Agent Avoidance

Quantum implements a variation of the collision avoidance technique called Hybrid Reciprocal Velocity Obstacles (HRVO).

Setting up Avoidance Agents

The NavMeshAvoidanceAgent component requires the entity to already have a NavMeshPathfinder and a NavMeshSteeringAgent component.

Simulation Config

The avoidance requires the following global parameters located on the SimulationConfig in the Navigation section.

Disable EnableAvoidance to completely remove any overhead from the avoidance system.

AvoidanceRange is crucial to the quality and performance cost of the avoidance system. It defines the range in which agents start to influence each other. The range is measured between the radii of two agents. (A) is the avoidance radius of an individual agent, and (B) is the avoidance radius of the agent plus the global AvoidanceRange.

inRange = Distance(positionAgentA, positionAgentB) - radiusAgentA - radiusAgentB < AvoidanceRange

MaxAvoidanceCandidates defines the maximum number of avoidance candidates used by each agent. More candidates requires more memory and CPU but also increase the quality. The higher the AvoidanceQuality and the more agents that are influencing each other, the higher this number has to be.

VelocityObstacleTruncationFactor defines how much a VO is truncated for non-moving obstacles.

NavMeshAgentConfig - Avoidance

Setting up Avoidance Obstacles

Avoidance Obstacles are static or moving entities that influence the avoidance behavior of Navmesh agents but are not agents themselves. They do not influence the path finder and should not be used to block parts of the game level.

A NavMeshAvoidanceObstacle component requires a Transform2D or Transform3D component to work properly.

If the entity that has a NavMeshAvoidanceObstacle component is moving, other agents require its velocity information to predict its future position and the NavMeshAvoidanceObstacle.Velocity has to be set manually.

Add a NavMeshAvoidanceObstacle to a Quantum Entity Prototype in Unity.

Or add it in code.

C#

var c = f.Create();
f.Set(c, new Transform2D { Position = new FPVector2(8,-2) });
var obstacle = new NavMeshAvoidanceObstacle();
obstacle.AvoidanceLayer = 0;
obstacle.Radius = FP._0_50;
obstacle.Velocity = FPVector2.Zero;
f.Set(c, obstacle);

Jittering Agents

The agent movement, particularly their movement direction, can be unstable due to the nature of the avoidance calculations in conjunction with fixed-point math. This causes the agents to jitter visibly.

To mitigate this, the Angular Speed of the agents can be tuned down, or view smoothing can be added. This can be done by overriding the QuantumEntityView class and adding blending to the rotation when applying the transforms.

C#

namespace Quantum {
  using UnityEngine;

  public class SmoothRotationEntityView : QuantumEntityView {
    public float Blending = 15;

    private Quaternion rotation;

    protected override void ApplyTransform(ref UpdatePositionParameter param) {
      // Override this in subclass to change how the new position is applied to the transform.
      transform.position = param.NewPosition + param.ErrorVisualVector;

      // Unity's quaternion multiplication is equivalent to applying rhs then lhs (despite their doc saying the opposite)
      rotation = param.ErrorVisualQuaternion * param.NewRotation;
      transform.rotation = Quaternion.Lerp(transform.rotation, rotation, Time.deltaTime * Blending);
    }
  }
}