Occlusion 和 Detail Map

1. Occlusion  环境光遮蔽图，在3D游戏经常会听到一个词环境光遮蔽（Ambient Occlusion）。

百度百科的说明 大概意思了解下就好。

AO是来描绘物体和物体相交或靠近的时候遮挡周围漫反射光线的效果，可以解决或改善漏光、飘和阴影不实等问题，解决或改善场景中缝隙、褶皱与墙角、角线以及细小物体等的表现不清晰问题，综合改善细节尤其是暗部阴影，增强空间的层次感、真实感，同时加强和改善画面明暗对比，增强画面的艺术性

上面的斯坦福龙呈现在一个均匀照明的环境中。 模型中有一些较黑和较亮的区域，但照明大部分都是均匀的。 尽管有相当复杂的几何形状，但龙看上去很平，没有明显的深度感觉。

下面是启用了环境光遮蔽的相同模型。

环境光遮蔽 从字面上就是对于环境光影响。对于直接光照不影响。

Unity里面实现下

 1 half Occlusion(float2 uv)
 2 {
 3 #if (SHADER_TARGET < 30)
 4     // SM20: instruction count limitation
 5     // SM20: simpler occlusion
 6     return tex2D(_OcclusionMap, uv).g;
 7 #else
 8     half occ = tex2D(_OcclusionMap, uv).g;
 9     return LerpOneTo (occ, _OcclusionStrength);
10 #endif
11 }
inline UnityGI UnityGI_Base(UnityGIInput data, half occlusion, half3 normalWorld)
{
    UnityGI o_gi;
    ResetUnityGI(o_gi);

    // Base pass with Lightmap support is responsible for handling ShadowMask / blending here for performance reason
    #if defined(HANDLE_SHADOWS_BLENDING_IN_GI)
        half bakedAtten = UnitySampleBakedOcclusion(data.lightmapUV.xy, data.worldPos);
        float zDist = dot(_WorldSpaceCameraPos - data.worldPos, UNITY_MATRIX_V[2].xyz);
        float fadeDist = UnityComputeShadowFadeDistance(data.worldPos, zDist);
        data.atten = UnityMixRealtimeAndBakedShadows(data.atten, bakedAtten, UnityComputeShadowFade(fadeDist));
    #endif

    o_gi.light = data.light;
    o_gi.light.color *= data.atten;

    #if UNITY_SHOULD_SAMPLE_SH
        o_gi.indirect.diffuse = ShadeSHPerPixel(normalWorld, data.ambient, data.worldPos);
    #endif

    #if defined(LIGHTMAP_ON)
        // Baked lightmaps
        half4 bakedColorTex = UNITY_SAMPLE_TEX2D(unity_Lightmap, data.lightmapUV.xy);
        half3 bakedColor = DecodeLightmap(bakedColorTex);

        #ifdef DIRLIGHTMAP_COMBINED
            fixed4 bakedDirTex = UNITY_SAMPLE_TEX2D_SAMPLER (unity_LightmapInd, unity_Lightmap, data.lightmapUV.xy);
            o_gi.indirect.diffuse += DecodeDirectionalLightmap (bakedColor, bakedDirTex, normalWorld);

            #if defined(LIGHTMAP_SHADOW_MIXING) && !defined(SHADOWS_SHADOWMASK) && defined(SHADOWS_SCREEN)
                ResetUnityLight(o_gi.light);
                o_gi.indirect.diffuse = SubtractMainLightWithRealtimeAttenuationFromLightmap (o_gi.indirect.diffuse, data.atten, bakedColorTex, normalWorld);
            #endif

        #else // not directional lightmap
            o_gi.indirect.diffuse += bakedColor;

            #if defined(LIGHTMAP_SHADOW_MIXING) && !defined(SHADOWS_SHADOWMASK) && defined(SHADOWS_SCREEN)
                ResetUnityLight(o_gi.light);
                o_gi.indirect.diffuse = SubtractMainLightWithRealtimeAttenuationFromLightmap(o_gi.indirect.diffuse, data.atten, bakedColorTex, normalWorld);
            #endif

        #endif
    #endif

    #ifdef DYNAMICLIGHTMAP_ON
        // Dynamic lightmaps
        fixed4 realtimeColorTex = UNITY_SAMPLE_TEX2D(unity_DynamicLightmap, data.lightmapUV.zw);
        half3 realtimeColor = DecodeRealtimeLightmap (realtimeColorTex);

