From 482e6bea3f4c843bfe9ecb6d35b5d7e5168f6e6b Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <brunobelanyi@gmail.com>
Date: Mon, 6 Apr 2020 14:57:08 +0200
Subject: [PATCH] library: render: add basics for Pathtracer

This is simple ray-tracing, with a binary white-or-black color depending
on whether we hit an object or not.
---
 pathtracer/src/render/pathtrace/pathtracer.rs | 48 ++++++++++++++++++-
 pathtracer/src/render/progress.rs             | 11 ++++-
 pathtracer/src/render/utils.rs                | 21 ++++++++
 3 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/pathtracer/src/render/pathtrace/pathtracer.rs b/pathtracer/src/render/pathtrace/pathtracer.rs
index a73c2db..8c4a8b7 100644
--- a/pathtracer/src/render/pathtrace/pathtracer.rs
+++ b/pathtracer/src/render/pathtrace/pathtracer.rs
@@ -1,5 +1,8 @@
+use super::super::utils::{buffer_to_image, prepare_buffer};
 use super::super::Renderer;
-use crate::scene::Scene;
+use crate::core::LinearColor;
+use crate::scene::{Object, Scene};
+use beevee::ray::Ray;
 use image::RgbImage;
 
 /// Render the [`Scene`] using Pathtracing
@@ -23,7 +26,48 @@ impl Pathtracer {
     ///
     /// [`Scene`]: ../scene/scene/struct.Scene.html
     pub fn render(&self) -> RgbImage {
-        todo!()
+        let (width, height) = (
+            self.scene.camera.film().width(),
+            self.scene.camera.film().height(),
+        );
+        let total = width * height;
+        let mut buffer = prepare_buffer(total);
+
+        // (total passes, film)
+        // FIXME: use MultiProgress because of rendering issues
+        let (pa, pb) = super::super::progress::get_multiple_progress(total, self.scene.shot_rays);
+
+        // Ensure at least one round of shots
+        for _ in 0..self.scene.shot_rays.max(1) {
+            pb.reset(); // We're rendering the whole film again, reset the pixel counter
+            for y in 0..self.scene.camera.film().height() {
+                for x in 0..self.scene.camera.film().width() {
+                    let i = x + y * self.scene.camera.film().width();
+                    buffer[i as usize] += self.pixel_ray(x as f32, y as f32);
+                    pb.inc(1);
+                }
+            }
+            pa.inc(1); // Increment the number of passes
+        }
+
+        pa.finish();
+        pb.finish_and_clear();
+
+        buffer_to_image(buffer, self.scene.shot_rays, width, height)
+    }
+
+    fn pixel_ray(&self, x: f32, y: f32) -> LinearColor {
+        let (x, y) = self.scene.camera.film().pixel_ratio(x, y);
+        let ray = self.scene.camera.ray_with_ratio(x, y);
+        if let Some(_) = self.cast_ray(ray) {
+            LinearColor::new(1., 1., 1.) // FIXME: calculate real color
+        } else {
+            LinearColor::black()
+        }
+    }
+
+    fn cast_ray(&self, ray: Ray) -> Option<(f32, &Object)> {
+        self.scene.bvh.walk(&ray, &self.scene.objects)
     }
 }
 
diff --git a/pathtracer/src/render/progress.rs b/pathtracer/src/render/progress.rs
index 30698ee..15d5851 100644
--- a/pathtracer/src/render/progress.rs
+++ b/pathtracer/src/render/progress.rs
@@ -2,9 +2,18 @@ use indicatif::ProgressBar;
 
 pub fn get_progressbar(total: u64) -> ProgressBar {
     let pb = ProgressBar::new(total);
-    pb.set_draw_delta(total / 10000);
+    pb.set_draw_delta((total / 10000).max(1));
     pb.set_style(indicatif::ProgressStyle::default_bar().template(
         "{spinner:.green} [{elapsed_precise}] [{wide_bar:.cyan/blue}] {percent:>3}%: {pos}/{len} pixels (ETA: {eta})",
     ));
     pb
 }
+
+pub fn get_multiple_progress(total: u32, passes: u32) -> (ProgressBar, ProgressBar) {
+    let pb = ProgressBar::new(passes as u64);
+    pb.set_draw_delta((passes as u64 / 100).max(1));
+    pb.set_style(indicatif::ProgressStyle::default_bar().template(
+        "{spinner:.green} [{elapsed_precise}] [{wide_bar:.cyan/blue}] {percent:>3}%: {pos}/{len} passes (ETA: {eta})",
+    ));
+    (pb, get_progressbar(total as u64))
+}
diff --git a/pathtracer/src/render/utils.rs b/pathtracer/src/render/utils.rs
index 2ff48ce..905f117 100644
--- a/pathtracer/src/render/utils.rs
+++ b/pathtracer/src/render/utils.rs
@@ -1,4 +1,6 @@
+use crate::core::LinearColor;
 use crate::Vector;
+use image::RgbImage;
 use nalgebra::Unit;
 use rand::prelude::thread_rng;
 use rand::Rng;
@@ -103,6 +105,25 @@ pub fn sample_hemisphere(normal: Vector) -> (Vector, f32) {
     (scattered, 1. / scattered.dot(&normal))
 }
 
+pub fn prepare_buffer(total: u32) -> Vec<LinearColor> {
+    let mut ans = Vec::with_capacity(total as usize);
+    for _ in 0..total {
+        ans.push(LinearColor::black());
+    }
+    ans
+}
+
+pub fn buffer_to_image(buffer: Vec<LinearColor>, passes: u32, width: u32, height: u32) -> RgbImage {
+    let mut image = RgbImage::new(width, height);
+
+    for (x, y, pixel) in image.enumerate_pixels_mut() {
+        let i = x as usize + y as usize * width as usize;
+        *pixel = (buffer[i].clone() / passes as f32).into();
+    }
+
+    image
+}
+
 #[cfg(test)]
 mod test {
     use super::*;