Physics Games and Physics-Based Game Downloads

The Evolution of an Idea: Rolling Assault

Wednesday, April 26th, 2006 by Matthew in Physics Games,Virtools
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Rolling Assault represents the evolution of a simple physics prototype I created a few years ago. This prototype had some merit so an artistic friend, Creath Carter, took it upon himself to create some content to the replace the lifeless polygons. We fleshed out the game a bit more in order to enter it into the IGF that year. This is the result:

Humble Beginnings

Over the summer of 2003 I spent a lot of time creating physics-based gameplay experiments. I used Virtools, our middleware of choice, and even posted all of the source code for the benefit of the Virtools developer community. The now-hibernating site was called DevLab–it’s still online, although it hasn’t been updated in awhile.

Anyway, one of the tests I created attempted to simulate the motion of a tank tread. Here is the resulting prototype, which took a few hours to create:

Rolling Assault Screenshot
(Rolling Assault Physics Prototype 1)

The game is playable through the Virtools’ plug-in. Use the left and right arrows for control.

This was generally the scope of the prototypes I was creating at the time. The controls are there, along a first pass at balancing the motion so it “feels” pretty good. A goal structure is clearly absent, though, along with such pleasantries as a reset key (right-click and do reset through the Virtools web player if you need to).

Life’s First Creath

As bare as it was, the treads test was fun to screw around with. Creath Carter, a friend from my school days, thought the mechanic had enough potential to bestow upon it some sexy artwork. I had worked with Creath in the past and he knew his way around Virtools. It was a welcome turn of events and saved the project from being completed shelved along with the rest of the physics game experiments.

A mere six days after this first prototype, this version was posted to DevLab:

Rolling Assault Screenshot
(Rolling Assault Physics Prototype 2)

Here is the playable Virtools link. Use A/D for left/right controls and mouse movement/click for turret control.

In addition to the new artwork, this version took a second pass at tuning the physics. The addition of the turret also added the ability for the player to right themselves when they get flipped over. On the whole, this new version seemed like a lot of fun to play. Even though there were no enemies to blast, yet, it was easy to imagine what it would be like to play an actual game from this point.

The IGF Version

In August–a month after the first version was created–we decided to put together a playable level of the game and submit it to the Independent Games Festival. The game wasn’t selected as a finalist, but the IGF did serve as a very useful deadline. The contest rules require that your game be roughly in “beta” form with one playable level of content. I had about 5 days that I could spend on the game, in between other projects, but it felt like a feasible goal. I had a lot of energy back then.

We came awfully close to achieving our goal. The final version of the prototype has four enemies, a longer level, music, some sound effects, and slightly-refined controls. There were a few pieces of content that didn’t make it in, unfortunately, including a sweet multi-stage end boss.

Rolling Assault Screenshot Screenshot of Physics Games
(Rolling Assault Game Screenshots)

It’s Judgment Play

One the big issues with physics-based game design is the issue of inertia. Naturally, any Newtonian physics engine that mimics reality will have such things as inertia, the conservation of angular momentum, and so on. But are those things necessarily conducive to a fun, responsive play experience? Not really. More often than not the limitations of reality actually get in the way.

Rolling Assault suffers in this regard. The control seemed fine in the early prototypes. It was satisfying to roll around; the wheels’ motion was aesthetically pleasing. However, as soon as we introduced very specific movement goals–dodge this missile, jump over this barrier–the sluggishness in the tank’s motion becomes apparent. The tank simply isn’t nimble enough to perform directed tasks without some degree of player frustration.

Solutions to Sluggishness

There are two obvious solutions to this problem. One is simply to remove high-fidelity movement requirements from the game’s design. This could be accomplished by putting more emphasis on accurate aiming and the game’s overall weaponry. The tank’s motion would change from a focal point to an abstracted means of scrolling the level forward. The player’s attention would instead be drawn to predictive aiming and observing enemy movement rather than the exact position of the tank. This would require completely rethinking enemy design.

Another solution is to tune the tank’s physics setup to be more responsive. One way to accomplish this is to exaggerate directional changes. For instance, if the tank is moving right and the player wants to go left, the game would provide additional impulses to overcome inertia. As soon as the tank is moving left properly, though, it would scale back the leftward impulses. This sort of anti-inertia logic is actually present in Amoeball and did help make the game feel more responsive. The complexity of the tank would require some additional tweaking–do you boost the torque of the wheels (which are already pretty slippery to begin with, since they are perfect spheres with infinitesimally small contact points)? Or do you fake it with impulses? Add torque on the main body so the player can arbitrarily control rotation mid-air? It would be an interesting design exercise, to say the least.

Play It! It’s Free!

All told, I’m pleased with how Rolling Assault came out. The game is well under a man-month of combined effort, and reasonably entertaining for how little time has been invested in it.

The one-level prototype of Rolling Assault is available exclusively at Fun-Motion. It’s a wee download, weighing in at 5 MB, and completely free. If you’ve read this far definitely check the game out. My rambling words can only do so much good without hands-on experience.

