前言

笔者曾使用UE实现过一个较为完整的写实水材质系统，但是因为UE的管线是定死的，导致高光无法实现，且后来做笔试题发现关于水的交互还未实现，因此本文将实现一个完整的风格化水，考虑到水的实现部分过多，这里不再使用代码展示，而是使用ASE，原理都差不多

管线设置

“Shader Type” 为 “Universal/Unlit”
“Surface” 为 “Transparent”
“Vertex Position” 为 “Relative”

深度

水深不必多讲，在UE的water shader中曾实现过，就是用scene depth - pixel depth
实现如下
这里需要根据相机的深度图重建世界坐标，请注意该方法会忽略半透明物体

颜色

有了深度就可以用深度来实现水的颜色了，这里会实现浅水、深水、海岸线、水底的颜色

浅水、深水

思路：根据深度对浅水颜色和深水颜色进行lerp
实现

HSV颜色空间

因为人眼对灰颜色更加敏感，所以对RGB的lerp是不对的，而HSV空间可以解决这个问题

实现

RGB转HSV

half3 RGBToHSV(half3 In)
{
    half4 K = half4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
    half4 P = lerp(half4(In.bg, K.wz), half4(In.gb, K.xy), step(In.b, In.g));
    half4 Q = lerp(half4(P.xyw, In.r), half4(In.r, P.yzx), step(P.x, In.r));
    half D = Q.x - min(Q.w, Q.y);
    half E = 1e-10;
    
    return half3(abs(Q.z + (Q.w - Q.y)/(6.0 * D + E)), D / (Q.x + E), Q.x);
}

HSV转RGB

half3 HSVToRGB(half3 In)
{
    half4 K = half4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
    half3 P = abs(frac(In.xxx + K.xyz) * 6.0 - K.www);
    return In.z * lerp(K.xxx, saturate(P - K.xxx), In.y);
}

在HSV空间进行lerp

half4 HSVLerp(half4 A, half4 B, half T)
{
    half4 Out = 0.f;
    A.xyz = RGBToHSV(A.xyz);
    B.xyz = RGBToHSV(B.xyz);

    half t = T; // used to lerp alpha, needs to remain unchanged

    half hue;
    half d = B.x - A.x; // hue difference

    if(A.x > B.x)
    {
        half temp = B.x;
        B.x = A.x;
        A.x = temp;

        d = -d;
        T = 1-T;
    }

    if(d > 0.5)
    {
        A.x = A.x + 1;
        hue = (A.x + T * (B.x - A.x)) % 1;
    }

    if(d <= 0.5) hue = A.x + T * d;

    half sat = A.y + T * (B.y - A.y);
    half val = A.z + T * (B.z - A.z);
    half alpha = A.w + t * (B.w - A.w);

    half3 rgb = HSVToRGB(half3(hue,sat,val));

    Out = half4(rgb, alpha);

    return Out;
}

海岸线

海岸线是因为fresnel效应，导致水平看向水面的颜色肯定是不同的
实现
使用Fresnel即可
效果

不透明度

思路：根据深度控制opacity
实现

表面涟漪

思路：使用normal map来模拟凹凸感，为了防止涟漪看着太假，可以使用两张normal map最后进行blend即可
实现

高光

思路：Blinn-Phong
实现

Light Hardness用于控制高光的软硬程度，step计算结果是最硬的高光
效果

折射

思路：基于normalized screen space(uv : 0 - 1)进行扰动
实现
效果

反射

因为平面反射使用一个摄像机从镜像角度渲染场景到RenderTexture上，再将结果合并至反射平面，开销不小，适用于PC端，这种方式实现的反射效果十分准确，但缺点是需要重新渲染一次场景，想想如果有多个镜面，那开销着实受不了，所以笔者选择使用对移动端友好的屏幕空间平面反射(ssrp)，原理是在屏幕空间中计算镜面反射，开销很低，但效果不是很准确，只能反射屏幕中的像素，容易露馅。对于水面来说，ssrp足以

实现

因为ssrp基于屏幕空间，可以将其看作一种后处理技术，Volume代码如下

using UnityEngine;
using UnityEngine.Rendering;

namespace UnityEditor.Rendering.Universal
{
    [SerializeField]
    public class SSPRVolume : VolumeComponent
    {
        [Tooltip("是否启用SSPR")]
        public BoolParameter m_Enable = new BoolParameter(false);
        
