Vulkan SDK Demo 之一 熟悉

DiligentEngine的API是D3d11和D3D12风格的，vulkan也被封装成了这种风格的API。 在了解Diligent Engine是如何对vulkan进行封装之前，我准备先学习下Vulkan。知乎funchun的编程指南是中文版，英文不好，准备先看一版中文版，回头再去研习其他的内容。

1.Vulkan编程指南阅读摘要

1.1 Vulkan SDK

安装完成之后，安装目录有如下文件。在阅读编程指南的过程中，我并未采用指南中的demo code来进行研究，而是使用的SDK自带的demo进行学习。

1.2 Vulkan SDK Demo

• validation layers

      /*
       * This is info for a temp callback to use during CreateInstance.
       * After the instance is created, we use the instance-based
       * function to register the final callback.
       */
      VkDebugUtilsMessengerCreateInfoEXT dbg_messenger_create_info;
      if (demo->validate) {
          // VK_EXT_debug_utils style
          dbg_messenger_create_info.sType = VK_STRUCTURE_TYPE_DEBUG_UTILS_MESSENGER_CREATE_INFO_EXT;
          dbg_messenger_create_info.pNext = NULL;
          dbg_messenger_create_info.flags = ;
          dbg_messenger_create_info.messageSeverity =
              VK_DEBUG_UTILS_MESSAGE_SEVERITY_WARNING_BIT_EXT | VK_DEBUG_UTILS_MESSAGE_SEVERITY_ERROR_BIT_EXT;
          dbg_messenger_create_info.messageType = VK_DEBUG_UTILS_MESSAGE_TYPE_GENERAL_BIT_EXT |
                                                  VK_DEBUG_UTILS_MESSAGE_TYPE_VALIDATION_BIT_EXT |
                                                  VK_DEBUG_UTILS_MESSAGE_TYPE_PERFORMANCE_BIT_EXT;
          dbg_messenger_create_info.pfnUserCallback = debug_messenger_callback;
          dbg_messenger_create_info.pUserData = demo;
          inst_info.pNext = &dbg_messenger_create_info;
      }

    if (demo->validate) {
          // Setup VK_EXT_debug_utils function pointers always (we use them for
          // debug labels and names).
          demo->CreateDebugUtilsMessengerEXT =
              (PFN_vkCreateDebugUtilsMessengerEXT)vkGetInstanceProcAddr(demo->inst, "vkCreateDebugUtilsMessengerEXT");
          demo->DestroyDebugUtilsMessengerEXT =
              (PFN_vkDestroyDebugUtilsMessengerEXT)vkGetInstanceProcAddr(demo->inst, "vkDestroyDebugUtilsMessengerEXT");
          demo->SubmitDebugUtilsMessageEXT =
              (PFN_vkSubmitDebugUtilsMessageEXT)vkGetInstanceProcAddr(demo->inst, "vkSubmitDebugUtilsMessageEXT");
          demo->CmdBeginDebugUtilsLabelEXT =
              (PFN_vkCmdBeginDebugUtilsLabelEXT)vkGetInstanceProcAddr(demo->inst, "vkCmdBeginDebugUtilsLabelEXT");
          demo->CmdEndDebugUtilsLabelEXT =
              (PFN_vkCmdEndDebugUtilsLabelEXT)vkGetInstanceProcAddr(demo->inst, "vkCmdEndDebugUtilsLabelEXT");
          demo->CmdInsertDebugUtilsLabelEXT =
              (PFN_vkCmdInsertDebugUtilsLabelEXT)vkGetInstanceProcAddr(demo->inst, "vkCmdInsertDebugUtilsLabelEXT");
          demo->SetDebugUtilsObjectNameEXT =
              (PFN_vkSetDebugUtilsObjectNameEXT)vkGetInstanceProcAddr(demo->inst, "vkSetDebugUtilsObjectNameEXT");
          if (NULL == demo->CreateDebugUtilsMessengerEXT || NULL == demo->DestroyDebugUtilsMessengerEXT ||
              NULL == demo->SubmitDebugUtilsMessageEXT || NULL == demo->CmdBeginDebugUtilsLabelEXT ||
              NULL == demo->CmdEndDebugUtilsLabelEXT || NULL == demo->CmdInsertDebugUtilsLabelEXT ||
              NULL == demo->SetDebugUtilsObjectNameEXT) {
              ERR_EXIT("GetProcAddr: Failed to init VK_EXT_debug_utils\n", "GetProcAddr: Failure");
          }
  
