Star Defense: The Tuning Challenge

Tuning defines Star Defense—possibly even more so than its 3D play-scapes. It is an important and essential part of game design. The tuning of a game’s individual components is what makes it a unique and compelling experience. Changing just one element would transform it into a completely different game.

For example, if the game allowed you to pause it while you placed towers or if there were a few more seconds between wave launches, Star Defense would lose its fast pace. If we altered the strength of the towers or how much it cost to upgrade them, it would influence how you played the game. If we handed out more credits for each enemy unit killed, it would change how you managed tower purchases and upgrades.

The tuning decisions we made in Star Defense transformed what is otherwise a turn-based genre into something that feels and plays a bit more like a real-time strategy game. Because the action never stops—and you can actually choose to advance waves—you’re forced to constantly survey the action. It changes the way you have to think about defending.

But defining the kind of game Star Defense would become was only half of our tuning challenge. We needed to craft a difficulty curve that would encourage players to explore new tactics and learn all of the game’s systems. If it were too hard, players would grow too frustrated to continue playing. With too little challenge, they would soon grow bored.

The past few weeks have been spent nailing this balance.

The core Star Defense experience is made up of seven planets that can be played on three difficulties. On average there are 60 waves per planet (although you can opt to play against an endless stream of S’rath). We also slowly introduce new S’rath unit types as the player progresses through the game. For each of the 21 levels to present a unique challenge, we ultimately had to create at least 21 distinct difficulty curves and 420 individual waves.

The first task was to understand the different variables we could use to create the dynamic, hand-tuned waves we were gunning for. We had already learned that changing hit points alone was not enough.

After a few experiments, we realized that we should not rely on changes in speed because we defined some of our enemy archetypes based on how quickly they moved. We could not rely on incremental shifts in unit spacing because it was too difficult for players to identify these changes until the S’rath had slipped through their defenses and were pounding on the shield walls.

We were left to play around with hit points, the number of S’rath found in each wave, and obvious changes in spacing.

With this knowledge, we settled in to start locking down levels by hand. It took us an entire week to tune three planets across one difficulty level. Then all that work was effectively undone when we decided to alter some S’rath behaviors and reorder the planets.

We needed a way to procedurally generate the waves in Star Defense—or we’d end up spending two months attempting to tune levels that could ultimately be undone if we changed any other part of the game.

In the end, we used procedurally generated waves as a rough framework, which then allowed us to jump in and strategically fine tune individual waves.  Those hand-crafted waves ensured that each planet felt like a unique character with its own difficulty pacing and surprises that would catch players off guard.

The tuning, combined with tower characteristics, wave timing and the unique paths along 3D planets, has created a level progression that will drive players to master Star Defense as they internalize enemy behaviors, towers’ strengths, and the ultimate placement of such weapons systems.

Most of all, our tuning has created a unique tower defense experience. Let us know what you think once the game lands in the App Store.

—Allen Ma