【UE5】将2D切片图渲染为体积纹理，最终实现使用RT实时绘制体积纹理【第六篇-阶段总结篇】

因为马上就要进入下一个阶段，制作动态编辑体积纹理的模块。

但在这之前，要在这一章做最后一些整理。

首先，我们完成没完成的部分。
其次，最后整理一下图表。
最后，本文附上正在用的贴图

完善Shader

还记得我们之前注释掉了"阶梯纹理修复"的部分吗？
在这里插入图片描述

在第二章第七节中，我们已经修复了这个阶梯纹理。

CurPos += LocalCamVec * (1 - FinalStepSize);//只留了它

然而，在第三章对Shader进行大幅修改时，我们暂时将其注释掉并未继续处理。现在，我们将重新着手修复这个阶梯纹理问题。

希望你还记得，修复阶梯纹理的原理是将for循环的一步单独再以一个小步FinalStepSize执行一次。
因此，基本上就是将for循环中的内容复制出来，在for之后再运行一次。

//创建变量，从0开始累加沿相机方向步进过程中的总密度
float accumdens = 0;//Shadow部分
//创建变量，透射率和光线的能量
float transmittance =1;
float3 lightenergy = 0;
//基本和相机方向步进一样，但这些都是常量，不需要写进for里
Density *= StepSize;
LightVector *= ShadowStepSize;
ShadowDensity *= ShadowStepSize;
//一个对数来计算阈值，用来判断光线是否还值得计算
float shadowthresh = -log(ShadowThreshold)/ShadowDensity;//使用 MaxSteps 作为最大步数进行循环，每次循环执行以下操作
for (int i = 0; i < MaxSteps; i++)
{float cursample = PseudoVolumeTexture(Tex, TexSampler, saturate(CurPos), XYFrames, NumFrames).r;// 在当前步进位置进行纹理采样//Shadow部分if(cursample > 0.001)//如果采样位置没有密度，则跳过{float3 Lpos = CurPos;//Lpos将作为光线步进的起始位置float shadowdist = 0;//和之前的accumdens一样，积累阴影//自阴影for(int s = 0; s < ShadowSteps; s++){Lpos += LightVector;//移动步进位置float Lsample = PseudoVolumeTexture(Tex, TexSampler, saturate(Lpos), XYFrames, NumFrames).r;//采样//判断是否在框内，不是则直接break退出forfloat3 shadowboxtest = floor( 0.5+ (abs(0.5-Lpos)));//float exitshadowbox = shadowboxtest.x + shadowboxtest.y + shadowboxtest.z;float exitshadowbox = dot(shadowboxtest,1);//简短的通道相加if(shadowdist > shadowthresh || exitshadowbox >= 1) break;shadowdist += Lsample;//累计}//接收阴影float3 dfpos = 2 * (CurPos -0.5) * LocalObjectBoundsMax;//-0.5 * 2，得到一个居中的Bounddfpos = LWCToFloat(TransformLocalPositionToWorld(Parameters,dfpos)) - CameraPosWS;//将dfpos转换为世界空间，需要LWC精度所以在代码里转换，减去相机位置float dftracedist = 1; //创建四个变量float dfshadow = 1;//这是我们最终要的float curdist = 0;float DistanceAlongTrace = 0;for (int d = 0; d < DFSSteps; d++)//又一次的光线步进{DistanceAlongTrace += curdist;//增加距离curdist = GetDistanceToNearestSurfaceGlobal(dfpos);//采样全局距离场，他和蓝图里`DistanceToNearestSurface`是相同函数float SphereSize = DistanceAlongTrace * LightTangent;//采样距离场软阴影的球形距离dfshadow = min( saturate(curdist/SphereSize),dfshadow);//用小于它的结果来更新变量dfpos.xyz += LightVectorWS * dftracedist * curdist;//继续移动位置dftracedist *= 1.0001;//增加一个很小的因子}//更新样本和光能，算法是BeersLaw函数cursample = 1 -exp(-cursample * Density);lightenergy += exp(-shadowdist * ShadowDensity) * cursample * transmittance * LightColor * dfshadow;//在结果上乘dfshadowtransmittance *= 1-cursample;//环境光照部分shadowdist = 0;//重置一下阴影距离，继续利用它计算光照Lpos = CurPos + float3(0,0,0.025);//新位置float Lsample = PseudoVolumeTexture(Tex, TexSampler, saturate(Lpos), XYFrames, NumFrames).r;//采样shadowdist += Lsample;Lpos = CurPos + float3(0,0,0.05);Lsample = PseudoVolumeTexture(Tex, TexSampler, saturate(Lpos), XYFrames, NumFrames).r;//采样shadowdist += Lsample;Lpos = CurPos + float3(0,0,0.15);Lsample = PseudoVolumeTexture(Tex, TexSampler, saturate(Lpos), XYFrames, NumFrames).r;//采样shadowdist += Lsample;lightenergy += exp(-shadowdist * AmbientDensity) *cursample * SkyColor * transmittance;//累计到光}CurPos += -LocalCamVec;
}CurPos += LocalCamVec * (1 - FinalStepSize);
float cursample = PseudoVolumeTexture(Tex, TexSampler, saturate(CurPos), XYFrames, NumFrames).r;//从上面复制过来，使用 FinalStepSize 结果再 Step 一次，进行阶梯修复if(cursample > 0.001){float3 Lpos = CurPos;float shadowdist = 0;for(int s = 0; s < ShadowSteps; s++){Lpos += LightVector;float Lsample = PseudoVolumeTexture(Tex, TexSampler, saturate(Lpos), XYFrames, NumFrames).r;float3 shadowboxtest = floor( 0.5+ (abs(0.5-Lpos)));float exitshadowbox = dot(shadowboxtest,1);if(shadowdist > shadowthresh || exitshadowbox >= 1) break;shadowdist += Lsample;}float3 dfpos = 2 * (CurPos -0.5) * LocalObjectBoundsMax;dfpos = LWCToFloat(TransformLocalPositionToWorld(Parameters,dfpos)) - CameraPosWS;float dftracedist = 1; float dfshadow = 1;float curdist = 0;float DistanceAlongTrace = 0;for (int d = 0; d < DFSSteps; d++){DistanceAlongTrace += curdist;curdist = GetDistanceToNearestSurfaceGlobal(dfpos);float SphereSize = DistanceAlongTrace * LightTangent;dfshadow = min( saturate(curdist/SphereSize),dfshadow);dfpos.xyz += LightVectorWS * dftracedist * curdist;dftracedist *= 1.0001;}cursample = 1 -exp(-cursample * Density);lightenergy += exp(-shadowdist * ShadowDensity) * cursample * transmittance * LightColor * dfshadow;transmittance *= 1-cursample;shadowdist = 0;Lpos = CurPos + float3(0,0,0.025);float Lsample = PseudoVolumeTexture(Tex, TexSampler, saturate(Lpos), XYFrames, NumFrames).r;shadowdist += Lsample;Lpos = CurPos + float3(0,0,0.05);Lsample = PseudoVolumeTexture(Tex, TexSampler, saturate(Lpos), XYFrames, NumFrames).r;shadowdist += Lsample;Lpos = CurPos + float3(0,0,0.15);Lsample = PseudoVolumeTexture(Tex, TexSampler, saturate(Lpos), XYFrames, NumFrames).r;shadowdist += Lsample;lightenergy += exp(-shadowdist * AmbientDensity) *cursample * SkyColor * transmittance;}return float4(lightenergy, transmittance);