          err = demo->CreateDebugUtilsMessengerEXT(demo->inst, &dbg_messenger_create_info, NULL, &demo->dbg_messenger);
          switch (err) {
              case VK_SUCCESS:
                  break;
              case VK_ERROR_OUT_OF_HOST_MEMORY:
                  ERR_EXIT("CreateDebugUtilsMessengerEXT: out of host memory\n", "CreateDebugUtilsMessengerEXT Failure");
                  break;
              default:
                  ERR_EXIT("CreateDebugUtilsMessengerEXT: unknown failure\n", "CreateDebugUtilsMessengerEXT Failure");
                  break;
          }
      }

• instance extensions
• CreateVulkanInstance

   const VkApplicationInfo app = {
          .sType = VK_STRUCTURE_TYPE_APPLICATION_INFO,
          .pNext = NULL,
          .pApplicationName = APP_SHORT_NAME,
          .applicationVersion = ,
          .pEngineName = APP_SHORT_NAME,
          .engineVersion = ,
          .apiVersion = VK_API_VERSION_1_0,
      };
      VkInstanceCreateInfo inst_info = {
          .sType = VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO,
          .pNext = NULL,
          .pApplicationInfo = &app,
          .enabledLayerCount = demo->enabled_layer_count,
          .ppEnabledLayerNames = (const char *const *)instance_validation_layers,
          .enabledExtensionCount = demo->enabled_extension_count,
          .ppEnabledExtensionNames = (const char *const *)demo->extension_names,
      };
  
      /*
       * This is info for a temp callback to use during CreateInstance.
       * After the instance is created, we use the instance-based
       * function to register the final callback.
       */
      VkDebugUtilsMessengerCreateInfoEXT dbg_messenger_create_info;
      if (demo->validate) {
          // VK_EXT_debug_utils style
          dbg_messenger_create_info.sType = VK_STRUCTURE_TYPE_DEBUG_UTILS_MESSENGER_CREATE_INFO_EXT;
          dbg_messenger_create_info.pNext = NULL;
          dbg_messenger_create_info.flags = ;
          dbg_messenger_create_info.messageSeverity =
              VK_DEBUG_UTILS_MESSAGE_SEVERITY_WARNING_BIT_EXT | VK_DEBUG_UTILS_MESSAGE_SEVERITY_ERROR_BIT_EXT;
          dbg_messenger_create_info.messageType = VK_DEBUG_UTILS_MESSAGE_TYPE_GENERAL_BIT_EXT |
                                                  VK_DEBUG_UTILS_MESSAGE_TYPE_VALIDATION_BIT_EXT |
                                                  VK_DEBUG_UTILS_MESSAGE_TYPE_PERFORMANCE_BIT_EXT;
          dbg_messenger_create_info.pfnUserCallback = debug_messenger_callback;
          dbg_messenger_create_info.pUserData = demo;
          inst_info.pNext = &dbg_messenger_create_info;
      }
  
      uint32_t gpu_count;
  
      err = vkCreateInstance(&inst_info, NULL, &demo->inst);