        #ifdef DIRLIGHTMAP_COMBINED
            half4 realtimeDirTex = UNITY_SAMPLE_TEX2D_SAMPLER(unity_DynamicDirectionality, unity_DynamicLightmap, data.lightmapUV.zw);
            o_gi.indirect.diffuse += DecodeDirectionalLightmap (realtimeColor, realtimeDirTex, normalWorld);
        #else
            o_gi.indirect.diffuse += realtimeColor;
        #endif
    #endif

    o_gi.indirect.diffuse *= occlusion;
    return o_gi;
}

使用的地方影响的diffuse 环境光的强度。

Detail Map Unity提供两个，一个DetailAlbedo 一个是DetailNormal

DetailAlbodo

float4 TexCoords(VertexInput v)
{
    float4 texcoord;
    texcoord.xy = TRANSFORM_TEX(v.uv0, _MainTex); // Always source from uv0
    texcoord.zw = TRANSFORM_TEX(((_UVSec == 0) ? v.uv0 : v.uv1), _DetailAlbedoMap);
    return texcoord;
}

VertexOutputForwardBase vertForwardBase (VertexInput v)
{
    UNITY_SETUP_INSTANCE_ID(v);
    VertexOutputForwardBase o;
    UNITY_INITIALIZE_OUTPUT(VertexOutputForwardBase, o);
    UNITY_TRANSFER_INSTANCE_ID(v, o);
    UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);

    float4 posWorld = mul(unity_ObjectToWorld, v.vertex);
    #if UNITY_REQUIRE_FRAG_WORLDPOS
        #if UNITY_PACK_WORLDPOS_WITH_TANGENT
            o.tangentToWorldAndPackedData[0].w = posWorld.x;
            o.tangentToWorldAndPackedData[1].w = posWorld.y;
            o.tangentToWorldAndPackedData[2].w = posWorld.z;
        #else
            o.posWorld = posWorld.xyz;
        #endif
    #endif
    o.pos = UnityObjectToClipPos(v.vertex);

    o.tex = TexCoords(v);
    o.eyeVec = NormalizePerVertexNormal(posWorld.xyz - _WorldSpaceCameraPos);
    float3 normalWorld = UnityObjectToWorldNormal(v.normal);
    #ifdef _TANGENT_TO_WORLD
        float4 tangentWorld = float4(UnityObjectToWorldDir(v.tangent.xyz), v.tangent.w);

        float3x3 tangentToWorld = CreateTangentToWorldPerVertex(normalWorld, tangentWorld.xyz, tangentWorld.w);
        o.tangentToWorldAndPackedData[0].xyz = tangentToWorld[0];
        o.tangentToWorldAndPackedData[1].xyz = tangentToWorld[1];
        o.tangentToWorldAndPackedData[2].xyz = tangentToWorld[2];
    #else
        o.tangentToWorldAndPackedData[0].xyz = 0;
        o.tangentToWorldAndPackedData[1].xyz = 0;
        o.tangentToWorldAndPackedData[2].xyz = normalWorld;
    #endif

    //We need this for shadow receving
    UNITY_TRANSFER_SHADOW(o, v.uv1);

    o.ambientOrLightmapUV = VertexGIForward(v, posWorld, normalWorld);

    #ifdef _PARALLAXMAP
        TANGENT_SPACE_ROTATION;
        half3 viewDirForParallax = mul (rotation, ObjSpaceViewDir(v.vertex));
        o.tangentToWorldAndPackedData[0].w = viewDirForParallax.x;
        o.tangentToWorldAndPackedData[1].w = viewDirForParallax.y;
        o.tangentToWorldAndPackedData[2].w = viewDirForParallax.z;
    #endif

    UNITY_TRANSFER_FOG(o,o.pos);
    return o;
}

在顶点着色器的 先填充UV

o.tex = TexCoords(v);

像素着色器

inline FragmentCommonData RoughnessSetup(float4 i_tex)
{
    half2 metallicGloss = MetallicRough(i_tex.xy);
    half metallic = metallicGloss.x;
    half smoothness = metallicGloss.y; // this is 1 minus the square root of real roughness m.

    half oneMinusReflectivity;
    half3 specColor;
    half3 diffColor = DiffuseAndSpecularFromMetallic(Albedo(i_tex), metallic, /*out*/ specColor, /*out*/ oneMinusReflectivity);

    FragmentCommonData o = (FragmentCommonData)0;
    o.diffColor = diffColor;
    o.specColor = specColor;
    o.oneMinusReflectivity = oneMinusReflectivity;
    o.smoothness = smoothness;
    return o;
}

