RayMarching-渲染3D纹理时的伪影

Question

我正在为客户开发一个项目，并尝试复制在 Unity Inspector 中完成的 3D 体渲染，以便我可以实时查看 3D 体数据的更改。 以下是最终输出的示例（有或没有透明度）： https://i.sstatic.net/NtVbv.jpg 然而，当我使用 Unity 提供的默认 Raymarching 着色器的稍微修改版本进行实时渲染时 - 我的结果完全不同。 https://i.sstatic.net/0K2YA.jpg 以下是用于渲染 3D 纹理的着色器代码：

 Shader "Unlit/3DVolumeShader"
 {
 Properties
 {
     _Alpha ("Alpha", float) = 0.8
     _StepSize ("Step Size", float) = 0.01
 }
 SubShader
 {
     Tags { "Queue" = "Transparent" "RenderType" = "Transparent" }
     Blend One OneMinusSrcAlpha
     LOD 100

     Pass
     {
         CGPROGRAM
         #pragma vertex vert
         #pragma fragment frag

         #include "UnityCG.cginc"

         #define TEX_WIDTH 512
         #define TEX_HEIGHT 64
         #define TEX_LENGTH 384

         // Maximum amount of raymarching samples
         #define MAX_STEP_COUNT 128

         // Allowed floating point inaccuracy for hit detection
         #define EPSILON 0.00001f

         struct appdata
         {
             float4 vertex : POSITION;
         };

         struct v2f
         {
             float4 vertex : SV_POSITION;
             float3 objectVertex : TEXCOORD0;
             float3 vectorToSurface : TEXCOORD1;
         };

         float _Alpha;
         float _StepSize;

         StructuredBuffer<float4> DensityMap;
         
         v2f vert (appdata v)
         {
             v2f o;

             // Vertex in object space this will be the starting point of raymarching
             o.objectVertex = v.vertex;

             // Convert vertex in object space to camera coordinates
             o.vertex = UnityObjectToClipPos(v.vertex);

             // Calculate vector from camera to vertex in world space
             float3 worldVertex = mul(unity_ObjectToWorld, v.vertex).xyz;
             o.vectorToSurface = worldVertex - _WorldSpaceCameraPos;

             return o;
         }

         // This method blends colors based on their alpha transparency
         // If color.a == 1 then no blending will occur
         // Otherwise multiply the difference in the alpha's by the new color
         float4 BlendColors(float4 color, float4 newColor)
         {
             color.rgb += (1.0 - color.a) * newColor.a * newColor.rgb;
             color.a += (1.0 - color.a) * newColor.a;
             return color;
         }

         fixed4 frag(v2f i) : SV_Target
         {
             // Start raymarching at the front surface of the object
             float3 rayOrigin = i.objectVertex;

             // Use vector from camera to object surface to get the ray direction
             float3 rayDirection = mul(unity_WorldToObject, float4(normalize(i.vectorToSurface), 1));

             float4 color = float4(0, 0, 0, 0);

             float3 bounds = float3(TEX_WIDTH, TEX_LENGTH, TEX_HEIGHT);
             float3 samplePosition = rayOrigin;

             // Raymarch through object space
             for (int i = 0; i < MAX_STEP_COUNT; i++)
             {
                 // Accumulate color only within unit cube bounds
                 if(max(abs(samplePosition.x), max(abs(samplePosition.y), abs(samplePosition.z))) < 0.5f + EPSILON)
                 {
                     // Sample the color at the position in our density map. Add an offset for UV coordinate transformation.
                     // float4 sampledColor = tex3D(_DensityMap, samplePosition + float3(0.5f, 0.5f, 0.5f));

                     float3 textureCoord = (samplePosition + float3(0.5f, 0.5f, 0.5f)) * bounds;
                     int index = int(textureCoord.x) + (int(textureCoord.y) * bounds.x) + (int(textureCoord.z) * bounds.x * bounds.y);

                     float4 sampledColor = DensityMap[index];
                     sampledColor.a *= _Alpha;

                     // Blend the colors based on alpha transparency
                     color = BlendColors(color, sampledColor);

                     samplePosition += rayDirection * _StepSize;
                 }
             }

             return color;
         }
         ENDCG
     }
 }
 }

我正在使用 raymarching 索引 3D 纹理数组，我认为这就是可能发生此问题的地方。我想知道 Unity 使用的缩放/坐标系统是否有问题。 我的纹理大小是 512x64x384，我正在渲染到缩放比例为 1x0.1x0.75 的立方体。 如果需要任何其他信息来解决此问题，请告诉我。