, including youth who feel they have nowhere to run, as well as police brutality and class politics.

“That’s actually what I relished most,” Jock told Comic Riffs. “This issue does have a very different feel to the main arc and [to] what Scott and Greg [Capullo] have been doing. I knew that hopefully I could do the material justice.

“The [artistic] approach that I have lends itself to the more kind of reality-based stories — the grimmer, the grittier and, particularly with this issue, dealing with an element of gangs and urban culture, I love doing that stuff.”

Snyder said that he began plotting No. 44 before production on Superheavy began, but that he understands how the story can be applied to current events.

“With this issue, I know that it touches on things that are pretty contemporary right now in the news,” Snyder said. “I know Batman is a place that we go for escape and entertainment. But honestly, the stuff that I’ve always enjoyed the most, and what we’ve tried to do with Batman on my run with Greg in general, has tried to sort of speak to what’s going on now and why Batman matters in different ways.”

As the issue’s mystery is investigated, Snyder has Batman discover some hard-to-accept truths about the police department — how Gotham cops handle certain areas and citizens of the city. Batman’s mere presence is often enough to deter evil — in this case, Batman comes upon something that can’t be scared with a mask and shadows.

“For this issue, I really felt like, instead of doing it in a way that’s more veiled, just go straight for it,” Snyder said. “Batman, he’s starting out, it’s his early years and he’s coming face to face with problems that are much larger than himself.

“We wanted to go centrally into issues like police brutality, the stratification of wealth in a place like Gotham, political corruption,” he continued. “The issue isn’t meant to focus on any one issue more than the other, even though some of them are in the news now. It’s meant to be a story about a kid who, everywhere he looks, sees nothing but hopelessness. He sees no way out of the situation he’s in, and everyone he goes to for help lets him down in tremendous ways. And that includes Bruce Wayne.

“It’s meant to be both resonant and be in dialogue with things that are happening now in contemporary America and in a larger way when it comes to Superheavy as an arc, about why Batman matters in today’s world.”

Snyder also praised Brian Azzarello (who receives a writing credit on Batman 44). He caught up with Azzarello each time he was in New York working on “The Dark Knight III: The Master Race” with Frank Miller, receiving help with the sometimes emotional and serious tone of a stand-alone issue that also serves as an important part of the Superheavy storyline.

Snyder and Azzarello “had an opportunity to get together and talk Batman a lot,” Snyder said. “When I started this issue, I knew he’d be somebody who would bring a really strong ethical compass to it, and make sure it remained raw and true and brutal, and there’s a lot of dialogue and a lot of moments in scenes that he designed.”

Snyder lauded, too, colorist Lee Loughridge, offering: “I hope people notice as they’re reading the issue the way that the color seeps out as it goes forward in the present storyline and things become more and more gray,” the writer said. That’s one of the brilliant things that I think Lee did.”

Loughridge and Jock’s visual ideas (Batman using his cape as a club) added to an experience in which Snyder said, everyone brought his “A”-game.

The writer also said that a favorite moment from issue 44 is when Batman addresses his methods of inflicting fear and trying to scare kids off of the streets and away from trouble. In a touching scene, the Dark Knight swoops down to a group of kids he frightened away earlier and shouts out to them, much to their disbelief, and tells the kids that he wants to talk to them.

“Our Batman has made a move in our run to be more about inspiring bravery in the population of Gotham, than sort of scarring villains back into the shadows,” Snyder said. “I wanted that lesson to be apparent in this issue. I hope that comes across. It’s more about, Batman needs to be somebody who listens and understands and is humbled by the struggles of everyday people and becomes a symbol of inspiration and bravery, instead of being a demon and a terror to the criminals of Gotham City.”