Unity

2024-02-09 00:33| 来源: 网络整理| 查看: 265

UnityStandardBRDF包含文件包含Unity_GlossyEnvironment函数。它包含所有用于转换粗糙度，对立方体贴图采样以及从HDR转换的代码。

作用：根据粗糙度采样对应mipmap级别的环境贴图

采样环境贴图得到间接光的环境反射的例子（镜面反射）：

UnityIndirect CreateIndirectLight(Interpolators i, float3 viewDir) { UnityIndirect indirectLight; indirectLight.diffuse = 0; indirectLight.specular = 0; // base pass 才计算环境光 if defined(FORWARD_BASE_PASS) // 计算从反射出来的方向 // viewDir是片元到摄像机的向量 // i.normal是片元在世界空间下的法线方向 float3 reflectionDir = reflect(-viewDir, i.normal) // 用于计算的结构体 Unity_GlossyEnvironmentData envData; envData.roughness = 1 - _Smoothness; // 粗糙度 envData.reflUVW = reflectionDir; // 对CubeMap采样的方向 indirectLight.specular = Unity_GlossyEnvironment(UNITY_PASS_TEXCUBE(unity_SpecCube0), unity_SpecCube0_HDR, envData); #endif return indirectLight; } UNITY_PASS_TEXCUBE是什么？

源码：

// Macros to declare textures and samplers, possibly separately. For platforms // that have separate samplers & textures (like DX11), and we'd want to conserve // the samplers. // - UNITY_DECLARE_TEX*_NOSAMPLER declares a texture, without a sampler. // - UNITY_SAMPLE_TEX*_SAMPLER samples a texture, using sampler from another texture. // That another texture must also be actually used in the current shader, otherwise // the correct sampler will not be set. #if defined(SHADER_API_D3D11) || defined(SHADER_API_XBOXONE) || defined(UNITY_COMPILER_HLSLCC) || defined(SHADER_API_PSSL) || (defined(SHADER_TARGET_SURFACE_ANALYSIS) && !defined(SHADER_TARGET_SURFACE_ANALYSIS_MOJOSHADER)) #define UNITY_PASS_TEXCUBE(tex) tex, sampler##tex #else // DX9 style HLSL syntax; same object for texture+sampler #define UNITY_PASS_TEXCUBE(tex) tex #endif

如果是D3D11：

Unity_GlossyEnvironment(UNITY_PASS_TEXCUBE(unity_SpecCube0), unity_SpecCube0_HDR, envData);

就相当于

Unity_GlossyEnvironment(unity_SpecCube0， samplerunity_SpecCube0, unity_SpecCube0_HDR, envData);

Unity_GlossyEnviroment源码： half perceptualRoughnessToMipmapLevel(half perceptualRoughness) { // 0~1的粗糙度转换成mipmap级别，UNITY_SPECCUBE_LOD_STEPS是mipmap的最大级别 return perceptualRoughness * UNITY_SPECCUBE_LOD_STEPS; } half3 Unity_GlossyEnvironment (UNITY_ARGS_TEXCUBE(tex), half4 hdr, Unity_GlossyEnvironmentData glossIn) { half perceptualRoughness = glossIn.roughness; // TODO: CAUTION: remap from Morten may work only with offline convolution, see impact with runtime convolution! // For now disabled #if 0 // 涉及如何创建mipmap的详细信息, 注释掉的内容 // 真正的计算三线性过滤mipmap不同级别之间的关系 float m = PerceptualRoughnessToRoughness(perceptualRoughness); // m is the real roughness parameter const float fEps = 1.192092896e-07F; // smallest such that 1.0+FLT_EPSILON != 1.0 (+1e-4h is NOT good here. is visibly very wrong) float n = (2.0/max(fEps, m*m))-2.0; // remap to spec power. See eq. 21 in --> https://dl.dropboxusercontent.com/u/55891920/papers/mm_brdf.pdf n /= 4; // remap from n_dot_h formulatino to n_dot_r. See section "Pre-convolved Cube Maps vs Path Tracers" --> https://s3.amazonaws.com/docs.knaldtech.com/knald/1.0.0/lys_power_drops.html perceptualRoughness = pow( 2/(n+2), 0.25); // remap back to square root of real roughness (0.25 include both the sqrt root of the conversion and sqrt for going from roughness to perceptualRoughness) #else // MM: came up with a surprisingly close approximation to what the #if 0'ed out code above does. // 得到与上面#if 0差不多效果的代码，修正了粗糙度与mipmap级别之间的关系不是线性的问题，计算量小很多。 perceptualRoughness = perceptualRoughness*(1.7 - 0.7*perceptualRoughness); #endif half mip = perceptualRoughnessToMipmapLevel(perceptualRoughness); half3 R = glossIn.reflUVW; half4 rgbm = UNITY_SAMPLE_TEXCUBE_LOD(tex, R, mip); // 对cubemap进行采样 return DecodeHDR(rgbm, hdr); } UNITY_ARGS_TEXCUBE(tex)是什么？

