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Comment by faanghacker | Hacker News Reader

So basically, everything is difficult, including doors.

That makes the OP article sound like clickbait, making doors out to be the most difficult thing about game design.

Also, I wonder how much of it is due to the disconnect between design and software implementation. From a software perspective, it doesn't seem that difficult to define doors as a separate class or type of game object behavior, and hard code that behavior into sequences.

It seems like the difficulty is mostly on the design/animation side. Controversial opinion: Maybe the problem is that designers and animators are just not as good at solving these logic problems as the software engineers.

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Sounds like you'd benefit from giving it a try. I'm going to go out on a limb here; you're at that stage of your life where everything you haven't tried sounds simple and you don't understand why other people struggle so much. I'm guessing this because on hearing that something is difficult your first suggestion is to.. simply design a class, and then suggest that the problem resides in the kinds of people approaching the problem.

Its a sort of arrogance that I think will be familiar to many people. But it sort of assumes that other people are too stupid or incompetent to try <insert obvious easy solution>. You might do better by trying to figure out what went wrong with the 'obvious' solution, or what you are missing in your own understanding that makes the problem appear so much simpler. If you figure out novel solutions, great! That's real genius. I think mostly you'll find out how tough most problems are.

Thank you for writing up a clear headed response. I had started to write a response to the comment, but decided I didn't know a way to phrase it in a way that would be constructive and decided not to submit.

Watch the video, it goes into detail about why doors are hard, especially as you start moving from "press space when near the door to make it slide into the wall" to "the door is a physics-simulated object that interacts with all the other physics-simulated objects in the game, and which players and NPCs will open in a realistic fashion that involves blending pre-fab animation with the location of the handle/knob relative to the character instead of vaguely waving a canned animation in the direction of the door as it magically opens".

Never mind a door simulated at the level of "I am opening it just wide enough for me to get outside with some food and water for the semi-feral cats who live under my house, with minimum opportunity for them to run inside before they're distracted with that food, also I have to kick it to get it open now because this is New Orleans and the house just settled a little more after Ida and now the frame's a little less square". Which is an interaction I have with a door every morning without ever thinking about the door.

There's also a quote from a lead developer at an AAA team saying that doors are the hardest thing to get right. Everything in a video game is a thin veneer of illusion, and doors are surprisingly complex in how they have to interact with every level of that illusion.

Move, shoot, and drive are easy, or at least well worked out, and everything else is hard. Doors are just a common case of "everything else" Sitting down realistically is hard. Standing up realistically is hard. Picking up stuff realistically is hard. Interacting with any object via contact is hard. Interacting with moving avatars is really hard.

The hard problems come up when you actually have to do motion planning, in the robotic sense. Few games do that. In most games, you're just moving the avatar while running canned animations. UE5 has a new dynamic animation system which is supposed to help with this. In the UE5 demo video, you see the character walk through an open doorway, and she reaches out and touches the doorframe. That's some kind of IK-driven animation triggered by proximity. Not clear if the mechanism behind that is general enough to handle door opening. Anyone know?

In virtual worlds, where you don't have pre-planned gameplay, it's a big problem. Second Life has hundreds of thousands of doors, and at least three vendors of door control software. Usually, doors have to be clicked on to open them, although stores often have automatic sliding doors.

Doors are one of those things that seem simple but actually is not, due to it being an interaction point between players and the game.

I watched the video again. Still don't see what the big deal is. For example...

NPCs blocking doors? Don't put NPCs there, and tell AI to avoid door zones rather than trying to make them know how to move out of the way when doors open.

Car on the other side of the door? Don't let the door open all the way.

In the elevator example in the IGN article: Implement an elevator door like in modern elevators, or if it's more primitive, don't let players or NPCs walk under the elevator, or worst case, kill the character -- can't call the AI dumb if they avoid being under the elevator that can kill them.

This isn't an unsolved problem. Halo did this with telefragging someone who is blocking a teleporter, and StarCraft did this by destroying the siege tank under a landed building.

Everything you describe is an ugly hack that ruins immersion and suspense of disbelief. Are you proposing the AI shouldn't be able to use doors? What if an NPC wants to open a door at the same time as a player? Are you suggesting that gamedevs should add an entire myriad of these exceptions to all the interactive aspects of the game? That's wholly infeasible. Players can and will break sort of game design in wild abandon.

You are trying to build a believable world, or at least one with as few uncanny valleys as possible.

Doors are hard, as is everything interactive. That doesn't mean people shouldn't try to make these things better. And at the same time, we need to acknowledge that doing this is bloody hard.

So your first solution means that NPCs can't interact with doors. What if your game needs NPCs to be able to move around freely and not be trapped in the rooms they spawn in.

Your blocked door solution also has some issues. How do I represent the state of a partially open door? Can a partially open door block bullets? Can I move through a partially open door? Can NPCs? What happens if the car moves towards the door while it is partly open? What if the car moves away? What happens if I try to interact with a partially open blocked door? What happens if I try to interact with a partially open unblocked door?

> StarCraft did this by destroying the siege tank under a landed building

If this in StarCraft I? In StarCraft II even a burrowed zergling can prevent the landing of a Command Center. (That makes no sense from a realistic point of view.)

Yes. And it only became relevant if you exploited a race condition by ordering the building to land, then ordering a siege tank to move under that landing point while the landing animation was in progress. You couldn't order a building to land on top of a unit, and a queued order to land would fail if any units were in the way, but once the building started to land, it wouldn't stop, and any units under it would be trapped. The bug fix added a second check which would kill any units under the building when it finished landing.

In principle, you could do this with any unit, but it was mostly useful for siege tanks, since those were the only Terran ground unit which really benefited from sitting in place.

Yes, StarCraft I. The issue wasn't physical realism. The problem was that a player could move a tank under a building during mid-landing, siege it up, and the boundaries of the building protected the siege tank from melee attacks.

Killing the tank was the "creative" solution, instead of a "brute force" solution to change the game dynamics to prevent the tank from sieging up under the building in the first place.

In SC2 the tanks will be forced to move out from under the building when it lands, but SC2 also has a much improved unit movement system over SC1 that allows this to be done more easily.

I've never seen this in any of the BW games I watched. I wonder if they fixed it. You just can't land a building where a unit is. There was a crazy bug where you could load units into a flying CC and use it as a mobile fortress but that too is patched.

That was the whole point -- it was fixed early on by killing the tank, rendering the exploit useless, which is why you never see it in games anymore.

Search on YT for the tank glitch.

I only found buildings crushing interceptors https://www.starcraftai.com/wiki/Tricks,_Glitches_and_Exploi...

Doors are complicated? Just don't have doors, problem solved. Game is complicated? Just don't create game. Such easy solutions.

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