[005-Shader-Water Ripple Special Effect]

// 水波纹特效
/**

wave y = A sin(wt+theta)

amount = A/(speed*len)
**/
Shader "Study/05-WaveShader"
{
    
    
    Properties
    {
    
    
        _MainTex ("Texture", 2D) = "white" {
    
    }
        // 震幅
        _Amount("Amount",Range(0.0,0.4)) = 0.2
        // 频率
        _W("W",Range(0,200)) = 100
        // 衰减速度
        _Speed("Speed",Range(0,1000)) = 500

        // _Center("Center",fixed2) = fixed2(0,0)
    }
    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 _Amount;
            float _W;
            float _Speed;

            fixed4 frag (v2f i) : SV_Target
            {
    
    
                //中心点
                fixed2 center_uv = {
    
    0.5,0.5};
                fixed2 uv = i.uv;
                // 到中心距离
                float2 dt = center_uv-uv;
                float2 len = sqrt(dot(dt,dt));

                // 振幅
                float amount = _Amount/(0.01+len*_Speed);

                if(amount<0.01){
    
    
                    amount = 0;
                }

                uv.y +=amount*cos(len*_W* UNITY_PI);
            

                fixed4 col = tex2D(_MainTex, uv);
                return col;
            }
            ENDCG
        }
    }
}