• vkEnumeratePhysicalDevices

      /* Make initial call to query gpu_count, then second call for gpu info*/
      err = vkEnumeratePhysicalDevices(demo->inst, &gpu_count, NULL);
      assert(!err);
  
      if (gpu_count > ) {
          VkPhysicalDevice *physical_devices = malloc(sizeof(VkPhysicalDevice) * gpu_count);
          err = vkEnumeratePhysicalDevices(demo->inst, &gpu_count, physical_devices);
          assert(!err);
          /* For cube demo we just grab the first physical device */
          demo->gpu = physical_devices[];
          free(physical_devices);
      } else {
          ERR_EXIT(
              "vkEnumeratePhysicalDevices reported zero accessible devices.\n\n"
              "Do you have a compatible Vulkan installable client driver (ICD) installed?\n"
              "Please look at the Getting Started guide for additional information.\n",
              "vkEnumeratePhysicalDevices Failure");
      }

      vkGetPhysicalDeviceProperties(demo->gpu, &demo->gpu_props);
  
      /* Call with NULL data to get count */
      vkGetPhysicalDeviceQueueFamilyProperties(demo->gpu, &demo->queue_family_count, NULL);
      assert(demo->queue_family_count >= );
  
      demo->queue_props = (VkQueueFamilyProperties *)malloc(demo->queue_family_count * sizeof(VkQueueFamilyProperties));
      vkGetPhysicalDeviceQueueFamilyProperties(demo->gpu, &demo->queue_family_count, demo->queue_props);
  

    // Query fine-grained feature support for this device.
      //  If app has specific feature requirements it should check supported
      //  features based on this query
      VkPhysicalDeviceFeatures physDevFeatures;
      vkGetPhysicalDeviceFeatures(demo->gpu, &physDevFeatures);

• device extensions需要找到对应的 VK_KHR_SWAPCHAIN_EXTENSION_NAME，这个是一个交换链的扩展

•     /* Look for device extensions */
      uint32_t device_extension_count = ;
      VkBool32 swapchainExtFound = ;
      demo->enabled_extension_count = ;
      memset(demo->extension_names, , sizeof(demo->extension_names));
  
      err = vkEnumerateDeviceExtensionProperties(demo->gpu, NULL, &device_extension_count, NULL);
      assert(!err);
  
      if (device_extension_count > ) {
          VkExtensionProperties *device_extensions = malloc(sizeof(VkExtensionProperties) * device_extension_count);
          err = vkEnumerateDeviceExtensionProperties(demo->gpu, NULL, &device_extension_count, device_extensions);
          assert(!err);
  
          for (uint32_t i = ; i < device_extension_count; i++) {
              if (!strcmp(VK_KHR_SWAPCHAIN_EXTENSION_NAME, device_extensions[i].extensionName)) {
                  swapchainExtFound = ;
                  demo->extension_names[demo->enabled_extension_count++] = VK_KHR_SWAPCHAIN_EXTENSION_NAME;
              }
              assert(demo->enabled_extension_count < );
          }
  
          if (demo->VK_KHR_incremental_present_enabled) {
              // Even though the user "enabled" the extension via the command
              // line, we must make sure that it's enumerated for use with the
              // device.  Therefore, disable it here, and re-enable it again if
              // enumerated.
              demo->VK_KHR_incremental_present_enabled = false;
              for (uint32_t i = ; i < device_extension_count; i++) {
                  if (!strcmp(VK_KHR_INCREMENTAL_PRESENT_EXTENSION_NAME, device_extensions[i].extensionName)) {
                      demo->extension_names[demo->enabled_extension_count++] = VK_KHR_INCREMENTAL_PRESENT_EXTENSION_NAME;
                      demo->VK_KHR_incremental_present_enabled = true;
                      DbgMsg("VK_KHR_incremental_present extension enabled\n");
                  }
                  assert(demo->enabled_extension_count < );
              }
              if (!demo->VK_KHR_incremental_present_enabled) {
                  DbgMsg("VK_KHR_incremental_present extension NOT AVAILABLE\n");
              }
          }
  
