体积光渲染——SRP实现
参考网址：
https://zhuanlan.zhihu.com/p/124297905
https://zhuanlan.zhihu.com/p/21425792?refer=c_37032701
效果图：
原git中有两个错误，需要修改，很是费解！！！
LightVolumePass.cs
void RenderLightVolume(ScriptableRenderContext context, RenderingData renderingData)
{
……
switch (light.lightType)
{
case LightType.Point:
case LightType.Spot:
cmd.DrawMesh(volumeData.Volume.VolumeMesh, volumeData.Volume.transform.localToWorldMatrix, volumeMat, 0, PassVolumeScattering);
break;
case LightType.Directional:
cmd.BlitFullScreen(BuiltinRenderTextureType.None, rt, volumeMat, PassFullScreenVolumeScattering);
break;
}
cmd.Blit(rt, renderingData.ColorTarget, volumeMat, PassVolumeResolve);
cmd设置绘制目的地：
cmd.GetTemporaryRT(rt, renderSize.x, renderSize.y, 0, FilterMode.Point, RenderTextureFormat.Default);
cmd.SetRenderTarget(rt, rt);
cmd.ClearRenderTarget(false, true, Color.black);
绘制完之后再：cmd.Blit(rt, renderingData.ColorTarget, volumeMat, PassVolumeResolve);
体积光核心shader部分：
float4 volumeLight(v2f_default i) : SV_TARGET
{
i.screenPos /= i.screenPos.w;
float3 ray = normalize(i.worldPos - _WorldCameraPos);
float cameraDepth = tex2D(_CameraDepthTex, i.screenPos.xy).r;
float near, far, depth;
depth = getBoundary(ray, near, far);
// Perform z culling with camera depth buffer
float3 nearWorldPos = _WorldCameraPos + ray * near;
float4 p = UnityWorldToClipPos(nearWorldPos);
p /= p.w;
//clip(p.z - cameraDepth);
// Limit far distance with camera depth buffer
float cameraWorldDepth = depthToWorldDistance(i.screenPos.xy, cameraDepth);
far = min(far, cameraWorldDepth);
near = max(_RangeLimit.x, near);
far = min(_RangeLimit.y, far);
// Jitter sample
float offset = sampleOffset(i.screenPos.xy) * (far - near) / _Steps;
far += offset;
near +=offset;
// Volumetric ray-marching
float3 transmittance = 1;
float3 color = 0;
color = scattering(ray, near, far, transmittance);
return float4(color, 1);
}
getBoundary函数：
float getBoundary(float3 ray, out float near, out float far)
{
float maxNear = _ProjectionParams.y;
float minFar = _ProjectionParams.z;
bool intersected = false;
for(int i = 0; i < _BoundaryPlaneCount; i++)
{
float t = intersectPlane(_BoundaryPlanes[i], _WorldCameraPos, ray, intersected);
if(intersected && dot(ray, _BoundaryPlanes[i].xyz) < 0) // frontface
maxNear = max(maxNear, t);
else if(intersected)
minFar = min(minFar, t);
}
near = maxNear;
far = minFar;
return minFar - maxNear;
}
这个函数求解，是当前射线方向上，近平面和远平面，已经far-near的深度。
如图所示：
float cameraWorldDepth = depthToWorldDistance(i.screenPos.xy, cameraDepth);
far = min(far, cameraWorldDepth);
near = max(_RangeLimit.x, near);
far = min(_RangeLimit.y, far);
经过这段代码：
far前移至自己的顶点位置。
只要步进这6个点，然后计算每个步进点的颜色值，累加，即得到黑色点的颜色值。
其中near到绿色的far，直接的距离就是体积光的效果。
float3 scattering(float3 ray, float near, float far, out float3 transmittance) // Alpha is total transmittance
{
transmittance = 1;
float3 totalLight = 0;
float stepSize = (far - near) / _Steps;
[loop]
for(int i = 1; i <= _Steps; i++) //这个for就是步进的代码体现
{
float3 pos = _WorldCameraPos + ray * (near + stepSize * i);
transmittance *= exp(-stepSize * extinctionAt(pos));
