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

// std
use std::f32::consts::PI;
use std::sync::Arc;
// pbrt
use crate::core::geometry::{nrm_abs_dot_vec3f, nrm_dot_vec3f, vec3_coordinate_system};
use crate::core::geometry::{Normal3f, Point2f, Ray, Vector3f, XYEnum};
use crate::core::interaction::{Interaction, InteractionCommon};
use crate::core::light::{LightFlags, VisibilityTester};
use crate::core::medium::{Medium, MediumInterface};
use crate::core::pbrt::{Float, Spectrum};
use crate::core::rng::FLOAT_ONE_MINUS_EPSILON;
use crate::core::sampling::{cosine_hemisphere_pdf, cosine_sample_hemisphere};
use crate::core::scene::Scene;
use crate::core::shape::Shape;
use crate::core::transform::Transform;

// see diffuse.h

pub struct DiffuseAreaLight {
    pub l_emit: Spectrum,
    pub shape: Arc<Shape>,
    pub two_sided: bool,
    pub area: Float,
    // inherited from class Light (see light.h)
    pub flags: u8,
    pub n_samples: i32,
    pub medium_interface: MediumInterface,
    // light_to_world: Transform,
    // world_to_light: Transform,
}

impl DiffuseAreaLight {
    pub fn new(
        _light_to_world: &Transform,
        medium_interface: &MediumInterface,
        l_emit: &Spectrum,
        n_samples: i32,
        shape: Arc<Shape>,
        two_sided: bool,
    ) -> Self {
        let area: Float = shape.area();
        let mut inside: Option<Arc<Medium>> = None;
        let mut outside: Option<Arc<Medium>> = None;
        if let Some(ref mi_inside) = medium_interface.inside {
            inside = Some(mi_inside.clone());
        }
        if let Some(ref mi_outside) = medium_interface.outside {
            outside = Some(mi_outside.clone());
        }
        DiffuseAreaLight {
            l_emit: *l_emit,
            shape,
            two_sided,
            area,
            // inherited from class Light (see light.h)
            flags: LightFlags::Area as u8,
            n_samples: std::cmp::max(1_i32, n_samples),
            medium_interface: MediumInterface { inside, outside },
            // light_to_world: *light_to_world,
            // world_to_light: Transform::inverse(*light_to_world),
        }
    }
    // Light
    pub fn sample_li<'a, 'b>(
        &'b self,
        iref: &'a InteractionCommon,
        light_intr: &'b mut InteractionCommon,
        u: Point2f,
        wi: &mut Vector3f,
        pdf: &mut Float,
        vis: &mut VisibilityTester<'a, 'b>,
    ) -> Spectrum {
        // TODO: ProfilePhase _(Prof::LightSample);
        *light_intr = self.shape.sample_with_ref_point(iref, u, pdf);
        // TODO: iref.mediumInterface = mediumInterface;
        if *pdf == 0.0 as Float || (light_intr.p - iref.p).length_squared() == 0.0 as Float {
            *pdf = 0.0 as Float;
            return Spectrum::default();
        }
        *wi = (light_intr.p - iref.p).normalize();
        vis.p0 = Some(&iref);
        vis.p1 = Some(light_intr);
        self.l(&light_intr, &-*wi)
    }
    pub fn power(&self) -> Spectrum {
        // return (twoSided ? 2 : 1) * Lemit * area * Pi;
        let factor = if self.two_sided {
            2.0 as Float
        } else {
            1.0 as Float
        };
        self.l_emit * factor * self.area * PI
    }
    pub fn preprocess(&self, _scene: &Scene) {
        // TODO?
    }
    pub fn le(&self, _ray: &Ray) -> Spectrum {
        Spectrum::default()
    }
    pub fn pdf_li(&self, iref: &dyn Interaction, wi: &Vector3f) -> Float {
        // TODO: ProfilePhase _(Prof::LightPdf);
        self.shape.pdf_with_ref_point(iref, &wi)
    }
    pub fn sample_le(
        &self,
        u1: Point2f,
        u2: Point2f,
        _time: Float,
        ray: &mut Ray,
        n_light: &mut Normal3f,
        pdf_pos: &mut Float,
        pdf_dir: &mut Float,
    ) -> Spectrum {
        // TODO: ProfilePhase _(Prof::LightSample);

        // sample a point on the area light's _Shape_, _p_shape_
        let ic: InteractionCommon = self.shape.sample(u1, pdf_pos);
        // TODO: p_shape.mediumInterface = mediumInterface;
        *n_light = ic.n;
        // sample a cosine-weighted outgoing direction _w_ for area light
        let mut w: Vector3f;
        if self.two_sided {
            let mut u: Point2f = Point2f { x: u2.x, y: u2.y };
            // choose a side to sample and then remap u[0] to [0,1]
            // before applying cosine-weighted hemisphere sampling for
            // the chosen side.
            if u[XYEnum::X] < 0.5 as Float {
                u[XYEnum::X] = (u[XYEnum::X] * 2.0 as Float).min(FLOAT_ONE_MINUS_EPSILON);
                w = cosine_sample_hemisphere(&u);
            } else {
                u[XYEnum::X] =
                    ((u[XYEnum::X] - 0.5 as Float) * 2.0 as Float).min(FLOAT_ONE_MINUS_EPSILON);
                w = cosine_sample_hemisphere(&u);
                w.z *= -1.0 as Float;
            }
            *pdf_dir = 0.5 as Float * cosine_hemisphere_pdf(w.z.abs());
        } else {
            w = cosine_sample_hemisphere(&u2);
            *pdf_dir = cosine_hemisphere_pdf(w.z);
        }
        let n: Vector3f = Vector3f::from(ic.n);
        let mut v1: Vector3f = Vector3f::default();
        let mut v2: Vector3f = Vector3f::default();
        vec3_coordinate_system(&n, &mut v1, &mut v2);
        w = v1 * w.x + v2 * w.y + n * w.z;
        *ray = ic.spawn_ray(&w);
        self.l(&ic, &w)
    }
    pub fn pdf_le(&self, ray: &Ray, n: &Normal3f, pdf_pos: &mut Float, pdf_dir: &mut Float) {
        *pdf_pos = self.shape.pdf(&InteractionCommon::default());
        if self.two_sided {
            *pdf_dir = 0.5 as Float * cosine_hemisphere_pdf(nrm_abs_dot_vec3f(&n, &ray.d));
        } else {
            *pdf_dir = cosine_hemisphere_pdf(nrm_dot_vec3f(&n, &ray.d));
        }
    }
    pub fn get_flags(&self) -> u8 {
        self.flags
    }
    pub fn get_n_samples(&self) -> i32 {
        self.n_samples
    }
    // AreaLight
    pub fn l(&self, intr: &InteractionCommon, w: &Vector3f) -> Spectrum {
        if self.two_sided || nrm_dot_vec3f(&intr.n, &w) > 0.0 as Float {
            self.l_emit
        } else {
            Spectrum::new(0.0 as Float)
        }
    }
}