Download Rolling Assault physics game here (5 MB).
(there is no quit key, just alt-F4 when you’re done playing)

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17 Responses to 'The Evolution of an Idea: Rolling Assault'

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  1. Dave said,

    on April 27th, 2006 at 12:08 am

    Ha-haa, this is pretty cool. I love the way the tank moves and handles, although you are right, any ideas of split-second manouevres to avoid incoming fire go out the window pretty quickly. Maybe another solution would be to give the tank a defense mechanism – perhaps a rechargeable energy shield? That could make game play more tactical although again it might marginalise your main gameplay mechanic.

    BTW there are a few things I want to ask you about the content of this post:

    “There were a few pieces of content that didn’t make it in, unfortunately, including a sweet” …what? Don’t hold out on me!

    “…the conversation of angular momentum” – this is either a typo or a very very funny play on words :)

    Thanks for the site, I love reading the reviews and look forward to future installments :)

  2. PoV said,

    on April 27th, 2006 at 3:38 am

    Despite the flaws you pointed out, it’s still a nice concept. Using the turret to right yourself is kinda cool.

  3. Blinx said,

    on April 27th, 2006 at 7:17 am

    For some reason, a file is missing. MSVCR7.dll is missing. I’ve downloaded it numerous times, and extracted it into different places but is still does not work.

  4. fluffy bunny said,

    on April 27th, 2006 at 9:54 am

    Pretty enjoyable, though as you note, it gets frustrating when you have to deal with the enemies as well as tank movement. If you do develop this concept further, I’d be interested in seeing how it turns out.

  5. Matthew said,

    on April 27th, 2006 at 9:57 am

    Dave: Whoops, thanks for the typo catches. I missed a line when I pasted in from Word–the never-implemented content was a level boss with multiple stages (so after a certain amount of damage it would transform, etc).

    Blinx: Try downloading the game again–I included that DLL in the archive.

  6. Jack (Wunderbear) said,

    on April 27th, 2006 at 11:09 am

    Very cool little game! I liked it. Although, trying to right the tank whilst being fired on from all sides was a bit aggravating. Perhaps the torque idea (so you can move the tank in the air) would be a good implementation.

    What would the sweet multi-stage boss look like?

  7. Krakle said,

    on April 27th, 2006 at 3:03 pm

    This is a very fun little toy, I actually enjoyed playing the second version of it more than the finished one. I just wish you could damage those turrents by running over them or into them. Also there is a small bug in the final one, after you defeat the helicopters and go back, they reapear. I also noted that if you continue on past the base you can see 2 miniguns. :) Was that going to be part of the boss or something you just left in. (My spacebar didn’t reset me :P) Overall, a fun little time waster, good in small doses. Do not operate heavy machinery while using. :)

  8. Alex said,

    on April 28th, 2006 at 9:37 am

    Great game! really great physics there. looking forward to seeing how this develops

    found a small (but rather annoying) bug in the game though, if you shoot and hit a turret before it has popped up, it become invunerable and can’t be damaged though it still fires

  9. Creath said,

    on April 29th, 2006 at 6:28 pm

    I think Alex just figured out that one, nagging bug we had never gotten around to finding. Sweet.

    I always say I’d be up for finishing this game. I still continued to make content for it long after both our schedules didn’t allow us to move it any further towards completion. On the player-defense topic, I had always wanted to do a color-coded ro-sham-bo style weapon system that allowed for immobile defense of the tank, and still managed to make you think outside of just hitting a shield button. Something like a guns>missiles>energy-weapons>guns deal.

    This was a fun project.

  10. Matteo said,

    on April 30th, 2006 at 1:33 pm

    awesome game!

  11. John H. said,

    on April 30th, 2006 at 2:03 pm

    Why don’t you just “move the camera back?” I think the problem may be that you don’t see enough of the game world at a time, and when enemies fire their shots are too close to react to. Make everything a bit smaller, and you give the the player more information to work with, and simultaneously give him a little more time to respond to threats. It would make it a more thoughtful game, but there’s not anything necessarily wrong with that….

    Anyway, that’s my opinion after roughly ten seconds of thought, heh.

  12. case said,

    on June 15th, 2006 at 3:58 pm

    creeth where is that content could you reply with a link on where to get it. for the defence topic how about a small glass or energy panel or something attached to the tip of the turret barrel. I’d really like to see more content.

  13. case said,

    on June 16th, 2006 at 10:23 am

    i found a way to right your self while airborne… you simply shoot missles in the opposite direction that you want to spin.

  14. Beakless said,

    on July 28th, 2006 at 2:12 am


    But ragdoll physics wouldn’t have gone a miss…

  15. Darren said,

    on January 22nd, 2007 at 6:44 pm

    Cool game or should I say demo there is one level and space dosnt restart

  16. Drunkman said,

    on February 8th, 2007 at 3:58 pm

    Press “R” to reset…

  17. Drunkman said,

    on February 8th, 2007 at 4:05 pm

    Are you still working on this? If you are, or already have, please tell me where I can get it.

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