float3 lightDir;
totalLight += transmittance * lightAt(pos, lightDir) * stepSize * phaseHG(lightDir, -ray);
}
return totalLight;
}
某个步进点的颜色值：
float3 lightAt(float3 pos, out float3 lightDir)
{
lightDir = normalize(_LightPosition.xyz - pos * _LightPosition.w);
float lightDistance = lerp(_LightDistance, distance(_LightPosition.xyz, pos), _LightPosition.w);
float3 transmittance = lerp(1, exp(-lightDistance * _TransmittanceExtinction), _IncomingLoss);
float3 inScatter = _TransmittanceExtinction * (1 - _AbsorptionRatio);
float3 lightColor = _LightColor.rgb;
lightColor *= step(_LightCosHalfAngle, dot(lightDir, _LightDirection));
lightColor *= shadowAt(pos);
lightColor *= inScatter;
lightColor *= transmittance;
return lightColor;
}
聚光灯的网格：
视椎体的平面方程：
List<Vector4> planes = new List<Vector4>(6);
public List<Vector4> GetVolumeBoundFaces(Camera camera)
{
planes.Clear();
Matrix4x4 viewProjection = Matrix4x4.identity;
if(light.type == LightType.Spot)
{
viewProjection = Matrix4x4.Perspective(light.spotAngle, 1, 0.03f, light.range) * Matrix4x4.Scale(new Vector3(1, 1, -1)) * light.transform.worldToLocalMatrix;
var m0 = viewProjection.GetRow(0);
var m1 = viewProjection.GetRow(1);
var m2 = viewProjection.GetRow(2);
var m3 = viewProjection.GetRow(3);
planes.Add( -(m3 + m0));
planes.Add( -(m3 - m0));
planes.Add( -(m3 + m1));
planes.Add( -(m3 - m1));
// planes.Add( -(m3 + m2)); // ignore near
planes.Add( -(m3 - m2));
}
else if(light.type == LightType.Directional)
{
viewProjection = camera.projectionMatrix * camera.worldToCameraMatrix;
var m2 = viewProjection.GetRow(2);
var m3 = viewProjection.GetRow(3);
planes.Add(-(m3 + m2)); // near plane only
}
return planes;
}
射线和平面相交的判断：
https://blog.csdn.net/a435262767/article/details/104700156
float intersectPlane(float4 plane, float3 origin, float3 dir, out bool intersect)
{
// t = -(O . P) / (D . P)
float d = dot(dir, plane.xyz);
intersect = d != 0;
return -dot(float4(origin.xyz, 1), plane) / d;
}
总的shader：
Shader "SarRP/LightVolume/Raymarching" {
Properties {
[HideInInspector] _MainTex ("MainTex", 2D) = "white" {
}
_ExtinctionTex ("Extinction", 3D) = "white" {
}
_AbsorptionRatio ("Absorption Ratio", Range(0, 1)) = 0.5
_UVScale ("UV Scale", Vector) = (1, 1, 1, 1)
//[HDR] _TransmittanceExtinction ("Extinction Scale", Color) = (1, 1, 1, 1)
// _IncomingLoss ("Light Attenuation", Range(0, 1)) = 1
//_Steps ("Steps", Int) = 64
_Seed ("Seed", Float) = 1
_HGFactor ("HG Phase Factor", Range(-1, 1)) = 0
//_SampleNoise ("Sample Noise", 2D) = "black" {}
}
HLSLINCLUDE
#include "../Lib.hlsl"
#include "../Light.hlsl"
#include "../Noise.hlsl"
#include "../Shadow/ShadowLib.hlsl"
float intersectPlane(float4 plane, float3 origin, float3 dir, out bool intersect)
{
// t = -(O . P) / (D . P)
float d = dot(dir, plane.xyz);
intersect = d != 0;
return -dot(float4(origin.xyz, 1), plane) / d;
}
uint _VolumeIndex;
RWTexture2DArray<half2> _RWVolumeDepthTexture;
Texture2DArray<half2> _VolumeDepthTexture;
sampler3D _ExtinctionTex;
float4x4 _LightProjectionMatrix;
float3 _UVScale;
int _Steps;
