May 20, 2020
AI For Beginners
Crowd Simulations
Part 1
Beginner Programming: Unity Game Dev Courses
Unity Learn Course – AI For Beginners
Intro
This is the first part of the Crowd Simulations section of the AI course that I covered. This was the first two major tutorials of four, Moving As One & Creating a City Crowd. These introduce the basic concepts of crowd simulations, and at least cover ways to start moving groups of agents with Nav Mesh Agents in Unity to help visualize these concepts (more so than particularly creating agent crowd AI behaviors yourself).
1: Moving As One
Crowd Behavior: agents move enmasse, as opposed to solely as individual units; their movements are usually also dependent on each other’s movements
Reynold’s Flocking Algorithm:
- Common flocking logic based on 3 simple rules:
- Turn towards average heading of group
- Turn towards average center of the group
- Avoid those around you
They start with a really basic Nav Mesh setup with a bunch of blue capsule agents on one side of a tight corridor, and a bunch of red capsule agents on the other side, and they each need to navigate to a goal on the opposite side, running through/past each group of capsules. The standard Nav Mesh Agent setups with colliders gives interesting group interactions by themselves already to start. This simulation was mostly to help visualize the idea of lines of flow in crowds, as well as instances of turbulence within crowd simulations.
2: Creating A City Crowd
Part 1
Starting setup is adding Street Crowd Simulation package to a Unity project. They included a starting scene of a street with several different characters with basic idle, walk, and run animations. This setup just helps visualize crowd behavior in a more interesting and realistic setting. Initially the agents select a random object from all the objects tagged “goal” as their destination and move there.
The additions done in the tutorial were having the agents continue finding new destinations after reaching the first one and adding more static meshes as obstacles for the agents to move around. The first goal used a distance check for once the agents were close enough to their destination, and then they would select another goal randomly from the initialized goal array. To accomplish the second part, they just added large cubes to simulate buildings to make a more realistic street walking setup with the characters.
Part 2
They added a bunch of buildings to the center of the street scene so agents would walk around the outter edge as normal street traffic.
Alternating Character Animations:
All the characters are using the same animations, so they look strange because they are all doing the exact same animations on the exact same time cycles. To rectify this, they looked into the “Cycle Offset” parameter within the standard walking animation for all the characters in the Animator.
They suggest setting this value with the SetFloat method within Unity’s Animator class. I tried doing this to set the value for the float parameter they added and tied to Cycle Offset, but it was not working for me. The string I entered matches the parameter name, and I connected the value to the parameter as they showed, but it was having no effect for me.
FIXED:
I was able to rectify this issue by explicitly stating within the Random.Range method setting the values to use floats for 0 and 1 (with 0.0f, and 1.0f). Without this explicit declaration, it must’ve been using ints and it was only setting everything to 0 every time (so initializing it as it was originally). Making them floats fixed the issue and they were being put on different cycles as expected.
They also set varied starting speeds for the agents. This included changing the speed of their animations along with their actual Nav Mesh Agent travel speed. To keep these working together well, they just randomly selected a float value and applied this same value to both of these parameters.
Dynamic Nav Mesh Obstacle (with First Person Controller):
They then move on to adding dynamic Nav Mesh obstacles by adding a First Person controller and making the player an obstacle on the Nav Mesh. This is done simply by adding a Nav Mesh Obstacle to the First Person controller. It creates a wireframe similar to a collider that can be shaped and controlled to control the area it removes from the Nav Mesh itself.
Summary
Overall the tutorials have been extremely basic so far and have not really delved into the actual AI behaviours of groups yet really. I am hoping they explore implementing Reynold’s Flocking theorem at some point so I can get some experience with that. If not I may take a detour into the world of “boids” to expose myself to more crowd behavior AIs.