        [Tooltip("是否启用HDR")] 
        public BoolParameter m_EnableHDR = new BoolParameter(false);
        
        [Tooltip("反射平面分辨率")]
        public ClampedIntParameter m_RTSize = new ClampedIntParameter(512, 128, 1024, false);
        
        [Tooltip("反射平面深度")]
        public FloatParameter m_ReflectPlaneHeight = new FloatParameter(0.5f, false);
        
        [Tooltip("根据距离对屏幕边缘进行平滑")]
        public ClampedFloatParameter m_FadeOutEdge = new ClampedFloatParameter(0.5f, 0f, 1f, false);

        [Tooltip("控制分辨率")] 
        public ClampedIntParameter m_Downsample = new ClampedIntParameter(1, 1, 5);

        [Tooltip("模糊算法循环次数，越高效果越好")]
        public ClampedIntParameter m_PassLoop = new ClampedIntParameter(1, 1, 5);

        [Tooltip("模糊强度")] 
        public ClampedFloatParameter m_BlurIntensity = new ClampedFloatParameter(1, 0, 10);
        
        public bool IsActive() => m_Enable.value;
        public bool IsTileCompatible() => false;
    }
}

compute shader

参数

#define THREADCOUNTX 8
#define THREADCOUNTY 8
#define THREADCOUNTZ 1

RWTexture2D<half4> _ResultRT;  // 反射后的RT
RWTexture2D<half> _ResultDepthRT;  // 反射后的depth
Texture2D<float4> _ScreenColorTex;    // scene color
Texture2D<float4> _ScreenDepthTex;   // scene depth

float2 _RTSize; // 反射后的RT分辨率
float _ReflectPlaneHeight;  //  反射平面高度(基于screen space uv)
float _FadeOutEdge; // 屏幕边缘的衰减程度
float _BlurIntensity;   // DualBlur 模糊强度

SamplerState PointClampSampler;    // 点采样
SamplerState LinearClampSampler;   // 线性采样

初始化

将RT和Depth清0

[numthreads(THREADCOUNTX, THREADCOUNTY, THREADCOUNTZ)]
void ClearRT(uint3 id : SV_DispatchThreadID)
{
    _ResultRT[id.xy] = half4(0.f, 0.f, 0.f, 0.f);
    _ResultDepthRT[id.xy] = half4(0.f, 0.f, 0.f, 0.f);
}

SSRP计算

重建世界坐标

[numthreads(THREADCOUNTX, THREADCOUNTY, THREADCOUNTZ)]
void CSMain (uint3 id : SV_DispatchThreadID)
{
    float2 uvSS = id.xy / _RTSize;  // [0,RTSize-1] -> screen [0,1] uv
    
    float posNDCZ = _ScreenDepthTex.SampleLevel(PointClampSampler, uvSS, 0.f).r;    // raw depth

    float3 absoluteWolrdPos = ComputeWorldSpacePosition(uvSS, posNDCZ, UNITY_MATRIX_I_VP);  // 求得重建后的世界坐标
}

重建反射后的世界坐标

if(absoluteWolrdPos.y < _ReflectPlaneHeight) return;    // 丢弃位于平面下方的像素
float3 reflectPosWS = absoluteWolrdPos;
reflectPosWS.y = -(reflectPosWS.y - _ReflectPlaneHeight) + _ReflectPlaneHeight; // 先将坐标减去_ReflectPlaneHeight，使其基于y = 0进行翻转(取负)

构建并测试屏幕空间uv

// 因为重建后的屏幕空间uv可以超出屏幕范围，需要进行测试
float4 reflectPosCS = mul(UNITY_MATRIX_VP, float4(reflectPosWS, 1.f));   // posWS -> posCS
float2 reflectPosNDCxy = reflectPosCS.xy / reflectPosCS.w;  // posCS -> posNDC
if(abs(reflectPosNDCxy.x) > 1.f || abs(reflectPosNDCxy.y) > 1.f) return; // uv范围在[0,1]
float2 reflectPosSSxy = reflectPosNDCxy * 0.5 + 0.5;	// ndc->ss