          if (demo->VK_GOOGLE_display_timing_enabled) {
              // Even though the user "enabled" the extension via the command
              // line, we must make sure that it's enumerated for use with the
              // device.  Therefore, disable it here, and re-enable it again if
              // enumerated.
              demo->VK_GOOGLE_display_timing_enabled = false;
              for (uint32_t i = ; i < device_extension_count; i++) {
                  if (!strcmp(VK_GOOGLE_DISPLAY_TIMING_EXTENSION_NAME, device_extensions[i].extensionName)) {
                      demo->extension_names[demo->enabled_extension_count++] = VK_GOOGLE_DISPLAY_TIMING_EXTENSION_NAME;
                      demo->VK_GOOGLE_display_timing_enabled = true;
                      DbgMsg("VK_GOOGLE_display_timing extension enabled\n");
                  }
                  assert(demo->enabled_extension_count < );
              }
              if (!demo->VK_GOOGLE_display_timing_enabled) {
                  DbgMsg("VK_GOOGLE_display_timing extension NOT AVAILABLE\n");
              }
          }
  
          free(device_extensions);
      }
  
      if (!swapchainExtFound) {
          ERR_EXIT("vkEnumerateDeviceExtensionProperties failed to find the " VK_KHR_SWAPCHAIN_EXTENSION_NAME
                   " extension.\n\nDo you have a compatible Vulkan installable client driver (ICD) installed?\n"
                   "Please look at the Getting Started guide for additional information.\n",
                   "vkCreateInstance Failure");
      }

• 凡事带有KHR结尾的函数，都是vulkan对于制定平台的一些扩展， 下面的代码创建一个窗口表面，当然如果你不需要展示图像，这个表面不是必须的。

// Create a WSI surface for the window:
#if defined(VK_USE_PLATFORM_WIN32_KHR)
    VkWin32SurfaceCreateInfoKHR createInfo;
    createInfo.sType = VK_STRUCTURE_TYPE_WIN32_SURFACE_CREATE_INFO_KHR;
    createInfo.pNext = NULL;
    createInfo.flags = ;
    createInfo.hinstance = demo->connection;
    createInfo.hwnd = demo->window;

    err = vkCreateWin32SurfaceKHR(demo->inst, &createInfo, NULL, &demo->surface);

• vkCreateDevice

      VkResult U_ASSERT_ONLY err;
      float queue_priorities[] = {0.0};
      VkDeviceQueueCreateInfo queues[];
      queues[].sType = VK_STRUCTURE_TYPE_DEVICE_QUEUE_CREATE_INFO;
      queues[].pNext = NULL;
      queues[].queueFamilyIndex = demo->graphics_queue_family_index;
      queues[].queueCount = ;
      queues[].pQueuePriorities = queue_priorities;
      queues[].flags = ;
  
      VkDeviceCreateInfo device = {
          .sType = VK_STRUCTURE_TYPE_DEVICE_CREATE_INFO,
          .pNext = NULL,
          .queueCreateInfoCount = ,
          .pQueueCreateInfos = queues,
          .enabledLayerCount = ,
          .ppEnabledLayerNames = NULL,
          .enabledExtensionCount = demo->enabled_extension_count,
          .ppEnabledExtensionNames = (const char *const *)demo->extension_names,
          .pEnabledFeatures = NULL,  // If specific features are required, pass them in here
      };
      if (demo->separate_present_queue) {
          queues[].sType = VK_STRUCTURE_TYPE_DEVICE_QUEUE_CREATE_INFO;
          queues[].pNext = NULL;
          queues[].queueFamilyIndex = demo->present_queue_family_index;
          queues[].queueCount = ;
          queues[].pQueuePriorities = queue_priorities;
          queues[].flags = ;
          device.queueCreateInfoCount = ;
      }
      err = vkCreateDevice(demo->gpu, &device, NULL, &demo->device);
      assert(!err);

• Get the list of VkFormat's that are supported:

    uint32_t formatCount;
      err = demo->fpGetPhysicalDeviceSurfaceFormatsKHR(demo->gpu, demo->surface, &formatCount, NULL);
      assert(!err);
      VkSurfaceFormatKHR *surfFormats = (VkSurfaceFormatKHR *)malloc(formatCount * sizeof(VkSurfaceFormatKHR));
      err = demo->fpGetPhysicalDeviceSurfaceFormatsKHR(demo->gpu, demo->surface, &formatCount, surfFormats);
      assert(!err);
      // If the format list includes just one entry of VK_FORMAT_UNDEFINED,
      // the surface has no preferred format.  Otherwise, at least one
      // supported format will be returned.
      if (formatCount ==  && surfFormats[].format == VK_FORMAT_UNDEFINED) {
          demo->format = VK_FORMAT_B8G8R8A8_UNORM;
      } else {
          assert(formatCount >= );
          demo->format = surfFormats[].format;
      }
      demo->color_space = surfFormats[].colorSpace;
      free(surfFormats);

