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krohmerNVkrohmerNV
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MDL 1.7 dielectric and generalized schlick improvements (#1321)
- Change the `Dielectric` MDL implementation to use custom curve instead of Fresnel because of issues with diffuse transmission. This comes with limited thin_film support, which will be restored by MDL 1.8 - Improve `Generalized Schlick` MDL implementation so Reflect, Transmit and ReflectTransmit are more plausible. The OSL backend produces very similar results.
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Lines changed: 100 additions & 29 deletions

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‎resources/Materials/TestSuite/pbrlib/bsdf/generalized_schlick.mtlx‎

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Original file line numberDiff line numberDiff line change
@@ -45,5 +45,51 @@
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<input name="bsdf" type="BSDF" nodename="layer_RT" />
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</surface>
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<output name="layer_RT_out" type="surfaceshader" nodename="surface_layer_RT" />
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<generalized_schlick_bsdf name="schlick_R2" type="BSDF">
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<input name="weight" type="float" value="1.0" />
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<input name="color0" type="color3" value="0.5, 0.0, 0.0" />
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<input name="color90" type="color3" value="0.0, 1.0, 0.0" />
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<input name="exponent" type="float" value="5.0" />
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<input name="scatter_mode" type="string" value="R" />
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</generalized_schlick_bsdf>
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<surface name="surface_R2" type="surfaceshader">
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<input name="bsdf" type="BSDF" nodename="schlick_R2" />
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</surface>
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<output name="R2_out" type="surfaceshader" nodename="surface_R2" />
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<generalized_schlick_bsdf name="schlick_T2" type="BSDF">
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<input name="weight" type="float" value="1.0" />
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<input name="color0" type="color3" value="0.5, 0.0, 0.0" />
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<input name="color90" type="color3" value="0.0, 1.0, 0.0" />
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<input name="exponent" type="float" value="5.0" />
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<input name="scatter_mode" type="string" value="T" />
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</generalized_schlick_bsdf>
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<surface name="surface_T2" type="surfaceshader">
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<input name="bsdf" type="BSDF" nodename="schlick_T2" />
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</surface>
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<output name="T2_out" type="surfaceshader" nodename="surface_T2" />
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<generalized_schlick_bsdf name="schlick_RT2" type="BSDF">
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<input name="weight" type="float" value="1.0" />
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<input name="color0" type="color3" value="0.5, 0.0, 0.0" />
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<input name="color90" type="color3" value="0.0, 1.0, 0.0" />
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<input name="exponent" type="float" value="5.0" />
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<input name="scatter_mode" type="string" value="RT" />
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</generalized_schlick_bsdf>
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<surface name="surface_RT2" type="surfaceshader">
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<input name="bsdf" type="BSDF" nodename="schlick_RT2" />
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</surface>
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<output name="RT2_out" type="surfaceshader" nodename="surface_RT2" />
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<layer name="layer_RT2" type="BSDF">
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<input name="top" type="BSDF" nodename="schlick_R2" />
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<input name="base" type="BSDF" nodename="schlick_T2" />
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</layer>
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<surface name="surface_layer_RT2" type="surfaceshader">
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<input name="bsdf" type="BSDF" nodename="layer_RT2" />
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</surface>
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<output name="layer_RT2_out" type="surfaceshader" nodename="surface_layer_RT2" />
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</nodegraph>
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</materialx>

