Unity Shader 系列(三十七):体素渲染完整实战——Chunk 系统与 URP 体素 Shader

Unity 体素游戏的技术全景

Minecraft 风格的体素游戏在 Unity 中实现需要解决三个核心工程问题:数据组织(如何高效存储亿级体素)、网格生成(如何将体素数据转换为可渲染的三角面)、渲染(如何高效渲染大量体素面)。本篇从零到一覆盖整个技术栈:Chunk 系统设计、Greedy Meshing 算法、纹理集 UV 计算、顶点 AO,以及完整的 URP 体素 Shader。

Chunk 系统架构

体素世界不能一次性加载全部数据——即使是 256×256×256 的小地图也需要 16MB 内存。标准做法是将世界分割为固定大小的 Chunk(区块),只加载玩家周围的区块。

Chunk 数据结构

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using UnityEngine;
using System.Collections.Generic;

// 单个方块类型
public enum BlockType : byte
{
Air = 0,
Grass = 1,
Dirt = 2,
Stone = 3,
Sand = 4,
Water = 5,
}

// 体素世界常量
public static class VoxelConfig
{
public const int CHUNK_SIZE = 16; // X/Z 方向大小
public const int CHUNK_HEIGHT = 256; // Y 方向高度
public const int RENDER_DISTANCE = 8; // 渲染距离(Chunk 数)

// 六个面的方向
public static readonly Vector3Int[] FaceDirections = {
Vector3Int.up, Vector3Int.down,
Vector3Int.left, Vector3Int.right,
Vector3Int.forward, Vector3Int.back
};
}

// 单个 Chunk 的数据类
public class ChunkData
{
public Vector2Int ChunkCoord; // Chunk 的世界坐标(以 Chunk 为单位)
private BlockType[] blocks; // 扁平化的三维数组

public ChunkData(Vector2Int coord)
{
ChunkCoord = coord;
blocks = new BlockType[VoxelConfig.CHUNK_SIZE
* VoxelConfig.CHUNK_HEIGHT
* VoxelConfig.CHUNK_SIZE];
}

// 三维坐标 → 一维索引
private int GetIndex(int x, int y, int z)
{
return x + VoxelConfig.CHUNK_SIZE * (y + VoxelConfig.CHUNK_HEIGHT * z);
}

public BlockType GetBlock(int x, int y, int z)
{
if (x < 0 || x >= VoxelConfig.CHUNK_SIZE ||
y < 0 || y >= VoxelConfig.CHUNK_HEIGHT ||
z < 0 || z >= VoxelConfig.CHUNK_SIZE)
return BlockType.Air;
return blocks[GetIndex(x, y, z)];
}

public void SetBlock(int x, int y, int z, BlockType type)
{
if (x < 0 || x >= VoxelConfig.CHUNK_SIZE ||
y < 0 || y >= VoxelConfig.CHUNK_HEIGHT ||
z < 0 || z >= VoxelConfig.CHUNK_SIZE)
return;
blocks[GetIndex(x, y, z)] = type;
}

public bool IsAir(int x, int y, int z)
{
return GetBlock(x, y, z) == BlockType.Air;
}
}

Greedy Meshing:减少三角面数

朴素的体素渲染为每个可见面生成两个三角形。一个 16×16×16 的 Chunk 最多可见面约 16384 个,但 Greedy Meshing 可以将相邻相同材质的面合并为一个大矩形,大幅减少三角面数(实测减少 60~80%)。

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public class GreedyMeshBuilder
{
// 面方向枚举(0=+Y, 1=-Y, 2=+X, 3=-X, 4=+Z, 5=-Z)
private struct FaceInfo
{
public BlockType blockType;
public bool merged; // 是否已被合并
}

