A handcrafted, 2d, retro, tower defense game
Feedback Loops & The Death Spiral Effect
I've played a crap ton of tower defense games and there's this one design choice that has always bugged me. I've always had to just deal with it because I was powerless to change it. Well, now that I'm creating my own tower defense game I finally have the opportunity to fix it! The central idea that I will be talking about revolves around the concept of a Positive Feedback Loop. I'll dive into more detail on that but first let me explain the design flaw.
The Design Flaw
Your ability to defend in a tower defense game is mostly based on the number of towers you can build. The number of towers you can build is mostly based on how much in-game money you have. The amount of in-game money you have is mostly based on how many enemies you destroy. The design flaw lies within that logic. Let me show you what I mean.
The in-game money increases with each kill
Kingdom Rush - Gold increases with each kill
Desktop Tower Defense - Gold increases with each kill
Skibi's Castle TD (Warcraft 3) - Gold increases with each kill
In both Desktop Tower Defense and Skibi's Castle TD you can even see a floating +1 above the enemies head after a kill.
That feels pretty good because you're getting rewarded for doing a good job. What that boils down to is the better you defend, the better you'll be able to defend in the future. Take a look at the diagram below for an illustration of this.
I'm going to take a brief detour and talk about what a feedback loop is.
"A positive feedback loop enhances or amplifies changes in a system; this tends to move a system away from its equilibrium state and make it more unstable. Negative feedback loops tend to dampen or buffer changes; this tends to hold a system to some equilibrium state making it more stable."
These feedback loops are found in many places throughout the world. In nature, the human body, weather, & engineering. The diagram above illustrates a feedback loop that positive and constructive. Constructive simply means the loop is beneficial to the player.
Ok back tower defenses. But let's think about the opposite effect. What if you place a tower in a bad position, don't build the correct tower to counter the enemy type, or you don't upgrade in time before the next wave starts? Well you still get a positive feedback loop except it works against the player, a destructive positive feedback loop.
Inevitable failure with one mistake
So if you make one mistake as a player, it puts you on a path towards an inevitable failure. If you mess up in the first few waves, you might as well quit. But most player's won't quit that early. They will give it their all and try to make the best out of a bad situation. This often ends up with the player wasting 20 - 40 minutes of their time thinking they can win, when it may be impossible. As a player it feels really crappy.
Ok so how does Whitevale Defender fix this design flaw?
Solution - Earn Fixed & Make Your Own Money
Whitevale Defender fixes the design issue in 2 different ways.
1) You get a fixed amount of in-game money (minerals) each wave, regardless of performance
So if you place your towers in great positions and you have a perfect wave, you receive 30 minerals. Also, if you don't build enough towers before the wave begins and you leak 10 enemies, you still receive 30 minerals. So there is always an opportunity to re-adjust your strategy and still win the game, even if you only have 1 health left!
Minerals you receive each wave
2) You can build a special tower that gives you in-game money (minerals) over time
The special tower is called the mining drill. You can build them over the top of mineral stones randomly placed around the map. Then the drill will give you a small amount of minerals over time. You can also build multiple drills at once to really get the income flowing. This allows you tightly control the positive feedback loop in your favor. The more drills you build, the more money you get, the more towers you can build.
Two Mining Drills in action
So there you have it. I explained the design flaw in most tower defenses and how my game Whitevale Defender fixes it. I think it is a breath of fresh air to tower defense games. If you are a fan of the tower defense genre, I know you will really enjoy how the new system works.