一、创建ScreenCutout.shader

Shader "Custom/Screen Cutout"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
	_ClipX0 ("Clip x0", float) = 0
	_ClipY0 ("Clip y0", float) = 0
	_ClipX1 ("Clip x1", float) = 0
	_ClipY1 ("Clip y1", float) = 0
    }
    SubShader
    {
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 3.0 //屏幕坐标必须使用3.0
	    #include "UnityCG.cginc"

            // note: no SV_POSITION in this struct
            struct v2f {
                float2 uv : TEXCOORD0;
            };

            v2f vert (
                float4 vertex : POSITION, // vertex position input
                float2 uv : TEXCOORD0, // texture coordinate input
                out float4 outpos : SV_POSITION // clip space position output
                )
            {
                v2f o;
                o.uv = uv;
                outpos = UnityObjectToClipPos(vertex);
                return o;
            }

            sampler2D _MainTex;
			float _ClipX0;
			float _ClipY0;
			float _ClipX1;
			float _ClipY1;

            fixed4 frag (v2f i, UNITY_VPOS_TYPE screenPos : VPOS) : SV_Target
            {
				if(screenPos.x > _ClipX0 && screenPos.x < _ClipX1 && screenPos.y > _ClipY0 && screenPos.y < _ClipY1)
					clip(-1);//结束渲染

                fixed4 c = tex2D (_MainTex, i.uv);
                return c;
            }
            ENDCG
        }
    }
}

效果