Working thread impl

example02_threaded_raytracing/src/rayTracer.cpp

@@ -3,6 +3,8 @@
 #include <cmath>
 #include <fstream>
 #include <array>
+#include <thread>
+#include <mutex>
 
 #include <glm/matrix.hpp>
 #include <glm/gtc/matrix_transform.hpp>
@@ -316,8 +318,7 @@ Ex02::RT::Image Ex02::RT::renderColorsWithSpheres(
     lights[2].falloffStart = 3.0f;
     lights[2].falloffEnd = 7.0f;
 
-    if(threadCount <= 1) {
-        for(unsigned int j = 0; j < outputHeight; ++j) {
+    const auto yIteration = [&spheres, &lights, &image, outputWidth, outputHeight, rayPos] (unsigned int j, std::mutex *mutex) {
         float offsetY = ((float)j + 0.5f - ((float)outputHeight / 2.0f));
         for(unsigned int i = 0; i < outputWidth; ++i) {
             float offsetX = ((float)i + 0.5f - ((float)outputWidth / 2.0f));
@@ -378,12 +379,46 @@ Ex02::RT::Image Ex02::RT::renderColorsWithSpheres(
 
                 // at this point, it is known that no spheres blocks ray
                 // to light
+                if(mutex) {
+                    std::lock_guard<std::mutex> lock(*mutex);
+                    light.applyLight(
+                        std::get<0>(*closestResult),
+                        image.getPixel(i, j));
+                } else {
                     light.applyLight(
                         std::get<0>(*closestResult),
                         image.getPixel(i, j));
                 }
             }
         }
+    };
+
+    if(threadCount <= 1) {
+        for(unsigned int j = 0; j < outputHeight; ++j) {
+            yIteration(j, nullptr);
+        }
+    } else {
+        std::vector<std::thread> threads;
+        std::mutex mutex;
+        unsigned int range = outputHeight / threadCount;
+        for(unsigned int threadIdx = 0; threadIdx < threadCount; ++threadIdx) {
+            unsigned int start = range * threadIdx;
+            unsigned int end = range * (threadIdx + 1);
+            if(threadIdx + 1 == threadCount) {
+                end = outputHeight;
+            }
+            threads.emplace_back(std::thread([&yIteration] (unsigned int start, unsigned int end, std::mutex *mutex) {
+                for(unsigned int y = start; y < end; ++y) {
+                    yIteration(y, mutex);
+                }
+            },
+                start,
+                end,
+                &mutex));
+        }
+        for(std::thread &thread : threads) {
+            thread.join();
+        }
     }
 
     return image;