分别新建一个材质，一个Shader和一个用于挂在到MainCamera上的C#脚本，将Shader设置到材质球上，然后编写C#脚本，C#代码如下:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Blood : MonoBehaviour {
    public Material material;
    public float speed=10;
    public float range=0;
    public float timer = 0;
	// Update is called once per frame
	void Update () {
        timer += Time.deltaTime * speed;
        range = Mathf.Sin(timer) + 1;
        range = (range * 0.25f) + 1;

    }
    private void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        material.SetFloat("_Length", range);
        Graphics.Blit(source, destination, material);
    }
}

完成后开始编写Shader代码:

Shader "Hidden/Blood"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
		_Length("Length",Float) = 1
	}
	SubShader
	{
		// No culling or depth
		//Cull Off ZWrite Off ZTest Always

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			
			#include "UnityCG.cginc"

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

			struct v2f
			{
				float2 uv : TEXCOORD0;
				float4 vertex : SV_POSITION;
			};

			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = v.uv;
				return o;
			}
			
			sampler2D _MainTex;
			float _Length;
			fixed4 frag (v2f i) : SV_Target
			{
				
				float2 tempUV = i.uv;
				float tempLength = 0;

				if (tempUV.x < 0.5)
				{
					tempLength = length(tempUV +float2(0.5,-0.5));
				}
				else
				{
					tempLength = length(float2(1.5, 0.5)-tempUV);
				}
				tempLength *= _Length;
				fixed4 col = tex2D(_MainTex, i.uv);
				col = lerp(col, fixed4(1, 0, 0, 1), 1-clamp(tempLength, 0, 1));
				return col;
			}
			ENDCG
		}
	}
}