Getting a Foot in the Door of Game Design

First of all – sorry about the misleading title – this post is about getting the doors working in the Endless Elevator game that we are currently developing. I thought it was a good pun and that as this post is all about our development process that it wasn’t too bad. The only career advice I got is just to start making games…any games.

You’d think making a door that opens and closes would be a pretty simple thing to do but surprisingly it wasn’t.

I designed and built some 3D models of building components in MagicaVoxel and exported them as .obj files. I use MagicaVoxel because it’s free and really quick and simple to use. When I model components I can be sure that they are all exactly the same scale and that all the different bits (no matter when I made them) are going to fit together without any hassle. But the models are not optimised for game engines as they have a reasonably high poly count due to the modelling process within the program. Most of the models come out with heaps of unnecessary triangles that need to be managed first. In most cases I will import the object into Blender and use the “decimate” modifier on the planes (with an angle of about 20 if you are interested). In the case of the door object it was pretty simple, it is just a door after all, and I didn’t need to optimise it.

Here is what the door looks like in MagicaVoxel:

Notice that the door object is sitting just forward of the enclosing frame and that when exporting the object the center is at the middle bottom plane of that frame. The door is off center because it’s modelled to fit exactly in a doorway that sits exactly in that position within the frame. This saves me a huge amount of time lining everything up when it gets to Unity as the position of the door (or any other object for that matter) is already in the right spot. The problem is that the point of origin for the door is in the wrong spot. It exports a few units behind the door and on the floor! This becomes important when you try and rotate that object (like you would when opening and closing a door) and the pivot point is not where the hinges should be.

To fix this I had to import the .obj file into Blender and reposition the point of origin for the model.

This is what it looks like in Blender when I did this:

To do it I selected the edge that I wanted the door to pivot on when opened.

Then in Edit Mode:
Mesh -> Snap -> Curser to Selected

In Object Mode:
Object -> Transform -> Origin to 3D Curser

So that puts the curser onto the correct position in the middle of that edge where the hinges would be and resets the point of origin (which is where it will pivot when rotated in Unity) to the right spot.

Once we were all imported into Unity and looking good I set up a prefab for the “Doorway” object with the door as a child object. The doorway object has a bunch of colliders to stop the player walking through the walls and a big sphere collider where the door would be to trigger the open / close function when the player walks into it.

This is what the doorway looks like in Unity:

Next I scripted up a few options for opening the door. I’ll post the script at the end of this article but basically there were three options of opening the door that I wanted to test. (Actually I tried it about six ways but whittled it down to the most simple methods – and just as an aside there is an actual “hinge” object type in Unity if you ever need it).

This is how the script looks in the editor:

Notice the slider at the bottom to control how far I want the door to open. It’s really handy to have this when playing in the editor and getting your settings right. If you want to know more about using it see this post

The three tick boxes are for testing the three different ways of opening the door.

Snappy was a quick simple transform of the position from open to closed with no “in betweening”. It looks a bit unnatural as the door magically goes from closed to open but it’s not too bad and most people are pretty used to similar behaviour in video games.

The active line in the code is:
the_door.transform.Rotate(-Vector3.up * 90 * Time.deltaTime);

The next method works more like a door should. In that it swings open and closed the whole way in a steady fashion. But the big problem with this method was that it was OK when the character was going into the doorway and with the swing of the door but when it was time to come back out of the doorway the door was in the way. There was not enough room to trigger the door opening from the other side without being hit by the door as it opened. Plus if the player enters the collider from the wrong trajectory the character gets pushed through a wall by the swinging door which is sub-optimal. I called this method InTheWay!

The active line here is:
the_door.transform.rotation = Quaternion.Euler(targetPositionOpen);

In an effort to combat this I chose to do a hybrid method that opened the door to a point that wouldn’t hit the player and then do the magic transform to get all the way open. I call this one aBitBoth. It looks a little weird too. Like there is an angry fairy pulling the door closed with a snap after the character enters.

Here are all three to compare.


In The Way

A Bit of Both

I’m not too sure which one I’m going to use at this stage as the Snappy method works best for now but I like the In The Way method better. I looks more normal and I like that you have to wait just a few milliseconds for the door to swing (adds tension when you are in a hurry to escape a bullet in the back). I could do something like halt the player movement from the rear of the door when it triggers to open from the closed side or maybe play around with the radius of the sphere. Neither solutions seem like great ideas to me right now but something like that will need to be done if I’m going to use that method. Maybe I could just have the door swing both ways and open to the outside when he is behind it but that’s probably a bit weird for a hotel door.

Here is that script that I was testing with:

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