// dx平台uv坐标起点在上方
#if defined UNITY_UV_STARTS_AT_TOP
    reflectPosSSxy.y = 1 - reflectPosSSxy.y;
#endif

uint2 reflectSSUVID = reflectPosSSxy * _RTSize;  // 根据正确的屏幕uv计算得到新的thread id

输出
```
_ResultRT[reflectSSUVID] = float4(_ScreenColorTex.SampleLevel(LinearClampSampler, uvSS, 0).rgb, 1);
```
可以看到这存在一定的遮挡问题（物体的反射渲染顺序错误）。如下图所示，造成这一现象的原因是两个不同的像素反射后都位于同一UV

深度顺序矫正

很显然，这里可以用到深度缓冲区，写入深度更小的像素(dx平台因为z值翻转，需要写入深度更大的像素)。这样会导致无法反射sky box，后续需要在PS中合并

#if defined UNITY_REVERSED_Z
if(reflectPosCS.z / reflectPosCS.w <= _ResultDepthRT[reflectSSUVID]) return;
#else
if(rePosCS.z / rePosCS.w >= _ResultDepthRT[reSSUVID]) return;
#endif
    
_ResultDepthRT[reflectSSUVID] = reflectPosCS.z / reflectPosCS.w;

边缘缺失

在某些视角下，若反射所需要的信息在渲染后的RT外，会生成不少空白像素，这里有两种解决办法：拉伸uv和2d sdf

考虑到性能，笔者使用SDF。具体原理是：sdf 作为不透明度

// 计算pixel到屏幕边缘的距离
float SDF(float2 pos)
{
    float2 distance = abs(pos) - float2(1, 1);
    return length(max(0.f, distance) - min(max(distance.x, distance.y), 0.f));
}

float mask = SDF(uvSS * 2.f - 1.f);
mask = smoothstep(0.f, _FadeOutEdge, abs(mask));	// 做一个平滑，避免生硬
_ResultRT[reflectSSUVID] = float4(_ScreenColorTex.SampleLevel(LinearClampSampler, uvSS, 0).rgb, mask);

填充空洞

如下图所示，反射后的平面会存在许多黑点空洞。这是因为计算世界坐标进行了透视投影的计算(近大远小)，导致最后的像素索引进行了偏移(如本该渲染到(1,1)的，却渲染到(1,2))

解决方法有两个：计算像素明度和根据像素的透明度，这里笔者选择透明度

[numthreads(THREADCOUNTX, THREADCOUNTY, THREADCOUNTZ)]
void FillHoles (uint3 id : SV_DispatchThreadID)
{
    ////////////////////////////////
    // 
    ////////////////////////////////
    float4 center = _ResultRT[id.xy];
    float4 top = _ResultRT[id.xy + uint2(0, 1)];
    float4 bottom = _ResultRT[id.xy + uint2(0, -1)];
    float4 right = _ResultRT[id.xy + uint2(1, 0)];
    float4 left = _ResultRT[id.xy + uint2(-1, 0)];
    
    // 查找不是空洞的pixel
    float4 best = center;
    best = top.a > best.a + 0.5 ? top : best;
    best = bottom.a > best.a + 0.5 ? bottom : best;
    best = right.a > best.a + 0.5 ? right : best;
    best = left.a > best.a + 0.5 ? left : best;
    
    // 填充空洞
    _ResultRT[id.xy] = best.a > center.a + 0.5 ? best : center;
    _ResultRT[id.xy + uint2(0, 1)] = best.a > top.a + 0.5 ? best : top;
    _ResultRT[id.xy + uint2(0, -1)] = best.a > bottom.a + 0.5 ? best : bottom;
    _ResultRT[id.xy + uint2(1, 0)] = best.a > right.a + 0.5 ? best : right;
    _ResultRT[id.xy + uint2(-1, 0)] = best.a > left.a + 0.5 ? best : left;
}

闪烁

没有找到好的解决方案，对于水体可以使用折射来遮羞

skybox 截断

目前的实现还存在一个问题：当观察角度过于低时会绘制截断的skybox

解决之道：跳过skybox

void CSMain (uint3 id : SV_DispatchThreadID)
{
    float2 uvSS = id.xy / _RTSize;  // [0,RTSize-1] -> screen [0,1] uv
    float posNDCZ = _ScreenDepthTex.SampleLevel(PointClampSampler, uvSS, 0.f).r;    // raw depth
    if(Linear01Depth(posNDCZ, _ZBufferParams) > 0.99) return; 
}

