模拟 mia_material

如我们在上一页所见，mia_material 反射行为可以精确模拟。实际上，几乎每个方面都可以模拟，并且对于大多数设置而言，都可以构建现象来模仿 mia_material 的行为。

技巧可能在于 mia_material 中包含几个可以打开或关闭特征的开关，而且通常这可能需要使用不同分层设置进行模拟。例如，在“thin_walled”模式为开或关时，mia_material 本身会产生不同的行为 - 对于分层着色器而言，“thin_walled”选项在 mila_material 上为开裁切功能将实现为可见性，而任何给定层可以将透明度视为一种组件。

以下是 mia_material“类似行为”现象 mila_layer_mia_material 的列表。

这只是引用一个示例来说明可以创建类似于 mia_material 的行为。直接使用分层着色器可能会更好，但如果希望在场景中混合现有 mia_materials，则这种做法可能会有所帮助。

declare phenomenon
    color "mila_layer_mia_material" (
        scalar  "diffuse_weight"      default 1.0, #: min 0.0 max 1.0
        color   "diffuse"             default 0.5 0.5 0.5,
        scalar  "diffuse_roughness"   default 0.0, #: min 0.0 max 1.0

        scalar  "reflectivity"        default 0.6, #: min 0.0 max 1.0
        color   "refl_color"          default 1.0 1.0 1.0,
        scalar  "refl_gloss"          default 1.0, #: min 0.0 max 1.0
        scalar  "refl_gloss_quality"  default 1.0, #: min 0.0 softmax 4.0

        scalar  "transparency"        default 0.0, #: min 0.0 max 1.0
        color   "refr_color"          default 1.0 1.0 1.0,
        scalar  "refr_gloss"          default 1.0, #: min 0.0 max 1.0
        scalar  "refr_ior"            default 1.4, #: min 0.1 softmax 2.0
        scalar  "refr_gloss_quality"  default 1.0, #: min 0.0 softmax 4.0
        boolean "refr_translucency"   default off,
        color   "refr_trans_color"    default 0.7 0.6 0.5,
        scalar  "refr_trans_weight"   default 0.5, #: min 0.0 max 1.0

        scalar  "anisotropy"          default 1.0, #: min 0.1 softmax 10
        scalar  "anisotropy_rotation" default 0.0, #: softmin 0 softmax 1
        integer "anisotropy_channel"  default -1,  #: min -1  softmax 64

        integer "brdf_fresnel_mode"    default 1,  #Custom curve (aka manual), while 0 Fresnel uses refr_ior
        scalar  "brdf_0_degree_refl"   default 0.2, #: min 0.0 max 1.0
        scalar  "brdf_90_degree_refl"  default 1.0, #: min 0.0 max 1.0
        scalar  "brdf_curve"           default 5.0, #: min 0.1 softmax 20

        # Reflection/Refraction optimizations & falloffs

        boolean  "refl_falloff_on"       default off,
        scalar   "refl_falloff_dist"     default 0.0,
        boolean  "refl_falloff_color_on" default off,
        color    "refl_falloff_color"    default 0 0 0,

        boolean  "refr_falloff_on"       default off,
        scalar   "refr_falloff_dist"     default 0.0,
        boolean  "refr_falloff_color_on" default off,
        color    "refr_falloff_color"    default 0 0 0,

        # Factors

        scalar   "indirect"              default 1.0,  #: min 0 softmax 1.0

        # Built in AO
        
        scalar   "quality"        default 1.0,          #: min 0.0 softmax 2.0

        # Only one bump input
        vector   "overall_bump"
    )
    
    shader "refl_roughness" "mila_get_roughness" ("glossiness" = interface "refl_gloss")
    # Reflections
    shader "reflection" "mila_glossy_reflection" (
        "roughness"       = "refl_roughness",
        "quality"         = interface "refl_gloss_quality",

        "anisotropy"      = interface "anisotropy",
        "aniso_angle"     = interface "anisotropy_rotation",
        "aniso_channel"   = interface "anisotropy_channel",
        