采样颜色

inline half3 DiffuseAndSpecularFromMetallic (half3 albedo, half metallic, out half3 specColor, out half oneMinusReflectivity)
{
    specColor = lerp (unity_ColorSpaceDielectricSpec.rgb, albedo, metallic);
    oneMinusReflectivity = OneMinusReflectivityFromMetallic(metallic);
    return albedo * oneMinusReflectivity;
}
half3 Albedo(float4 texcoords)
{
    half3 albedo = _Color.rgb * tex2D (_MainTex, texcoords.xy).rgb;
#if _DETAIL
    #if (SHADER_TARGET < 30)
        // SM20: instruction count limitation
        // SM20: no detail mask
        half mask = 1;
    #else
        half mask = DetailMask(texcoords.xy);
    #endif
    half3 detailAlbedo = tex2D (_DetailAlbedoMap, texcoords.zw).rgb;
    #if _DETAIL_MULX2
        albedo *= LerpWhiteTo (detailAlbedo * unity_ColorSpaceDouble.rgb, mask);
    #elif _DETAIL_MUL
        albedo *= LerpWhiteTo (detailAlbedo, mask);
    #elif _DETAIL_ADD
        albedo += detailAlbedo * mask;
    #elif _DETAIL_LERP
        albedo = lerp (albedo, detailAlbedo, mask);
    #endif
#endif
    return albedo;
}

这里detailAlbedo有多种的混合模式。可以选择。

DetailNormal

// parallax transformed texcoord is used to sample occlusion
inline FragmentCommonData FragmentSetup (inout float4 i_tex, float3 i_eyeVec, half3 i_viewDirForParallax, float4 tangentToWorld[3], float3 i_posWorld)
{
    i_tex = Parallax(i_tex, i_viewDirForParallax);

    half alpha = Alpha(i_tex.xy);
    #if defined(_ALPHATEST_ON)
        clip (alpha - _Cutoff);
    #endif

    FragmentCommonData o = UNITY_SETUP_BRDF_INPUT (i_tex);
    o.normalWorld = PerPixelWorldNormal(i_tex, tangentToWorld);
    o.eyeVec = NormalizePerPixelNormal(i_eyeVec);
    o.posWorld = i_posWorld;

    // NOTE: shader relies on pre-multiply alpha-blend (_SrcBlend = One, _DstBlend = OneMinusSrcAlpha)
    o.diffColor = PreMultiplyAlpha (o.diffColor, alpha, o.oneMinusReflectivity, /*out*/ o.alpha);
    return o;
}
 o.normalWorld = PerPixelWorldNormal(i_tex, tangentToWorld);

在像素着色器中，计算顶点法线

float3 PerPixelWorldNormal(float4 i_tex, float4 tangentToWorld[3])
{
#ifdef _NORMALMAP
    half3 tangent = tangentToWorld[0].xyz;
    half3 binormal = tangentToWorld[1].xyz;
    half3 normal = tangentToWorld[2].xyz;

    #if UNITY_TANGENT_ORTHONORMALIZE
        normal = NormalizePerPixelNormal(normal);

        // ortho-normalize Tangent
        tangent = normalize (tangent - normal * dot(tangent, normal));

        // recalculate Binormal
        half3 newB = cross(normal, tangent);
        binormal = newB * sign (dot (newB, binormal));
    #endif

    half3 normalTangent = NormalInTangentSpace(i_tex);
    float3 normalWorld = NormalizePerPixelNormal(tangent * normalTangent.x + binormal * normalTangent.y + normal * normalTangent.z); // @TODO: see if we can squeeze this normalize on SM2.0 as well
#else
    float3 normalWorld = normalize(tangentToWorld[2].xyz);
#endif
    return normalWorld;
}
UNITY_TANGENT_ORTHONORMALIZE

这里正交归一化一般不开启，就是重新把法线 副法线，切线正交。但是一般的精度就够了，不需要在顶点着色器中，重新做。

half3 normalTangent = NormalInTangentSpace(i_tex);

采样出切线空间中，法线的方向。

#ifdef _NORMALMAP
half3 NormalInTangentSpace(float4 texcoords)
{
    half3 normalTangent = UnpackScaleNormal(tex2D (_BumpMap, texcoords.xy), _BumpScale);

