AppExperiments

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using UnityEngine;

namespace Leap.Unity.Examples {

  public class ProjectionPostProcessProvider : PostProcessProvider {
    
    [Header("Projection")]

    [Tooltip("The exponent of the projection of any hand distance from the approximated "
           + "shoulder beyond the handMergeDistance.")]
    [Range(0f, 5f)]
    public float projectionExponent = 3.50f;

    [Tooltip("The distance from the approximated shoulder beyond which any additional "
           + "distance is exponentiated by the projectionExponent.")]
    [Range(0f, 1f)]
    public float handMergeDistance = 0.30f;

    public override void ProcessFrame(ref Frame inputFrame) {
      // Calculate the position of the head and the basis to calculate shoulder position.
      var headPos = Camera.main.transform.position;
      var shoulderBasis = Quaternion.LookRotation(
        Vector3.ProjectOnPlane(Camera.main.transform.forward, Vector3.up),
        Vector3.up);

      foreach (var hand in inputFrame.Hands) {
        // Approximate shoulder position with magic values.
        var shoulderPos = headPos
                          + (shoulderBasis * (new Vector3(0f, -0.2f, -0.1f)
                          + Vector3.left * 0.1f * (hand.IsLeft ? 1f : -1f)));

        // Calculate the projection of the hand if it extends beyond the
        // handMergeDistance.
        var shoulderToHand = hand.PalmPosition.ToVector3() - shoulderPos;
        var handShoulderDist = shoulderToHand.magnitude;
        var projectionDistance = Mathf.Max(0f, handShoulderDist - handMergeDistance);
        var projectionAmount = Mathf.Pow(1 + projectionDistance, projectionExponent);
        hand.SetTransform(shoulderPos + shoulderToHand * projectionAmount,
                          hand.Rotation.ToQuaternion());
      }
    }

  }
}