liquid.shader

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'

Shader "Unlit/FX/Liquid"
{
    Properties
    {
        [Header(Main)]
        [HDR]_Tint ("Tint", Color) = (1,1,1,1)
        _MainTex ("Texture", 2D) = "white" {}
        [HDR]_TopColor ("Top Color", Color) = (1,1,1,1)
        [Header(Foam)]
        [HDR]_FoamColor ("Foam Line Color", Color) = (1,1,1,1)
        _Line ("Foam Line Width", Range(0,0.1)) = 0.0
        _LineSmooth ("Foam Line Smoothness", Range(0,0.1)) = 0.0
        [Header(Rim)]
        [HDR]_RimColor ("Rim Color", Color) = (1,1,1,1)
        _RimPower ("Rim Power", Range(0,10)) = 0.0
        [Header(Sine)]
        _Freq ("Frequency", Range(0,15)) = 8
        _Amplitude ("Amplitude", Range(0,0.5)) = 0.15
    }

    SubShader
    {
        Tags {"Queue"="Geometry"  "DisableBatching" = "True" }

        Pass
        {
            Zwrite On
            Cull Off // we want the front and back faces
            AlphaToMask On // transparency

            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;
                float3 normal : NORMAL;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
                float3 viewDir : COLOR;
                float3 normal : COLOR2;
                float3 fillPosition : TEXCOORD2;
                float3 worldNormal : TEXCOORD3;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float3 _FillAmount;
            float _WobbleX, _WobbleZ;
            float4 _TopColor, _RimColor, _FoamColor, _Tint;
            float _Line, _RimPower, _LineSmooth;
            float _Freq, _Amplitude;


            // https://docs.unity3d.com/Packages/[email protected]/manual/Rotate-About-Axis-Node.html
            float3 Unity_RotateAboutAxis_Degrees(float3 In, float3 Axis, float Rotation)
            {
                Rotation = radians(Rotation);
                float s = sin(Rotation);
                float c = cos(Rotation);
                float one_minus_c = 1.0 - c;

                Axis = normalize(Axis);
                float3x3 rot_mat =
                {   one_minus_c * Axis.x * Axis.x + c, one_minus_c * Axis.x * Axis.y - Axis.z * s, one_minus_c * Axis.z * Axis.x + Axis.y * s,
                    one_minus_c * Axis.x * Axis.y + Axis.z * s, one_minus_c * Axis.y * Axis.y + c, one_minus_c * Axis.y * Axis.z - Axis.x * s,
                    one_minus_c * Axis.z * Axis.x - Axis.y * s, one_minus_c * Axis.y * Axis.z + Axis.x * s, one_minus_c * Axis.z * Axis.z + c
                };
                float3 Out = mul(rot_mat,  In);
                return Out;
            }


            v2f vert (appdata v)
            {
                v2f o;

                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                // get world position of the vertex - transform position
                float3 worldPos = mul (unity_ObjectToWorld, v.vertex.xyz);
                float3 worldPosOffset = float3(worldPos.x, worldPos.y , worldPos.z) - _FillAmount;
                // rotate it around XY
                float3 worldPosX= Unity_RotateAboutAxis_Degrees(worldPosOffset, float3(0,0,1),90);
                // rotate around XZ
                float3 worldPosZ = Unity_RotateAboutAxis_Degrees(worldPosOffset, float3(1,0,0),90);
                // combine rotations with worldPos, based on sine wave from script
                float3 worldPosAdjusted = worldPos + (worldPosX  * _WobbleX)+ (worldPosZ* _WobbleZ);
                // how high up the liquid is
                o.fillPosition =  worldPosAdjusted - _FillAmount;
                o.viewDir = normalize(WorldSpaceViewDir(v.vertex));
                o.normal = v.normal;
                o.worldNormal  = mul ((float4x4)unity_ObjectToWorld, v.normal );
                return o;
            }

            fixed4 frag (v2f i, fixed facing : VFACE) : SV_Target
            {
                float3 worldNormal = mul( unity_ObjectToWorld, float4( i.normal, 0.0 ) ).xyz;
                // rim light
                float fresnel = pow(1 - saturate(dot(worldNormal, i.viewDir)), _RimPower);
                float4 RimResult = fresnel * _RimColor;
                RimResult *= _RimColor;

                // add movement based deform, using a sine wave
                float wobbleIntensity =  abs(_WobbleX) + abs(_WobbleZ);
                float wobble = sin((i.fillPosition.x * _Freq) + (i.fillPosition.z * _Freq ) + ( _Time.y)) * (_Amplitude *wobbleIntensity);
                float movingfillPosition = i.fillPosition.y + wobble;

                // sample the texture based on the fill line
                fixed4 col = tex2D(_MainTex, movingfillPosition) * _Tint;
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);

                // foam edge
                float cutoffTop = step(movingfillPosition, 0.5);
                float foam = cutoffTop * smoothstep(0.5 - _Line- _LineSmooth, 0.5 - _Line ,movingfillPosition);
                float4 foamColored = foam * _FoamColor;

                // rest of the liquid minus the foam
                float result = cutoffTop - foam;
                float4 resultColored = result * col;

                // both together, with the texture
                float4 finalResult = resultColored + foamColored;
                finalResult.rgb += RimResult;

                // little edge on the top of the backfaces
                float backfaceFoam = (cutoffTop * smoothstep(0.5 - (0.2 * _Line)- _LineSmooth,0.5 - (0.2 * _Line),movingfillPosition ));
                float4 backfaceFoamColor = _FoamColor * backfaceFoam;
                // color of backfaces/ top
                float4 topColor = (_TopColor * (1-backfaceFoam) + backfaceFoamColor) * (foam + result);

                // clip above the cutoff
                clip(result + foam - 0.01);

                //VFACE returns positive for front facing, negative for backfacing
                return facing > 0 ? finalResult: topColor;


            }
            ENDCG
        }

    }
}