• 同步

  // Create semaphores to synchronize acquiring presentable buffers before
      // rendering and waiting for drawing to be complete before presenting
      VkSemaphoreCreateInfo semaphoreCreateInfo = {
          .sType = VK_STRUCTURE_TYPE_SEMAPHORE_CREATE_INFO,
          .pNext = NULL,
          .flags = ,
      }; 
  
      // Create fences that we can use to throttle if we get too far
      // ahead of the image presents
      VkFenceCreateInfo fence_ci = {
          .sType = VK_STRUCTURE_TYPE_FENCE_CREATE_INFO, .pNext = NULL, .flags = VK_FENCE_CREATE_SIGNALED_BIT};
      for (uint32_t i = ; i < FRAME_LAG; i++) {
          err = vkCreateFence(demo->device, &fence_ci, NULL, &demo->fences[i]);
          assert(!err);
  
          err = vkCreateSemaphore(demo->device, &semaphoreCreateInfo, NULL, &demo->image_acquired_semaphores[i]);
          assert(!err);
  
          err = vkCreateSemaphore(demo->device, &semaphoreCreateInfo, NULL, &demo->draw_complete_semaphores[i]);
          assert(!err);
  
          if (demo->separate_present_queue) {
              err = vkCreateSemaphore(demo->device, &semaphoreCreateInfo, NULL, &demo->image_ownership_semaphores[i]);
              assert(!err);
          }
      }
      demo->frame_index = ;

• Get Memory information and properties

    vkGetPhysicalDeviceMemoryProperties(demo->gpu, &demo->memory_properties);

• demo_prepare: command buff, depth,mesh data,descriptor layout, render_pass, pipe lines

  static void demo_prepare(struct demo *demo) {
      VkResult U_ASSERT_ONLY err;
      if (demo->cmd_pool == VK_NULL_HANDLE) {
          const VkCommandPoolCreateInfo cmd_pool_info = {
              .sType = VK_STRUCTURE_TYPE_COMMAND_POOL_CREATE_INFO,
              .pNext = NULL,
              .queueFamilyIndex = demo->graphics_queue_family_index,
              .flags = ,
          };
          err = vkCreateCommandPool(demo->device, &cmd_pool_info, NULL, &demo->cmd_pool);
          assert(!err);
      }
  
      const VkCommandBufferAllocateInfo cmd = {
          .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO,
          .pNext = NULL,
          .commandPool = demo->cmd_pool,
          .level = VK_COMMAND_BUFFER_LEVEL_PRIMARY,
          .commandBufferCount = ,
      };
      err = vkAllocateCommandBuffers(demo->device, &cmd, &demo->cmd);
      assert(!err);
      VkCommandBufferBeginInfo cmd_buf_info = {
          .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO,
          .pNext = NULL,
          .flags = ,
          .pInheritanceInfo = NULL,
      };
      err = vkBeginCommandBuffer(demo->cmd, &cmd_buf_info);
      assert(!err);
  
      demo_prepare_buffers(demo);
  
      if (demo->is_minimized) {
          demo->prepared = false;
          return;
      }
  
      demo_prepare_depth(demo);
      demo_prepare_textures(demo);
      demo_prepare_cube_data_buffers(demo);
  
      demo_prepare_descriptor_layout(demo);
      demo_prepare_render_pass(demo);
      demo_prepare_pipeline(demo);
  
      for (uint32_t i = ; i < demo->swapchainImageCount; i++) {
          err = vkAllocateCommandBuffers(demo->device, &cmd, &demo->swapchain_image_resources[i].cmd);
          assert(!err);
      }
  