Render Feature

反射是有一定的模糊效果的，这里使用Dual Blur

using System;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Rendering.Universal;
using UnityEditor.Rendering.Universal;

public class SSPRPassFeature : ScriptableRendererFeature
{
    [System.Serializable]
    public class PassSetting
    {
        [Tooltip("显示于frame debugger")]
        public readonly string m_ProfilerTag = "SSRP Pass";
        
        [Tooltip("Pass执行位置")]
        public RenderPassEvent passEvent = RenderPassEvent.AfterRenderingTransparents;

        [Tooltip("compute shader")]
        public ComputeShader CS = null;

        [Tooltip("Pixel Shader")]
        public Material material = null;
    }
    
    class SSPRRenderPass : ScriptableRenderPass
    {
        // profiler tag will show up in frame debugger
        private const string m_ProfilerTag = "SSPR Pass";

        // 用于存储pass setting
        private PassSetting m_passSetting;
        private SSPRVolume m_SSPRVolume;

        private ComputeShader m_CS;
        private Material m_Material;
        
        // 反射RT的分辨率
        private int RTSizeWidth;
        private int RTSizeHeight;

        struct RTID
        {
            public static RenderTargetIdentifier m_ResultRT;
            public static RenderTargetIdentifier m_ResultDepthRT;
            public static RenderTargetIdentifier m_TempRT;
        }

        struct ShaderID
        {
            public static readonly int RTSizeID = Shader.PropertyToID("_RTSize");
            public static readonly int ReflectPlaneHeightID = Shader.PropertyToID("_ReflectPlaneHeight");
            public static readonly int FadeOutEdgeID = Shader.PropertyToID("_FadeOutEdge");
            public static readonly int ReflectColorRTID = Shader.PropertyToID("_ResultRT");
            public static readonly int ResultDepthRTID = Shader.PropertyToID("_ResultDepthRT");
            public static readonly int SceneColorRTID = Shader.PropertyToID("_ScreenColorTex");
            public static readonly int SceneDepthRTID = Shader.PropertyToID("_ScreenDepthTex");
            
            public static readonly int BlurIntensityID = Shader.PropertyToID("_BlurIntensity");
            public static readonly int TempRTID = Shader.PropertyToID("_TempRT");
        }
        private struct BlurLevelShaderID
        {
            internal int downLevelID;
            internal int upLevelID;
        }
        private BlurLevelShaderID[] blurLevel;
        private static int m_maxBlurLevel = 16;

        struct Dispatch
        {
            // 线程组id
            public static int ThreadGroupCountX;
            public static int ThreadGroupCountY;
            public static int ThreadGroupCountZ;
            // 线程id
            public static int ThreadCountX;
            public static int ThreadCountY;
            public static int ThreadCountZ;
        }

        struct Kernal
        {
            public static int ClearRT;
            public static int CSMain;
            public static int FillHoles;
        }
        
        // 用于设置material 属性
        public SSPRRenderPass(SSPRPassFeature.PassSetting passSetting) 
        {
            this.m_passSetting = passSetting;

            renderPassEvent = m_passSetting.passEvent;

            this.m_CS = m_passSetting.CS;
            this.m_Material = m_passSetting.material;

            Kernal.ClearRT = m_CS.FindKernel("ClearRT");
            Kernal.CSMain = m_CS.FindKernel("CSMain");
            Kernal.FillHoles = m_CS.FindKernel("FillHoles");
        }
        
        public override void OnCameraSetup(CommandBuffer cmd, ref RenderingData renderingData)
        {
            // 获取定义的volume
            var POSTStack = VolumeManager.instance.stack;
            m_SSPRVolume = POSTStack.GetComponent<SSPRVolume>();

