Trail效果

我觉得不是很完美，但意思多半是这个意思，主要是对SimpleNoise，以及通过 取反，subtract等方法得出一个变换的UV区域

shader代码

 Properties
    {
        _MainTex ("Texture", 2D) = "white" {}

        _NoiseSpeed("噪声纹理移动的速度",Vector)=(-0.5,0,0,0)
        _NoiseScale("噪声纹理板块的大小",float)=35
        
        _MainTexSpeed("主纹理移动的速度",Vector)= (-0.5,0,0,0)

        [HDR] MainColor("拖尾的颜色",color)=(1,1,1,1)
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // make fog work
            #pragma multi_compile_fog

            #include "UnityCG.cginc"

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

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            float4 _NoiseSpeed;
            float _NoiseScale;

            float4 MainColor;
            float4 _MainTexSpeed;

            inline float unity_noise_randomValue(float2 uv)
            {
                return frac(sin(dot(uv, float2(12.9898, 78.233))) * 43758.5453);
            }

            inline float unity_noise_interpolate(float a, float b, float t)
            {
                return (1.0 - t) * a + (t * b);
            }

            inline float unity_valueNoise(float2 uv)
            {
                float2 i = floor(uv);
                float2 f = frac(uv);
                f = f * f * (3.0 - 2.0 * f);

                uv = abs(frac(uv) - 0.5);
                float2 c0 = i + float2(0.0, 0.0);
                float2 c1 = i + float2(1.0, 0.0);
                float2 c2 = i + float2(0.0, 1.0);
                float2 c3 = i + float2(1.0, 1.0);
                float r0 = unity_noise_randomValue(c0);
                float r1 = unity_noise_randomValue(c1);
                float r2 = unity_noise_randomValue(c2);
                float r3 = unity_noise_randomValue(c3);

                float bottomOfGrid = unity_noise_interpolate(r0, r1, f.x);
                float topOfGrid = unity_noise_interpolate(r2, r3, f.x);
                float t = unity_noise_interpolate(bottomOfGrid, topOfGrid, f.y);
                return t;
            }

            float Unity_SimpleNoise_float(float2 UV, float Scale)
            {
                float t = 0.0;

                float freq = pow(2.0, float(0));
                float amp = pow(0.5, float(3 - 0));
                t += unity_valueNoise(float2(UV.x * Scale / freq, UV.y * Scale / freq)) * amp;

                freq = pow(2.0, float(1));
                amp = pow(0.5, float(3 - 1));
                t += unity_valueNoise(float2(UV.x * Scale / freq, UV.y * Scale / freq)) * amp;

                freq = pow(2.0, float(2));
                amp = pow(0.5, float(3 - 2));
                t += unity_valueNoise(float2(UV.x * Scale / freq, UV.y * Scale / freq)) * amp;

                return t;
            }

            float Ret(float a)
            {
                return a <= 0.2 ? -1 : 0;
            }

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
              
                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                
                // 噪声纹理输出一个Float值    UV偏离缩放                   噪声纹理板块密集度
                float Noisenum= Unity_SimpleNoise_float((i.uv + (_Time.y * _NoiseSpeed.xy)),_NoiseScale);

                //UV纹理中取R值
                float uvr = i.uv[0];

                //最终得到一个渐变区域，可显示区域以左右为界，黑白不规则渐变
                float NoiCol = (Noisenum + (1 - uvr)) - uvr;


               //主纹理的偏移
               float2 Mainuv = i.uv + (_Time.y * _MainTexSpeed.xy);
          
               fixed4 col = tex2D(_MainTex, Mainuv);
            
               
              fixed4 finalcol = col * NoiCol;

              clip(Ret(finalcol.r + finalcol.g + finalcol.b));


                return col+ MainColor;
            }
            ENDCG
        }
    }

unity自带的拖尾组件，材质球赋予给拖尾组件