// 对一个方向的切片进行贪心合并
// axis: 0=X, 1=Y, 2=Z 方向的切片
// positive: true=正方向面, false=负方向面
public void GenerateSliceMesh(
ChunkData chunk,
int sliceCoord, // 切片在 axis 方向的坐标
int axis,
bool positive,
List<Vector3> vertices,
List<int> triangles,
List<Vector2> uvs,
List<Color32> colors)
{
// 获取切片尺寸(axis=1 是 Y 轴,切片是 XZ 平面)
int uSize = axis == 0 ? VoxelConfig.CHUNK_HEIGHT : VoxelConfig.CHUNK_SIZE;
int vSize = axis == 2 ? VoxelConfig.CHUNK_HEIGHT : VoxelConfig.CHUNK_SIZE;

var faceGrid = new FaceInfo[uSize, vSize];

// 填充面网格:哪些位置需要生成这个方向的面
for (int u = 0; u < uSize; u++)
{
for (int v = 0; v < vSize; v++)
{
// 根据 axis 转换为 xyz 坐标
int x = axis == 0 ? sliceCoord : (axis == 2 ? v : u);
int y = axis == 1 ? sliceCoord : (axis == 2 ? sliceCoord : v);
int z = axis == 2 ? sliceCoord : (axis == 0 ? v : u);

BlockType current = chunk.GetBlock(x, y, z);
int nx = x + (axis == 0 ? (positive ? 1 : -1) : 0);
int ny = y + (axis == 1 ? (positive ? 1 : -1) : 0);
int nz = z + (axis == 2 ? (positive ? 1 : -1) : 0);
BlockType neighbor = chunk.GetBlock(nx, ny, nz);

// 面可见:当前格子不为空,且邻居为空
if (current != BlockType.Air && neighbor == BlockType.Air)
faceGrid[u, v] = new FaceInfo { blockType = current, merged = false };
else
faceGrid[u, v] = new FaceInfo { blockType = BlockType.Air, merged = true };
}
}

// Greedy Meshing:贪心合并
for (int u = 0; u < uSize; u++)
{
for (int v = 0; v < vSize; v++)
{
if (faceGrid[u, v].merged) continue;
BlockType type = faceGrid[u, v].blockType;

// 沿 V 方向扩展
int vEnd = v + 1;
while (vEnd < vSize && !faceGrid[u, vEnd].merged && faceGrid[u, vEnd].blockType == type)
vEnd++;

// 沿 U 方向扩展(检查整行是否都满足条件)
int uEnd = u + 1;
while (uEnd < uSize)
{
bool canExpand = true;
for (int vi = v; vi < vEnd; vi++)
{
if (faceGrid[uEnd, vi].merged || faceGrid[uEnd, vi].blockType != type)
{
canExpand = false;
break;
}
}
if (!canExpand) break;
uEnd++;
}

// 标记已合并的区域
for (int ui = u; ui < uEnd; ui++)
for (int vi = v; vi < vEnd; vi++)
faceGrid[ui, vi].merged = true;

// 添加合并后的大矩形面
AddFace(vertices, triangles, uvs, colors,
u, v, uEnd - u, vEnd - v,
sliceCoord, axis, positive, type);
}
}
}

void AddFace(List<Vector3> verts, List<int> tris, List<Vector2> uvs, List<Color32> colors,
int u, int v, int uSize, int vSize,
int sliceCoord, int axis, bool positive, BlockType type)
{
int baseIdx = verts.Count;

// 构建矩形的四个顶点(根据 axis 方向转换坐标)
Vector3[] faceVerts = new Vector3[4];
Vector3[] positions = {
ToWorldPos(u, v, sliceCoord, axis, positive),
ToWorldPos(u + uSize,v, sliceCoord, axis, positive),
ToWorldPos(u + uSize,v + vSize,sliceCoord, axis, positive),
ToWorldPos(u, v + vSize,sliceCoord, axis, positive),
};

verts.AddRange(positions);

// 法线方向决定三角形绕序
if (positive)
{
tris.AddRange(new[] { baseIdx, baseIdx+1, baseIdx+2, baseIdx, baseIdx+2, baseIdx+3 });
}
else
{
tris.AddRange(new[] { baseIdx, baseIdx+2, baseIdx+1, baseIdx, baseIdx+3, baseIdx+2 });
}

