water effect(2)

	//数字4代表4个波的混合，dirAB.xy代表A波方向，dir.zw指B波，dirCD.xy指C波，dirCD.zw指D波
	half3 GerstnerOffset4 (half2 xzVtx, half4 steepness, half4 amp, half4 freq, half4 speed, half4 dirAB, half4 dirCD) 
	{
		half3 offsets;
		//计算四个波的参数，对应于Gerstner中的Q*A*D
		half4 AB = steepness.xxyy * amp.xxyy * dirAB.xyzw;
		half4 CD = steepness.zzww * amp.zzww * dirCD.xyzw;
		
		//计算四个波的cos参数，对应于 W*D*(x,y)
		half4 dotABCD = freq.xyzw * half4(dot(dirAB.xy, xzVtx), dot(dirAB.zw, xzVtx), dot(dirCD.xy, xzVtx), dot(dirCD.zw, xzVtx));
		half4 TIME = _Time.yyyy * speed;
		
		half4 COS = cos (dotABCD + TIME);
		half4 SIN = sin (dotABCD + TIME);
		
		偏移量的计算
		offsets.x = dot(COS, half4(AB.xz, CD.xz));
		offsets.z = dot(COS, half4(AB.yw, CD.yw));
		offsets.y = dot(SIN, amp);

		return offsets;			
	}

	half4 frag300( v2f_noGrab i ) : COLOR
	{		
	//计算出pixel的世界法线，这里边的基准向量不再用(0,1,0)表示，而是使用顶点着色器计算出来的法线向量。
		half3 worldNormal = PerPixelNormal(_BumpMap, i.bumpCoords, normalize(VERTEX_WORLD_NORMAL), PER_PIXEL_DISPLACE);

		half3 viewVector = normalize(i.viewInterpolator.xyz);

//屏幕纹理的扭曲
		half4 distortOffset = half4(worldNormal.xz * REALTIME_DISTORTION * 10.0, 0, 0);
		half4 screenWithOffset = i.screenPos + distortOffset;
		
//利用相机计算出来的贴图来设置反射颜色。
		#ifdef WATER_REFLECTIVE		
			half4 rtReflections = tex2Dproj(_ReflectionTex, UNITY_PROJ_COORD(screenWithOffset));	
		#endif
		
//与上一节类似，反射计算高光效果。
		half3 reflectVector = normalize(reflect(viewVector, worldNormal));          
		half3 h = normalize (_WorldLightDir.xyz + viewVector.xyz);
		float nh = max (0, dot (worldNormal, -h));
		float spec = max(0.0,pow (nh, _Shininess));	
		
//边缘混合，利用相机的纹理深度与当前pixel的纹理深度做对比，差距越小，edgeBlendFactors.x越小，
//最后计算basecolor的alpha与edgeBlendFactors.x正相关；效果就是水面离水底越近，水面颜色越透明。
		half4 edgeBlendFactors = half4(1.0, 0.0, 0.0, 0.0);
		
		#ifdef WATER_EDGEBLEND_ON
			half depth = UNITY_SAMPLE_DEPTH(tex2Dproj(_CameraDepthTexture, UNITY_PROJ_COORD(i.screenPos)));
			depth = LinearEyeDepth(depth);
			edgeBlendFactors = saturate(_InvFadeParemeter * (depth-i.screenPos.z));		
			edgeBlendFactors.y = 1.0-edgeBlendFactors.y;
		#endif		
		
//与上一节类似，通过fresnel公式计算反射率。
		worldNormal.xz *= _FresnelScale;		
		half refl2Refr = Fresnel(viewVector, worldNormal, FRESNEL_BIAS, FRESNEL_POWER);
		
		half4 baseColor = _BaseColor;

//先混合整体的环境纹理和反射颜色，然后再混合基础颜色。
		#ifdef WATER_REFLECTIVE	
			baseColor = lerp (baseColor, lerp (rtReflections,_ReflectionColor,_ReflectionColor.a), saturate(refl2Refr * 2.0));
		#else
			baseColor = lerp (baseColor, _ReflectionColor, saturate(refl2Refr * 2.0));		
		#endif
		
		baseColor = baseColor + spec * _SpecularColor;
		
//计算最后改点的alpha值，与反射率和边缘程度相关。
		baseColor.a = edgeBlendFactors.x * saturate(0.5 + refl2Refr * 1.0);
		return baseColor;
	}