flocking

Ludum Dare 31, the last jam of the year, ended up very well for me. I created “baa ram ewe“, a game where you must herd sheeps with the mouse, moving them from a thin grass to a plentiful pasture. The game has a good – and solid, for an experimental game made in 48 hours – mechanics and a good overall aesthetics, I really liked the final result of this game. I also received a lot of positive feedbacks, mostly asking me to create a mobile version, which I decided to do.

Baa Ram Ewe uses a boiding algorithm (also known as flocking algorithm) to move the sheeps, to keep them together, and to avoid obstacles and dangerous elements. The boiding algorithm is a method to simulate collective movement of animals, such as fishes, birds, sheep, etc. For example, take a look a the following video, which shows a simulation of buffaloes running:

The algorithm is very simple. All agents in the simulation follow a set of simple rules. These rules defines how each agent will move accordingly to its neighbors flock-mates. The interaction between the agents generate an emergent behavior, as you can see in the video.

The rules used in these kind of simulation are really simple. Commonly, all boiding applications have the following ones:

  • Separation: the agent must avoid the nearest flock-mates by steering away from them;
  • Alignment: the agent try to head to the average position of the nearest flock-mates;
  • Cohesion: the agent try to move to the average position considering the nearest flock-mates;

You can see a visual example of these rules on the figure below (copied of the Craig Reynold’s site, the creator of this algorithm)

boiding_rules

(a) separation rule; (b) alignment rule; and (c) cohesion rule. From (http://www.red3d.com/cwr/boids/)

In Baa Ram Ewe, I used the algorithms presented by Conrad Parker in his site as basis. Summarizing, I have a FLOCKING function that moves the sheeps accordingly to a set of rules:

FUNCTION FLOCKING
  VECTOR v1, v2, ..., vN

  FOR EACH boid IN boids
    v1 = rule1(boid)
    v2 = rule2(boid)
    ...
    vN = ruleN(boid)

    boid.velocity += v1 + v2 + ... + vN
    boid.position += boid.velocity
  END FOR EACH
END FUNCTION

As you can see, you can define any number of rules, but be careful with that! More rules mean more complexity, you probably won’t be able to generate the behavior you want. Check it out the Conrad Parker site to a nice description of the basic rules.

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Finally I finished my entry for this Ludum Dare (LD31, the theme is The Entire Game on One Screen). This time, I am so exhausted that I couldn’t do any progress report during the weekend, but, on the other hand, I could finish the game, including the mechanics, graphics and sounds.

My idea was creating something with artificial intelligence (again) and for some reason, after the theme announcement, I remembered that I never touched at a flocking algorithm and this would be a good opportunity for it. The game idea is to take some sheeps from one point and bring them to another, without letting them to leave the map or to be killed. The player uses the mouse to herd the sheeps, which will behave accordingly to their neighbor mates and some tiles in the environment.

As tradition, I writing here a summary of the competition:

What was good:

  • Could finish the game!
  • Cute sheeps with nice behavior;
  • I could follow the schedule without any change;
  • I could do some music and sound effects;
  • I drawn my first tileset!

What wasn’t good:

  • Lot of problems with collisions ;/
  • Spend a lot of time with rotation math (shame on me);
  • The sound effects are pretty limited and the music is too simple;
  • The graphics are cool but some things I’m hating, such as the windmill;
  • I had to redraw the tileset 2 times!

Which technologies and techniques I used:

  • The sheeps are controlled by a flocking algorithm, (or boid algorithm) as described here and here;
  • The graphics were made in Inkscape;
  • The map were built in Tiled, using a 32×32 tileset;
  • I recorded the audio for the sound effects in Audacity;
  • The music were made in Guitar Pro and converted in audacity;
  • CreateJS and Creatine were used as programming base;

anim1

(VIEW LUDUM DARE ENTRY | PLAY BAA-RAM-EWE)

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Ludum Dare 31 has begun! I was expecting the snowman theme, the favorite on the previous voting rounds, but, thanks to all gods, snowman melted in the flames of hell. The winner theme was “The Entire Game on One Screen“.

I finally have an idea (hopefully, a good one): a game where you command a dog herding a group of sheeps where the goal is keeping the maximum number of sheeps inside the screen area.

 

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