diff --git a/src/ThreadPool.cpp b/src/ThreadPool.cpp
index df0f0b3..391a887 100644
--- a/src/ThreadPool.cpp
+++ b/src/ThreadPool.cpp
@@ -27,7 +27,6 @@ void ThreadPool::cancel()
   {
     std::unique_lock l(queueLock);
     numRemaining = numRunning;
-    taskQueue.clear();
   }
   while (true)
   {
@@ -79,7 +78,7 @@ void ThreadPool::work()
       if (numRemaining == 0)
       {
         taskQueue.pop_front();
-        completedCV.notify_one();
+        completedCV.notify_all();
       }
     }
   }
diff --git a/src/main.cpp b/src/main.cpp
index 329b399..25f1ea9 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -22,9 +22,18 @@ int main()
     while (true)
     {
         window.beginFrame();
-        if (ImGui::Button("Test"))
+        if (ImGui::Button("Render"))
         {
-            std::cout << "Test" << std::endl;
+          scene.startRender(
+              Camera{
+                  .position = glm::vec3(0, 10, 10),
+                  .direction = glm::vec3(0, -1, -1),
+              },
+              RenderParameter{
+                  .width = 1920,
+                  .height = 1080,
+                  .numSamples = 10000,
+              });
         }
         window.update(scene.getImage());
     }
diff --git a/src/scene/Scene.cpp b/src/scene/Scene.cpp
index a3d426e..c30ce97 100644
--- a/src/scene/Scene.cpp
+++ b/src/scene/Scene.cpp
@@ -18,6 +18,10 @@ static bool firstTime = true;
 void Scene::startRender(Camera cam, RenderParameter params)
 {
   threadPool.cancel();
+  pendingCancel = true;
+  if (worker.joinable())
+    worker.join();
+  pendingCancel = false;
   image.clear();
   accumulator.clear();
   image.resize(params.width * params.height);
@@ -36,6 +40,8 @@ void Scene::render(Camera camera, RenderParameter params)
 {
   for (int samp = 0; samp < params.numSamples; ++samp)
   {
+    if (pendingCancel)
+      return;
     Batch batch;
     for (int w = 0; w < params.width; ++w)
     {
diff --git a/src/scene/Scene.h b/src/scene/Scene.h
index ddd1c8f..d71f9ef 100644
--- a/src/scene/Scene.h
+++ b/src/scene/Scene.h
@@ -35,6 +35,7 @@ class Scene
     virtual void render(Camera cam, RenderParameter params);
     ThreadPool threadPool;
     std::thread worker;
+    std::atomic_bool pendingCancel = false;
     // the thing being displayed
     std::vector<glm::vec3> image;
     // radiance accumulator