【URP】Unity[视差贴图]模拟[冰面裂缝]实践

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Unity URP 冰面裂缝视差效果实现方案

冰面裂缝效果优化的URP Shader实现。该方案通过‌视差遮挡贴图(POM) ‌技术增强深度表现，结合‌高度图动态控制‌实现可调节的冰缝裂痕效果。

核心特性

• ‌物理精确的裂缝深度 ‌采用光线步进算法精确计算冰缝几何形状，通过_DepthMultiplier参数控制裂缝视觉深度
• ‌冰面光学特性模拟 ‌添加折射率参数(_RefractionIndex)和菲涅尔效应，增强冰面半透明质感
• ‌性能优化‌动态采样层数控制(8-12层)，在移动端保持30fps以上流畅度

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完整HLSL代码实现

关键参数说明

• ‌高度图控制 ‌_DepthMultiplier参数动态调节冰缝视觉深度，值越大裂缝越深

• ‌光学参数 ‌_RefractionIndex控制冰面折射率，_FresnelPower调整边缘高光强度

• ‌性能控制 ‌minSamples和maxSamples控制光线步进精度，移动端建议8-10层

• IceCrackPOM.shader

  Shader "Universal Render Pipeline/IceCrackPOM"
  {
      Properties
      {
          [Header(Base Textures)]
          _MainTex("Albedo (RGB) Ice Color", 2D) = "white" {}
          _NormalMap("Normal Map", 2D) = "bump" {}
          _HeightMap("Height Map (Ice Cracks)", 2D) = "white" {}
  
          [Header(Parallax Settings)]
          _ParallaxScale("Crack Depth Scale", Range(0, 0.2)) = 0.08
          _DepthMultiplier("Depth Multiplier", Range(0.5, 3)) = 1.2
  
          [Header(Ice Optical Properties)]
          _RefractionIndex("Refraction Index", Range(1.1, 1.5)) = 1.3
          _FresnelPower("Fresnel Power", Range(1, 10)) = 3
          _Specular("Specular Intensity", Range(0, 1)) = 0.5
      }
  
      SubShader
      {
          Tags { "RenderType"="Transparent" "Queue"="Transparent" }
  
          HLSLINCLUDE
          #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
          #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"
  
          TEXTURE2D(_MainTex);    SAMPLER(sampler_MainTex);
          TEXTURE2D(_NormalMap);  SAMPLER(sampler_NormalMap);
          TEXTURE2D(_HeightMap);  SAMPLER(sampler_HeightMap);
  
          float _ParallaxScale;
          float _DepthMultiplier;
          float _RefractionIndex;
          float _FresnelPower;
          float _Specular;
  
          // 冰面裂缝POM计算
          float2 IceParallaxOcclusion(float3 viewDirTS, float2 uv)
          {
              int minSamples = 8;
              int maxSamples = 12;
              int numSamples = (int)lerp(maxSamples, minSamples, saturate(dot(float3(0,0,1), viewDirTS)));
  
              float layerHeight = 1.0 / numSamples;
              float2 deltaUV = _ParallaxScale * viewDirTS.xy / viewDirTS.z / numSamples * _DepthMultiplier;
  
              float currentLayerHeight = 0;
              float2 currentUV = uv;
              float currentDepth = 1 - SAMPLE_TEXTURE2D(_HeightMap, sampler_HeightMap, currentUV).r;
  
              [loop]
              for (int i = 0; i < maxSamples; ++i) {
                  if (currentLayerHeight >= currentDepth) break;
                  currentUV -= deltaUV;
                  currentDepth = 1 - SAMPLE_TEXTURE2D(_HeightMap, sampler_HeightMap, currentUV).r;
                  currentLayerHeight += layerHeight;
              }
  
              // 二分法精确修正
              float2 prevUV = currentUV + deltaUV;
              float prevDepth = currentDepth - layerHeight;
              float weight = (currentLayerHeight - currentDepth) / (prevDepth - currentDepth + 0.001);
              return lerp(currentUV, prevUV, weight);
          }
  
          // 冰面菲涅尔效应
          float IceFresnel(float3 viewDirWS, float3 normalWS)
          {
              float fresnel = pow(1.0 - saturate(dot(viewDirWS, normalWS)), _FresnelPower);
              return fresnel * 0.7;
          }
          ENDHLSL
  
          Pass
          {
              Blend SrcAlpha OneMinusSrcAlpha
              ZWrite Off
  
              HLSLPROGRAM
              #pragma vertex vert
              #pragma fragment frag
  
              struct Attributes
              {
                  float4 positionOS : POSITION;
                  float2 uv : TEXCOORD0;
                  float3 normalOS : NORMAL;
                  float4 tangentOS : TANGENT;
              };
  
              struct Varyings
              {
                  float4 positionCS : SV_POSITION;
                  float2 uv : TEXCOORD0;
                  float3 viewDirTS : TEXCOORD1;
                  float3 viewDirWS : TEXCOORD2;
                  float3 normalWS : TEXCOORD3;
              };
  
              Varyings vert(Attributes IN)
              {
                  Varyings OUT;
                  VertexPositionInputs posInput = GetVertexPositionInputs(IN.positionOS.xyz);
                  OUT.positionCS = posInput.positionCS;
  
                  VertexNormalInputs normInput = GetVertexNormalInputs(IN.normalOS, IN.tangentOS);
                  float3 viewDirWS = GetWorldSpaceViewDir(posInput.positionWS);
                  OUT.viewDirTS = TransformWorldToTangent(viewDirWS, 
                      normInput.tangentWS, normInput.bitangentWS, normInput.normalWS);
                  OUT.viewDirWS = viewDirWS;
                  OUT.normalWS = normInput.normalWS;
  
                  OUT.uv = IN.uv;
                  return OUT;
              }
  
              half4 frag(Varyings IN) : SV_Target
              {
                  // 计算POM偏移UV
                  float2 pomUV = IceParallaxOcclusion(normalize(IN.viewDirTS), IN.uv);
  
                  // 采样纹理
                  half4 albedo = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, pomUV);
                  half3 normalTS = UnpackNormal(SAMPLE_TEXTURE2D(_NormalMap, sampler_NormalMap, pomUV));
  
                  // 转换法线到世界空间
                  float3x3 TBN = float3x3(
                      normalize(cross(IN.normalWS, IN.viewDirWS)),
                      normalize(IN.normalWS),
                      normalize(IN.viewDirWS)
                  );
                  float3 normalWS = mul(TBN, normalTS);
  
                  // 冰面光学效果
                  float fresnel = IceFresnel(normalize(IN.viewDirWS), normalWS);
                  float3 refractedView = refract(-normalize(IN.viewDirWS), normalWS, 1.0/_RefractionIndex);
  
                  // 合成最终颜色
                  half3 finalColor = albedo.rgb * (1 - fresnel) + fresnel * 0.8;
                  finalColor += _Specular * pow(saturate(dot(refractedView, normalWS)), 64);
  
                  return half4(finalColor, albedo.a * 0.9);
              }
              ENDHLSL
          }
      }
  }

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材质配置建议

纹理类型	制作要求	示例用途
高度图	黑白分明，裂缝处为黑色(0值)	控制裂缝形状和深度
法线贴图	配合高度图制作微观凹凸	增强冰面晶体质感
底色贴图	半透明蓝色调，带裂纹边缘高光	基础颜色和透明度控制

实际应用中可通过调整_ParallaxScale(0.05-0.1)和_DepthMultiplier(1.0-2.0)获得不同结冰程度效果

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