        "use_max_dist"       = interface "refl_falloff_on",
        "max_dist"           = interface "refl_falloff_dist",
        "use_max_dist_color" = interface "refl_falloff_color_on",
        "max_dist_color"     = interface "refl_falloff_color",
    )

    shader "refr_roughness" "mila_get_roughness" ("glossiness" = interface "refr_gloss")    
    # Refractions
    shader "refraction" "mila_glossy_transmission" (
        "roughness"       = "refr_roughness",
        "quality"         = interface "refr_gloss_quality",
        "ior"             = interface "refr_ior",
        
        "anisotropy"      = interface "anisotropy",
        "aniso_angle"     = interface "anisotropy_rotation",
        "aniso_channel"   = interface "anisotropy_channel",
        
        "use_max_dist"       = interface "refr_falloff_on",
        "max_dist"           = interface "refr_falloff_dist",
        "use_max_dist_color" = interface "refr_falloff_color_on",
        "max_dist_color"     = interface "refr_falloff_color"        

    )

    # Translucency
    shader "translucency" "mila_diffuse_transmission" (
        "tint"            = interface "refr_trans_color",
        "indirect"        = interface "indirect_multiplier"
    )    

    # Diffuse
    shader "diffuse" "mila_diffuse_reflection" (
        "roughness"        = interface "diffuse_roughness",
        "indirect"         = interface "indirect_multiplier",
        "quality"          = interface "quality"
    )

    # Transparency and Translucency live in a 
    # separate "sub layers" because they steal
    # energy from eachother

    shader "transmission" "mila_layer" (
        "layers" [
            {
                "shader" "translucency",
                "weight_tint" 1 1 1,
                "weight"  = interface "refr_trans_weight",
		"use_directional_weight" off,
                "on"      = interface "refr_translucency"
            },
            {
                "shader" "refraction",
                "weight_tint" 1 1 1, 
                "weight" 1,
		"use_directional_weight" off,
                "on" on
            }
        ]
    )

    #
    # The main layers, mimicking mia_materials
    # energy conservation logic
    #

    shader "mia_layers" "mila_layer" (
        "layers" [
            {
                "shader" "reflection",   # Reflection layer
                "weight_tint"          = interface "refl_color",
                "bump"                 = interface "overall_bump",
                "weight"               = interface "reflectivity",
		"use_directional_weight" on,
                "directional_weight_mode" = interface "brdf_fresnel_mode",
                "normal_reflectivity"  = interface "brdf_0_degree_refl",
                "grazing_reflectivity" = interface "brdf_90_degree_refl",
                "exponent"             = interface "brdf_curve",
                "ior"                  = interface "refr_ior",
                "on" on
            },
            {
                "shader" "transmission", # Transparency+Translucency
                "bump"                 = interface "overall_bump",
                "weight_tint"          = interface "refr_color", 
                "weight"               = interface "transparency",
		"use_directional_weight" off,
                "on" on
            },
            {
                "shader" "diffuse",      # Diffuse
                "bump"                 = interface "overall_bump",
                "weight_tint"          = interface "diffuse", 
                "weight"               = interface "diffuse_weight",
		"use_directional_weight" off,
                "on" on
            }
        ]
    )

    root = "mia_layers"
    
    apply material, texture, shadow, photon
    version 1
end declare

mia_material_emulator 与 mia_material(_x) 具有相同的参数，以下参数除外。其中的某些差别在用户界面中或是使用简单的映射着色器时可能体现不出来

mia_material 中缺少以下参数或是以下参数有所不同：

cutout_opacity
应该直接输入到 mila_material 的“可见性”输入中。
brdf_fresnel
为 mia_material 中的布尔开关。通过 mila_layer，我们首先选择在定向依赖权重中是否开启了“use_directional_weight”，如果为“开”，我们可以从当前两个值（0 = 菲涅尔，1 = 自定义曲线）中选择定向依赖权重的具体模式当使用定向依赖权重时，值 1 与旧参数“关”值一致，并且值 0 与其“开”值一致。在 mia_material 中，为获得非定向依赖权重，必须调整“自定义曲线”的输入，因为它始终为定向依赖。
refl_is_metal
缺失 - 通过使反射颜色与漫反射颜色相同达到相同效果。
brdf_conserve_energy
缺少；这些着色器始终会节约能量。
refl_gloss
refr_gloss
具有不同的范围；默认情况下分层粗糙度行为逆向与 mia_material 镜面反射高光的光泽度参数相似。但是，该曲线的行为应当采用更线性的视觉方式，以更改粗糙度。还有其他选项允许您更改该曲线的指数（当前默认值为 3），以调整粗糙度映射到材质模糊度的方式。请参见 mila_glossy_reflection 以了解更多详细信息。
overall_bump
standard_bump
no_diffuse_bump
bump_mode
将替换为一个凹凸输入 overall_bump。该现象的不同变体可轻松写入，以支持这些开关的各种变体（例如单独的漫反射凹凸输入）。
multiple_outputs
默认情况下在分层着色器中始终处于打开状态。
refl_interpolate
refl_hl_only
refl_interpolate
intr_*
fg_quality*
no_visible_area_hl
do_refractive_caustics
skip_inside_refl
backface_cull
hl_vs_refl_balance
additional_color
mode
lights
全都是此现象或分层着色器不支持的特征。

