融合、融球效果shader，重点在等势面公式上

Shader "Custom/MetaballsShader"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Color("Color",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 _Color;
			//等势面公式
            float energy(float r, float2 point1, float2 point2) {
                return (r * r) / ((point1.x - point2.x) * (point1.x - point2.x) + (point1.y - point2.y) * (point1.y - point2.y));
            }

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

            fixed4 frag (v2f i) : SV_Target
            {
               float4 color = tex2D(_MainTex, i.uv);
               float2 center = float2(0.5,0.5);
               float fragEnergy = energy(0.1, i.uv.xy, float2(0.5, 0.5));
               fragEnergy += energy(0.1, i.uv.xy, lerp(float2(0.2, 0.2), center,sin(_Time.y)));
               fragEnergy += energy(0.1, i.uv.xy, lerp(float2(0.8, 0.8), center,sin(_Time.y)));
               fragEnergy += energy(0.1, i.uv.xy, lerp(float2(0.2, 0.8), center,sin(_Time.y)));
               fragEnergy += energy(0.1, i.uv.xy, lerp(float2(0.8, 0.2), center,sin(_Time.y)));
               color = smoothstep(0.95, 1.0, fragEnergy) * _Color;

                // apply fog
                //UNITY_APPLY_FOG(i.fogCoord, col);
                return color;
            }
            ENDCG
        }
    }
}