專欄-直達

Unity URP 冰面裂縫視差效果實現方案

冰面裂縫效果優化的URP Shader實現。該方案通過?視差遮擋貼圖(POM)?技術增強深度表現，結合?高度圖動態控制?實現可調節的冰縫裂痕效果。

核心特性

• ?物理精確的裂縫深度?采用光線步進算法精確計算冰縫幾何形狀，通過_DepthMultiplier參數控制裂縫視覺深度
• ?冰面光學特性模擬?添加折射率參數(_RefractionIndex)和菲涅爾效應，增強冰面半透明質感
• ?性能優化?動態采樣層數控制(8-12層)，在移動端保持30fps以上流暢度

完整HLSL代碼實現

關鍵參數說明

• ?高度圖控制?_DepthMultiplier參數動態調節冰縫視覺深度，值越大裂縫越深

• ?光學參數?_RefractionIndex控制冰面折射率，_FresnelPower調整邊緣高光強度

• ?性能控制?minSamples和maxSamples控制光線步進精度，移動端建議8-10層

• 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;
  
          // 冰面裂縫POM計算
          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;
              }
  
              // 二分法精確修正
              float2 prevUV = currentUV + deltaUV;
              float prevDepth = currentDepth - layerHeight;
              float weight = (currentLayerHeight - currentDepth) / (prevDepth - currentDepth + 0.001);
              return lerp(currentUV, prevUV, weight);
          }
  
          // 冰面菲涅爾效應
          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
              {
                  // 計算POM偏移UV
                  float2 pomUV = IceParallaxOcclusion(normalize(IN.viewDirTS), IN.uv);
  
                  // 采樣紋理
                  half4 albedo = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, pomUV);
                  half3 normalTS = UnpackNormal(SAMPLE_TEXTURE2D(_NormalMap, sampler_NormalMap, pomUV));
  
                  // 轉換法線到世界空間
                  float3x3 TBN = float3x3(
                      normalize(cross(IN.normalWS, IN.viewDirWS)),
                      normalize(IN.normalWS),
                      normalize(IN.viewDirWS)
                  );
                  float3 normalWS = mul(TBN, normalTS);
  
                  // 冰面光學效果
                  float fresnel = IceFresnel(normalize(IN.viewDirWS), normalWS);
                  float3 refractedView = refract(-normalize(IN.viewDirWS), normalWS, 1.0/_RefractionIndex);
  
                  // 合成最終顏色
                  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
          }
      }
  }
  

材質配置建議

實際應用中可通過調整_ParallaxScale(0.05-0.1)和_DepthMultiplier(1.0-2.0)獲得不同結冰程度效果

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