arendur 0.0.5

Just another physically based renderer.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247

// Copyright 2017 Dasein Phaos aka. Luxko
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Accounts for the Fresnel reflectance
use geometry::prelude::*;
use std::mem;
use spectrum::{Spectrum, RGBSpectrumf};
use super::*;

/// compute fresnel reflectance for dielectrics
fn fresnel_dielectric(mut cos_theta_i: Float, mut etai: Float, mut etat: Float) -> Float {
    if cos_theta_i < 0.0 as Float {
        // swap direction
        mem::swap(&mut etai, &mut etat);
        cos_theta_i = -cos_theta_i;
    }
    let sin2_theta_i = (1.0 as Float - cos_theta_i * cos_theta_i).max(0. as Float);
    let eta = etai / etat;
    let sin2_theta_t = eta*eta*sin2_theta_i;
    if sin2_theta_t >= 1.0 as Float {
        // total reflection
        return 1.0 as Float;
    }
    let cos_theta_t = (1.0 as Float - sin2_theta_t).sqrt();
    let etci = etat * cos_theta_i;
    let eict = etai * cos_theta_t;
    let r_para = (etci - eict) / (etci + eict);
    let eici = etai * cos_theta_i;
    let etct = etat * cos_theta_t;
    let r_perp = (eici - etct) / (eici + etct);
    (r_para * r_para + r_perp * r_perp) * 0.5 as Float
}

/// compute fresnel reflectance for conductors
fn fresnel_conductor(mut cos_theta_i: Float, mut etai: RGBSpectrumf, mut etat: RGBSpectrumf, k: RGBSpectrumf) -> RGBSpectrumf {
    if cos_theta_i < 0.0 as Float {
        // swap direction
        mem::swap(&mut etai, &mut etat);
        cos_theta_i = -cos_theta_i;
    }

    let sin_theta_i2 = 1.0 as Float - cos_theta_i * cos_theta_i;
    let cos_theta_i2 = cos_theta_i * cos_theta_i;
    let sin_theta_i4 = sin_theta_i2 * sin_theta_i2;
    let sin_theta_i2 = RGBSpectrumf::grey_scale(sin_theta_i2);
    let sin_theta_i4 = RGBSpectrumf::grey_scale(sin_theta_i4);
    let cos_theta_i2 = RGBSpectrumf::grey_scale(cos_theta_i2);
    
    let eta = etat/etai;
    let eta2 = eta * eta;
    let k2 = k * k;
    let tmp0 = eta2 - k2 - sin_theta_i2;
    let a2pb2 = (tmp0 * tmp0 + 4.0 as Float * eta2 * k2).sqrt();
    // FIXME: wrong
    let am2 = (a2pb2 * 2.0 as Float).sqrt();

    let r_perp = (a2pb2 + cos_theta_i2 - am2 * cos_theta_i) / (a2pb2 + cos_theta_i2 + am2 * cos_theta_i);
    let tmpa = a2pb2 * cos_theta_i2;
    let tmpb = am2 * cos_theta_i * sin_theta_i2 + sin_theta_i4;
    let r_para = r_perp * (tmpa - tmpb) / (tmpa + tmpb);
    (r_para * r_para + r_perp * r_perp) * 0.5 as Float   
}

/// A fresnel interface
pub trait Fresnel {
    /// given an incoming direction, specify the reflectance factor
    fn evaluate(&self, cos_theta_i: Float) -> RGBSpectrumf;
}

/// A fresnel conductor
#[derive(Copy, Clone, Debug)]
pub struct Conductor {
    pub etai: RGBSpectrumf,
    pub etat: RGBSpectrumf,
    pub k: RGBSpectrumf,
}

impl Conductor {
    /// construction
    #[inline]
    pub fn new(etai: RGBSpectrumf, etat: RGBSpectrumf, k: RGBSpectrumf) -> Conductor {
        Conductor {
            etai: etai, etat: etat, k: k
        }
    }
}

impl Fresnel for Conductor {
    #[inline]
    fn evaluate(&self, cos_theta_i: Float) -> RGBSpectrumf {
        fresnel_conductor(cos_theta_i, self.etai, self.etat, self.k)
    }
}

/// A fresnel dielectric
#[derive(Copy, Clone, Debug)]
pub struct Dielectric {
    pub eta0: Float,
    pub eta1: Float,
}

impl Dielectric {
    /// Construction
    #[inline]
    pub fn new(etai: Float, etat: Float) -> Dielectric {
        Dielectric{
            eta0: etai, eta1: etat
        }
    }
}

impl Fresnel for Dielectric {
    #[inline]
    fn evaluate(&self, cos_theta_i: Float) -> RGBSpectrumf {
        RGBSpectrumf::grey_scale(fresnel_dielectric(cos_theta_i, self.eta0, self.eta1))
    }
}