图像示例

模拟车漆

模拟车漆着色器实际上更困难，但这通常是由于车漆着色器更老、物理真实性较低。此模拟看起来并不是非常精确 - 它看起来更逼真，并且更加具有物理真实性。旧车漆现象具有以下问题：

更有意义的做法是尝试克隆更“合理”的车漆参数并构建更具物理真实性的新现象，新现象会保留旧着色器的一些特征，但逼真效果将会大大提高。下面就尝试构建这种现象 - 可能会存在其他版本：

declare phenomenon
    color "mila_layer_car_paint" 
    (
        color   "base_color"             default 0.8 0.1 0,
        color   "edge_color"             default 0 0 0,
        scalar  "edge_color_bias"        default 1.0,
        color   "lit_color"              default 0.6 0 0.2,
        scalar  "diffuse_weight"         default 1.0,

        color   "flake_color"            default 1 1 1,
        scalar  "flake_weight"           default 1.0,

        scalar  "flake_density"          default  0.8,
        scalar  "flake_strength"         default  0.8,
        scalar  "flake_scale"            default 0.1,
        integer "flake_type"             default  0,
        integer "flake_cell_style"       default 0,
        scalar  "flake_cell_size"        default  0.3,
        
        # New - more physical - parameters
        scalar  "flake_roughness"        default 0.4,

        scalar  "glossy_paint_weight"    default 0.1,
        scalar  "glossy_paint_roughness" default 0.6,
        
        color   "clearcoat_1_color"      default 1 1 1,
        scalar  "clearcoat_1_weight"     default 1.0,
        scalar  "clearcoat_1_roughness"  default 0.0,
        
        color   "clearcoat_2_color"      default 1 1 1,
        scalar  "clearcoat_2_weight"     default 0.0,
        scalar  "clearcoat_2_roughness"  default 0.4,
        
        scalar  "clearcoat_ior"          default 1.8,
        
        scalar  "quality"                default 1.0,
        scalar  "max_distance"           default 0.0,

        # Dirt
        color   "dirt_color"             default .3 .3 .3,
        scalar  "dirt_weight"            default 0.0,

        scalar  "irradiance_weight"      default 1.0,
    )

    shader "flakes"  "mila_bump_flakes" (
        "weight"    = interface "flake_weight",
        "scale"    = interface "flake_scale",
        "perturbation" = interface "flake_strength",
        "density"  = interface "flake_density",
        "type"    = interface "flake_type",
        "circle_size"  = interface "flake_cell_size",
        "cell_style" = interface "flake_cell_style",

    )
    
    shader "dirt" "mila_diffuse_reflection" (
        "tint"  = interface "dirt_color",
        "indirect" = interface "irradiance_weight"
    )

    shader "clearcoat_2" "mila_glossy_reflection" (
        "roughness" = interface "clearcoat_2_roughness",
        "quality"   = interface "quality"
    )

    shader "clearcoat_1" "mila_glossy_reflection" (
        "roughness" = interface "clearcoat_1_roughness",
        "quality"   = interface "quality"
    )

    shader "flakes_gloss"  "mila_glossy_reflection" (
        "tint"      = interface "flake_color",
        "roughness" = interface "flake_roughness",
        "quality"   = interface "quality"
    )

    shader "glossy_paint" "mila_glossy_reflection" (
        "roughness"      = interface "glossy_paint_roughness",
        "quality"        = interface "quality"
    )
    
