Handling Vulkan Swapchain Recreation During Window Resize

The Problem: Out-of-Date Swapchains

In Vulkan, the swapchain is a collection of buffers used to present images to the screen. Because these buffers are tied to the specific dimensions of the window surface, any change in window size renders the existing swapchain "out of date." Attempting to present to an outdated swapchain results in a VK_ERROR_OUT_OF_DATE_KHR error, and continuing to use the old image extents will cause visual corruption or application crashes.

The Takeaway: To maintain a stable render loop, you must detect the resize event, synchronize the GPU to ensure no resources are in use, recreate the swapchain using the old one as a template for efficiency, and rebuild all dependent resources (image views, framebuffers, and depth buffers) to match the new dimensions.

Prerequisites

• A functional Vulkan logical device with graphics and present queues.
• An existing swapchain and associated resources (image views, framebuffers).
• A window system integration (WSI) like GLFW or Win32 that provides resize callbacks.
• Validation layers enabled to detect mismatched extent errors during development.

Recreation Procedure

1. Detect the Resize Event: Use your windowing library's callback to set a boolean flag (e.g., framebufferResized = true). Do not recreate the swapchain inside the callback; handle it at the start of your next frame logic to avoid threading conflicts.
2. Synchronize the GPU: You cannot destroy resources currently being read or written by the GPU. Use vkDeviceWaitIdle to ensure all pending queues are empty.

   // Run on the main render thread
   vkDeviceWaitIdle(logicalDevice);

3. Query New Surface Extents: Retrieve the updated dimensions from the physical device. This ensures you use the actual surface size rather than the window size, which may differ on high-DPI displays.

   VkSurfaceCapabilitiesKHR caps;
   vkGetPhysicalDeviceSurfaceCapabilitiesKHR(physicalDevice, surface, &caps);
   VkExtent2D newExtent = caps.currentExtent;

4. Create the New Swapchain: Pass the handle of the current swapchain to the oldSwapchain field of VkSwapchainCreateInfoKHR. This allows the driver to reuse internal memory and speeds up the transition.

   VkSwapchainCreateInfoKHR swapInfo = {};
   swapInfo.sType = VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR;
   swapInfo.surface = surface;
   swapInfo.imageExtent = newExtent;
   swapInfo.oldSwapchain = oldSwapchain; // Optimization: reuse existing resources
   // ... other required fields (format, presentMode, etc.)
   
   VkSwapchainKHR newSwapchain;
   VkResult result = vkCreateSwapchainKHR(logicalDevice, &swapInfo, nullptr, &newSwapchain);

5. Cleanup and Update: Destroy the old swapchain only after the new one is successfully created. Then, update your local handle.

   vkDestroySwapchainKHR(logicalDevice, oldSwapchain, nullptr);
   oldSwapchain = newSwapchain;

6. Rebuild Dependent Resources: This is the most common point of failure. You must recreate everything that depends on the swapchain's image handles or its extent:
   • Image Views: Create new VkImageView handles for the new swapchain images.
   • Depth/Resolve Images: If you use a depth buffer, it must be destroyed and recreated to match newExtent.
   • Framebuffers: Recreate VkFramebuffer objects using the new image views.
   • Command Buffers: If your command buffers are recorded with hard-coded viewport/scissor dimensions, they must be re-recorded.

Verification and Checks

Check	Expected Result	Diagnostic Tool
Swapchain Creation	VK_SUCCESS or VK_SUBOPTIMAL_KHR	Return value of vkCreateSwapchainKHR
Image Extent	Matches window client area exactly	Log caps.currentExtent
Resource Validity	No "Object Destroyed" warnings	Vulkan Validation Layers
Presentation	No VK_ERROR_OUT_OF_DATE_KHR after recreation	Return value of vkQueuePresentKHR

Recovery and Edge Cases

• Recursive Out-of-Date: If vkCreateSwapchainKHR returns VK_ERROR_OUT_OF_DATE_KHR, the window was resized again during the recreation process. Wrap the procedure in a while loop or retry the logic once more.
• Surface Loss: If VK_ERROR_SURFACE_LOST_KHR occurs, the window surface itself is invalid. You must destroy the VkSurfaceKHR and recreate it via your WSI (e.g., glfwCreateWindowSurface) before attempting swapchain recreation.
• Suboptimal State: VK_SUBOPTIMAL_KHR means the swapchain can still present, but the image doesn't perfectly match the surface. You can continue rendering, but you should trigger a recreation at the next convenient break to avoid clipping.