Chopper Defense pushes the player to the edge of their ability, requiring quick decisions and precise aiming and maneuvering. The game would be impossible to play without its usability features.

Game controls

I wrote two extensive blog posts explaining the usability defects of two most popular action game control choices on iDevices – Accelerometer-based controls and Dual sticks – and how I designed Chopper Defense controls, which let you move and shoot very smoothly and precisely without having to think about it.

Here are some of the many defects of iOS game controls that Chopper Defense does not have: hard to aim at moving targets, hard to aim while moving, need to stop moving or aiming to switch weapons, unpredictable moving/aiming, lack of configuration options.

Feedback and situational awareness

The player is about to be overwhelmed by rockets.

The gameplay is full of visual and audial* cues that give the player immediate understanding of what's going on right now and what's about to happen. The explosions of your buildings and of enemy units have very distinct sounds and flashes, the rockets that enemy jets fire at you are bright orange and come right before the jets themselves arrive from the same direction. The fast and deadly battleship rockets make a very distinct launch sound, so that the player can start evading them immediately, etc.

* Sound effects have a huge advantage in usability – they let you convey information to the player without interrupting whatever it is they're doing right now.

Forgiveness

The #1 rule of creating any experience is that it should feel right, not necessarily be mathematically correct. It is important that the game is not perceived as unfair by the player.

Hitboxes of enemy jets and player's chopper

In Chopper Defense the most obvious examples are hitboxes. For enemy units, a hitbox is much larger than the unit itself, so if your bullet passes just next to an enemy jet, it still gets shot down despite the fact that if we could pause the video and examine it in slow motion we would see that the bullet did not actually hit the jet itself. The reason for such deliberate cheating is that without it, it would be unnecessarily hard to shoot down such small and fast-moving jets, and it would often seem as if the game is just not registering bullet hits properly. By contrast, your chopper's hitbox is much smaller than itself, so you can have more exciting near miss encounters with enemy rockets.

Another example: enemy jets drop bombs on your island. You can blow up the jets in the vicinity of your cursor by using a blast cannon. It usually goes unnoticed, however, that the bombs that have already been dropped by those jets but have not yet reached the land would also disappear in the blast, and this often comes as a tacit life-saver. If the bombs were allowed to reach land and explode, frustration would build up.

The player just blew up two enemy jets with a blast cannon.