GGX\u4f5c\u4e3a\u63cf\u8ff0\u9ad8\u5149\u5f62\u72b6\u7684\u51fd\u6570\uff0c\u975e\u5e38\u91cd\u8981\uff0c\u4f46\u540c\u65f6\u5b83\u4e5f\u6bd4\u8f83\u6d88\u8017\u6027\u80fd\uff0c\u9002\u5408PC\u7aef\u4f7f\u7528\uff0c\u867d\u7136Walter\u4e5f\u63d0\u51fa\u4e00\u79cd\u9002\u5408\u79fb\u52a8\u7aef\u7684GGX\uff0c\u4f46\u5e76\u6ca1\u6709\u89e3\u51b3fp16\u7cbe\u5ea6\u4e0b\u5bfc\u81f4\u7684\u95ee\u9898<\/p>\n
\u672c\u6587\u5c06\u4ecb\u7ecdWalter GGX\u5b58\u5728\u7684\u95ee\u9898\uff0c\u5e76\u5206\u4eab\u4e00\u79cd\u53ef\u4ee5\u89e3\u51b3Walter GGX\u95ee\u9898\u7684GGX\u7b97\u6cd5<\/p>\n
\/\/ GGX \/ Trowbridge-Reitz\n\/\/ [Walter et al. 2007, \"Microfacet models for refraction through rough surfaces\"]\nfloat D_GGX(float a2, float NoH)\n{\n float d = (NoH * a2 - NoH) * NoH + 1.f; \/\/ 2 mad\n return a2 \/ (PI * d * d + 1e-4); \/\/ 4 mul, 1 rcp\n}\n<\/code><\/pre>\n\n- \u7279\u70b9<\/p>\n<\/li>\n
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\u5229\u7528\u6307\u4ee4\u4f18\u5316\u3002\u901a\u8fc7\u591a\u9879\u5f0f\u5c55\u5f00\u89c4\u907f\u4e86\u6807\u51c6\u516c\u5f0f\u4e2d\u7684 (1\u2212NoH2) \u8fd9\u79cd\u9700\u8981\u591a\u6b21\u51cf\u6cd5\u7684\u8fd0\u7b97<\/p>\n<\/li>\n
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\u7f3a\u70b9<\/p>\n<\/li>\n
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\u03b12\u4f9d\u8d56\u9ad8\u7cbe\u5ea6\u3002\u5f53 a2<\/code> \u975e\u5e38\u5c0f\uff0c\u5206\u6bcd\u7684 d \u4f1a\u8d8b\u5411\u4e8e 0\uff0c\u82e5\u662ffp16\uff0c\u4f1a\u6709\u53ef\u80fd\u5f97\u5230NaN<\/p>\n\u5f53roughness\u975e\u5e38\u5c0f\u59820.01\uff0ca2 = 0.0001\uff0c\u4e14normal\u4e0ehalf vec\u521a\u597d\u5bf9\u9f50\u2014\u2014NoH = 1\uff0cd = 0.0001\uff0c\u5206\u6bcd = $3.14 * 10^{-8}$<\/strong><\/p>\n\u95ee\u9898\u5c31\u5728\u4e8e\u5206\u6bcd\uff0c\u7531\u4e8efp16\u7684\u6700\u5c0f\u503c\u4e3a6.1\u00d710\u22125<\/strong>\uff0c\u5206\u6bcd\u5df2\u7ecf\u8fdc\u8fdc\u8d85\u8fc7fp16\u7684\u7cbe\u5ea6\u8303\u56f4<\/p>\n<\/li>\n<\/ul>\n<\/li>\n- \n
Walter Mobile GGX<\/p>\n
float D_GGX_Mobile(float Roughness, float NoH)\n{\n \/\/ Walter et al. 2007, \"Microfacet Models for Refraction through Rough Surfaces\"\n float OneMinusNoHSqr = 1.0 - NoH * NoH;\n float a = Roughness * Roughness;\n float n = NoH * a;\n float p = a \/ (OneMinusNoHSqr + n * n);\n float d = (1.0 \/ PI) * p * p;\n \/\/ clamp to avoid overlfow in a bright env\n return min(d, 2048.0);\n}\n<\/code><\/pre>\n\n- \u7279\u70b9\uff1a\u9488\u5bf9FP16\u505a\u4e86\u4fdd\u62a4\u4f4e\u7cbe\u5ea6\u6ea2\u51fa\u7684\u8bbe\u8ba1<\/p>\n<\/li>\n
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\u7f3a\u70b9\uff1a\u727a\u7272\u4e86\u9ad8\u5149\u7ec6\u8282<\/p>\n<\/li>\n<\/ul>\n
\u56e0\u4e3a\u505a\u4e86min(d, 2048.0)<\/span><\/p>\n<\/li>\n- \n
Filament GGX<\/p>\n
#define MEDIUMP_FLT_MAX 65504.0\n#define saturateMediump(x) min(x, MEDIUMP_FLT_MAX)\n\nfloat D_GGX(float roughness, float NoH, const vec3 n, const vec3 h) {\n vec3 NxH = cross(n, h);\n float a = NoH * roughness;\n float k = roughness \/ (dot(NxH, NxH) + a * a);\n float d = k * k * (1.0 \/ PI);\n return saturateMediump(d);\n}\n<\/code><\/pre>\n\n- \u4e3a\u4ec0\u4e48cross\u53ef\u4ee5\u4ee3\u66ff1- NoH^2<\/span><\/li>\n<\/ul>\n
\u4f7f\u7528\u5230\u4e86\u62c9\u683c\u6717\u65e5\u7b49\u5f0f\uff1a|a\u00d7b|^2 = |a|^2|b|^2 - (a\u00b7b)^2<\/span><\/p>\n\u53c8\u56e0\u4e3aa\u3001b\u90fd\u662f\u5355\u4f4d\u5411\u91cf\uff0c\u90a3\u4e48|a\u00d7b|^2 = 1 - (a\u00b7b)^2<\/span><\/p>\n\n- \u7279\u70b9\uff1a\u652f\u6301FP16\uff0c\u4e14\u4fdd\u7559\u9ad8\u5149\u7ec6\u8282<\/p>\n<\/li>\n
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\u7f3a\u70b9\uff1a\u8ba1\u7b97\u6d88\u8017\u6bd4Walter Mobile GGX\u7565\u9ad8\u4e00\u4e9b<\/p>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
\u603b\u7ed3<\/h1>\n
\n\n\n\u65b9\u6848<\/th>\n \u4f18\u70b9<\/th>\n \u7f3a\u70b9<\/th>\n<\/tr>\n<\/thead>\n \n\nWalter GGX<\/td>\n \u901f\u5ea6\u5feb\u3001\u9ad8\u5149\u7ec6\u8282\u9ad8<\/td>\n fp16\u4e0b\u9ad8\u5149\u4e0d\u7a33\u5b9a<\/td>\n<\/tr>\n \nWalter Mobile GGX<\/td>\n \u6bd4GGX\u6027\u80fd\u66f4\u597d<\/td>\n fp16\u4e0b\u635f\u5931\u9ad8\u5149\u7ec6\u8282<\/td>\n<\/tr>\n \nFilament GGX<\/td>\n fp16\u4e0b\u4fdd\u7559\u9ad8\u5149\u7ec6\u8282\u4e14\u7a33\u5b9a<\/td>\n \u6027\u80fd\u6bd4Walter Mobile GGX\u7565\u9ad8<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nReference<\/h1>\n