Why do game developers dislike doors?

Game developers have been chatting on Twitter about one of the most difficult features in games.

Although I don't like brags, I have been through many doors in my life and made only occasional errors that caused pain or embarrassment. Although opening and closing doors are something we all know, how do you translate that skill into a videogame? It's not easy. It's not easy. That's what hundreds upon hundreds of developers said when Stephan Hovelbrinks (the developer of Death Trash) spoke out about the difficult task of implementing basic doors into games.

Hovelbrinks posted a screenshot from his Discord post, in which he explained all the problems that doors can cause in games. Hovelbrinks said that doors are difficult to use in games and can cause all kinds of bugs. They are a dynamic block and funnel in pathfinding.

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It is easy to see that doors can multiply the complexity of a game's logic. Imagine an NPC in The Witcher 3 who wants to go to bed for the night. The AI doesn't need to consider any doors. It just needs to map a route that leads from the current position of the character to their bed. However, if there are a few doors in the way, the NPC will need to be able to recognize that the door is in their way and use logic to control the interaction with it. What happens if there are two NPCs using the same door? How can an NPC tell if a door opens towards them or away? This is a deeply intertwined problem that Liz England, a game designer who worked on games such as Sunset Overdrive and Watch Dogs Legion, has called "The Door Problem".

Hovelbrinks tweets that "AAA developers hate them". He also points out that the Assassin’s Creed games fix the problem by pretending that doors never existed. However, Valhalla, the latest Assassin’s Creed game, does include some doors in certain puzzles. The tweet quickly went viral, as developers from all walks of the game industry weighed in to discuss all the problems caused by doors.

Sergey Mohov is a leading gameplay designer at Remedy. "I don’t know exactly how many man-months went in the door system of Control, but it was more than most abilities or weapons," he said. Many of his peers joined him to confirm that doors are an issue in Remedy games.

Damion Schubert, former BioWare Austin designer and creative director at Boss Fight, responded to Hovelbrink's tweet by posting an entire thread explaining the challenges of making good videogame doors.

Doors are a nightmare for even The Last of Us 2's director. "IT WAS THE THING THAT TOOK THE LONGEST TO GET RIGHT WHAT WERE WE THINKING," wrote Kurt Margenau. Margenau explains in several tweets the tedious process Naughty Dog underwent to make doors work properly, as well as the clever hacks that were required. In combat situations, doors will automatically close behind players to stop them from being pursued by enemies. However, in regular exploration, all doors remain open to allow players to remember where they have been.

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Marcin Pieprzowski was a former QA Lead for The Witcher 3. He said that the door in the boss fight had a lock that could be unlocked after players defeat a boss. The team discovered 12 scenarios that would lock the door and trap the player. Pieprzowski claims that the solution was to not lock the door at all. Then there's the hilarious tale of how a quest bug opened every door to The Witcher 3 - even those that were supposed to be purely cosmetic.

You can find many more examples of doors interfering with games in the tweets attributed to Hovelbrink's original tweet. This just shows how simple things can become in games that appear so stupid. Next time you open a door, thank the poor developer for trying to make it work.