      if (demo->separate_present_queue) {
          const VkCommandPoolCreateInfo present_cmd_pool_info = {
              .sType = VK_STRUCTURE_TYPE_COMMAND_POOL_CREATE_INFO,
              .pNext = NULL,
              .queueFamilyIndex = demo->present_queue_family_index,
              .flags = ,
          };
          err = vkCreateCommandPool(demo->device, &present_cmd_pool_info, NULL, &demo->present_cmd_pool);
          assert(!err);
          const VkCommandBufferAllocateInfo present_cmd_info = {
              .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO,
              .pNext = NULL,
              .commandPool = demo->present_cmd_pool,
              .level = VK_COMMAND_BUFFER_LEVEL_PRIMARY,
              .commandBufferCount = ,
          };
          for (uint32_t i = ; i < demo->swapchainImageCount; i++) {
              err = vkAllocateCommandBuffers(demo->device, &present_cmd_info,
                                             &demo->swapchain_image_resources[i].graphics_to_present_cmd);
              assert(!err);
              demo_build_image_ownership_cmd(demo, i);
          }
      }
  
      demo_prepare_descriptor_pool(demo);
      demo_prepare_descriptor_set(demo);
  
      demo_prepare_framebuffers(demo);
  
      for (uint32_t i = ; i < demo->swapchainImageCount; i++) {
          demo->current_buffer = i;
          demo_draw_build_cmd(demo, demo->swapchain_image_resources[i].cmd);
      }
  
      /*
       * Prepare functions above may generate pipeline commands
       * that need to be flushed before beginning the render loop.
       */
      demo_flush_init_cmd(demo);
      if (demo->staging_texture.buffer) {
          demo_destroy_texture(demo, &demo->staging_texture);
      }
  
      demo->current_buffer = ;
      demo->prepared = true;
  }

• vulkan都是提前把渲染命令准备好

  /*
       * Prepare functions above may generate pipeline commands
       * that need to be flushed before beginning the render loop.
       */
      demo_flush_init_cmd(demo);
      if (demo->staging_texture.buffer) {
          demo_destroy_texture(demo, &demo->staging_texture);
      }
  
      demo->current_buffer = ;
      demo->prepared = true;

• 渲染主循环

  #if defined(VK_USE_PLATFORM_WIN32_KHR)
  static void demo_run(struct demo *demo) {
      if (!demo->prepared) return;
  
      demo_draw(demo);
      demo->curFrame++;
      if (demo->frameCount != INT32_MAX && demo->curFrame == demo->frameCount) {
          PostQuitMessage(validation_error);
      }
  }

  static void demo_draw(struct demo *demo) {
      VkResult U_ASSERT_ONLY err;
  
      // Ensure no more than FRAME_LAG renderings are outstanding
      vkWaitForFences(demo->device, , &demo->fences[demo->frame_index], VK_TRUE, UINT64_MAX);
      vkResetFences(demo->device, , &demo->fences[demo->frame_index]);
  
      do {
          // Get the index of the next available swapchain image:
          err =
              demo->fpAcquireNextImageKHR(demo->device, demo->swapchain, UINT64_MAX,
                                          demo->image_acquired_semaphores[demo->frame_index], VK_NULL_HANDLE, &demo->current_buffer);
  
          if (err == VK_ERROR_OUT_OF_DATE_KHR) {
              // demo->swapchain is out of date (e.g. the window was resized) and
              // must be recreated:
              demo_resize(demo);
          } else if (err == VK_SUBOPTIMAL_KHR) {
              // demo->swapchain is not as optimal as it could be, but the platform's
              // presentation engine will still present the image correctly.
              break;
          } else if (err == VK_ERROR_SURFACE_LOST_KHR) {
              vkDestroySurfaceKHR(demo->inst, demo->surface, NULL);
              demo_create_surface(demo);
              demo_resize(demo);
          } else {
              assert(!err);
          }
      } while (err != VK_SUCCESS);
  
      demo_update_data_buffer(demo);
  
      if (demo->VK_GOOGLE_display_timing_enabled) {
          // Look at what happened to previous presents, and make appropriate
          // adjustments in timing:
          DemoUpdateTargetIPD(demo);
  
