"Avengers" director Joss Whedon is one of the great script doctors of Hollywood. He's helped rework scripts for movies including "Toy Story," "Speed,""Twister," and "X-Men."During a Tribeca Talks conversation Monday evening, Mark Ruffalo asked Whedon if writing was difficult for him.Whedon noted one thing that is particularly difficult during the writing process for anyone."Structure is hard. Structure is always hard, and the most important thing," admitted Whedon. "Structure is work. It's math, it's graphs ...""Especially when you're writing for eight superheroes," saidRuffalo, referencing "Avengers: Age of Ultron." The 2015 sequel to Whedon's record-breaking "Avengers" starred a range of heroes, from Thor, Iron Man, and the Hulk, to Vision, the Scarlett Witch, Black Widow, and more.During the talk, Whedon explained his mental process for keeping plot points and characters in order while writing."I will do color charts that look like I'm doing aPowerPoint presentation where just ... 'This is where it's scary. This is where it's funny. This is where we know this ... and everything's got to find it's flow and intersect," he said.Hewent on to say that there is nothing that gives him more joy than writingsomething that's not difficult to believe since he began writing his own comics after being introduced to them around the age of nine."The act of writing, the macro and the micro which is having ideas and then actually writing scenes once you've figured out what they need to be, is perfect bliss," Whedon told the crowd. "It is the greatest thing anybody ever got paid to do. I'll never capture that feeling any other wayand I don't need to. What's great is that, as soon as I started writing again, it was there. It was just like, 'Oh my God. It's been so long my old friend.'"Whedon went on to describe hisprocess of writing particular scenes for "Buffy the Vampire Slayer" and how validated it made him feelafterwards."When I wrote Angel turns evil ...I wrote the scene where he basically pretends that he just doesn't care about her," said Whedon. "He just acts like a d---. And that was an actualI didn't drop my pen, but I actuallylooked at it and was like, 'Oh my God. I had no idea I was such a d---!' I accessed this terrible person and I was just so happy that I got this darkness in me that was just appalling.""I'll set out to write a sad scene," he said. "Sometimes I'll write for 90 minutes and then I'll have to stop because I'm all dried out. I just can't cry anymore. So, I'll go do something else and come back to it.""I'll laugh, if I think it's funny. I'll get pissed off," Whedon said of writing other scenes. "You know, many people have reported hearing thumps from upstairs while I'm writing stunts and falling down. I'm in it. I'm absolutely in it. I'm playing all the parts [from] every angle. It's the best."Whedon hinted that he's working on his next project after "Age of Ultron" after a bit of a break, but wouldn't tell fans what he was working on just yet. Though it sounds like it's a movie."The thing that I'm writing now, by which I will not, unfortunately, say a damn thing except that it's super good," he teased. "It's definitely a departure,not from the things I care about, but from the kind of storytelling I've done."Apparently, it will have an emotional ending so powerful Whedon said it left him crying in public."I wrote all the way through the end of the movie and was crying so hard in public that the restaurant closed, the valet guy came to me and then just went away without even talking to me," described Whedon. "I had to take off my shirt and blow my nose into it because they had taken away all the napkins and everything. I couldn't get up. I couldn't stop writing. Then I got in the car, luckily somebodyelse was driving, and I kept crying for about 20 more minutes."That was when Whedon realized he wrote the end of the movie. Whatever it is, we can't wait to see his next project if it's like anything else he has done in the past.Join the conversation about this storyNOW WATCH: 4.2 million Americans could be displaced by rising sea levels this century ' see if your county is at risk Click here to read full news..