Shader "Custom/WaterWave Effect"
{
	Properties
	{
		_MainTex("Base (RGB)", 2D) = "white" {}
	}

	SubShader
	{
		Pass
		{
			ZTest Always
			Cull Off
			ZWrite Off
			Fog{ Mode off }

			CGPROGRAM
			#pragma vertex vert_img  
			#pragma fragment frag  
			#pragma fragmentoption ARB_precision_hint_fastest   
			#include "UnityCG.cginc"  

			uniform sampler2D _MainTex;
			float4 _MainTex_TexelSize;

			uniform float _distanceFactor;
			uniform float _timeFactor;
			uniform float _totalFactor;
			uniform float _wavePower;
			uniform float _timeFade;
			uniform float4 _startPos;
			uniform float _effectDis;

			fixed4 frag(v2f_img i) : SV_Target
			{
				//DX下纹理坐标反向问题  
				#if UNITY_UV_STARTS_AT_TOP  
				if (_MainTex_TexelSize.y < 0)
				_startPos.y = 1 - _startPos.y;
				#endif

				//计算uv到中间点的向量(向外扩，反过来就是向里缩)  
				float2 dv = _startPos.xy - i.uv;
				//按照屏幕长宽比进行缩放  
				dv *= float2(_ScreenParams.x / _ScreenParams.y, 1);
				//计算像素点距中点的距离  
				float dis = sqrt(dv.x * dv.x + dv.y * dv.y);

				float2 uv = i.uv;
				if (_effectDis == 0 || dis < _effectDis)
				{
					//用sin函数计算出波形的偏移值factor  
					//dis在这里都是小于1的，所以我们需要乘以一个比较大的数，比如60，这样就有多个波峰波谷  
					//sin函数是（-1，1）的值域，我们希望偏移值很小，所以这里我们缩小100倍，据说乘法比较快,so...  
					float sinFactor = sin(dis * _distanceFactor + _Time.y * _timeFactor) * _totalFactor * 0.01;
					//计算每个像素uv的偏移值  
					float2 offset = normalize(dv) * sinFactor;
					//像素采样时偏移offset  
					uv += offset * pow(dis, _wavePower) * _timeFade;
				}
				
				fixed4 c = tex2D(_MainTex, uv);

				return c;
			}
			ENDCG
		}
	}
	Fallback off
}