源码：

// Macros to declare textures and samplers, possibly separately. For platforms // that have separate samplers & textures (like DX11), and we'd want to conserve // the samplers. // - UNITY_DECLARE_TEX*_NOSAMPLER declares a texture, without a sampler. // - UNITY_SAMPLE_TEX*_SAMPLER samples a texture, using sampler from another texture. // That another texture must also be actually used in the current shader, otherwise // the correct sampler will not be set. #if defined(SHADER_API_D3D11) || defined(SHADER_API_XBOXONE) || defined(UNITY_COMPILER_HLSLCC) || defined(SHADER_API_PSSL) || (defined(SHADER_TARGET_SURFACE_ANALYSIS) && !defined(SHADER_TARGET_SURFACE_ANALYSIS_MOJOSHADER)) #define UNITY_ARGS_TEXCUBE(tex) TextureCube tex, SamplerState sampler##tex #else // DX9 style HLSL syntax; same object for texture+sampler #define UNITY_ARGS_TEXCUBE(tex) samplerCUBE tex #endif

如果是D3D11：

half3 Unity_GlossyEnvironment (UNITY_ARGS_TEXCUBE(tex), half4 hdr, Unity_GlossyEnvironmentData glossIn)

相当于

half3 Unity_GlossyEnvironment (TextureCube tex, SamplerState samplertex, half4 hdr, Unity_GlossyEnvironmentData glossIn)

其中samplertex是配合UNITY_SAMPLE_TEXCUBE_LOD的

UNITY_SAMPLE_TEXCUBE_LOD是什麽？

源码：

// Macros to declare textures and samplers, possibly separately. For platforms // that have separate samplers & textures (like DX11), and we'd want to conserve // the samplers. // - UNITY_DECLARE_TEX*_NOSAMPLER declares a texture, without a sampler. // - UNITY_SAMPLE_TEX*_SAMPLER samples a texture, using sampler from another texture. // That another texture must also be actually used in the current shader, otherwise // the correct sampler will not be set. #if defined(SHADER_API_D3D11) || defined(SHADER_API_XBOXONE) || defined(UNITY_COMPILER_HLSLCC) || defined(SHADER_API_PSSL) || (defined(SHADER_TARGET_SURFACE_ANALYSIS) && !defined(SHADER_TARGET_SURFACE_ANALYSIS_MOJOSHADER)) #define UNITY_SAMPLE_TEXCUBE_LOD(tex,coord,lod) tex.SampleLevel (sampler##tex,coord, lod) #else // DX9 style HLSL syntax; same object for texture+sampler #define UNITY_SAMPLE_TEXCUBE_LOD(tex,coord,lod) texCUBElod (tex, half4(coord, lod)) #endif

如果是D3D11：

half4 rgbm = UNITY_SAMPLE_TEXCUBE_LOD(tex, R, mip);

相当于：

half4 rgbm = tex.SampleLevel (samplertex, R, mip);

DecodeHDR是什么样的？

因为立方体贴图包含HDR（高动态范围）颜色，这使其可以包含大于1的亮度值。我们必须将样本从HDR格式转换为RGB。

HDR数据使用RGBM格式存储在四个通道中。因此，我们必须采样一个half4值，然后进行转换。

RGBM包含三个RGB通道，以及一个包含幅度因子的M通道。通过将它们乘以来计算最终的RGB值。这里，x 是标量，y 是指数，存储在解码指令的前两个部分中。

// Decodes HDR textures // handles dLDR, RGBM formats inline half3 DecodeHDR (half4 data, half4 decodeInstructions) { // Take into account texture alpha if decodeInstructions.w is true(the alpha value affects the RGB channels) half alpha = decodeInstructions.w * (data.a - 1.0) + 1.0; // If Linear mode is not supported we can skip exponent part #if defined(UNITY_COLORSPACE_GAMMA) return (decodeInstructions.x * alpha) * data.rgb; #else # if defined(UNITY_USE_NATIVE_HDR) return decodeInstructions.x * data.rgb; // Multiplier for future HDRI relative to absolute conversion. # else return (decodeInstructions.x * pow(alpha, decodeInstructions.y)) * data.rgb; # endif #endif }

M通道的转换是必需的，因为当存储在纹理中时，它被限制为0到1范围内的8位值。所以 X 指令将其放大，并且 y指令使它成为非线性的，就像伽玛空间一样。

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