From c4557adce1238700a48ecc242f02ace596df8748 Mon Sep 17 00:00:00 2001
From: Antoine Martin <antoine97.martin@gmail.com>
Date: Tue, 28 Apr 2020 11:56:48 +0200
Subject: [PATCH] bidirectional: implement path building

---
 .../bidirectional/bidirectional_pathtracer.rs | 38 +++++++++++++++----
 1 file changed, 30 insertions(+), 8 deletions(-)

diff --git a/pathtracer/src/render/bidirectional/bidirectional_pathtracer.rs b/pathtracer/src/render/bidirectional/bidirectional_pathtracer.rs
index f2bff2a..91fbf5b 100644
--- a/pathtracer/src/render/bidirectional/bidirectional_pathtracer.rs
+++ b/pathtracer/src/render/bidirectional/bidirectional_pathtracer.rs
@@ -1,7 +1,11 @@
 use super::super::Renderer;
 use super::path::*;
-use crate::scene::Scene;
+use crate::material::Material;
+use crate::render::utils::sample_hemisphere;
+use crate::scene::{Object, Scene};
+use crate::shape::Shape;
 use crate::{Point, Vector};
+use beevee::ray::Ray;
 use image::RgbImage;
 use nalgebra::Unit;
 
@@ -30,17 +34,35 @@ impl BidirectionalPathtracer {
     }
 
     #[allow(unused)]
-    fn construct_path(&self, point: Point, _direction: Unit<Vector>) -> Path {
-        let mut res = Path::new(point);
+    fn construct_path(&self, mut origin: Point, mut direction: Unit<Vector>) -> Path {
+        let mut res = Path::new(origin);
         for _ in 0..self.scene.reflection_limit {
-            // FIXME:
-            //  * cast_ray: if no intersection, return the empty path
-            //  * look-up information at intersection
-            //  * append to path
-            //  * start again with new origin
+            let ray = Ray::new(origin, direction);
+            match self.cast_ray(ray) {
+                Some((distance, obj)) => {
+                    let hit_pos = origin + direction.as_ref() * distance;
+                    let texel = obj.shape.project_texel(&hit_pos);
+                    let properties = obj.material.properties(texel);
+                    let normal = obj.shape.normal(&hit_pos);
+                    let p = PathPoint::new(origin, direction, normal, properties);
+
+                    res.push_point(p);
+
+                    let (new_direction, _) = sample_hemisphere(normal);
+                    // Calculate the incoming light along the new ray
+                    origin = hit_pos + new_direction.as_ref() * 0.001;
+                    direction = new_direction;
+                }
+                None => break,
+            }
         }
         res
     }
+
+    #[allow(unused)]
+    fn cast_ray(&self, ray: Ray) -> Option<(f32, &Object)> {
+        self.scene.bvh.walk(&ray, &self.scene.objects)
+    }
 }
 
 impl Renderer for BidirectionalPathtracer {