float2 _RangeLimit;
float3 _TransmittanceExtinction;
float _IncomingLoss;
float _LightDistance;
float4 _BoundaryPlanes[16];
int _BoundaryPlaneCount;
float _Seed;
float4 _FrameSize;
float _HGFactor;
float _AbsorptionRatio;
sampler2D _SampleNoise;
float4 _SampleNoise_TexelSize;
sampler2D _CameraDepthTex;
float4 volumeDepth(v2f_default i, fixed facing : VFACE) : SV_TARGET
{
uint3 coord = uint3(_ScreenParams.xy * i.pos.xy, _VolumeIndex);
half2 depth = _RWVolumeDepthTexture[coord].rg;
if(facing > 0)
depth.r = distance(i.worldPos, _WorldCameraPos);
else
depth.g = distance(i.worldPos, _WorldCameraPos);
_RWVolumeDepthTexture[coord] = depth;
return float4(depth.rg, 0, 0);
}
float phaseHG(float3 lightDir, float3 viewDir)
{
float g = _HGFactor;
return (1 - g * g) / (4 * PI * pow(1 + g * g - 2 * g * dot(viewDir, lightDir), 1.5));
}
float3 sampleExtinctionTex(float3 pos)
{
float3 noise = tex3D(_ExtinctionTex, pos * _UVScale).rgb;
noise *= .5;
noise += .5;
return noise;
}
float3 extinctionAt(float3 pos)
{
return 1 * _TransmittanceExtinction;
}
float3 lightAt(float3 pos, out float3 lightDir)
{
lightDir = normalize(_LightPosition.xyz - pos * _LightPosition.w);
float lightDistance = lerp(_LightDistance, distance(_LightPosition.xyz, pos), _LightPosition.w);
float3 transmittance = lerp(1, exp(-lightDistance * _TransmittanceExtinction), _IncomingLoss);
float3 inScatter = _TransmittanceExtinction * (1 - _AbsorptionRatio);
float3 lightColor = _LightColor.rgb;
lightColor *= step(_LightCosHalfAngle, dot(lightDir, _LightDirection));
lightColor *= shadowAt(pos);
lightColor *= inScatter;
lightColor *= transmittance;
return lightColor;
}
float3 scattering(float3 ray, float near, float far, out float3 transmittance) // Alpha is total transmittance
{
transmittance = 1;
float3 totalLight = 0;
float stepSize = (far - near) / _Steps;
[loop]
for(int i = 1; i <= _Steps; i++)
{
float3 pos = _WorldCameraPos + ray * (near + stepSize * i);
transmittance *= exp(-stepSize * extinctionAt(pos));
//transmittance = exp(-far * extinctionAt(pos));
/*if(transmittance.x < 0.01 && transmittance.y < 0.01 && transmittance.z < 0.01)
break;*/
float3 lightDir;
totalLight += transmittance * lightAt(pos, lightDir) * stepSize * phaseHG(lightDir, -ray);
//totalLight = transmittance;
}
return totalLight;
}
float getBoundary(float3 ray, out float near, out float far)
{
float maxNear = _ProjectionParams.y;
float minFar = _ProjectionParams.z;
bool intersected = false;
for(int i = 0; i < _BoundaryPlaneCount; i++)
{
float t = intersectPlane(_BoundaryPlanes[i], _WorldCameraPos, ray, intersected);
if(intersected && dot(ray, _BoundaryPlanes[i].xyz) < 0) // frontface
maxNear = max(maxNear, t);
else if(intersected)
minFar = min(minFar, t);
}
near = maxNear;
far = minFar;
return minFar - maxNear;
}
float sampleOffset(float2 screenPos)
{
//return 0;
// return gold_noise(screenPos, _Seed);
return tex2D(_SampleNoise, screenPos * _FrameSize.xy * _SampleNoise_TexelSize.xy) * 2 - 1;
}
float4 volumeLight(v2f_default i) : SV_TARGET
{
i.screenPos /= i.screenPos.w;