‎source/MaterialXGenMdl/mdl/materialx/pbrlib.mdl‎

Lines changed: 54 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -159,11 +159,16 @@ export material mx_dielectric_bsdf(
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]]
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= let {
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float coatIor = mxp_thinfilm_ior <= 0.0 ? 1.0 : mxp_thinfilm_ior;
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float grazing_refl = math::max((1.0 - math::average(mxp_roughness)), 0.0);
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float root_r = (mxp_ior-1)/(mxp_ior+1);
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bsdf bsdf_R = df::thin_film(
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thickness: mxp_thinfilm_thickness,
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ior: color(coatIor),
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base: df::fresnel_layer(
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ior: mxp_ior,
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// fresnel layer has issues if base is a diffuse transmission, use custom curve for now
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// this will break thin_film but improves standard_surface with diffuse transmission
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base: df::custom_curve_layer(
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normal_reflectivity: root_r*root_r,
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grazing_reflectivity: grazing_refl,
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weight: mxp_weight,
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layer: df::microfacet_ggx_smith_bsdf(
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roughness_u: mxp_roughness.x,
@@ -172,16 +177,16 @@ export material mx_dielectric_bsdf(
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tangent_u: mxp_tangent,
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mode: df::scatter_reflect),
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base: mxp_base.surface.scattering,
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normal: mxp_normal));
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normal: mxp_normal));
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bsdf bsdf_T = df::weighted_layer(
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weight: mxp_weight,
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layer: df::microfacet_ggx_smith_bsdf(
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roughness_u: mxp_roughness.x,
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roughness_v: mxp_roughness.y,
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tint: mxp_tint,
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tangent_u: mxp_tangent,
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mode: df::scatter_transmit),
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roughness_u: mxp_roughness.x,
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roughness_v: mxp_roughness.y,
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tint: mxp_tint,
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tangent_u: mxp_tangent,
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mode: df::scatter_transmit),
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normal: mxp_normal);
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bsdf bsdf_RT = df::weighted_layer(
@@ -255,7 +260,7 @@ export material mx_generalized_schlick_bsdf(
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color mxp_color0 = color(1.0),
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color mxp_color90 = color(1.0),
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float mxp_exponent = 5.0,
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float2 mxp_roughness = float2(0.0),
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float2 mxp_roughness = float2(0.05),
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float3 mxp_normal = state::normal(),
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float3 mxp_tangent = state::texture_tangent_u(0),
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uniform mx_distribution_type mxp_distribution = mx_distribution_type_ggx [[ anno::unused() ]],
@@ -268,31 +273,51 @@ export material mx_generalized_schlick_bsdf(
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]]
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= let {
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float coatIor = mxp_thinfilm_ior <= 0.0 ? 1.0 : mxp_thinfilm_ior;
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df::scatter_mode mode = ::mx_map_scatter_mode(mxp_scatter_mode);
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bsdf ggx_model = df::microfacet_ggx_smith_bsdf(
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roughness_u: mxp_roughness.x * mxp_roughness.x,
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roughness_v: mxp_roughness.y * mxp_roughness.y,
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float avgF0 = math::average(float3(mxp_color0));
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bsdf ggx_model_R = df::microfacet_ggx_smith_bsdf(
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roughness_u: mxp_roughness.x,
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roughness_v: mxp_roughness.y,
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tint: color(1.0),
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tangent_u: mxp_tangent,
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mode: df::scatter_reflect);
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284+
bsdf ggx_model_T = df::microfacet_ggx_smith_bsdf(
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roughness_u: mxp_roughness.x,
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roughness_v: mxp_roughness.y,
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tint: color(1.0),
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tangent_u: mxp_tangent,
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mode: mode);
289+
mode: df::scatter_transmit);
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} in material(
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surface: material_surface(
280-
scattering: df::thin_film(
281-
thickness: mxp_thinfilm_thickness,
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ior: color(coatIor),
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base: df::color_custom_curve_layer(
284-
normal_reflectivity: mxp_color0,
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grazing_reflectivity: mxp_color90,
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exponent: mxp_exponent,
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weight: color(mxp_weight),
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layer: ggx_model,
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base: mxp_base.surface.scattering,
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normal: mxp_normal
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)
292+
scattering: df::weighted_layer(
293+
weight: mxp_weight,
294+
layer: mxp_scatter_mode == mx_scatter_mode_T
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? df::color_custom_curve_layer(
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normal_reflectivity: mxp_color0,
297+
grazing_reflectivity: mxp_color90,
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exponent: mxp_exponent,
299+
layer: bsdf(),
300+
base: ggx_model_T)
301+
: df::thin_film(
302+
thickness: mxp_thinfilm_thickness,
303+
ior: color(coatIor),
304+
base: df::color_custom_curve_layer(
305+
normal_reflectivity: mxp_color0,
306+
grazing_reflectivity: mxp_color90,
307+
exponent: mxp_exponent,
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layer: ggx_model_R,
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base: mxp_scatter_mode == mx_scatter_mode_R
310+
? mxp_base.surface.scattering
311+
: ggx_model_T)),
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base: mxp_base.surface.scattering,
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normal: mxp_normal
292314
)
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),
316+
// we can't use the computed ior here because it's varying
317+
// assuming that we have something glass like when transmission is used
318+
ior: color(1.5), // color(mx_f0_to_ior(avgF0))
319+
294320
// we need to carry volume properties along for SSS
295-
ior: mxp_base.ior,
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volume: mxp_base.volume
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);
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@@ -513,7 +538,7 @@ export material mx_surface(
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material mxp_bsdf = material() [[ anno::usage( "materialx:bsdf") ]],
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material mxp_edf = material() [[ anno::usage( "materialx:edf") ]],
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float mxp_opacity = 1.0,
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uniform float mxp_transmission_ior = 1.0 // extra parameter for setting transmission IOR
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uniform float mxp_transmission_ior = 0.0 // extra parameter for setting transmission IOR
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) [[
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anno::usage( "materialx:surfaceshader")
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]]
@@ -528,7 +553,7 @@ export material mx_surface(
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scattering: bsdf_node,
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emission: edf_node
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),
531-
ior: color(mxp_transmission_ior),
556+
ior: mxp_transmission_ior > 0.0 ? color(mxp_transmission_ior) : mxp_bsdf.ior,
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volume: bsdf_volume,
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geometry: material_geometry(
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cutout_opacity: mxp_opacity

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