Game development: Techniques to keep your users playing (plus discussion of scoring system in Play The Field)

One of the big challenges in game development, whether at hobbyist or pro level, is creating replay value so the user can enjoy the game for an extended period of time. Even if the game is free, the longer they play it the more likely they are to tell other people about it, hence increasing popularity and total number of users. If the game is ad supported, keeping the users interest is even more critical (currently PTF has no ads).

In games which are level based, hand-designing levels is tedious and requires a great deal of testing to balance the elements of each level. Random level generation is one idea, but usually users will get tired of that unless some very special algorithms are used.

Multiplayer against one or more human players is another good way to extend enjoyment, and if you can elevate your game to the level of a “e-sport” where pro-gamers will play it for money, then you user count will likely skyrocket. Or course, being a professional e-sport brings with a great responsibility for fairness and balance in gameplay.

Games where the opponent is generated from artificial intelligence are typically either too easy or too hard, though lately some games have improved in this area. Making a graded system of levels can be effective, especially if there is some way to auto adjust to the user’s performance.

In my mobile game Play The Field, I choose to utilize a classic, time-tested system to increase re-playability: scoring. When a board is completed, the user receives a score base on their performance, and that score is saved and displayed on the main level map screen. Users can replay levels, aiming for a higher score by using more creative and effective tactics.

For those who are interested, I’ll outline the algorithm for generating the score in PTF. It’s relatively simple and contains the sum of these three factors:

  • The total money remaining
  • The total cost of all friendly units in play
  • The number of seconds since the level started, subtracted from 300, i.e. (300 – secondsSoFar)

The idea of this formula is to judge how efficiently the board was solved, by factoring in the number of units lost plus the total time spend. The more units lost, which is factored in indirectly via the total money remaining and total cost of units in play, the lower the score. The longer the user takes, the lower the score.

By choosing to use a sum of the first two factors, the fact the user has chosen to purchase a certain unit doesn’t matter – what is important is that he/she uses it effectively. Sqeaking by with a single unit left isn’t nearly impressive as dominating without loosing a single friendly unit.

The reason for the 300 factor is to give the user 5 minutes (60 seconds x 5 minutes = 300) to try and complete the level. After that, the contribution of the time falls to zero (negative values are rounded up to 0), leaving only the amount of money (in terms of unspent money and cost of created units) remaining.

In my playtesting, I found this to be a pretty accurate way to gauge the user’s skill, though I am always open for suggestions to optimize the scoring algorithm.

Download PTF on iTunes (free): https://itunes.apple.com/us/app/play-the-field/id985621862?mt=8

Play The Field: advanced controls

In a previous post, I talked about the basic rules of the game and the fundamentals of the interface. This time I’ll go over some of the advanced controls that can help you further optimize your tactics.

First is the usage of swipes, by which I mean touching a point with your finger, moving that finger to another location, and then raising it. A swipe can be used to quickly place a series of units in a certain formation, for example to encircle a small number of enemy units. The swipe doesn’t have to be in any pre-defined shape (line, circle, etc.), as any arbitrary shape will work. I think you’ll find it tedious and time consuming to tap several times quickly when trying to overcome the opponent, and using swipes makes it so much faster and easier.

Another thing you can use swipes for is to select units. Begin the swipe by clicking one of your units and then move your finger across any other units you want to select. As your finger crosses each friendly unit it will become selected. That way you can then issue commands (like attack a specific unit or move to a specific location) with a group of units. If you want to select all of your units on the screen, you can do that quickly with a button on the top right of the screen. It has three green units, shown in a triangle formation.

There are two other commands which you can issue to one or more units and aren’t immediately obvious. The first of these is to quickly tap on one or more units that are already selected. This will cancel any actions they have been given (for example if they were told to attack a specific enemy unit), and they will revert to the default behavior of heading towards, and attacking the nearest enemy. This will also unselect those unit(s).

The other command is to cause one or more units to hold still (called ‘hold position’ in some RTS games). This is done simply by touching a unit that is already selected and holding for roughly a half of second or more. A red box will be drawn around units holding still, and they will not automatically head towards the nearest enemy. However they will still attack any enemies in range. This technique can be used at some of the later stages in order to avoid units going off by themselves and getting captured needlessly.

Tactics in Play The Field

For those of you haven’t played Play The Field or found it challenging, it might be unclear what I mean by ‘tactics’, so in this post I’ll talk a little about that term.

You probably have some vague idea what tactics means, but lets review by looking at the dictionary (according to Dictionary.com, edited slightly below):

  1. The art or science of disposing military or naval forces for battle and maneuvering them in battle.
  2. The maneuvers themselves.
  3. Any mode of procedure for gaining advantage or success.