          // Note: a real application would position its geometry to that it's in
          // the correct locatoin for when the next image is presented.  It might
          // also wait, so that there's less latency between any input and when
          // the next image is rendered/presented.  This demo program is so
          // simple that it doesn't do either of those.
      }
  
      // Wait for the image acquired semaphore to be signaled to ensure
      // that the image won't be rendered to until the presentation
      // engine has fully released ownership to the application, and it is
      // okay to render to the image.
      VkPipelineStageFlags pipe_stage_flags;
      VkSubmitInfo submit_info;
      submit_info.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
      submit_info.pNext = NULL;
      submit_info.pWaitDstStageMask = &pipe_stage_flags;
      pipe_stage_flags = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
      submit_info.waitSemaphoreCount = ;
      submit_info.pWaitSemaphores = &demo->image_acquired_semaphores[demo->frame_index];
      submit_info.commandBufferCount = ;
      submit_info.pCommandBuffers = &demo->swapchain_image_resources[demo->current_buffer].cmd;
      submit_info.signalSemaphoreCount = ;
      submit_info.pSignalSemaphores = &demo->draw_complete_semaphores[demo->frame_index];
      err = vkQueueSubmit(demo->graphics_queue, , &submit_info, demo->fences[demo->frame_index]);
      assert(!err);
  
      if (demo->separate_present_queue) {
          // If we are using separate queues, change image ownership to the
          // present queue before presenting, waiting for the draw complete
          // semaphore and signalling the ownership released semaphore when finished
          VkFence nullFence = VK_NULL_HANDLE;
          pipe_stage_flags = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
          submit_info.waitSemaphoreCount = ;
          submit_info.pWaitSemaphores = &demo->draw_complete_semaphores[demo->frame_index];
          submit_info.commandBufferCount = ;
          submit_info.pCommandBuffers = &demo->swapchain_image_resources[demo->current_buffer].graphics_to_present_cmd;
          submit_info.signalSemaphoreCount = ;
          submit_info.pSignalSemaphores = &demo->image_ownership_semaphores[demo->frame_index];
          err = vkQueueSubmit(demo->present_queue, , &submit_info, nullFence);
          assert(!err);
      }
  
      // If we are using separate queues we have to wait for image ownership,
      // otherwise wait for draw complete
      VkPresentInfoKHR present = {
          .sType = VK_STRUCTURE_TYPE_PRESENT_INFO_KHR,
          .pNext = NULL,
          .waitSemaphoreCount = ,
          .pWaitSemaphores = (demo->separate_present_queue) ? &demo->image_ownership_semaphores[demo->frame_index]
                                                            : &demo->draw_complete_semaphores[demo->frame_index],
          .swapchainCount = ,
          .pSwapchains = &demo->swapchain,
          .pImageIndices = &demo->current_buffer,
      };
  
      VkRectLayerKHR rect;
      VkPresentRegionKHR region;
      VkPresentRegionsKHR regions;
      if (demo->VK_KHR_incremental_present_enabled) {
          // If using VK_KHR_incremental_present, we provide a hint of the region
          // that contains changed content relative to the previously-presented
          // image.  The implementation can use this hint in order to save
          // work/power (by only copying the region in the hint).  The
          // implementation is free to ignore the hint though, and so we must
          // ensure that the entire image has the correctly-drawn content.
          uint32_t eighthOfWidth = demo->width / ;
          uint32_t eighthOfHeight = demo->height / ;
  
          rect.offset.x = eighthOfWidth;
          rect.offset.y = eighthOfHeight;
          rect.extent.width = eighthOfWidth * ;
          rect.extent.height = eighthOfHeight * ;
          rect.layer = ;
  
