Did you know that the Wicked Witch of the West is a gay and lesbian icon? Well, surely you knew that Ben Hur is a gay romance? The same goes for Lord of the Rings, of course. Frodo and Sam Gamgee are the first gay couple of Middle-earth, according to this reading.

One of the beautiful things about movies is that no two people see the same one. I may look at Lawrence of Arabia and see a story of magnificent folly, the rise and fall of an unusual Englishman, but the film is more notorious in gay circles. "Florence of the Desert" is one of its nicknames, based on the idea that Peter O'Toole wore so much make-up he turned it into a drag show.

There is a clear subtext in the original film too: when Orrens is captured and tortured by the Turkish officer, the implication is that he is raped. Worse, he can't face the idea that he liked the pain. That becomes one of the reasons for the hardening of his attitude towards the Turks. "No prisoners", and all that guff.

Before the 1960s, homosexuality was largely invisible in movies, except to those who were looking for it. As the 1995 documentary based on Vito Russo's book The Celluloid Closet made clear, gay audiences always saw things that straight audiences didn't. That was part of the allure of movies for gay men and women: the secret looks, the knowing glances.

For a brief moment about  1930, when Marlene Dietrich dressed as a man and kissed a woman on the lips in Morocco, a new freedom seemed possible. But the Catholic League of Decency made sure it wasn't, by threatening a nationwide boycott of American cinemas if Hollywood didn't clean up its act. They weren't just against gay sex, they were against all sex, except within marriage and maybe not even then.

From 1934 until the early '60s, the Hays Code, a voluntary system of self-censorship established by the American studios, warped the depiction of love in all its forms. Married couples had to have separate beds, in the same bedroom; when they kissed, one foot had to stay on the floor. The kiss could not be "French", let alone same-sex. Naturally, screenwriters and directors found ways around the rules – none better than Preston Sturges, whose comedies are full of direct and indirect challenges to the moral guardians.

Gay characters in the 1930s were largely sissies, based on popular stereotypes, often played by the same actors: Edward Everett Horton, Franklin Pangborn, Eric Blore. The word gay still had its original connotation in the Fred Astaire and Ginger Rogers comedy The Gay Divorcee (1934), but that had changed by 1939, when Cary Grant used the word in its new sense in Bringing up Baby, for the first time. Forced to answer the door wearing a flimsy negligee, Grant offers the only explanation he can think of: "I just went gay all of a sudden". If you believe the rumours about him and Randolph Scott, it wasn't so sudden.

A thaw began during the war. Gay characters were still being written out of popular books when they were adapted for the screen, but some survived the process. Sal Mineo's character in Rebel Without a Cause was clearly gay and in love with James Dean. In The Maltese Falcon (1941), Peter Lorre's character, Joel Cairo, announces himself with a gardenia-scented name card. Alfred Hitchcock had Farley Granger and Robert Walker as gay thrill killers in Strangers on a Train in 1951. Even that movie, with its horrible connotations, has gay admirers. At least they were visible as gay men: out and proud and dangerously well-dressed.

Sometimes straight directors gave the audience a nod and a wink, as in the famous scene in Red River (1946), when Howard Hawks cooked up an hilariously suggestive scene between John Ireland and Montgomery Clift, as two cowboys on a cattle drive with John Wayne. Ireland asks if he can examine Clift's pistol. "There's only two things more beautiful than a good gun: a Swiss watch and a woman from anywhere," says Ireland, holding Monty's weapon. "Have you ever had a good Swiss watch?" he asks. Clift, who was gay, can hardly keep a straight face.

How things have changed. In the early 1990s the New Queer Cinema movement exploded, producing some great films and filmmakers: Derek Jarman, Todd Haynes, Gregg Araki, Isaac Julien. Television brought gay characters and stories into the mainstream, in drama and comedy. Gay characters are everywhere now, which has surely had some effect on the shifting attitudes towards marriage equality in many Western countries. The repression, the writing out, the sublimation of sexual drives into signs that only a certain section of the audience could read, has mostly disappeared. There's no need. The battle has been won, hasn't it?

I wonder. Straight and gay actors still worry about playing gay roles; few directors come out as gay, in case they don't get offered "straight" films (meaning action). Moronic "gay" comedies, where straight characters pretend to be gay, still get made. The "sissy" stereotype hasn't disappeared. And the New Queer Cinema has lost some of the energy it had 20 years ago.

When gay and lesbian lives were absent from, or suppressed, on our screens, there was something to fight for. I would never argue that the new freedom is a bad thing, but it becomes harder to see the frontier when many of the bridges have been crossed.

Twitter: @ptbyrnes