This weeks game went quite well! I was able to implement a game mechanic that I’d previously thought of as being quite complex: displaying the future positions of a physics object. In this case, I display the orbital trajectory of the spacecraft that the player is controlling. But I’m getting ahead of myself, I should start at the beginning of the week.

At the start of the week I had no idea what I was going to make. I spent some time looking through itch.io, trying to get inspiration. I decided that I wanted to make a puzzle game, and I had only watched The Matrix movies over the weekend. So I decided that I was going to make a hacker puzzle game. After a day of working on it and coming up with ideas, I had this to show for it…

So, I realize I’m not having fun, I don’t really have a solid vision for the game, and I don’t actually want to make… whatever this is. It’s still early in the week, and thankfully (or unfortunately?) at this point I’ve had enough experiences like this where I know the best thing to do is scrap the prototype and make something new. No Sunk-Cost Fallacy over here.

I then decide to look through Adriel Wallick’s 1 Game a Week blog for some inspiration. Her blog and this GDC talk by her was recommended to me by Rami Ismael (@tha_rami), and is what inspired me to start making a game a week in the first place!

One game that stood out to me was her game on Week 45 (I don’t think I’ll be doing 1 Game a Week for that long!) – I liked the idea of making a space game using gravity around planets, and the trails that Adriel added to her game looked really cool. I also tried (and failed) to make a gravity based game last year, so I decided I’d give it another shot. I then thought about one of my favourite games ever: Kerbal Space Program.

In KSP, when you are orbiting a planet you can see your future trajectory. I felt that it would be cool to make a super stripped down version of this mechanic, where you have a ship in 2D, and you need to perform orbital maneuvers to enter a specific orbit.

So I started making the new game in the same codebase as the last one, because I had to get the game done before the end of Friday. I first setup the code to apply gravity to objects in the scene. That was very simple to do, I just implemented the formula I found here and implemented it in code like this:

public Vector2 CalculateGravity(Vector2 otherPosition)
{
    Vector2 dir = ((Vector2)transform.position - otherPosition).normalized;

    float distanceToSurface = Vector2.Distance(transform.position, otherPosition) - m_radius;

    float gravity = m_surfaceGravity * Mathf.Pow(1 + distanceToSurface, -2);

    return dir * gravity;
}

The hard part was actually adding in the orbital prediction itself. I thought of a few ways to do it, but it turns out that you can now create separate Physics scenes in Unity. This is great, because I can create a new Physics scene, copy over the objects I want to get the trajectories from, run the simulation on the scene and then track the positions of the objects over each step. It took me about a day (and a lot of hacky code) to get it working since I’d never used this Unity feature before, but I got it working in the end! Unfortunately the code was a total mess, but it worked for the purposes of just getting this game done.

I then had the great idea of adding in an editor function where I can place objects in the scene and then see their orbital trajectory without going into Play Mode. I spent way too long on this and ran into some walls. One of which was the fact that you apparently can’t create Physics scenes in Edit Mode, which meant I had to hack together some solution to prevent existing objects from being simulated. I even asked for help on Twitter, but unfortunately nobody seemed to know the answer…

In Unity, does anyone know how to create a scene with EditorSceneManager that also has its own PhysicsScene2D? Can't find anything on Google for this 🤔 #gamedev #indiedev #unity2d #unity3d #unity

— Aaron Meaney (@TheReccy) September 17, 2021

The plan was that by adding this editor feature, I’d be able to build and iterate on levels more quickly. I once again remembered my own warning with the Sunk-Cost Fallacy, and abandoned the feature. I then added in the asteroids, the bullets, and then the Delta-V and Ammunition systems. Stuck together some basic levels, and got the game finished just before midnight on Friday. I actually finished the game on Friday for once! 🥳

What went well

• I was able to finish on Friday for once! (and played Deltarune over the weekend!)
• I made a game that I thought was fun to play, and has potential.
• I learned how to use Unity’s Physics Scene feature to make predictions.
• I got better at writing “quick code” to get features out for prototypes

What could have gone better

• I could have spent way less time trying to add the unnecessary editor feature.
• I could have had a game idea that I wanted to make ready to go on Monday.
• I would have liked to add sound effects or music, but ran out of time.
• I would have liked to write this post-mortem on Friday, instead of Sunday night.
• More levels would have been nice too, but once again I ran out of time.

What I learned

• I learned more about Unity’s physics system and how it can be leveraged to make certain game mechanics.
• I learned how fast I can code features for a short game by cutting programming best practices. (But I still know how to use best practices for “real projects”!)
• I learned how important it is to work on a project I’m excited about, for my motivation and ability to design the game as I go

Summary

Overall, this is my favourite game so far! I’m really happy that I was able to add the orbit trajectory mechanic as I enjoyed figuring out how to implement it, as the solution isn’t immediately obvious.

Not many people have played the game as of writing this, and I haven’t really gotten any feedback. I have some ideas on how I’d improve the game to make a full version, and if enough people like it, I’d definitely spend a few months making a full game.

As always, if you want to try out the game, the link is right here:

If you wanna play around with the code, I also have a link to the GitHub repo if you click here!