【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;}ENDHLSLPass{Blend SrcAlpha OneMinusSrcAlphaZWrite OffHLSLPROGRAM#pragma vertex vert#pragma fragment fragstruct 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UVfloat2 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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