MDL Specification Simplified

mdl_specification_simplified.txt

// source: http://www.mdlhandbook.com/pdf/mdl_handbook.150810.LTR.pdf

// Material definition:

- Surface properties of front-facing surfaces
  - Reflection
  - Transmission
  - Emission
- Surface properties of back-facing surfaces
  - Reflection
  - Transmission
  - Emission
- Volume properties
- Geometric properties
- Shared properties
   - Index of refraction
   - Surface treated as boundary or volume

struct material_emission {
	edf emission = edf(); // Light emission DF
	color intensity = color(0.0);
	intensity_mode mode = intensity_radiant_exitance;
};

struct material_surface {
	bsdf scattering = bsdf(); // Bidirectional scattering DF
	material_emission emission = material_emission();
};

struct material_volume {
	vdf scattering = vdf();
	color absorption_coefficient = 0.0;
	color scattering_coefficient = 0.0;
};

struct material_geometry {
	float3 displacement = float3(0.0);
	float cutout_opacity = 1.0;
	float3 normal = state::normal();
};


struct material {
	uniform bool thin_walled = false;
	material_surface surface = material_surface();
	material_surface backface = material_surface();
	uniform color ior = color(1.0);
	material_volume volume = material_volume();
	material_geometry geometry = material_geometry();
};


// BSDF

diffuse_reflection_bsdf:
	tint: color
	roughness: float

diffuse_transmission_bsdf:
	tint: color

specular_bsdf:
	tint: color
	mode: scatter_mode (scatter_reflect, scatter_transmit, scatter_reflect_transmit)

simple_glossy_bsdf:
	tint: color
	roughness_u: float
	roughness_v: float
	tangent_u: vector3
	mode: scatter_mode (scatter_reflect, scatter_transmit, scatter_reflect_transmit)

backscattering_glossy_reflection_bsdf:

measured_bsdf:




// EDF

// Light emitted in all directions from the surface of the object,
// called Lambertian light distribution by analogy to
// Lambertian diffuse reflection. 
diffuse_edf:

// Distribution of the emission based on the cosine between
// emission direction and surface normal (cosinek distribution)
spot_edf:

// Light distribution based on a measured light profile.
// Arbitrary geometric structure for light distribution from the
// emissive object can be specified based on standard industrial
// formats called light profiles
measured_edf:

// parametesr for all EDFs:
- intensity: color
- mode: intensity_mode (intensity_radiant_exitance, intensity_power)






// VDF

// Addition of absorption effects and subsurface scattering to
// the material’s volume
anisotropic_vdf


// custom IORs

abbe_number_ior




// Layers

weighted_layer:
	weight: float
	layer: bsdf
	base: bsdf

// (layer * reflection-factor) + (base * (1.0 - reflection-factor))
fresnel_layer:
	ior: float
	weight: float
	layer: bsdf
	base: bsdf

normalized_mix:
	components: [ weight, bsdf ]

clamped_mix:
	components: [ weight, bsdf ]

custom_curve_layer:
	weight: float
	normal_reflectivity: float
	grazing_reflectivity: float
	exponent: float
	layer: bsdf
	base: bsdf

measured_curve_layer: