From 6a829a96fd8a38e0da0a44811a3dd1ac04744bf6 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <brunobelanyi@gmail.com>
Date: Tue, 17 Mar 2020 23:44:13 +0100
Subject: [PATCH] library: render: add Scene implementation

---
 src/render/mod.rs   |   3 +
 src/render/scene.rs | 144 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 147 insertions(+)
 create mode 100644 src/render/scene.rs

diff --git a/src/render/mod.rs b/src/render/mod.rs
index 175aa06..257c216 100644
--- a/src/render/mod.rs
+++ b/src/render/mod.rs
@@ -3,3 +3,6 @@ pub use light_aggregate::*;
 
 pub mod object;
 pub use object::*;
+
+pub mod scene;
+pub use scene::*;
diff --git a/src/render/scene.rs b/src/render/scene.rs
new file mode 100644
index 0000000..6293864
--- /dev/null
+++ b/src/render/scene.rs
@@ -0,0 +1,144 @@
+use super::{light_aggregate::LightAggregate, object::Object};
+use crate::core::Camera;
+use crate::core::LinearColor;
+use crate::{Point, Vector};
+use bvh::ray::Ray;
+use image::RgbImage;
+use rand::prelude::thread_rng;
+use rand::Rng;
+
+/// Represent the scene being rendered.
+pub struct Scene<'a> {
+    camera: Camera,
+    lights: LightAggregate,
+    objects: Vec<Object<'a>>,
+    aliasing_limit: u32,
+}
+
+impl<'a> Scene<'a> {
+    pub fn new(
+        camera: Camera,
+        lights: LightAggregate,
+        objects: Vec<Object<'a>>,
+        aliasing_limit: u32,
+        reflection_limit: u32,
+    ) -> Self {
+        Scene {
+            camera,
+            lights,
+            objects,
+            aliasing_limit,
+            reflection_limit,
+        }
+    }
+
+    /// Render the scene into an image.
+    pub fn render(&self) -> RgbImage {
+        let mut image = RgbImage::new(self.camera.film().width(), self.camera.film().height());
+        let pixel_func = if self.aliasing_limit > 0 {
+            Self::anti_alias_pixel
+        } else {
+            Self::pixel
+        };
+        for (x, y, pixel) in image.enumerate_pixels_mut() {
+            *pixel = pixel_func(&self, x as f32, y as f32).into()
+        }
+        image
+    }
+
+    /// Get pixel color for (x, y) a pixel **coordinate**
+    fn pixel(&self, x: f32, y: f32) -> LinearColor {
+        let (x, y) = self.camera.film().pixel_ratio(x, y);
+        let pixel = self.camera.film().pixel_at_ratio(x, y);
+        let direction = (pixel - self.camera.origin()).normalize();
+        self.cast_ray(Ray::new(pixel, direction))
+            .map_or_else(LinearColor::black, |(t, obj)| {
+                self.color_at(pixel + direction * t, obj, direction, self.reflection_limit)
+            })
+    }
+
+    /// Get pixel color with anti-aliasing
+    fn anti_alias_pixel(&self, x: f32, y: f32) -> LinearColor {
+        let range = 0..self.aliasing_limit;
+        let mut rng = thread_rng();
+        let acc: LinearColor = range
+            .map(|_| {
+                let random_x: f32 = rng.gen();
+                let random_y: f32 = rng.gen();
+                self.pixel(x + random_x, y + random_y)
+            })
+            .sum();
+        acc / self.aliasing_limit as f32
+    }
+
+    fn cast_ray(&self, ray: Ray) -> Option<(f32, &Object)> {
+        // NOTE(Bruno): should be written using iterators
+        let mut shot_obj: Option<&Object> = None;
+        let mut t = std::f32::INFINITY;
+        for object in self.objects.iter() {
+            match object.shape.intersect(&ray) {
+                Some(dist) if dist < t => {
+                    t = dist;
+                    shot_obj = Some(&object);
+                }
+                _ => {}
+            }
+        }
+        shot_obj.map(|obj| (t, obj))
+    }
+
+    fn color_at(&self, point: Point, object: &Object, incident_ray: Vector) -> LinearColor {
+        self.illuminate(point, object, incident_ray)
+        // FIXME: add reflection
+    }
+
+    fn illuminate(&self, point: Point, object: &Object, incident_ray: Vector) -> LinearColor {
+        let texel = object.shape.project_texel(&point);
+        let normal = object.shape.normal(&point);
+        let reflected = reflected(incident_ray, normal);
+
+        self.illuminate_ambient(object.texture.texel_color(texel))
+            + self.illuminate_spatial(point.clone(), object, normal, reflected)
+    }
+
+    fn illuminate_ambient(&self, color: LinearColor) -> LinearColor {
+        self.lights
+            .ambient_lights_iter()
+            .map(|light| color.clone() * light.illumination(&Point::origin()))
+            .sum()
+    }
+
+    fn illuminate_spatial(
+        &self,
+        point: Point,
+        object: &Object,
+        normal: Vector,
+        reflected: Vector,
+    ) -> LinearColor {
+        let texel = object.shape.project_texel(&point);
+        let k_d = object.material.diffuse(texel);
+        let k_s = object.material.specular(texel);
+        self.lights
+            .spatial_lights_iter()
+            .map(|light| {
+                let (direction, t) = light.to_source(&point);
+                let light_ray = Ray::new(point + 0.001 * direction, direction);
+                match self.cast_ray(light_ray) {
+                    // Take shadows into account
+                    Some((obstacle_t, _)) if obstacle_t < t => return LinearColor::black(),
+                    _ => {}
+                }
+                let lum = light.illumination(&point);
+                let diffused = k_d.clone() * normal.dot(&direction);
+                let specular = k_s.clone() * reflected.dot(&direction);
+                lum * (diffused + specular)
+            })
+            .sum()
+    }
+}
+
+fn reflected(incident: Vector, normal: Vector) -> Vector {
+    let proj = incident.dot(&normal);
+    let delt = normal * (proj * 2.);
+    incident - delt
+}