[游戏开发]cannot implicitly convert from ‘float4x4‘ to ‘float4‘

Unity升级到5.6及以后，所有跟UNITY_MATRIX_MVP运算的矩阵或者向量的mul方法，会被自动转成UnityObjectToClipPos方法

float4x4 m = mul(Unity_MATRIX_MVP, rm);
// 自动变成如下
float4x4 m = UnityObjectToClipPos(rm);

在代码中遇到了这样的报错：

void Update()
    {
        Matrix4x4 RM = new Matrix4x4();
        RM[0, 0] = Mathf.Cos(Time.realtimeSinceStartup);
        RM[0, 2] = Mathf.Sin(Time.realtimeSinceStartup);
        RM[1, 1] = 1;
        RM[2, 0] = -Mathf.Sin(Time.realtimeSinceStartup);
        RM[2, 2] = Mathf.Cos(Time.realtimeSinceStartup);
        RM[3, 3] = 1;
        
        GetComponent<Renderer>().material.SetMatrix("rm", RM);
    }
   
float4x4 rm;
struct v2f {
	float4 pos:POSITION;
};

v2f vert(appdata_base v)
{
	v2f o;
  	float4x4 m = UnityObjectToClipPos(rm);// 报错 cannot implicitly convert from
   	o.pos = mul(m,v.vertex);
	return o;
}

解决办法如下：

v2f vert(appdata_base v)
{
    v2f o;
    float4x4 m1 = UNITY_MATRIX_MVP;
    float4x4 m = mul(m1,rm);
    o.pos = mul(m,v.vertex);
    return o;
}

原因是mul和UnityObjectToClipPos所需的参数不一样，查文档如下：


这里我们可以看到UnityObjectToClipPos与mul传入的参数类型不一致，不能隐式转换导致的报错