Unity3D Camera透视相机到正交相机插值

using UnityEngine;
using System.Collections;

public class ProjectionLerp : MonoBehaviour
{
    [Range(0, 0.9f)]
    public float lerp;

    public float nearClip = -0.1f;
    public float size =3f;


    void Update()
    {
        var ratio = Screen.width / (float)Screen.height;

        var a = Matrix4x4.Perspective(45, ratio, 0.1f, 5000f);
        var b = Matrix4x4.Ortho(-size * ratio, size * ratio, -size, size, nearClip, 5000f);

        Camera.main.projectionMatrix = Lerp(a, b, lerp);
    }

    Matrix4x4 Lerp(Matrix4x4 a, Matrix4x4 b, float lerp)
    {
        var result = new Matrix4x4();
        result.SetRow(0, Vector4.Lerp(a.GetRow(0), b.GetRow(0), lerp));
        result.SetRow(1, Vector4.Lerp(a.GetRow(1), b.GetRow(1), lerp));
        result.SetRow(2, Vector4.Lerp(a.GetRow(2), b.GetRow(2), lerp));
        result.SetRow(3, Vector4.Lerp(a.GetRow(3), b.GetRow(3), lerp));

        return result;
    }
}