Although PTF is essentially non-violent (if you can exclude the extremely cartoony explosions and laser beams), the first definition above is a perfect match to what the game is about – disposing (placing) forces and maneuvering (moving, controlling) them to achieve a goal. The other definitions (#2 and #3) are also strongly related.

For those of you unfamiliar with the RTS genre or similar games, you may try a few levels and get frustrated with the difficulty. To be sure, the game’s difficulty quickly ramps up and is not too forgiving (I may add a difficulty setting option if requested), but there are some tricks that will help you overcome these middle stages. As for the last few – those will definitely take some tactics, some time, and a lot of luck (:

  • Think of what angle you attack an enemy formation and how it effects the battle. For example, if the enemy units are lined up horizontally, if you attack from above (with a similar line formation), you will be fighting on even ground, with maybe 50-50 odds. But if you attack from the side, you can focus several of your units on one of theirs, before they have time to regroup
  • Remember you get money each time you capture an enemy unit, and therefore add units to an in-progress battle as soon as you get enough money. Think about the best place to add these units: right in the middle or battle or a bit outside it?
  • Think about the characteristics of each unit: speed, hit points, damage, size, etc. Which units are they weak against and which strong?
  • If you save up enough money, you can buy one strong unit, or several weak ones. Think about the tradeoffs between these two choices and when you would favor one option over the other.

This is just a starting point. When you start to take in consideration things like ‘maker’ units (essentially stationary buildings that periodically create new units), things get much more complicated.

[PTF on iTunes: https://itunes.apple.com/us/app/play-the-field/id985621862?ls=1&mt=8]

(Play The Field iTunes link: https://itunes.apple.com/us/app/play-the-field/id985621862?ls=1&mt=8)

Play The Field: What kind of game is it?

In my last post I showed a brief demonstration of the gameplay for my iPad game Play The Field. However from that alone it may be hard to tell what is going on, except that there is some sort of action happening. So in this post I’ll talk in detail about what the game is about.

For each stage in Play The Field, there are only two objectives: never go down to zero units, and try to reduce the enemy to zero units by capturing theirs. At any time during the game if you have zero units on screen (except the start of each stage) you immediately loose that stage, and if the enemy goes to zero you pass that level. It’s as simple as that.

In order to achieve said goals, you have two actions to take: placing new units and managing ones already on the screen.

Placing a unit is as simple as clicking on an empty space on the map. If you have enough money to create the unit it will automatically join the game at that location. Money comes from two places, an initial amount given at the start of the game, and an amount received from capturing each enemy unit.

Except for the first few stages, there is usually a choice of several different types of units, and the ones available are shown on the top of the screen. The currently selected type is highlighted, and to change that simply tap on another type.

Units on screen are managed by issuing commands. This is done by first selecting a unit by tapping on it, and then clicking on either an enemy unit or a location on the map. There are a few more advanced commands, but I’ll leave those for a future post.

Units will typically attack enemy units in range, unless they were commanded to attack a different unit. A unit without any commands will also move towards the nearest enemy unit. When a unit takes damage, it’s HP (hit points) will decrease a certain amount, and if any units HPs reach zero (or below), they will disappear and be considered as captured by the opponent’s team.

The gameplay is somewhat reminiscent of the Real Time Strategy (RTS) genre, with it’s well known classics like Starcraft and Age of Empires, and without a doubt these game were a major influence. However the gameplay is vastly simplified (as well as the graphics – more on that later) so it’s much easier to pick up as a casual game. In fact, the short stages, some of which have a “trick” to solve them quickly, have some similarities to the puzzle genre.

Play The Field – quick demo video

Due to a problem with the app preview video for 1.0 there is only static screen shots viewable at present, show in this post I’ve included the video which was supposed to be included in iTunes.

When you see a line of units being spawned quickly, that is done by simply moving your finger across the screen to create any sort of formation.

Play The Field 1.0 released on Apple app store!

I’m very pleased to announce Play The Field, the minimalist real time tactics game, has been approved by Apple and is now available on the app store, free of charge. The game is currently only available for iPad, but with enough interest I may create a iPhone version as well.

Here is the link to see it in iTunes:

https://itunes.apple.com/us/app/play-the-field/id985621862?ls=1&mt=8

For anyone who is curious, it took roughly 9 days (including the weekend) in the queue before Apple began reviewing it. The review itself was pretty quick, lasting around three and a half hours.

In the near future I’m planning on making some posts on what inspired the game, it’s gameplay, and how it was developed, so check back sometime soon.