#if _DETAIL && defined(UNITY_ENABLE_DETAIL_NORMALMAP)
    half mask = DetailMask(texcoords.xy);
    half3 detailNormalTangent = UnpackScaleNormal(tex2D (_DetailNormalMap, texcoords.zw), _DetailNormalMapScale);
    #if _DETAIL_LERP
        normalTangent = lerp(
            normalTangent,
            detailNormalTangent,
            mask);
    #else
        normalTangent = lerp(
            normalTangent,
            BlendNormals(normalTangent, detailNormalTangent),
            mask);
    #endif
#endif

    return normalTangent;
}
#endif

这样就全部搞定。

这里有个非常重要的一点。为什么早期渲染，金属感弱的问题。

#define unity_ColorSpaceDielectricSpec half4(0.04, 0.04, 0.04, 1.0 - 0.04) // standard dielectric reflectivity coef at incident angle (= 4%)

 specColor = lerp (unity_ColorSpaceDielectricSpec.rgb, albedo, metallic);

根据材料的金属度不一样，高光颜色是不一样的。根据物质的导电性特性区分。可以根据龚大的这篇文章

金属，塑料，傻傻分不清楚

// parallax transformed texcoord is used to sample occlusion
inline FragmentCommonData FragmentSetup (inout float4 i_tex, float3 i_eyeVec, half3 i_viewDirForParallax, float4 tangentToWorld[3], float3 i_posWorld)
{
    i_tex = Parallax(i_tex, i_viewDirForParallax);

    half alpha = Alpha(i_tex.xy);
    #if defined(_ALPHATEST_ON)
        clip (alpha - _Cutoff);
    #endif

    FragmentCommonData o = UNITY_SETUP_BRDF_INPUT (i_tex);
    o.normalWorld = PerPixelWorldNormal(i_tex, tangentToWorld);
    o.eyeVec = NormalizePerPixelNormal(i_eyeVec);
    o.posWorld = i_posWorld;

    // NOTE: shader relies on pre-multiply alpha-blend (_SrcBlend = One, _DstBlend = OneMinusSrcAlpha)
    o.diffColor = PreMultiplyAlpha (o.diffColor, alpha, o.oneMinusReflectivity, /*out*/ o.alpha);
    return o;
}

代码流程有点长，在顶点着色器的入口函数

half4 fragForwardBaseInternal (VertexOutputForwardBase i)
{
    UNITY_APPLY_DITHER_CROSSFADE(i.pos.xy);

    FRAGMENT_SETUP(s)

    UNITY_SETUP_INSTANCE_ID(i);
    UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i);

    UnityLight mainLight = MainLight ();
    UNITY_LIGHT_ATTENUATION(atten, i, s.posWorld);

    half occlusion = Occlusion(i.tex.xy);
    UnityGI gi = FragmentGI (s, occlusion, i.ambientOrLightmapUV, atten, mainLight);

    half4 c = UNITY_BRDF_PBS (s.diffColor, s.specColor, s.oneMinusReflectivity, s.smoothness, s.normalWorld, -s.eyeVec, gi.light, gi.indirect);
    c.rgb += Emission(i.tex.xy);

    UNITY_APPLY_FOG(i.fogCoord, c.rgb);
    return OutputForward (c, s.alpha);
}

通过宏，获取基本的diff颜色和高光，法线一些基础信息

#define FRAGMENT_SETUP(x) FragmentCommonData x = 
    FragmentSetup(i.tex, i.eyeVec, IN_VIEWDIR4PARALLAX(i), i.tangentToWorldAndPackedData, IN_WORLDPOS(i));
inline FragmentCommonData FragmentSetup (inout float4 i_tex, float3 i_eyeVec, half3 i_viewDirForParallax, float4 tangentToWorld[3], float3 i_posWorld)
{
    i_tex = Parallax(i_tex, i_viewDirForParallax);

    half alpha = Alpha(i_tex.xy);
    #if defined(_ALPHATEST_ON)
        clip (alpha - _Cutoff);
    #endif

    FragmentCommonData o = UNITY_SETUP_BRDF_INPUT (i_tex);
    o.normalWorld = PerPixelWorldNormal(i_tex, tangentToWorld);
    o.eyeVec = NormalizePerPixelNormal(i_eyeVec);
    o.posWorld = i_posWorld;

    // NOTE: shader relies on pre-multiply alpha-blend (_SrcBlend = One, _DstBlend = OneMinusSrcAlpha)
    o.diffColor = PreMultiplyAlpha (o.diffColor, alpha, o.oneMinusReflectivity, /*out*/ o.alpha);
    return o;
}
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原文地址：https://www.cnblogs.com/wbaoqing/p/9244365.html