描述：

在網上看到很多效果很好的水，比如根據水的深度，顏色有深淺變化，能讓水變得更真實，但是又會涉及到比較複雜的計算，在移動端上面還是有些吃力的。

最近研究了一下，想在移動端上面模擬這樣的效果 ：

1 水的深淺透明度變化

2 水的深淺顏色變化

3 水上的陰影模擬（大面積的水通過烘焙比較浪費烘焙圖）

根據上面的3點，可以通過一張黑白圖的rg通道來實現深淺以及陰影的模擬 效果如下

如圖，淺色的偏綠，深色的偏藍 ，顏色可以手動調節，左邊為陰影位置

程式碼如下：

Shader "Game_XXX/whater"
{
	Properties 
	{
		_WaterTex ("Normal Map (RGB), Foam (A)", 2D) = "white" {}
		_AlphaTex("AlphaTex", 2D) = "black" {}
		_shadowLight ("shadowLight",range(0,1)) = 0
		_Tiling ("Wave Scale", Range(0.00025, 0.007)) = 0.25
		_WaveSpeed("Wave Speed", Float) = 0.4
		_SpecularRatio ("Specular Ratio", Range(10,500)) = 200
		_outSideColor("outSideColor",Color) = (0,0,0,0)
		_outSideLight("outSideLight",Range(0,10))=1
		_inSideColor("inSideColor",Color) = (0,0,0,0)
		_inSideLight("intSideLight",Range(0,10))=1
		_Alpha("Alpha",Range(0,1)) = 1
		//模擬燈光顏色
		_LightColorSelf ("LightColorSelf",Color) = (1,1,1,1)
		//模擬燈光方向
		_LightDir ("LightDir",vector) = (0,1,0,0)
		//高光強度
		_specularLight("specularLight",range(0.1,2)) =1	
	}
	
	SubShader {  
		Tags {
			"Queue"="Transparent-200"
			"RenderType"="Transparent" 
			"IgnoreProjector" = "True"
			"LightMode" = "ForwardBase"
		}
		LOD 250
		Pass
		{

			 ZWrite Off
			 Blend SrcAlpha OneMinusSrcAlpha
			 CGPROGRAM

			 #pragma vertex Vert
			 #pragma fragment Frag
			 #include "UnityCG.cginc"
			
			 float _Tiling;
			 float _WaveSpeed;
			 float _SpecularRatio;
			 sampler2D _WaterTex;
			 sampler2D _AlphaTex;
			 float4 _LightColorSelf;
			 float4 _LightDir;
			 float4 _outSideColor;
			 float _outSideLight;
			 float4 _inSideColor;
			 float _inSideLight;
			 float _shadowLight;
			 float _specularLight;
			 float _Alpha;

			struct v2f
			{
			 float4 position  : POSITION;
			 float3 worldView  : TEXCOORD0;
			 float3 tilingAndOffset:TEXCOORD2;
			 float3x3 tangentTransform:TEXCOORD4;  
			 float2 alphaUV :TEXCOORD7;

			};

			

			v2f Vert(appdata_full v)
			{
			 v2f o;
			 float4 worldPos = mul(unity_ObjectToWorld, v.vertex);
			 //視向量（世界空間）
			 o.worldView = -normalize(worldPos - _WorldSpaceCameraPos);
			 o.position = UnityObjectToClipPos(v.vertex);
			 //uv動畫
			 o.tilingAndOffset.z =frac( _Time.x * _WaveSpeed);//frac :返回標量或向量的小數
			 o.tilingAndOffset.xy = worldPos.xz*_Tiling;
			 o.alphaUV = v.texcoord;
			 //求世界法線三件套  
			 float3 normal =normalize( UnityObjectToWorldNormal(v.normal));  
             float3 tangentDir = normalize( mul( unity_ObjectToWorld, float4( v.tangent.xyz, 0.0 ) ).xyz );//切線空間轉化為世界空間  
             float3 bitangentDir = normalize(cross(normal, tangentDir) * v.tangent.w);//切線 法線 計算副切線  

			 o.tangentTransform = float3x3( tangentDir, bitangentDir, normal);  
			 return o;
			}

			float4 Frag(v2f i):COLOR
			{

			  

			  //法線取樣
			  fixed3 BumpMap01 = UnpackNormal(tex2D(_WaterTex,i.tilingAndOffset.xy + i.tilingAndOffset.z ));
			  fixed3 BumpMap02 = UnpackNormal(tex2D(_WaterTex,i.tilingAndOffset.xy*1.1 - i.tilingAndOffset.z));
			  //兩張法線相混合
			  //fixed3 N1 =saturate( normalize(mul( BumpMap01.rgb, i.tangentTransform )));
			  //fixed3 N2 =saturate( normalize(mul( BumpMap02.rgb, i.tangentTransform )));
			  //fixed3 worldNormal  =  N1 - float3(N2.x,0,N2.z);

			  fixed3 N1 = normalize(mul( BumpMap01.rgb, i.tangentTransform ));
			  fixed3 N2 = normalize(mul( BumpMap02.rgb, i.tangentTransform ));
			  fixed3 worldNormal = N1*0.5 +N2*0.5;




			  float LdotN = dot(worldNormal, _LightDir.xyz); //_LightDir為模擬燈光
			 

			  //高光 
			  float dotSpecular = dot(worldNormal,  normalize( i.worldView+_LightDir.xyz));
			  fixed3 specularReflection = pow(saturate(dotSpecular), _SpecularRatio)*_specularLight;


			  //通道貼圖取樣
			  fixed4 alphaTex = tex2D (_AlphaTex,i.alphaUV);
			  //模擬燈光的顏色 * 漫反射係數= 基礎水的顏色
			  fixed4 col =_LightColorSelf*2 * saturate (LdotN) ;
			  //用alpha貼圖的r通道來模擬水的深淺的顏色，白色為深色，黑色為淺色 ，同時乘以想要的顏色
			  col.rgb = col.rgb * alphaTex.r *_inSideColor * _inSideLight  +  col.rgb * (1-alphaTex.r) * _outSideColor *_outSideLight + specularReflection;

			  //控制透明度，根據alpha的r通道 來控制深淺的透明度，深色的透明度小 淺色的透明度大
			  col.a = _Alpha * alphaTex.r;

			  //手動繪製陰影 用alpha貼圖的g通道 跟col相乘 來模擬陰影 
			  alphaTex.g = saturate(alphaTex.g + _shadowLight);
			  col.rgb *= alphaTex.g;
			  return col;
			}
		      ENDCG	
	    }  
	}

	FallBack "Diffuse"
}