float3 ray = normalize(i.worldPos - _WorldCameraPos);
float cameraDepth = tex2D(_CameraDepthTex, i.screenPos.xy).r;
float near, far, depth;
depth = getBoundary(ray, near, far);
// Perform z culling with camera depth buffer
float3 nearWorldPos = _WorldCameraPos + ray * near;
float4 p = UnityWorldToClipPos(nearWorldPos);
p /= p.w;
//clip(p.z - cameraDepth);
// Limit far distance with camera depth buffer
float cameraWorldDepth = depthToWorldDistance(i.screenPos.xy, cameraDepth);
far = min(far, cameraWorldDepth);
near = max(_RangeLimit.x, near);
far = min(_RangeLimit.y, far);
// Jitter sample
float offset = sampleOffset(i.screenPos.xy) * (far - near) / _Steps;
far += offset;
near +=offset;
// Volumetric ray-marching
float3 transmittance = 1;
float3 color = 0;
color = scattering(ray, near, far, transmittance);
return float4(color, 1);
}
float _GlobalFogExtinction;
float4 globalFog(v2f_ray i) : SV_TARGET
{
float3 ray = normalize(i.ray);
float depth = tex2D(_CameraDepthTex, i.uv).r;
float3 worldPos = _WorldCameraPos + LinearEyeDepth(depth) * i.ray;
float z = distance(_WorldCameraPos, worldPos);
float transmittance = exp(-_GlobalFogExtinction * z);
float3 color = _AmbientLight * (1 - transmittance);
return float4(color.rgb, 1 - transmittance);
}
sampler2D _MainTex;
float4 _MainTex_TexelSize;
float randf(float2 pos, float seed)
{
return gold_noise(pos, seed) *.5 + .5;
}
float4 mixScreen(v2f_default i) : SV_TARGET
{
float4 col = 0;
float R = 4;
for(int j = 0; j < 4; j++)
{
float dist = j * R;
dist += randf(i.uv.xy, _Seed + j);
dist = sqrt(dist);
float2 rot;
float ang = randf(i.uv.xy, _Seed + j) * 2 * PI;
sincos(ang, rot.x, rot.y);
float2 offset = rot * dist * _MainTex_TexelSize.xy;
col += tex2D(_MainTex, i.uv.xy + offset).rgba;
}
//return tex2D(_MainTex, i.uv.xy);
return col / 4;
}
ENDHLSL
SubShader {
// #0 Distance between front & backface
Pass {
Name "Light Volume Raymarching"
ZTest Off
ZWrite Off
Cull Off
Blend One Zero
HLSLPROGRAM
#pragma vertex vert_default
#pragma fragment volumeDepth
#pragma target 5.0
ENDHLSL
}
// #1 Volumetric scattering
Pass {
Name "Light Volume Scattering"
ZTest Less
ZWrite Off
Cull Front
Blend One One
HLSLPROGRAM
#pragma vertex vert_default
#pragma fragment volumeLight
#pragma target 5.0
//#pragma enable_d3d11_debug_symbols
ENDHLSL
}
// #2 Full-screen volumetric scattering
Pass {
Name "Full-screne Light Volume Scattering"
ZTest Less
ZWrite Off
Cull Off
Blend One One
HLSLPROGRAM
#pragma vertex vert_blit_default
#pragma fragment volumeLight
#pragma target 5.0
//#pragma enable_d3d11_debug_symbols
ENDHLSL
}
// #3 Blit to Screen Buffer
Pass {
Name "Light Volume Scattering"
ZTest Off
ZWrite On
Cull Back
Blend One One
HLSLPROGRAM
#pragma vertex vert_default
#pragma fragment mixScreen
#pragma target 5.0
//#pragma enable_d3d11_debug_symbols
ENDHLSL
}
// #4 Global Fog
Pass {
Name "Global Fog"
ZTest Off
ZWrite On
Cull Off
Blend One OneMinusSrcAlpha
HLSLPROGRAM
#pragma vertex vert_ray
#pragma fragment globalFog
#pragma target 5.0
//#pragma enable_d3d11_debug_symbols
ENDHLSL
}
}
}