// 纹理集 UV(见下节)
var atlasUV = GetAtlasUV(type, axis, positive, uSize, vSize);
uvs.AddRange(atlasUV);

// 顶点 AO 颜色(见下节)
colors.AddRange(new Color32[] {
new Color32(255, 255, 255, 255),
new Color32(255, 255, 255, 255),
new Color32(255, 255, 255, 255),
new Color32(255, 255, 255, 255)
});
}

Vector3 ToWorldPos(int u, int v, int s, int axis, bool positive)
{
float offset = positive ? 1 : 0;
switch (axis)
{
case 0: return new Vector3(s + offset, u, v);
case 1: return new Vector3(u, s + offset, v);
default: return new Vector3(u, v, s + offset);
}
}

Vector2[] GetAtlasUV(BlockType type, int axis, bool positive, int uSize, int vSize)
{
// 见下节纹理集实现
return new Vector2[4] {
new Vector2(0, 0), new Vector2(uSize, 0),
new Vector2(uSize, vSize), new Vector2(0, vSize)
};
}
}

纹理集(Texture Atlas)与防漏色

体素游戏的所有方块纹理通常打包在一张大纹理(纹理集)上,通过 UV 坐标选择不同的子纹理。

防止纹理漏色(Bleeding)

漏色是指纹理集中相邻纹理的像素”渗入”到当前纹理边界,在 Mipmap 降采样时尤为严重。

解决方案:UV 坐标向内收缩半个纹素(Texel Padding):

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public class TextureAtlas
{
private int atlasWidth; // 纹理集宽度(像素)
private int atlasHeight; // 纹理集高度
private int tileSize; // 每个方块纹理大小(如 16px)

public int TilesPerRow => atlasWidth / tileSize;
public int TilesPerColumn=> atlasHeight / tileSize;

// 获取某方块类型在纹理集中的 UV 偏移(左下角 UV)
public Vector2 GetTileOffset(int tileX, int tileY)
{
return new Vector2(
(float)tileX * tileSize / atlasWidth,
(float)tileY * tileSize / atlasHeight
);
}

// 获取防漏色 UV 坐标(向内缩进半个 Texel)
public Vector2[] GetSafeTileUVs(int tileX, int tileY, int uSize, int vSize)
{
// 半个 Texel 的 UV 偏移(防止漏色)
float halfTexelX = 0.5f / atlasWidth;
float halfTexelY = 0.5f / atlasHeight;

float u0 = (float)tileX * tileSize / atlasWidth + halfTexelX;
float v0 = (float)tileY * tileSize / atlasHeight + halfTexelY;
float u1 = u0 + (float)tileSize / atlasWidth - halfTexelX * 2;
float v1 = v0 + (float)tileSize / atlasHeight - halfTexelY * 2;

// UV 按面的 uSize/vSize 重复(贪心合并的大面需要 UV 重复)
return new Vector2[]
{
new Vector2(u0, v0),
new Vector2(u0 + (u1-u0) * uSize, v0),
new Vector2(u0 + (u1-u0) * uSize, v0 + (v1-v0) * vSize),
new Vector2(u0, v0 + (v1-v0) * vSize)
};
}
}

顶点 AO(Vertex Ambient Occlusion)

体素 AO 不需要光线追踪,通过检查顶点周围邻居体素的遮蔽情况计算环境光遮蔽值,存储在顶点颜色中。

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// 计算单个顶点的 AO 值(0=完全遮蔽,1=完全开放)
byte CalculateVertexAO(ChunkData chunk, Vector3Int vertexPos, int axis, bool positive)
{
// 顶点在面的角落,需要检查周围的 3 个邻居
// side1, side2: 相邻的两个侧面体素
// corner: 对角体素
Vector3Int normal = new Vector3Int(
axis == 0 ? (positive ? 1 : -1) : 0,
axis == 1 ? (positive ? 1 : -1) : 0,
axis == 2 ? (positive ? 1 : -1) : 0
);