            float aspect = (float)Screen.height / Screen.width;	// 屏幕分辨率
            // 线程对应compute shader中的线程数
            Dispatch.ThreadCountX = 8;
            Dispatch.ThreadCountY = 8;
            Dispatch.ThreadCountZ = 1;
            // 使得一个线程对应一个uv
            Dispatch.ThreadGroupCountY = m_SSPRVolume.m_RTSize.value / Dispatch.ThreadCountY;    // RT高度
            Dispatch.ThreadGroupCountX = Mathf.RoundToInt(Dispatch.ThreadGroupCountY / aspect); // RT 宽度
            Dispatch.ThreadGroupCountZ = 1;
            // 反射面的分辨率大小
            this.RTSizeWidth = Dispatch.ThreadGroupCountX * Dispatch.ThreadCountX;
            this.RTSizeHeight = Dispatch.ThreadGroupCountY * Dispatch.ThreadCountY;
            
            // alpha作为mask
            RenderTextureDescriptor descriptor = new RenderTextureDescriptor(this.RTSizeWidth, this.RTSizeHeight, RenderTextureFormat.ARGB32);
            if (m_SSPRVolume.m_EnableHDR.value == true)
            {
                // 每位16字节，支持HDR
                descriptor.colorFormat = RenderTextureFormat.ARGBHalf;
            }
            descriptor.enableRandomWrite = true;    // 用于D3D的UAV(无序视图)
            
            // 申请RT
            cmd.GetTemporaryRT(ShaderID.ReflectColorRTID, descriptor);
            RTID.m_ResultRT = new RenderTargetIdentifier(ShaderID.ReflectColorRTID);
            descriptor.colorFormat = RenderTextureFormat.R16;    // 深度图只有r channel
            cmd.GetTemporaryRT(ShaderID.ResultDepthRTID, descriptor);
            RTID.m_ResultDepthRT = new RenderTargetIdentifier(ShaderID.ResultDepthRTID);

            blurLevel = new BlurLevelShaderID[m_maxBlurLevel];
            for (int t = 0; t < m_maxBlurLevel; ++t)
            {
                blurLevel[t] = new BlurLevelShaderID
                {
                    downLevelID = Shader.PropertyToID("_BlurMipDown" + t),
                    upLevelID = Shader.PropertyToID("_BlurMipU" + t)
                };
            }
        }
        
        public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
        {
            if (m_CS == null)
            {
                Debug.LogError("Custom:SSPR compute shader missing");
            }

            if (m_SSPRVolume.m_Enable.value == true)
            {
                // Grab a command buffer. We put the actual execution of the pass inside of a profiling scope
                CommandBuffer cmd = CommandBufferPool.Get();

                using (new ProfilingScope(cmd, new ProfilingSampler(m_ProfilerTag)))
                {
                    cmd.SetComputeTextureParam(this.m_CS, Kernal.ClearRT, ShaderID.ReflectColorRTID, RTID.m_ResultRT);
                    cmd.SetComputeTextureParam(this.m_CS, Kernal.ClearRT, ShaderID.ResultDepthRTID, RTID.m_ResultDepthRT);
                    cmd.DispatchCompute(this.m_CS, Kernal.ClearRT, Dispatch.ThreadGroupCountX, Dispatch.ThreadGroupCountY, Dispatch.ThreadGroupCountZ);
                    
                    cmd.SetComputeVectorParam(this.m_CS, ShaderID.RTSizeID, new Vector2(this.RTSizeWidth, this.RTSizeHeight));
                    cmd.SetComputeFloatParam(this.m_CS, ShaderID.ReflectPlaneHeightID, m_SSPRVolume.m_ReflectPlaneHeight.value);
                    cmd.SetComputeFloatParam(this.m_CS, ShaderID.FadeOutEdgeID, m_SSPRVolume.m_FadeOutEdge.value);
                    cmd.SetComputeTextureParam(this.m_CS, Kernal.CSMain, ShaderID.ReflectColorRTID, RTID.m_ResultRT);
                    cmd.SetComputeTextureParam(this.m_CS, Kernal.CSMain, ShaderID.ResultDepthRTID, RTID.m_ResultDepthRT);
                    cmd.SetComputeTextureParam(this.m_CS, Kernal.CSMain, ShaderID.SceneColorRTID, new RenderTargetIdentifier("_CameraOpaqueTexture"));
                    cmd.SetComputeTextureParam(this.m_CS, Kernal.CSMain, ShaderID.SceneDepthRTID, new RenderTargetIdentifier("_CameraDepthTexture"));
                    cmd.DispatchCompute(this.m_CS, Kernal.CSMain, Dispatch.ThreadGroupCountX, Dispatch.ThreadGroupCountY, Dispatch.ThreadGroupCountZ);
                    