/// This interface always returns `Spectrum::gray_scale(1)`.
pub struct Noop;

impl Fresnel for Noop {
    #[inline]
    fn evaluate(&self, _cos_theta_i: Float) -> RGBSpectrumf {
        RGBSpectrumf::grey_scale(1.0 as Float)
    }
}

/// Defines a perfect scattering model described by fresnel
#[derive(Copy, Clone, Debug)]
pub struct FresnelBxdf {
    /// The reflectance term
    pub reflectance: RGBSpectrumf,
    /// The transmittance term
    pub transmittance: RGBSpectrumf,
    /// eta above
    pub eta0: Float,
    /// eta below
    pub eta1: Float,
}

impl FresnelBxdf {
    pub fn new(reflectance: RGBSpectrumf, transmittance: RGBSpectrumf, eta0: Float, eta1: Float) -> FresnelBxdf {
        FresnelBxdf{
            reflectance, transmittance, eta0, eta1
        }
    }
}

impl Bxdf for FresnelBxdf {
    #[inline]
    fn kind(&self) -> BxdfType {
        BXDF_REFLECTION | BXDF_TRANSMISSION | BXDF_SPECULAR
    }

    #[inline]
    fn evaluate(&self, _wo: Vector3f, _wi: Vector3f) -> RGBSpectrumf {
        RGBSpectrumf::black()
    }

    fn evaluate_sampled(&self, wo: Vector3f, u: Point2f) -> (RGBSpectrumf, Vector3f, Float, BxdfType) {
        let cos_theta = normal::cos_theta(wo);
        let f = fresnel_dielectric(cos_theta, self.eta0, self.eta1);
        if u.x < f {
            // reflection
            let wi = Vector3f::new(-wo.x, -wo.y, wo.z);
            let pdf = f;
            debug_assert!(pdf <= 1. as Float);
            debug_assert!(pdf > 0. as Float);
            let f = pdf * self.reflectance / cos_theta.abs();
            (f, wi, pdf, BXDF_REFLECTION | BXDF_SPECULAR)
        } else {
            // transmition
            let pdf = 1. as Float - f;
            debug_assert!(pdf>= 0. as Float);
            let (etai, etao, n) = if cos_theta > 0. as Float {
                (self.eta0, self.eta1, Vector3f::new(0. as Float, 0., 1.))
            } else {
                // println!("in to out");
                (self.eta1, self.eta0, Vector3f::new(0. as Float, 0., -1.))
            };
            let eta = etai/etao;
            let wt = normal::refract(wo, n, eta);
            if let Some(wt) = wt {
                let f = self.transmittance *eta * eta* pdf/wt.z.abs();
                // println!("{:?}, {:?}, {}", f, wt, pdf);
                (f, wt, pdf, BXDF_TRANSMISSION | BXDF_SPECULAR)
            } else {
                (RGBSpectrumf::black(), Vector3f::zero(), pdf, BXDF_TRANSMISSION | BXDF_SPECULAR)
            }
        }
    }

    #[inline]
    fn pdf(&self, _wo: Vector3f, _wi: Vector3f) -> Float {
        0. as Float
    }
}

/// A refracting model
#[derive(Copy, Clone, Debug)]
pub struct FresnelTBxdf {
    pub transmittance: RGBSpectrumf,
    pub eta0: Float,
    pub eta1: Float,
}

impl Bxdf for FresnelTBxdf {
    #[inline]
    fn kind(&self) -> BxdfType {
        BXDF_TRANSMISSION | BXDF_SPECULAR
    }

    #[inline]
    fn evaluate(&self, _wo: Vector3f, _wi: Vector3f) -> RGBSpectrumf {
        RGBSpectrumf::black()
    }

    fn evaluate_sampled(&self, wo: Vector3f, _u: Point2f) -> (RGBSpectrumf, Vector3f, Float, BxdfType) {
        let (etai, etao, n) = if wo.z > 0. as Float {
                (self.eta0, self.eta1, Vector3f::new(0. as Float, 0., 1.))
        } else {
            (self.eta1, self.eta0, Vector3f::new(0. as Float, 0., -1.))
        };
        let eta = etai/etao;
        let wt = normal::refract(wo, n, eta);
        if let Some(wt) = wt {
            let f = self.transmittance *eta * eta*(
                1. as Float - fresnel_dielectric(wo.z, self.eta0, self.eta1)
            ) /wt.z.abs();
            // println!("{:?}, {:?}, {}", f, wt, pdf);
            (f, wt, 1. as Float, BXDF_TRANSMISSION | BXDF_SPECULAR)
        } else {
            (RGBSpectrumf::black(), Vector3f::zero(), 1. as Float, BXDF_TRANSMISSION | BXDF_SPECULAR)
        }
    }

    #[inline]
    fn pdf(&self, _wo: Vector3f, _wi: Vector3f) -> Float {
        0. as Float
    }
}