// 根据顶点位置确定两个侧面方向(简化实现)
// 完整实现需要根据顶点在面的四个角分别计算

// AO 公式:0 个邻居遮蔽 → AO=3, 1个 → AO=2, 2个 → AO=1, side1+side2都遮蔽 → AO=0
int side1Occluded = 0; // 0 or 1
int side2Occluded = 0;
int cornerOccluded = 0;

// 如果两个侧面都有体素,角落方向不可见(不检查 corner)
int aoValue;
if (side1Occluded == 1 && side2Occluded == 1)
aoValue = 0;
else
aoValue = 3 - (side1Occluded + side2Occluded + cornerOccluded);

// 归一化到 0-255(存入 Color32.r)
return (byte)(aoValue * 255 / 3);
}

完整 URP 体素地形 Shader

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Shader "Custom/URP/VoxelTerrain"
{
Properties
{
_AtlasTex ("Texture Atlas", 2D) = "white" {}
_AtlasTileSize ("Tile Size (0-1 UV)", Float) = 0.0625 // 1/16,16×16 纹理集
_FogColor ("Fog Color", Color) = (0.6, 0.7, 0.8, 1.0)
_FogStart ("Fog Start Distance", Float) = 80
_FogEnd ("Fog End Distance", Float) = 160
_AmbientColor ("Ambient Color", Color) = (0.3, 0.35, 0.4, 1.0)
_AOStrength ("AO Strength", Range(0, 1)) = 0.7
}
SubShader
{
Tags { "RenderType"="Opaque" "RenderPipeline"="UniversalPipeline" }

Pass
{
Tags { "LightMode"="UniversalForward" }
HLSLPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile _ _MAIN_LIGHT_SHADOWS
#pragma multi_compile _ _MAIN_LIGHT_SHADOWS_CASCADE
#pragma multi_compile _ _SHADOWS_SOFT
#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"

struct Attributes
{
float4 positionOS : POSITION;
float3 normalOS : NORMAL;
float2 uv : TEXCOORD0;
float4 color : COLOR; // 顶点 AO 存储在顶点颜色的 R 通道
};

struct Varyings
{
float4 positionHCS : SV_POSITION;
float3 positionWS : TEXCOORD0;
float3 normalWS : TEXCOORD1;
float2 uv : TEXCOORD2;
float ao : TEXCOORD3; // AO 值
float fogFactor : TEXCOORD4;
};

TEXTURE2D(_AtlasTex); SAMPLER(sampler_AtlasTex);

CBUFFER_START(UnityPerMaterial)
float4 _AtlasTex_ST;
float _AtlasTileSize;
float4 _FogColor;
float _FogStart;
float _FogEnd;
float4 _AmbientColor;
float _AOStrength;
CBUFFER_END

Varyings vert(Attributes IN)
{
Varyings OUT;
VertexPositionInputs posInputs = GetVertexPositionInputs(IN.positionOS.xyz);
OUT.positionHCS = posInputs.positionCS;
OUT.positionWS = posInputs.positionWS;
OUT.normalWS = TransformObjectToWorldNormal(IN.normalOS);
OUT.uv = IN.uv; // UV 直接来自网格生成(已包含纹理集偏移)

// AO 从顶点颜色 R 通道读取,映射到 [AOStrength, 1] 范围
OUT.ao = lerp(_AOStrength, 1.0, IN.color.r);

// 线性雾计算(在顶点阶段计算,Fragment 阶段 Lerp)
float dist = length(_WorldSpaceCameraPos - posInputs.positionWS);
OUT.fogFactor = saturate((dist - _FogStart) / (_FogEnd - _FogStart));

return OUT;
}

half4 frag(Varyings IN) : SV_Target
{
// ===== 纹理采样 =====
half4 albedo = SAMPLE_TEXTURE2D(_AtlasTex, sampler_AtlasTex, IN.uv);

// ===== 光照 =====
float3 normalWS = normalize(IN.normalWS);

// 获取主光源(含阴影衰减)
float4 shadowCoord = TransformWorldToShadowCoord(IN.positionWS);
Light mainLight = GetMainLight(shadowCoord);
float NdotL = saturate(dot(normalWS, mainLight.direction));

// 面方向光照(顶部面最亮,底部面最暗)
// 体素游戏常用此技巧替代复杂光照,性能更好
float faceDimming = 1.0;
if (abs(normalWS.y + 1.0) < 0.1) faceDimming = 0.5; // 底部面
else if (abs(normalWS.x) > 0.5 || abs(normalWS.z) > 0.5) faceDimming = 0.75; // 侧面

// 漫反射:主光源 + 环境光
half3 diffuse = mainLight.color * NdotL * mainLight.shadowAttenuation * faceDimming;
half3 ambient = _AmbientColor.rgb;
half3 lighting = diffuse + ambient;

// ===== 应用 AO =====
half3 color = albedo.rgb * lighting * IN.ao;

// ===== 距离雾 =====
color = lerp(color, _FogColor.rgb, IN.fogFactor);

return half4(color, 1.0);
}
ENDHLSL
}

// 阴影投射
UsePass "Universal Render Pipeline/Lit/ShadowCaster"
}
}

体素破坏特效 Shader

方块被破坏时,碎片飞散的顶点动画 Shader:

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Shader "Custom/URP/VoxelBreakEffect"
{
Properties
{
_MainTex ("Block Texture", 2D) = "white" {}
_LifeTime ("Life Time", Float) = 1.0
_Gravity ("Gravity", Float) = 9.8
_SpreadRadius ("Spread Radius", Float) = 2.0
_RotateSpeed ("Rotate Speed", Float) = 5.0
_ElapsedTime ("Elapsed Time", Float) = 0.0 // C# 每帧传入
}
SubShader
{
Tags
{
"RenderType" = "Transparent"
"RenderPipeline" = "UniversalPipeline"
"Queue" = "Transparent"
}
Blend SrcAlpha OneMinusSrcAlpha
ZWrite Off

Pass
{
Tags { "LightMode"="UniversalForward" }
HLSLPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

struct Attributes
{
float4 positionOS : POSITION;
float3 normalOS : NORMAL;
float2 uv : TEXCOORD0;
float4 color : COLOR; // R=碎片ID(决定飞散方向)
};

struct Varyings
{
float4 positionHCS : SV_POSITION;
float2 uv : TEXCOORD0;
float alpha : TEXCOORD1;
};

TEXTURE2D(_MainTex); SAMPLER(sampler_MainTex);

CBUFFER_START(UnityPerMaterial)
float4 _MainTex_ST;
float _LifeTime;
float _Gravity;
float _SpreadRadius;
float _RotateSpeed;
float _ElapsedTime;
CBUFFER_END

// 伪随机数(基于碎片 ID)
float3 RandomDir(float id)
{
float a = id * 137.508;
float b = id * 98.76543;
return normalize(float3(sin(a) * cos(b), abs(sin(b)) + 0.3, cos(a) * cos(b)));
}

float3x3 RotationMatrix(float3 axis, float angle)
{
float s = sin(angle), c = cos(angle);
float oc = 1.0 - c;
return float3x3(
oc * axis.x * axis.x + c,
oc * axis.x * axis.y - axis.z * s,
oc * axis.z * axis.x + axis.y * s,
oc * axis.x * axis.y + axis.z * s,
oc * axis.y * axis.y + c,
oc * axis.y * axis.z - axis.x * s,
oc * axis.z * axis.x - axis.y * s,
oc * axis.y * axis.z + axis.x * s,
oc * axis.z * axis.z + c
);
}

Varyings vert(Attributes IN)
{
Varyings OUT;
float t = _ElapsedTime;
float life = t / _LifeTime; // [0, 1]

// 碎片 ID(从顶点颜色读取,每个碎片的顶点有相同 ID)
float id = IN.color.r * 255.0;

// 飞散方向(随机)
float3 flyDir = RandomDir(id);
float3 flyPos = flyDir * _SpreadRadius * t;

