Game Component: Spaceship editor, part 4

Last year I decided that I just don't have the time and energy to work
on a full game, and instead I should work on quick prototypes
instead. I had planned to try an idea every few weeks. The space
station
generator
was one of these; the spaceship
editor
was another. Spaceship physics turned out to be really interesting
and I kept working on it. It's been months now. I have lots of other
things I want to try, so I need to wrap this up, even if there's more I could do.

In the last
post
I talked about the physics. The final step was to figure out whether
there were interesting tradeoffs that a player could make when
designing a ship. I needed a spaceship editor.

I made a circle that could be dragged around with Flash's built-in
draggable object feature, but I switched to handling the mouse events
myself, so that I could add "snap to angle" and other constraints. It
wasn't long after having a draggable circle that I made a circle for
each thruster. And then two, one for the head and one for the tail. I
also wanted the thruster to move as a whole if you dragged the base,
but only the tip to move if you dragged the end. I overlaid these on a
large version of the ship to make a ship editor. Now I could start
answering the key question: are there interesting design choices?

After playing around with lots of configurations my answer was
no. It's always better to put the forward thrusters
near the wingtips. You don't lose any forward thrust, and you gain a
great deal of rotational speed. The other thrusters were less of an
issue, because they were used for less common motions.

To make this interesting I need some disadvantage of putting forward
thrusters at the tips. One thing I considered was that thrusters at
the edges of your ship are more vulnerable to damage. However, I don't
actually have a game here, so that's not something I can easily
test. So I turned to the other idea: thrusters require support that
have mass. Putting a thruster far from the center requires more
massive supports, which slow you down. I started with mass and moment
of inertia calculations from physics, and then used tuning and
experimentation to come up with something that felt reasonable. The
main tradeoff I focused on is between rotational and forward
acceleration, when both are from the same forward thrusters. If you
move the thrusters near the wingtips, you get lots of rotation, but
you need a lot of mass for the structural supports, and that slows
your forward acceleration. This plot shows acceleration versus
thruster distance from the center:

It shows that at least for the forward thrusters, there's a nice
tradeoff between rotational and forward acceleration, and you can't
get unlimited rotational power because the supports become too
massive. There are lots of other things I could look at, but I think
some tradeoffs depend on the game (for example, they may be completely
different if the ship is in an atmosphere than if it were in space),
and I'm not writing a game right now.

I eventually recognized that I could keep working on this for a long
time, but I need to move on and explore other topics. I've mostly
answered the question I set out to answer: if you let the player
design the spaceship, are there interesting tradeoffs arising from the
physics? I think the answer is yes, but probably not as many
interesting tradeoffs as Spore's approach would allow. In addition,
things weren't automatically interesting; I had to design a tradeoff
and then tune the physics to make that tradeoff show up, and I had to
be careful to avoid overpowered ships. That was unsatisfying. In a
real game I imagine I'd have to manually design lots of tradeoffs for
different game levels or areas of the world, and it'd be quite tough
to test all the combinations. And even if I could do that, controlling
sliders in a continuous tradeoff space seems less fun than picking
from some really interesting manually designed items in Spore or
Ur-Quan
Masters. So
yes, I was able to make what I set out to make, and it was fun to play
with, but probably would be a lot less work and more fun to give
people a few interesting choices.

The Demo

Of course after all that I should let you try designing your own ships
and see what you think. Instructions:

1. Press T to change ships (you may have to click on the
   map first to get focus). The demo ships are: yellow square (4
   thrusters), green square (like yellow but you can make it
   asymmetric), teal curved, purple curved (like teal but two
   thrusters are broken, so it can't fly properly), blue square (8
   thrusters!), red triangle (goes fast but can't turn well). I
   mostly play with the yellow and blue ships.
   

   
   
   




2. Change the ship by dragging the thrusters and adjusting their size
   and orientation. As you do this, watch the graphs. The bar charts
   show what happens if you press one key at a time. The polygons
   represent your current flight envelope for two keys at a time. I
   find that I use the W+A and
   W+D combinations often, so I watch the chart
   in the lower left. The shaded ovals show the "target" that you
   want to mostly cover if you want a reasonable ship. The yellow and
   blue ships are easy to improve: just increase the power of the
   thrusters and they will fly well. The teal and red ships are
   slightly harder, and the purple ship is near hopeless. In a real
   game the number and power of your thrusters would be limited, and
   fuel efficiency and fuel tank size would be additional factors to consider.
   

   
   
   




3. Fly the ship around with W=forwards,
   S=backwards, A=rotate left, D=rotate
   right, Q=slide left, E=slide right,
   Z=reset position.
   

   
   
   

Try the demo.

The demo is written with Flash 10 in mind. It should work with Flash 9
but there may be some visual artifacts (due to bugs in Flash 9 that I
didn't work around). There are some other minor bugs that I might fix
someday.

I'm finished with the spaceship editor mini-project and haven't
decided what the next mini-project will be. I really enjoyed working
on the spaceship physics and editor, but I spent too much time on it,
and hope to spend less time on the next mini-project.

Update: [2009-12-05] If you want to try a game that lets you create your own spaceships, check out Captain Forever. It's pretty neat.

Update: [2012-08-16] Another game that lets you design your own spaceships is Gimbal.

Update: [2012-10-15] Also see Evolving Spaceship Designs for Optimal Control and the Emergence of Interesting Behaviour [PDF], by Samuel A. Roberts and Simon M. Lucas, or watch the video.

Update: [2017-01-05] Another game that lets you design your own spaceships is Reassembly.