                    cmd.SetComputeTextureParam(this.m_CS, Kernal.FillHoles, ShaderID.ReflectColorRTID, RTID.m_ResultRT);
                    cmd.DispatchCompute(this.m_CS, Kernal.FillHoles, Dispatch.ThreadGroupCountX, Dispatch.ThreadGroupCountY, Dispatch.ThreadGroupCountZ);
                }

                if (m_Material == null)
                {
                    Debug.LogError("Custom:SSPR shader missing");
                }
                else
                {
                    m_Material.SetFloat(ShaderID.BlurIntensityID, m_SSPRVolume.m_BlurIntensity.value);
                    
                    RenderTextureDescriptor descriptor = new RenderTextureDescriptor(this.RTSizeWidth, this.RTSizeHeight, RenderTextureFormat.Default);
                    descriptor.width /= m_SSPRVolume.m_Downsample.value;
                    descriptor.height /= m_SSPRVolume.m_Downsample.value;
                    //descriptor.depthBufferBits = 0;     // 不会用到深度，精度设为0
                    cmd.GetTemporaryRT(ShaderID.TempRTID, descriptor);
                    RTID.m_TempRT = new RenderTargetIdentifier(ShaderID.TempRTID);
                    
                    Blit(cmd, RTID.m_ResultRT, RTID.m_TempRT);
                    
                    RenderTargetIdentifier lastDown = RTID.m_TempRT;
                    for (uint i = 0; i < m_SSPRVolume.m_PassLoop.value; ++i)
                    {
                        int midDown = blurLevel[i].downLevelID;
                        int midUp = blurLevel[i].upLevelID;
                        cmd.GetTemporaryRT(midDown, descriptor, FilterMode.Bilinear);
                        cmd.GetTemporaryRT(midUp, descriptor, FilterMode.Bilinear);
                        Blit(cmd, lastDown, midDown, m_Material, 1);
                        lastDown = midDown;

                        descriptor.width = Mathf.Max(descriptor.width / 2, 1);
                        descriptor.height = Mathf.Max(descriptor.height / 2, 1);
                    }

                    int lastUp = blurLevel[m_SSPRVolume.m_PassLoop.value - 1].downLevelID;
                    for (int i = m_SSPRVolume.m_PassLoop.value - 2; i >= 0; --i)
                    {
                        int midUp = blurLevel[i].upLevelID;
                        cmd.Blit(lastUp, midUp, m_Material, 2);
                        lastUp = midUp;
                    }
                    
                    cmd.Blit(lastUp, RTID.m_ResultRT, m_Material, 2);
                }
                context.ExecuteCommandBuffer(cmd);
                CommandBufferPool.Release(cmd);
            }
        }
        
        public override void OnCameraCleanup(CommandBuffer cmd)
        {
            if(cmd == null) throw new ArgumentNullException("cmd");
            
            cmd.ReleaseTemporaryRT(ShaderID.ReflectColorRTID);
            cmd.ReleaseTemporaryRT(ShaderID.SceneDepthRTID);
        }
    }

    public PassSetting m_Setting = new PassSetting();
    SSPRRenderPass m_SSPRPass;
    
    public override void Create()
    {
        m_SSPRPass = new SSPRRenderPass(m_Setting);
    }
    
    public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
    {
        // can queue up multiple passes after each other
        renderer.EnqueuePass(m_SSPRPass);
    }
}

Shader

最终效果还是得用material(pixel shader)实现(不过不用置于物体上)

Shader "URP/reflect"
{
    Properties
    {
        [HideInInspector] _MainTex("", 2D) = "white" {}
    }

    SubShader
    {
        Tags
        {
            "RenderPipeline"="UniversalRenderPipeline"
            "Queue"="Overlay"
        }
        Cull Off
        ZWrite Off
        ZTest Always

        HLSLINCLUDE
        #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

        CBUFFER_START(UnityPerMaterial)
        float _BlurIntensity;
        float4 _MainTex_TexelSize;
        CBUFFER_END
        
        TEXTURE2D(_MainTex);            SAMPLER(sampler_MainTex);
        TEXTURE2D(_ResultRT);
        sampler LinearClampSampler;

         struct VSInput
         {
             float4 positionOS : POSITION;
             float4 normalOS : NORMAL;
             float2 uv : TEXCOORD;
         };

         struct PSInput
         {
             float4 positionCS : SV_POSITION;
             float2 uv:TEXCOORD;
             float4 uv01 : TEXCOORD1;
             float4 uv23 : TEXCOORD2;
             float4 uv45 : TEXCOORD3;
             float4 uv67 : TEXCOORD4;
             float4 positionSS : TEXCOORD5;
             float3 positionWS : TEXCOORD6;
             float3 viewDirWS : TEXCOORD7;
             float3 normalWS : NORMAL;
         };
        ENDHLSL


        pass
        {
            NAME "Copy SSRP"
            Tags
            {
                "LightMode"="UniversalForward"
                "RenderType"="Overlay"
            }

            HLSLPROGRAM
            #pragma vertex VS
            #pragma fragment PS
            
            PSInput VS(VSInput vsInput)
            {
                PSInput vsOutput;

                VertexPositionInputs vertexPos = GetVertexPositionInputs(vsInput.positionOS);
                vsOutput.positionWS = vertexPos.positionWS;
                vsOutput.positionCS = vertexPos.positionCS;
                vsOutput.positionSS = ComputeScreenPos(vsOutput.positionCS);

                VertexNormalInputs vertexNormal = GetVertexNormalInputs(vsInput.normalOS);
                vsOutput.normalWS = vertexNormal.normalWS;

                return vsOutput;
            }

            half4 PS(PSInput psInput) : SV_Target
            {
                half2 screenUV = psInput.positionSS.xy / psInput.positionSS.w;
                float4 SSPRResult = SAMPLE_TEXTURE2D(_ResultRT, LinearClampSampler, screenUV);
                SSPRResult.xyz *= SSPRResult.w;
                
                return SSPRResult;
            }
            ENDHLSL
        }

        Pass
        {
            NAME "Down Samp[le"
            
            HLSLPROGRAM
            #pragma vertex VS
            #pragma fragment PS

            PSInput VS(VSInput vsInput)
            {
                PSInput vsOutput;

                vsOutput.positionCS = TransformObjectToHClip(vsInput.positionOS);

                // 在D3D平台下，若开启抗锯齿，_TexelSize.y会变成负值，需要进行oneminus，否则会导致图像上下颠倒
                #ifdef UNITY_UV_STARTS_AT_TOP
                if(_MainTex_TexelSize.y < 0)
                    vsInput.uv.y = 1 - vsInput.uv.y;
                #endif
            
                vsOutput.uv = vsInput.uv;
                vsOutput.uv01.xy = vsInput.uv + float2(1.f, 1.f) * _MainTex_TexelSize.xy * _BlurIntensity;
                vsOutput.uv01.zw = vsInput.uv + float2(-1.f, -1.f) * _MainTex_TexelSize.xy * _BlurIntensity;
                vsOutput.uv23.xy = vsInput.uv + float2(1.f, -1.f) * _MainTex_TexelSize.xy * _BlurIntensity;
                vsOutput.uv23.zw = vsInput.uv + float2(-1.f, 1.f) * _MainTex_TexelSize.xy * _BlurIntensity;

                return vsOutput;
            }

            float4 PS(PSInput psInput) : SV_TARGET
            {
                float4 outputColor = 0.f;

                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv.xy) * 0.5;
                
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv01.xy) * 0.125;
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv01.zw) * 0.125;
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv23.xy) * 0.125;
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv23.zw) * 0.125;

                return outputColor;
            }
            
            ENDHLSL
        }

        Pass
        {
            NAME "Up Sample"
            
            HLSLPROGRAM
            #pragma vertex VS
            #pragma fragment PS
            
            PSInput VS(VSInput vsInput)
            {
                PSInput vsOutput;

                vsOutput.positionCS = TransformObjectToHClip(vsInput.positionOS);

                #ifdef UNITY_UV_STARTS_AT_TOP
                if(_MainTex_TexelSize.y < 0.f)
                    vsInput.uv.y = 1 - vsInput.uv.y;
                #endif

                vsOutput.uv = vsInput.uv;
                // 1/12
                vsOutput.uv01.xy = vsInput.uv + float2(0, 1) * _MainTex_TexelSize.xy * _BlurIntensity;
                vsOutput.uv01.zw = vsInput.uv + float2(0, -1) * _MainTex_TexelSize.xy * _BlurIntensity;
                vsOutput.uv23.xy = vsInput.uv + float2(1, 0) * _MainTex_TexelSize.xy * _BlurIntensity;
                vsOutput.uv23.zw = vsInput.uv + float2(-1, 0) * _MainTex_TexelSize.xy * _BlurIntensity;
                // 1/6
                vsOutput.uv45.xy = vsInput.uv + float2(1, 1) * 0.5 * _MainTex_TexelSize.xy * _BlurIntensity;
                vsOutput.uv45.zw = vsInput.uv + float2(-1, -1) * 0.5 * _MainTex_TexelSize.xy * _BlurIntensity;
                vsOutput.uv67.xy = vsInput.uv + float2(1, -1) * 0.5 * _MainTex_TexelSize.xy * _BlurIntensity;
                vsOutput.uv67.zw = vsInput.uv + float2(-1, 1) * 0.5 * _MainTex_TexelSize.xy * _BlurIntensity;

                return vsOutput;
            }

            float4 PS(PSInput psInput) : SV_TARGET
            {
                float4 outputColor = 0.f;

                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv01.xy) * 1/12;
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv01.zw) * 1/12;
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv23.xy) * 1/12;
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv23.zw) * 1/12;

                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv45.xy) * 1/6;
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv45.zw) * 1/6;
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv67.xy) * 1/6;
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv67.zw) * 1/6;

                return outputColor;
            }
            ENDHLSL
        }
    }
}

焦散

思路：在UE中使用后处理实现过，这里尝试一种新方法，基于xz坐标绘制
实现

panner反向uv模拟焦散的运动
纹理
效果

浪花

参考了很多游戏中的风格化水体效果，发现很少实现波峰浪花的，仅仅实现了近岸浪花，这里偷个懒也只实现近岸浪花叭
实现
FoamMask基于深度实现，使用Foam Cutoff来控制Foam区域
效果

Wave

老朋友了GerstnerWave，考虑到移动端的性能，最多叠加4个波

实现

float3 GerstnerWave(float3 positionWS, float steepness, float wavelength, float speed, float direction, inout float3 tangentWS, inout float3 binormalWS)
{
    direction = direction * 2 - 1;
    float2 d = normalize(float2(cos(3.14 * direction), sin(3.14 * direction)));    
    float k = 2 * 3.14 / wavelength;   // 频率周期
    float f = k * (dot(d, positionWS.xz) - speed * _Time.y);   // sin/cos参数
    float a = steepness / k;   // 振幅(防止打结)

    tangentWS += float3(
    -d.x * d.x * (steepness * sin(f)),
    d.x * (steepness * cos(f)),
    -d.x * d.y * (steepness * sin(f))
    );

    binormalWS += float3(
    -d.x * d.y * (steepness * sin(f)),
    d.y * (steepness * cos(f)),
    -d.y * d.y * (steepness * sin(f))
    );

    return float3(
    d.x * (a * cos(f)),
    a * sin(f),
    d.y * (a * cos(f))
    );
}

float3 GerstnerWave4(float3 positionWS, float3 normalWS, float steepness, float waveLength, float speed, float4 direction)
{
    float3 offset = 0.f;
    float3 tangent = float3(1, 0, 0);
    float3 binormal = float3(0, 0, 1);

    offset += GerstnerWave(positionWS, steepness, waveLength, speed, direction.x, tangent, binormal);
    offset += GerstnerWave(positionWS, steepness, waveLength, speed, direction.y, tangent, binormal);
    offset += GerstnerWave(positionWS, steepness, waveLength, speed, direction.z, tangent, binormal);
    offset += GerstnerWave(positionWS, steepness, waveLength, speed, direction.w, tangent, binormal);

    normalWS = cross(tangent, binormal);
    return offset;
}