陡峭视差贴图(Steep Parallax Mapping)实现原理
陡峭视差贴图通过分层深度比较和动态UV偏移技术增强岩石表面立体感.
视角自适应分层采样
根据视线与表面法线的夹角动态分配采样层数（平视视角增加至12层，俯视视角减少至5层），解决标准视差贴图在平视角度下的失真问题
深度图梯度修正
引入_LayerBias参数（推荐值0.2-0.4）调整UV偏移量计算公式，避免陡峭区域出现采样断裂：
$\Delta UV=\frac{ParallaxScale \cdot ViewDir_{xy}}{(ViewDir_z+LayerBias) \cdot LayerCount}$
风格化深度增强
在最终插值阶段使用pow(weight,2)强化轮廓对比度，配合ramp贴图实现卡通化光影过渡效果
URP HLSL完整实现代码
关键特性说明
动态层数优化：通过lerp(_MaxLayers, _MinLayers, saturate(dot(float3(0,0,1), viewDirTS)))实现平视视角自动增加采样精度
抗失真处理：_LayerBias参数修正陡峭表面的UV偏移计算，避免采样断裂
风格化增强：ramp贴图控制光影过渡，边缘光强化轮廓立体感
StylizedRockParallax.shader
Shader "Universal Render Pipeline/StylizedRockParallax"
{
Properties
{
[Header(Base Textures)]
_MainTex("Albedo (RGB)", 2D) = "white" {}
_NormalMap("Normal Map", 2D) = "bump" {}
_HeightMap("Height Map", 2D) = "white" {}
_RampTex("Stylized Ramp", 2D) = "white" {}
[Header(Parallax Settings)]
_ParallaxScale("Depth Scale", Range(0, 0.15)) = 0.08
_LayerBias("Layer Bias", Range(0.1, 0.5)) = 0.3
_MinLayers("Min Layers", Int) = 5
_MaxLayers("Max Layers", Int) = 12
[Header(Stylized Lighting)]
_RimPower("Rim Power", Range(1, 10)) = 3
_ShadowTint("Shadow Tint", Color) = (0.3,0.3,0.4,1)
}
SubShader
{
Tags { "RenderType"="Opaque" "RenderPipeline"="UniversalPipeline" }
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);
TEXTURE2D(_RampTex); SAMPLER(sampler_RampTex);
float _ParallaxScale;
float _LayerBias;
int _MinLayers, _MaxLayers;
float _RimPower;
float4 _ShadowTint;
// 陡峭视差映射核心算法
float2 SteepParallaxMapping(float3 viewDirTS, float2 uv)
{
// 动态层数计算（平视视角增加层数）
int numLayers = (int)lerp(_MaxLayers, _MinLayers, saturate(dot(float3(0,0,1), viewDirTS)));
float layerHeight = 1.0 / numLayers;
float2 deltaUV = _ParallaxScale * viewDirTS.xy / (viewDirTS.z + _LayerBias) / numLayers;
// 光线步进初始化
float currentLayerHeight = 0;
float2 currentUV = uv;
float currentDepth = 1 - SAMPLE_TEXTURE2D(_HeightMap, sampler_HeightMap, currentUV).r;
// 分层深度检测
[loop]
for (int i = 0; i < _MaxLayers; ++i) {
if (currentLayerHeight >= currentDepth) break;
currentUV -= deltaUV;
currentDepth = 1 - SAMPLE_TEXTURE2D(_HeightMap, sampler_HeightMap, currentUV).r;
currentLayerHeight += layerHeight;
}
// 风格化插值修正
float2 prevUV = currentUV + deltaUV;
float prevDepth = currentDepth - layerHeight;
float weight = pow((currentLayerHeight - currentDepth) / (prevDepth - currentDepth + 0.001), 2);
return lerp(currentUV, prevUV, saturate(weight * 1.5));
}
// 风格化光照计算
half3 StylizedShading(float3 normalWS, float3 viewDirWS, float NdotL)
{
float rim = pow(1 - saturate(dot(normalWS, viewDirWS)), _RimPower);
float2 rampUV = float2(NdotL * 0.5 + 0.5, 0.5);
half3 rampColor = SAMPLE_TEXTURE2D(_RampTex, sampler_RampTex, rampUV).rgb;
return lerp(rampColor * _ShadowTint.rgb, rampColor, saturate(NdotL + rim));
}
ENDHLSL
Pass
{
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 normalWS : TEXCOORD2;
float3 viewDirWS : TEXCOORD3;
float4 shadowCoord : TEXCOORD4;
};
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.normalWS = normInput.normalWS;
OUT.viewDirWS = viewDirWS;
OUT.shadowCoord = GetShadowCoord(posInput);
OUT.uv = IN.uv;
return OUT;
}
half4 frag(Varyings IN) : SV_Target
{
// 计算陡峭视差UV
float2 parallaxUV = SteepParallaxMapping(normalize(IN.viewDirTS), IN.uv);
// 采样纹理
half4 albedo = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, parallaxUV);
half3 normalTS = UnpackNormal(SAMPLE_TEXTURE2D(_NormalMap, sampler_NormalMap, parallaxUV));
// 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);
// 光照计算
Light mainLight = GetMainLight(IN.shadowCoord);
float NdotL = saturate(dot(normalWS, mainLight.direction));
half3 lighting = StylizedShading(normalWS, normalize(IN.viewDirWS), NdotL);
return half4(albedo.rgb * lighting * mainLight.color, 1);
}
ENDHLSL
}
}
}
材质配置
参数组合 风格化效果
_ParallaxScale=0.05 + _RimPower=5 轻度凹凸+柔和边缘光
_ParallaxScale=0.1 + _LayerBias=0.4 强烈凹凸+抗失真处理
_ShadowTint=(0.4,0.2,0.6) 紫色调阴影增强风格化表现
)
