## Monday, August 1, 2011

### Symmetric Starship Doors

This week I took a break from working on my lunar-lander game to go back and fix the level symmetry in a simple game I made a couple years ago.

SpaceRL (unimaginative working title) is a turn-based, grid-based, Roguelike-inspired attempt to represent zero-gravity motion; in particular, the ability to shoot a gun in one direction whilst floating in another direction. It's inspired by the cover of Tobias Buckell's book Ragamuffin:

The game is very simple at the moment: survey derelict, monster-infested starship wrecks and identify the crew remains. The basic combat maneuver is shown above: get some monsters following you, find a straight corridor, kick off, and blow them away as they pursue.

Coming up with level design that suggests a starship was an interesting challenge. I want something that appears to have been constructed along an axis of symmetry but that due to barricades and debris can no longer be navigated straightforwardly.

This week I finished making door placement be symmetric across the central axis. I also experimented with making the levels into simply-connected mazes. If there is only one way to get to each room from the entrance, the player will need to backtrack more in the process of visiting every room. Whether this is fun or not is debatable; it depends on whether revisiting rooms is interesting. I've thought about having the player eventually find the artificial gravity controls, for instance. Gravity would remove your ability to move and shoot simultaneously, which would change the experience.

The more-likely solution will be the typical thing of having shortcuts back toward the root of the tree that the player can open up. For instance, there might be a door that is barricaded from one side; once the player gets to that other side via a round-about route they can un-barricade it and take the shortcut.

Here are four versions of the same map:

Asymmetric

Symmetric

Asymmetric Maze

Symmetric Maze

The percent signs in the maps represent destroyed doors. They are there to imply that the original layout was symmetric even if the current connectivity is not. The “symmetric” level style means the generation algorithm attempts to connect matching pairs of rooms on opposite sides of the symmetry axis at the same time, rather than leaving it to chance. Without it there tend to be more destroyed doors.

Here is one more ship layout, this time with a horizontal axis of symmetry: