Unity Shader学习：SSR屏幕空间反射

本文在前向渲染模式下实现，延迟渲染更适合SSR，这里只简单的实现下，未作更深入的优化。

思路:沿视线和法线的反射向量步进光线，判断打到物体(这里用的是深度比较)，采样这个点物体的颜色作为反射的颜色，使用dither进行了优化和模糊。

原文:https://blog.csdn.net/puppet_master/article/details/80808486

c#部分:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;public class SSR : MonoBehaviour {public Material mat;private Camera cam;[Range(0,1000f)]public float maxRayMarchingDistance = 500f;[Range(0,256)]public int maxRayMarchingStep = 64;[Range(0,2f)]public float rayMarchingStepSize = 0.05f;[Range(0,2f)]public float depthThickness = 0.01f;[Range(0,3)]public int downSample = 1;[Range(0f,3f)]public int samplerScale = 1;private void OnEnable(){cam.depthTextureMode = DepthTextureMode.DepthNormals;}private void Awake (){cam = GetComponent<Camera>();}private void Start(){mat.SetTexture("_DitherMap", GenerateDitherMap());}private void OnRenderImage(RenderTexture source, RenderTexture destination){if (mat){int width = source.width >> downSample;int height = source.height >> downSample;mat.SetFloat("_MaxRayMarchingDistance", maxRayMarchingDistance);mat.SetInt("_MaxRayMarchingStep", maxRayMarchingStep);mat.SetFloat("_RayMarchingStepSize", rayMarchingStepSize);mat.SetFloat("_DepthThickness", depthThickness);//得到光线追踪的反射图RenderTexture reflectRT = RenderTexture.GetTemporary(width, height, 0, source.format);RenderTexture tempBlurRT = RenderTexture.GetTemporary(width, height, 0, source.format);Graphics.Blit(source, reflectRT, mat, 0);//对反射图高斯模糊mat.SetVector("_Offsets", new Vector4(0, samplerScale, 0, 0));Graphics.Blit(reflectRT, tempBlurRT, mat, 1);mat.SetVector("_Offsets", new Vector4(samplerScale, 0, 0, 0));Graphics.Blit(tempBlurRT, reflectRT, mat, 1);//合并mat.SetTexture("_ReflectTex", reflectRT);            Graphics.Blit(source, destination, mat, 2);RenderTexture.ReleaseTemporary(reflectRT);RenderTexture.ReleaseTemporary(tempBlurRT);}}//游骑兵工作室的DitherMapprivate Texture2D GenerateDitherMap(){int texSize = 4;Texture2D ditherMap = new Texture2D(texSize, texSize, TextureFormat.Alpha8, false, true);ditherMap.filterMode = FilterMode.Point;Color32[] colors = new Color32[texSize * texSize];colors[0] = GetDitherColor(0.0f);colors[1] = GetDitherColor(8.0f);colors[2] = GetDitherColor(2.0f);colors[3] = GetDitherColor(10.0f);colors[4] = GetDitherColor(12.0f);colors[5] = GetDitherColor(4.0f);colors[6] = GetDitherColor(14.0f);colors[7] = GetDitherColor(6.0f);colors[8] = GetDitherColor(3.0f);colors[9] = GetDitherColor(11.0f);colors[10] = GetDitherColor(1.0f);colors[11] = GetDitherColor(9.0f);colors[12] = GetDitherColor(15.0f);colors[13] = GetDitherColor(7.0f);colors[14] = GetDitherColor(13.0f);colors[15] = GetDitherColor(5.0f);ditherMap.SetPixels32(colors);ditherMap.Apply();return ditherMap;}private Color32 GetDitherColor(float value){byte byteValue = (byte)(value / 16.0f * 255);return new Color32(byteValue, byteValue, byteValue, byteValue);}
}

shader部分:

Shader "Unlit/SSR"
{Properties{_MainTex ("Texture", 2D) = "white" {}}SubShader{//1.reflectPass{ZTest OffZWrite OffCull OffCGPROGRAM#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;float3 viewRay:TEXCOORD1;};sampler2D _MainTex;float4 _MainTex_ST;sampler2D _DitherMap;float _MaxRayMarchingDistance;float _MaxRayMarchingStep;float _RayMarchingStepSize;float _DepthThickness;sampler2D _CameraDepthNormalsTexture;bool checkDepthCollision(float3 viewPos,out float2 screenPos) {float4 clipPos = mul(unity_CameraProjection, float4(viewPos, 1.0));clipPos = clipPos / clipPos.w;screenPos = float2(clipPos.x*0.5 + 0.5, clipPos.y*0.5 + 0.5);float4 depthNormalTex = tex2Dlod(_CameraDepthNormalsTexture, float4(screenPos,0,0));//解码深度图,得到视空间深度float depth = DecodeFloatRG(depthNormalTex.zw)*_ProjectionParams.z+0.2;//防止远近裁面的闪动，原因暂时未知//判断当前反射点是否在屏幕外或超过了当前深度值//只取距离视空间深度附近的采样点,防止采样到背面在屏幕上没颜色的点return screenPos.x > 0.0 && screenPos.y > 0.0 && screenPos.x < 1.0 && screenPos.y < 1.0 && -viewPos.z >=depth&&depth+_DepthThickness>=-viewPos.z ;}bool viewSpaceRayMarching(float3 rayOri, float3 rayDir, out float2 hitScreenPos,float2 ditherUV) {//dither扰动采样点float2 offsetUV = fmod(floor(ditherUV), 4.0);float ditherValue = tex2D(_DitherMap, offsetUV*0.25).a;rayOri += ditherValue * rayDir;int maxStep = _MaxRayMarchingStep;hitScreenPos = float2(0, 0);UNITY_LOOPfor (int i = 0; i < maxStep; i++){float3 currentPos = rayOri + rayDir * _RayMarchingStepSize*i;if (_RayMarchingStepSize*i >_MaxRayMarchingDistance){return false;}//反射前进点超出深度，表示打到了物体if (checkDepthCollision(currentPos, hitScreenPos)) {        return true;}}return false;}v2f vert (appdata v){v2f o;o.vertex = UnityObjectToClipPos(v.vertex);o.uv = TRANSFORM_TEX(v.uv, _MainTex);float4 clipPos = float4(v.uv * 2 - 1.0, 1.0, 1.0);float4 viewRay = mul(unity_CameraInvProjection, clipPos);o.viewRay = viewRay.xyz / viewRay.w;return o;}fixed4 frag (v2f i) : SV_Target{float linear01Depth;float3 viewNormal;float4 cdn = tex2D(_CameraDepthNormalsTexture, i.uv);DecodeDepthNormal(cdn, linear01Depth, viewNormal);float3 viewPos = linear01Depth * i.viewRay;float3 viewDir = normalize(viewPos);viewNormal = normalize(viewNormal);float3 reflectDir = reflect(viewDir, viewNormal);float2 hitScreenPos = float2(0, 0);float4 reflectTex = float4(0, 0, 0, 0);if (viewSpaceRayMarching(viewPos,reflectDir,hitScreenPos,i.vertex.xy)){reflectTex = tex2D(_MainTex, hitScreenPos);}return float4(reflectTex);}ENDCG}//2.blurPass{ZTest OffZWrite OffCull OffCGPROGRAM#pragma vertex vert#pragma fragment frag#include "UnityCG.cginc"struct appdata{float4 vertex : POSITION;float2 uv : TEXCOORD0;};struct v2f{float4 vertex : SV_POSITION;float2 uv : TEXCOORD0;float4 uv01 : TEXCOORD1;float4 uv23 : TEXCOORD2;float4 uv45 : TEXCOORD3;};sampler2D _MainTex;float4 _MainTex_TexelSize;float4 _Offsets;v2f vert(appdata v) {v2f o;_Offsets *= _MainTex_TexelSize.xyxy;o.vertex = UnityObjectToClipPos(v.vertex);o.uv = v.uv;o.uv01 = v.uv.xyxy + _Offsets.xyxy*float4(1, 1, -1, -1);o.uv23 = v.uv.xyxy + _Offsets.xyxy*float4(1, 1, -1, -1)*2.0;o.uv45 = v.uv.xyxy + _Offsets.xyxy*float4(1, 1, -1, -1)*3.0;return o;}float4 frag(v2f i) :SV_Target{float4 color = float4(0,0,0,0);color += 0.40*tex2D(_MainTex, i.uv);color += 0.15*tex2D(_MainTex, i.uv01.xy);color += 0.15*tex2D(_MainTex, i.uv01.zw);color += 0.10*tex2D(_MainTex, i.uv23.xy);color += 0.10*tex2D(_MainTex, i.uv23.zw);color += 0.05*tex2D(_MainTex, i.uv45.xy);color += 0.05*tex2D(_MainTex, i.uv45.zw);return color;}ENDCG}//3.combinePass{ZTest OffZWrite OffCull OffCGPROGRAM#pragma vertex vert#pragma fragment frag#include "UnityCG.cginc"struct appdata{float4 vertex : POSITION;float2 uv : TEXCOORD0;};struct v2f{float4 vertex : SV_POSITION;float2 uv : TEXCOORD0;};sampler2D _MainTex;sampler2D _ReflectTex;v2f vert(appdata v) {v2f o;o.vertex = UnityObjectToClipPos(v.vertex);o.uv = v.uv;return o;}float4 frag(v2f i) :SV_Target{float4 ori = tex2D(_MainTex,i.uv);float4 reflect = tex2D(_ReflectTex, i.uv);return ori+reflect;}ENDCG}}
}

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