【数学】计算折射光线方向

/// <summary>
/// 计算折射光线
/// </summary>
/// <param name="I">入射向量,指向入射面</param>
/// <param name="N">法向量，反向入射面</param>
/// <param name="etaRatio">折射角的正弦值与入射角的正弦值的比</param>
/// <returns></returns>
public static Vector3 Refract(Vector3 I, Vector3 N, float etaRatio)
{
I = I.normalized;
N = N.normalized;

float cosI = Vector3.Dot(I, N);

float cosT2 = 1.0f - etaRatio * etaRatio * (1.0f - cosI * cosI);

Vector3 T = etaRatio * I - (etaRatio * cosI + Mathf.Sqrt(cosT2)) * N;

if (cosT2 > 0)
return T;
else
return Vector3.zero;
}