Animation in Defense Grid

01/04/2010 by Adam Crockett

Animation in Defense Grid

In this diary, I’ll be discussing aspects of the animation process for our tower defense title, Defense Grid: The Awakening.

The visual tone of the game was set by the various artists involved. 
This was done in a very collaborative environment – typical of game
development at Hidden Path.  We discussed and decided how the towers and
creatures should move, and what sort of impact the animations should


In the game, the player character erects defensive towers from
predefined slots in each level. Since we wanted to preserve the
fundamental strategy of tower positioning, we didn’t want to have towers
move around like characters, but we did want them to raise, lower,
attack, and scan for the next target. We also planned special idle
motions, and reload sequences, but most of the towers’ animation ‘zing’
is in the way they raise and lower, mechanically blossoming into death-
dealing machines of doom. As we were starting to spec out some of our
planned idles, T.J., one of the programmers, devised a procedural way
for the turrets to “scan” for the next target. I was happy enough with
the result to scratch most of the idle animations off the list. It was
much less repetitive and more convincing than a looping idle animation
created by an artist. Players will still see a standard idle here and
there, such as a rotating radar dish, but most were replaced by T.J.’s
great solution.

Accommodating the procedural motion wasn’t without its challenges – it
meant re-rigging some of the towers to have yaw and pitch bones that the
programmers could control (even in instances where a tower did not yaw
or pitch!) but it was ultimately worth it, and I still love the way the
towers all look around separately, searching for their next unlucky


The aliens consist of the invading hordes intent on robbing the player
of his precious power cores. They appear in increasingly difficult waves
made up of different types of creatures with different stats. They move
intently, focused on their goal, undeterred by the slaughter into which
they march.

As models were completed, I began rigging the most complex one first --
the Juggernaut. We used 3d Studio Max‘s biped rig, posed as a quadruped.
After rigging and skinning were completed, I created the first walk and
death cycles to set the look and feel for our animation team.  For
additional direction, I tweaked the animation timing to work
appropriately with the pacing of game play.  The animation crew took it
from there.

Though we started with a more complex list that included lots of
animations, gameplay evolved such that we narrowed the list down to
basically walking and dying. Those two animations had to convey each
alien’s personality.  Differentiating was a difficult task.  Each alien
has a couple of death animations, for variety, but the walks were pretty
standard and so presented a tougher problem.  To solve it, we added
“leans” that we blended into their animations as the aliens turned
corners.  That added a lot to an otherwise unremarkable animation.  I
was very pleased with the way the alien animations turned out.  Of
course, I’m never completely satisfied.  If we had additional time and
budget, I would have liked to see the deaths have a bit more inertia,
but they definitely convey what they need to with a lot of character
from game view.

Overall, I’m really happy with the animation in Defense Grid. I think it
is a substantially better experience than what other tower defense
games have to offer. I still get giddy watching the towers unfold, and
it’s always satisfying to watch a particularly tough alien finally
crumple to the ground. I hope you enjoy playing Defense Grid: The
Awakening, and thanks for reading!

Posted in Defense Grid | Keywords: aliens, Defense Grid