A simple 2d flock demo based on Unity2D game engine.
In this game demo, there are altogether 3 different flocks (orange, blue and green). For each single frame, every flock agent (single bird) will try to fly in a circle area with all its neighbors (same color), first gather, then align at same direction, next avoid colliding with each other. Each flock will ignore any other flocks.
I use Unity2019.3.11f1 and JetBrain's Rider IDE for this project under Windows 10 environment.
Unity and Unity hub download
archived Unity download
Jetbrains Rider download
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Download this repo, open(or unzip and open) the Unity2D_Flock-Demo folder.
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Open the Unity Hub, from the Home Screen, click Projects to view the Projects tab.
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To open an existing Unity Project stored on your computer, click the Project name in the Projects tab, or click Open to browse your computer for the Project folder.
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Note that a Unity Project is a collection of files and directories, rather than just one specific Unity Project file. To open a Project, you must select the main Project folder, rather than a specific file.
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For this game, just select the Unity2D_Flock-Demo folder and open this project.
The whole project in Unity contains two main folders, Assets folder and Package folder.
Under Assets folder, there are altogether 6 subfolders:
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Behavior Objects folder: contains 15 behavior objects (Alignment behavior object, stay in radius behavior object and so on) created by scriptable objects in Unity as assets.
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Filter Objects folder: contains 2 filter objects (same flock filter and obstacle layer filter) also created by scriptable objects in Unity as assets.
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Prefabs Objects folder: contains 4 prefabs (orange, green, blue and default white prefabs).
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Scenes folder: contains 1 main scene of this game demo.
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Scripts folder: contains 18 C# scripts I write for this game demo. Under Behavior Scripts subfolder, there are altogether 12 C# scripts about flock behaviors. Under Editor subfolder, there is 1 C# script called CompositeBehaviorEditor which uses Unity GUI module to generate a custom behaviors editor. Under Filter Scripts subfolder, there are 3 C# scripts about filters. In addition to these C# scripts, there are also Flock.cs and FlockAgent.cs files to represent a flock and each single bird.
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Sprites folder: contains 1 sprite for a single flock agent.
For each flock, I design that it should have 3 basic behaviors: cohesion, alignment, and avoidance. For each flock agent (single bird) in a flock, each frame it should first try to gather with all other possible neighbors, then get average direction as the flock’s current frame’s direction, last check to see if each pair of two flock agents in the same block has a distance that exceeds a certain value.
Next, I observe that the cohesion behavior is not smooth enough so that sometimes several flock agent objects may flick thus I write a SteeredCohesionBehavior class to solve this problem.
After all these designs, I find that maybe a composite behavior which contains all these 3 behaviors will be a better idea, then I just create a Composite Behavior Class (object) which will help us control all 3 basic behaviors in each frame.
Then I find that flocks will just leave the current scene and never come back which is not very similar to real life experience. Therefore, I create a StayInRadiusBehavior class to let each flock fly in a certain circle area.
Now all behaviors seem to be right for only one flock, in order to deal with multiple flocks’ issue, we need let each flock to know whether a specific flock agent belongs to it or not. Therefore, I design the filter part, create a SameFlockFilter to filter neighbors and attached this filter to generate all behaviors’ filtered version (no need for stay in radius behavior).
For multiple flocks, all behaviors also work now. Finally, I want to add obstacle avoidance feature thus I create a PhysicsLayerFilter to let orange flock to avoid the yellow obstacle. However, according to Unity issue, obstacle avoidance feature only cares about the center of the obstacle. In order to also consider the Collider of the obstacle, I had to add several lines of codes in FilteredAvoidanceBehavior class. However, this feature sometimes still fails.
For future plan, I will try to solve the obstacle avoidance issue first and then move this project to 3D version.