    shader "edge_diffuse" "mila_diffuse_reflection" (
        "tint"   = interface "edge_color",
        "indirect"  = interface "irradiance_weight"
    )

    shader "main_diffuse" "mila_diffuse_reflection" (
        "tint"   = interface "base_color",
        "indirect"  = interface "irradiance_weight"
    )

    shader "mia_layers" "mila_layer" (
        "layers" [
            {
                "shader"               "dirt",
                "weight"               = interface "dirt_weight",
                "weight_tint"          1 1 1,
                "on" on
            },
            {
                "shader"               "clearcoat_1",
                "weight"               = interface "clearcoat_1_weight",
                "weight_tint"          = interface "clearcoat_1_color",
		"use_directional_weight" on,
                "directional_weight_mode" 0,
                "ior"                  = interface "clearcoat_ior",
                "on" on
            },
            {
                "shader"               "clearcoat_2",
                "weight"               = interface "clearcoat_2_weight",
                "weight_tint"          = interface "clearcoat_2_color",
		"use_directional_weight" on,
                "directional_weight_mode" 0,
                "ior"                  = interface "clearcoat_ior",
                "on" on
            },
            {
                "shader"               "flakes_gloss",
                "weight"               = "flakes.visibility",
                "weight_tint"          1 1 1,
                "bump"                 = "flakes.normal",
                "on" on
            },
            {
                "shader"               "glossy_paint",
                "weight"               = interface "glossy_paint_weight",
                "weight_tint"          = interface "lit_color",
                "on" on
            },
            {
                "shader"               "edge_diffuse",
                "weight"               = interface "diffuse_weight",
                "weight_tint"          1 1 1,
                "use_directional_weight" on,
                "directional_weight_mode" 1,
                "normal_reflectivity"  0.0,
                "grazing_reflectivity" 1.0,
                "exponent"  = interface "edge_color_bias",
                "on" on
            },
            {
                "shader"               "main_diffuse",
                "weight_tint"          1 1 1,
                "weight"               = interface "diffuse_weight",
                "on" on
            }
        ]
    )

    root = "mia_layers"
    
    apply material, texture, shadow, photon
    version 2
end declare

该现象通过以下 7 个层（从上到下）构建：

以下是着色器的参数：

base_color
edge_color
edge_color_bias
diffuse_weight
与在原始车漆现象中的行为完全相同（请参见车漆库文档）。
lit_color
行为略微不同，但仍保留了它的名称。旧着色器中的对象会伪造为一种特殊的彩色高光，这实际上是新的彩色光泽反射层的颜色。
flake_color
flake_weight
flake_density
flake_strength
flake_scale
与原始车漆现象相同的作用基本上完全相同（请参见车漆库文档）。
flake_roughness
是薄片的粗糙度，范围为 0 到 1。
glossy_paint_weight
glossy_paint_roughness
是新的“彩色光泽车漆”层的权重和粗糙度，使用 lit_color 作为其反射颜色。
clearcoat_X_color
clearcoat_X_weight
clearcoat_X_roughness
clearcoat_ior
为透明涂层创建两个真实的光泽层。这两个层可以自动进行正确的反射，并始终应用菲涅尔效果（使用 clearcoat_ior 的 IOR）。大多数具有单独的高光和反射控件的旧混乱参数都已消失，因为所有这些参数都是奇怪的高光/反射“边”和“基础”权重设置，它们只是为了模拟菲涅尔效果。
max_distance
dirt_color
dirt_weight
irradiance_weight
……作用全都与之前相同。

旧现象中已被删除的过时参数：

lit_color_bias
大致替换为 glossy_paint_roughness
flake_reflect
flake_exp
油漆碎片现在始终进行物理反射。替换为 flake_roughness
flake_decay
global_weight
不受此现象支持。
ambient
diffuse_bias
reflection_color
edge_factor
reflection_edge_weight
reflection_base_weight
glossy_spread
spec_*
所有这些均不具有物理真实性或处于奇怪的范围内。它们会替换为使用粗糙度参数的光泽层，本身始终反射事物（即所有单独的反射设置均已移除）并遵循菲涅尔反射率曲线。
mode
lights
不应用于分层着色器。

图像示例