          region.rectangleCount = ;
          region.pRectangles = ▭
  
          regions.sType = VK_STRUCTURE_TYPE_PRESENT_REGIONS_KHR;
          regions.pNext = present.pNext;
          regions.swapchainCount = present.swapchainCount;
          regions.pRegions = &region;
          present.pNext = &regions;
      }
  
      if (demo->VK_GOOGLE_display_timing_enabled) {
          VkPresentTimeGOOGLE ptime;
          if (demo->prev_desired_present_time == ) {
              // This must be the first present for this swapchain.
              //
              // We don't know where we are relative to the presentation engine's
              // display's refresh cycle.  We also don't know how long rendering
              // takes.  Let's make a grossly-simplified assumption that the
              // desiredPresentTime should be half way between now and
              // now+target_IPD.  We will adjust over time.
              uint64_t curtime = getTimeInNanoseconds();
              if (curtime == ) {
                  // Since we didn't find out the current time, don't give a
                  // desiredPresentTime:
                  ptime.desiredPresentTime = ;
              } else {
                  ptime.desiredPresentTime = curtime + (demo->target_IPD >> );
              }
          } else {
              ptime.desiredPresentTime = (demo->prev_desired_present_time + demo->target_IPD);
          }
          ptime.presentID = demo->next_present_id++;
          demo->prev_desired_present_time = ptime.desiredPresentTime;
  
          VkPresentTimesInfoGOOGLE present_time = {
              .sType = VK_STRUCTURE_TYPE_PRESENT_TIMES_INFO_GOOGLE,
              .pNext = present.pNext,
              .swapchainCount = present.swapchainCount,
              .pTimes = &ptime,
          };
          if (demo->VK_GOOGLE_display_timing_enabled) {
              present.pNext = &present_time;
          }
      }
  
      err = demo->fpQueuePresentKHR(demo->present_queue, &present);
      demo->frame_index += ;
      demo->frame_index %= FRAME_LAG;
  
      if (err == VK_ERROR_OUT_OF_DATE_KHR) {
          // demo->swapchain is out of date (e.g. the window was resized) and
          // must be recreated:
          demo_resize(demo);
      } else if (err == VK_SUBOPTIMAL_KHR) {
          // demo->swapchain is not as optimal as it could be, but the platform's
          // presentation engine will still present the image correctly.
      } else if (err == VK_ERROR_SURFACE_LOST_KHR) {
          vkDestroySurfaceKHR(demo->inst, demo->surface, NULL);
          demo_create_surface(demo);
          demo_resize(demo);
      } else {
          assert(!err);
      }
  }

最终图形画出来的效果如下图所示。

总结

这里我只是简单的了解了Vulkan渲染的流程，但是其中的概念不是很清晰。按照张静的观点，Vulkan 很酷很炫，但是不适合你，早点分手吧 ，似乎

学习vulkan是一件得不偿失的事情，我自己思考了下，我为什么要学这个呢？

1） 我对图形API感兴趣，我想知道他是怎么和硬件结合的，Vulkan就是图形API内的汇编，吃透了他，估计其他的几种API都不是问题，手动狗头；

2） 工作需要，如果我要想采用商用引擎来接入合作项目，那必须对底层的硬件调用有所了解，这样才能做深入的定制集成；

3） 性能优化是我给自己的定位，如果我连这些都不清楚，如何优化。

所以不要再犹豫了，学哪个都不容易，坚持下去吧，一年之后再看。

Reference:

1、知乎Vulkan-高性能渲染

2、Life of a triangle - NVIDIA's logical pipeline

3、Round Robin 算法

4、NVIDIA Developer Vulkan

5、Vulkan SDK Tutorial

6、Vulkan In 30 Minutes

7、Vulkan Notes

8、GDC  2016 Talk

9、知乎： Vulkan编程指南

10、Shader交叉编译之梦

11、游戏引擎随笔： 现代图形API

12、SPIR-V

13、Khronos Vulkan Registry ： vulkan specifics

14、vulkan踩坑记

15、Vulkan C++ examples and demos

16、NVIDIA GameWorks Graphics Samples