Patch for https://github.com/Overv/VulkanTutorial/blob/master/code/15_hello_triangle.cpp that shows what is happening with fences.

15.c.patch

diff --git a/code/15_hello_triangle.cpp b/code/15_hello_triangle.cpp
index 532520e..31f2bd7 100644
--- a/code/15_hello_triangle.cpp
+++ b/code/15_hello_triangle.cpp
@@ -642,12 +642,15 @@ private:

     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
+        VkFence waited = inFlightFences[currentFrame];

         uint32_t imageIndex;
         vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);

+        VkFence waited2 = NULL;
         if (imagesInFlight[imageIndex] != VK_NULL_HANDLE) {
             vkWaitForFences(device, 1, &imagesInFlight[imageIndex], VK_TRUE, UINT64_MAX);
+            waited2 = imagesInFlight[imageIndex];
         }
         imagesInFlight[imageIndex] = inFlightFences[currentFrame];

@@ -673,6 +676,10 @@ private:
             throw std::runtime_error("failed to submit draw command buffer!");
         }

+        printf("Frame %d: waited for fence %p, acquired image %d, waited for fence %p, submitted with fence %p\n",
+          (int)currentFrame, waited, (int)imageIndex, waited2, inFlightFences[currentFrame]
+        );
+
         VkPresentInfoKHR presentInfo{};
         presentInfo.sType = VK_STRUCTURE_TYPE_PRESENT_INFO_KHR;