/* 
 * From "A sneak peek at NVIDIA's Material Definition Handbook" by Andy Kopra
 * http://on-demand.gputechconf.com/gtc/2015/presentation/S5303-Andy-Kopra.pdf
 */
 
mdl 1.0;

import df::*;
import state::*;
import base::*;
import tex::*;
import math::*;
import anno::*;

export const color magenta = color(.3, .22, .3); 
export const color green = color(.20, .3, .2);

export material anisotropic_glossy ( 
    color tint = color(0.7), 
    float roughness_u = 1.0, 
    float roughness_v = 0.15) =
material (
    surface: material_surface (
        scattering: df::simple_glossy_bsdf (
            tint: tint,
            roughness_u: roughness_u, roughness_v: roughness_v,
            mode: df::scatter_reflect)));

export float3 modify_normal_u(float factor = 1.0) {
    return math::normalize(
        state::normal()
            + state::texture_tangent_u(0)
            * factor);
}

export material anisotropic_glossy_three_lobes ( 
    color tint = color(0.7),
    float roughness = 0.1,
    uniform float normal_strength = 1.5) =
let {
    float3 start_normal = modify_normal_u(-normal_strength); 
    float3 middle_normal = state::normal();
    float3 end_normal = modify_normal_u(normal_strength); 
    bsdf glossy_component = anisotropic_glossy (
        tint: tint,
        roughness_v: 1,
        roughness_u: roughness).surface.scattering;
} in material (
    surface: material_surface ( 
        scattering: df::weighted_layer (
            weight: 0.5,
            normal: middle_normal, 
            layer: glossy_component, 
            base: df::weighted_layer (
                weight: 0.5,
                normal: end_normal,
                layer: glossy_component,
                base: df::weighted_layer (
                    weight: 1.0,
                    normal: start_normal,
                    layer: glossy_component)))));

export material warp_and_weft (
    color warp_color = magenta, 
    float warp_roughness = 0.3,
    color weft_color = green,
    float weft_roughness = 0.15,
    uniform float weft_normal_strength = 1.5,
    uniform float warp_to_weft = 3,
    float shadowing = 0.0) =
let {
    bsdf warp = anisotropic_glossy (
        tint: warp_color,
        roughness_u: 1.0,
        roughness_v: warp_roughness).surface.scattering;
    bsdf weft = anisotropic_glossy_three_lobes (
        tint: weft_color,
        roughness: weft_roughness,
        normal_strength: weft_normal_strength).surface.scattering;
    float warp_weight =
        warp_to_weft > 1 ? 1.0 - 1.0 / warp_to_weft : warp_to_weft;
} in material (
    surface: material_surface (
        scattering: df::custom_curve_layer (
        weight: shadowing, 
        normal_reflectivity: 0.05, 
        grazing_reflectivity: 1.0, 
        exponent: 3,
        base: df::weighted_layer (
            weight: warp_weight, 
            layer: weft,
            base: warp))));

export material translucency (
    color transmission_color = color(1)) =
material (
    thin_walled: true,
    surface: material_surface (
        scattering: df::diffuse_transmission_bsdf ( tint: transmission_color)));

export material iridescent_silk (
    color warp_color = magenta
    [[
        anno::display_name("Warp Color"),
        anno::description("Color of vertically woven (straight) threads")
    ]],
    float warp_roughness = 0.3
    [[
        anno::display_name("Warp Roughness"),
        anno::soft_range(0.0, 1.0)
    ]],
    color weft_color = green
    [[
        anno::display_name("Weft Color"),
        anno::description("Color of horizontally woven (curved) threads")
    ]],
    float weft_roughness = 0.15
    [[
        anno::display_name("Weft Roughness"),
        anno::soft_range(0.0, 1.0)
    ]],
    uniform float weft_normal_strength = 1.5
    [[
        anno::display_name("Weft Normal Strength"),
        anno::soft_range(0.0, 3.0)
    ]],
    uniform float warp_to_weft = 3
    [[
        anno::display_name("Warp to Weft Ratio"),
        anno::soft_range(1.0, 5.0)
    ]],
    float transmission_weight = 0.2
    [[
        anno::display_name("Transmission Weight"),
        anno::soft_range(0.0, 1.0)
    ]],
    color transmission_color = color(0.95,1.0,0.95)
    [[
        anno::display_name("Transmission Color"),
        anno::description("Color transmitted through the material")
    ]],
    float transmission_exponent = 3.0
    [[
        anno::display_name("Transmission Exponent"),
        anno::soft_range(0.5, 4.0)
    ]],
    float shadowing = 0.0
    [[
        anno::display_name("Shadowing"),
        anno::soft_range(0.0, 1.0)
    ]]) =
let {
    bsdf glossy = warp_and_weft (
        warp_color: warp_color,
        warp_roughness: warp_roughness,
        weft_color: weft_color,
        weft_roughness: weft_roughness, 
        weft_normal_strength: weft_normal_strength, 
        warp_to_weft: warp_to_weft,
        shadowing: shadowing).surface.scattering;
    bsdf translucent = translucency (
        transmission_color: transmission_color).surface.scattering;
} in material (
    thin_walled: true,
    surface: material_surface (
        scattering: df::custom_curve_layer (
            weight: 1.0,
            normal_reflectivity: 1.0 - transmission_weight, 
            grazing_reflectivity: 1.0,
            exponent: transmission_exponent,
            layer: glossy,
            base: translucent)));