From 3f2c7b40e85b7b3c00db35e34b2ac08b37cf33cf Mon Sep 17 00:00:00 2001
From: Antoine Martin <antoine97.martin@gmail.com>
Date: Tue, 7 Apr 2020 22:19:38 +0200
Subject: [PATCH] library: render: pathtracer: draft parallelize

---
 pathtracer/examples/cornell-box.yaml          |  1 +
 pathtracer/src/render/pathtrace/pathtracer.rs | 53 ++++++++++++-------
 pathtracer/src/render/progress.rs             |  9 ----
 pathtracer/src/render/utils.rs                |  8 ---
 4 files changed, 36 insertions(+), 35 deletions(-)

diff --git a/pathtracer/examples/cornell-box.yaml b/pathtracer/examples/cornell-box.yaml
index d6fa9bb..e6b0f46 100644
--- a/pathtracer/examples/cornell-box.yaml
+++ b/pathtracer/examples/cornell-box.yaml
@@ -1,4 +1,5 @@
 reflection_limit: 5
+shot_rays: 50
 
 camera:
   origin: [0.0, 1.0, 0.0]
diff --git a/pathtracer/src/render/pathtrace/pathtracer.rs b/pathtracer/src/render/pathtrace/pathtracer.rs
index a4363be..dec5700 100644
--- a/pathtracer/src/render/pathtrace/pathtracer.rs
+++ b/pathtracer/src/render/pathtrace/pathtracer.rs
@@ -1,4 +1,6 @@
-use super::super::utils::{buffer_to_image, prepare_buffer, sample_hemisphere};
+use rayon::prelude::*;
+
+use super::super::utils::{buffer_to_image, sample_hemisphere};
 use super::super::Renderer;
 use crate::{
     core::LinearColor,
@@ -35,29 +37,44 @@ impl Pathtracer {
             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);
+        let p = super::super::progress::get_progressbar(self.scene.shot_rays as u64);
 
         // 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);
+        let img_buf = (0..self.scene.shot_rays.max(1))
+            .into_par_iter()
+            .map(|_| {
+                let mut buffer: Vec<LinearColor> = Vec::new();
+                buffer.resize_with(total as usize, LinearColor::black);
+
+                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);
+                    }
                 }
-            }
-            pa.inc(1); // Increment the number of passes
-        }
+                p.inc(1); // Increment the number of passes
 
-        pa.finish();
-        pb.finish_and_clear();
+                buffer
+            })
+            .reduce(
+                || {
+                    let mut vec = Vec::new();
+                    vec.resize_with(total as usize, LinearColor::black);
+                    vec
+                },
+                |mut acc, buf| {
+                    for (i, pixel) in buf.into_iter().enumerate() {
+                        acc[i] += pixel;
+                    }
 
-        buffer_to_image(buffer, self.scene.shot_rays, width, height)
+                    acc
+                },
+            );
+
+        p.finish();
+
+        buffer_to_image(img_buf, self.scene.shot_rays, width, height)
     }
 
     fn pixel_ray(&self, x: f32, y: f32) -> LinearColor {
diff --git a/pathtracer/src/render/progress.rs b/pathtracer/src/render/progress.rs
index 15d5851..4d2c398 100644
--- a/pathtracer/src/render/progress.rs
+++ b/pathtracer/src/render/progress.rs
@@ -8,12 +8,3 @@ pub fn get_progressbar(total: u64) -> ProgressBar {
     ));
     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 4ed4c3a..086a31e 100644
--- a/pathtracer/src/render/utils.rs
+++ b/pathtracer/src/render/utils.rs
@@ -104,14 +104,6 @@ pub fn sample_hemisphere(normal: Unit<Vector>) -> (Unit<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);