From a4d7ccc1a559ace02900af902b14da68ea6e1492 Mon Sep 17 00:00:00 2001
From: Maximilian Giller <m.giller.dev@gmail.com>
Date: Sun, 29 Jan 2023 15:48:17 +0100
Subject: [PATCH] Parallel noise processing

---
 common/noise/worleynoise.cpp | 46 ++++++++++++++++++++++++++++--------
 common/noise/worleynoise.h   |  4 ++++
 fancy1.cpp                   |  2 +-
 shader/cloudshader.cpp       |  2 +-
 shader/cloudshader.h         |  2 +-
 5 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/common/noise/worleynoise.cpp b/common/noise/worleynoise.cpp
index 3d65749..d6ce4a9 100644
--- a/common/noise/worleynoise.cpp
+++ b/common/noise/worleynoise.cpp
@@ -2,9 +2,15 @@
 #include <iostream>
 #include <algorithm>
 #include <set>
+#include <thread>
 #include "worleynoise.h"
 #include "common/vector3d.h"
 
+void WorleyNoise::runWorleyNoiseInThread(int xOffset, int xSize, WorleyNoise *noise)
+{
+    noise->renderNoiseThread(xOffset, xSize);
+}
+
 void WorleyNoise::generateNoise()
 {
     auto start = std::chrono::high_resolution_clock::now();
@@ -36,17 +42,21 @@ void WorleyNoise::generateNoise()
     noiseMap.clear();
     noiseMap.resize(size * size * size);
 
-    for (int x = 0; x < size; x++)
+    int const nThreads = (int) std::thread::hardware_concurrency() - 1;
+    int threadSize = std::floor((float) size / (float) nThreads);
+    int remaining = size - nThreads * threadSize;
+    std::vector<std::thread> threads;
+    for (int n = 0; n < nThreads; n++)
     {
-        for (int y = 0; y < size; y++)
-        {
-            for (int z = 0; z < size; z++)
-            {
-                Vector3d point = Vector3d(x, y, z);
-                point /= (float) size;
-                setNoise(x, y, z, distanceToClosestPoint(point));
-            }
-        }
+        threads.emplace_back(runWorleyNoiseInThread, n * threadSize, threadSize, this);
+    }
+
+    renderNoiseThread(nThreads * threadSize, remaining);
+
+    // Rejoin the threads
+    for (int t = 0; t < nThreads; ++t)
+    {
+        threads[t].join();
     }
 
     // Normalize getNoise map to [0, 1]
@@ -66,6 +76,22 @@ void WorleyNoise::generateNoise()
               << duration.count() << " seconds" << std::endl;
 }
 
+void WorleyNoise::renderNoiseThread(int xOffset, int xSize)
+{
+    for (int x = 0; x < xSize; x++)
+    {
+        for (int y = 0; y < size; y++)
+        {
+            for (int z = 0; z < size; z++)
+            {
+                Vector3d point = Vector3d(x, y, z);
+                point /= (float) size;
+                setNoise(xOffset + x, y, z, distanceToClosestPoint(point));
+            }
+        }
+    }
+}
+
 WorleyNoise::WorleyNoise(int size, int numberOfPoints, unsigned int seed) : numberOfPoints(numberOfPoints), Noise(size)
 {
     // Init random
diff --git a/common/noise/worleynoise.h b/common/noise/worleynoise.h
index 3a37390..4994e5e 100644
--- a/common/noise/worleynoise.h
+++ b/common/noise/worleynoise.h
@@ -18,6 +18,8 @@ public:
      */
     WorleyNoise(int size, int numberOfPoints, unsigned int seed = 0);
 
+    void renderNoiseThread(int xOffset, int xSize);
+
 protected:
     int numberOfPoints;
     std::vector<Vector3d> points;   // 3D-Array, each cell represents a subcell. There are numberOfPoints^3 subcells.
@@ -32,6 +34,8 @@ protected:
     void generateNoise();
 
     std::vector<Vector3d> getSubcellPoints(Vector3d point);
+
+    static void runWorleyNoiseInThread(int xOffset, int xSize, WorleyNoise *noise);
 };
 
 
diff --git a/fancy1.cpp b/fancy1.cpp
index f55e46e..4c0cad3 100644
--- a/fancy1.cpp
+++ b/fancy1.cpp
@@ -72,7 +72,7 @@ int main()
     // Render the scene
     SuperRenderer sr;
     sr.setSuperSamplingFactor(1);
-    sr.renderImage(scene, camera, 512, 512).save("result.png");
+    sr.renderImage(scene, camera, 256, 256).save("result.png");
 
     return 0;
 }
diff --git a/shader/cloudshader.cpp b/shader/cloudshader.cpp
index dd8a11a..6358d1d 100644
--- a/shader/cloudshader.cpp
+++ b/shader/cloudshader.cpp
@@ -69,7 +69,7 @@ bool CloudShader::isTransparent() const
 }
 
 CloudShader::CloudShader(const CloudSettings &settings) : settings(settings),
-                                                          cloudNoise(CloudNoise(NOISE_SIZE, settings.seed))
+                                                          cloudNoise(CloudNoise(settings.noiseSize, settings.seed))
 {
     cloudNoise.invert = true;
 }
diff --git a/shader/cloudshader.h b/shader/cloudshader.h
index a85d394..edc78d1 100644
--- a/shader/cloudshader.h
+++ b/shader/cloudshader.h
@@ -7,11 +7,11 @@
 #include "primitive/primitive.h"
 #include "common/noise/worleynoise.h"
 
-int const NOISE_SIZE = 64;
 float const TRANSMITTANCE_BREAK = 0.0001f;  // If transmittance goes below this limit, the cloud is considered opaque
 
 struct CloudSettings
 {
+    int noiseSize = 256; // 64
     unsigned int seed = 0;  // 0 for random seed
     float densitySteps = .2f;   // .2f
     float scale = 30;   // 30