【URP】Unity[视差贴图]模拟[冰面裂缝]实践
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
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
}
}
}
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