// 重力(向下加速)
flyPos.y -= 0.5 * _Gravity * t * t;

// 旋转(碎片在飞行中旋转)
float3 rotAxis = normalize(float3(sin(id), cos(id * 2.3), sin(id * 1.7)));
float rotAngle = t * _RotateSpeed * (frac(id * 0.618) - 0.5) * 2.0;
float3x3 rotMat = RotationMatrix(rotAxis, rotAngle);

// 应用位移和旋转
float3 posOS = mul(rotMat, IN.positionOS.xyz) + flyPos;
OUT.positionHCS = TransformObjectToHClip(posOS);
OUT.uv = TRANSFORM_TEX(IN.uv, _MainTex);

// Alpha 随时间淡出
OUT.alpha = 1.0 - smoothstep(0.5, 1.0, life);
return OUT;
}

half4 frag(Varyings IN) : SV_Target
{
half4 col = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, IN.uv);
col.a *= IN.alpha;
return col;
}
ENDHLSL
}
}
}

GPU Instancing 与间接渲染优化

体素渲染的主要性能瓶颈是大量 Chunk 的 DrawCall。使用 GPU Instancing 和 DrawMeshInstancedIndirect 可以大幅降低 CPU 开销:

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// Chunk 管理器中批量渲染所有 Chunk
public class ChunkRenderer : MonoBehaviour
{
public Mesh chunkMesh; // 统一的区块 Mesh(或程序化生成)
public Material chunkMaterial;
private List<Matrix4x4> chunkTransforms = new List<Matrix4x4>();

void Update()
{
// 收集所有可见 Chunk 的变换矩阵
chunkTransforms.Clear();
foreach (var chunk in LoadedChunks)
{
if (IsChunkVisible(chunk))
chunkTransforms.Add(chunk.transform.localToWorldMatrix);
}

// 每次最多 1023 个实例(Unity GPU Instancing 限制)
for (int i = 0; i < chunkTransforms.Count; i += 1023)
{
int count = Mathf.Min(1023, chunkTransforms.Count - i);
var batch = chunkTransforms.GetRange(i, count).ToArray();
Graphics.DrawMeshInstanced(chunkMesh, 0, chunkMaterial, batch);
}
}
}

游戏应用场景

技术 具体游戏应用
Greedy Meshing 沙盒建造游戏的高效地形渲染
纹理集 + AO Minecraft 风格视觉效果
Chunk 流式加载 无缝大世界,内存控制在 500MB 以内
GPU Instancing 批量渲染 100+ Chunk,DrawCall < 10
破坏特效 Shader 方块破坏/爆炸视觉反馈
水面透明 Shader 体素水体(半透明 + 折射)

性能考量

  • Chunk 大小的选择:16×16 是最常见的选择,平衡了网格生成时间(约 0.5ms/Chunk)和 DrawCall 数量。32×32 减少 DrawCall 但网格重建更慢
  • Greedy Meshing 适用场景:均匀材质大面积(草地、石墙)效果显著;凌乱的自然地形(洞穴、矿脉)效果有限
  • AO 的性能影响:顶点 AO 计算在网格生成时完成(离线),运行时零额外开销,推荐始终启用
  • Mipmap 与纹理集漏色:建议在纹理集 Texture Import 中启用 Mipmap,但 Filter Mode 选 Trilinear,不要选 Bilinear。同时纹理集中每个方块纹理之间至少留 2px 间距

Unity 中的体素渲染是一个既考验数学(AO、Greedy Meshing)又考验工程(Chunk 系统、内存管理)的综合课题,但每一个技术点都有清晰的优化路径——从最简单的朴素实现出发,逐步引入优化,最终可以在 Unity 中构建出媲美商业体素游戏的流畅体验。


Unity Shader 系列(三十七):体素渲染完整实战——Chunk 系统与 URP 体素 Shader
https://alex-rachel.github.io/2026/04/01/37-voxel-rendering/
作者
Alex
发布于
2026年4月1日
许可协议