“Beware Planet Earth!”‘s level design consists of two important parts: map building and design of the Martian assault waves storming Barney’s barnyard. This article is not about the graphic aspect of level building; we’re dealing with one of the numerous aspects of game play.
Building a level is always a step by step process, always done with a lot of testing and iterated improvements. Very early in the development, we decided the game space would take the form of a 10×9-tile grid. Of course, the actual game screen is much larger than this, but we needed to save estate for the GUI (machine deck buttons, tools button such as the Zapper’s, Cogs available, etc.). After some testing, we felt it was the best balance between legibility and level design freedom, with regards to the specific type of Tower Defense game we were planning to create. It is very likely that for another Tower Defense game, the game grid would have been quite different.

Once the grid’s size was decided, and knowing how many levels the final game would consist of, we created several dozens of paths designs, each being unique. We did so to avoid redundancy and boredom on the player’s behalf…but also to give the wave designer more stuff to play with. Because some maps may comprise several entry points for the Martians, the array of possibilities is extremely wide. We tried several sketching methods and the most efficient and handy turned out to be…Excel. Nothing’s quite better to create a grid with a fixed tile size.

â–² Two examples of schematic maps

The final choice of which maps would be in the game was done knowing the progression of the player through the story. That is, depending on the introduction of a specific new Martian, some designs were more relevant than others. Other layouts are more tricky for the player to handle and were therefore chosen to be the final levels.

Once the layouts were picked, we had to create the actual maps and add obstacles, non buildable areas, number of cows to protect, the number of entry points, etc. All those elements were tools to adjust the levels’ difficulty and required several iterations to strike the right balance through the progression.
Those designs were then handed over to Gwen, the artist, who dealt with the graphic part, but even without this, it was already possible to work on the second aspect of the level design: creating Martians waves.

â–² Here is what it looks like in-game!

To do so, we used a tool that Quittouff developed specifically for the game. It allows us to place Martians on a timeline spanning the whole level in order to define when a Martian enters the level through an entrance (which is a crop circle). Of course, it is no random design: each Martian has its own speed, hit points and skills. Martians are introduced progressively within the game and are not all available right away in all levels. Moreover, the number of Martians sent within a wave and the delay to the next Martian varies greatly, allowing for building a tower. Of course there is also a graphic constraint, because if Martians spawned too quickly, they would quickly overlaps with each other. The wave design is, of course, a very important tool to manage game difficulty, and, therefore, fun.

â–² This is the tool with which we create the actual martian assaults

The parameters we must take into account while tweaking a level are numerous. They fall into three major categories: the Martian-related parameters (speed, hit points, skills), the tower-related one (direct damage, splash damage, range, firing rate, cost, etc.), and the environmental parameters (which we hold back as a surprise).

All those variables are at least partially interconnected and their interplay has an impact on the level’s difficulty and fun factor. For example, in order to make a tower more easily overwhelmed, it is possible to increase its cooldown, bring more Martian in a row, increase their speed, change the path’s layout, etc. Accurate metrics, playtesting sessions and in-house testing sessions, as well as several iterations help us to improve the quality of the levels.

We hope you’ll like it!