首先定义一个裁剪范围，

_DisappearOffset("offset",Range(-1,1)) = 1

在顶点着色器中，取某个轴的值与裁剪的数相减存储在UV的z分量中

  v2f vert (appdata v)
  {
      v2f o;
	  o.pos = UnityObjectToClipPos(v.pos);
	  o.uv.xy = v.uv;
	  o.uv.z = _DisappearOffset + v.pos.z;
      return o;
  }

在片元着色器中返回uv.z的数值，查看值

 fixed4 frag (v2f i) : SV_Target
 { 
        return i.uv.z;
 }

在片元着色器中使用Clip函数，将小于0的位置裁剪掉

  fixed4 frag (v2f i) : SV_Target
  { 
         clip(i.uv.z);
         fixed4 col = tex2D(_MainTex, i.uv);
         return col;
 }

Clip函数的实现如下：

如果x<0则裁剪掉此片断
void clip(float4 x)
{
    if (any(x < 0))
    discard;
}

最终效果:

代码：

Shader "Custom/ClipShader"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _DisappearOffset("offset",Range(-1,1)) = 1
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" "RenderQueue"="Geometry"}
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            struct appdata
            {
                float4 vertics : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float3 uv : TEXCOORD0;
                float4 vertics : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float _DisappearOffset;

            v2f vert (appdata v)
            {
              	v2f o;
				o.vertics = UnityObjectToClipPos(v.vertics);
				o.uv.xy = v.uv;
				o.uv.z = _DisappearOffset + v.vertics.z;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            { 
                clip(i.uv.z);
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                return i.uv.z;
            }
            ENDCG
        }
    }
}