The VK_KHR_swapchain extension is the device-level companion to the
VK_KHR_surface extension. It introduces VkSwapchainKHR
objects,
which provide the ability to present rendering results to a surface.
Extending VkStructureType
:
VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR
VK_STRUCTURE_TYPE_PRESENT_INFO_KHR
Extending VkImageLayout
:
VK_IMAGE_LAYOUT_PRESENT_SRC_KHR
Extending VkResult
:
VK_SUBOPTIMAL_KHR
VK_ERROR_OUT_OF_DATE_KHR
1) Does this extension allow the application to specify the memory backing of the presentable images?
RESOLVED: No. Unlike standard images, the implementation will allocate the memory backing of the presentable image.
2) What operations are allowed on presentable images?
RESOLVED: This is determined by the imageUsageFlags specified when creating the presentable image's swapchain.
3) Does this extension support MSAA presentable images?
RESOLVED: No. Presentable images are always single-sampled. Multi-sampled rendering must use regular images. To present the rendering results the application must manually resolve the multi- sampled image to a single-sampled presentable image prior to presentation.
4) Does this extension support stereo/multi-view presentable images?
RESOLVED: Yes. The number of views associated with a presentable image is determined by the imageArraySize specified when creating a swapchain. All presentable images in a given swapchain use the same array size.
5) Are the layers of stereo presentable images half-sized?
RESOLVED: No. The image extents always match those requested by the applicaton.
6) Do the "present" and "acquire next image" commands operate on a queue? If not, do they need to include explicit semaphore objects to interlock them with queue operations?
RESOLVED: The present command operates on a queue. The image ownership operation it represents happens in order with other operations on the queue, so no explicit semaphore object is required to synchronize its actions. Applications may want to acquire the next image in separate threads from those in which they manage their queue, or in multiple threads. To make such usage easier, the acquire next image command takes a semaphore to signal as a method of explicit synchronizatoin. The application must later queue a wait for this semaphore before queuing execution of any commands using the image.
7) Does vkAcquireNextImageKHR() block if no images are available?
RESOLVED: The command takes a timeout parameter. Special values for the timeout are 0, which makes the call a non-blocking operation, and UINT64_MAX, which blocks indefinitely. Values in between will block for up to the specified time. The call will return when an image becomes available or an error occurs. It may, but is not required to, return before the specified timeout expires if the swapchain becomes out of date.
8) Can multiple presents be queued using one QueuePresent call?
RESOLVED: Yes. VkPresentInfoKHR contains a list of swapchains and corresponding image indices that will be presented. When supported, all presentations queued with a single vkQueuePresentKHR call will be applied atomically as one operation. The same swapchain must not appear in the list more than once. Later extensions may provide applications stronger guarantees of atomicity for such present operations, and/or allow them to query whether atomic presentation of a particular group of swapchains is possible.
9) How do the presentation and acquire next image functions notify the application the targeted surface has changed?
RESOLVED: Two new result codes are introduced for this purpose:
VK_SUBOPTIMAL_KHR - Presentation will still succeed, subject to the window resize behavior, but the swapchain is no longer configured optimally for the surface it targets. Applications should query updated surface information and recreate their swapchain at the next convenient opportunity.
VK_ERROR_OUT_OF_DATE_KHR - Failure. The swapchain is no longer compatible with the surface it targets. The application must query updated surface information and recreate the swapchain before presentation will succeed.
These can be returned by both vkAcquireNextImageKHR and vkQueuePresentKHR.
10) Does the vkAcquireNextImageKHR command return a semaphore to the application via an output parameter, or accept a semaphore to signal from the application as an object handle parameter?
RESOLVED: Accept a semahpore to signal as an object handle. This avoids the need to specify whether the application must destroy the semaphore or whether it is owned by the swapchain, and if the latter, what its lifetime is and whether it can be re-used for other operations once it is received from vkAcquireNextImageKHR.
11) What types of swapchain queuing behavior should be exposed? Options include swap interval specification, mailbox/most recent Vs. FIFO queue management, targeting specific vertical blank intervals or absolute times for a given present opeation, and probably others. For some of these, whether they are specified at swapchain creation time or as per-present parameters needs to be decided as well.
RESOLVED: The base swapchain extension will expose 3 possible behaviors (of which, FIFO will always be supported):
-Immediate present: Does not wait for vertical blanking period to update the current image, likely resulting in visible tearing. No internal queue is used. Present requests are applied immediately.
-Mailbox queue: Waits for the next vetical blanking period to update the current image. No tearing should be observed. An internal single-entry queue is used to hold pending presentation requests. If the queue is full when a new presentation request is received, the new request replaces the existing entry, and any images associated with the prior entry become available for re-use by the application.
-FIFO queue: Waits for the next vertical blanking period to update the current image. No tearing should be observed. An internal queue containing (numSwapchainImages - 1) entries is used to hold pending presentation requests. New requests are appended to the end of the queue, and one request is removed from the beginning of the queue and processed during each vertical blanking period in which the queue is non-empty
Not all surfaces will support all of these modes, so the modes supported will be returned using a surface info query. All surfaces must support the FIFO queue mode. Applications must choose one of these modes up front when creating a swapchain. Switching modes can be accomplished by recreating the swapchain.
12) Can VK_PRESENT_MODE_MAILBOX_KHR provide non-blocking guarantees for vkAcquireNextImageKHR()? If so, what is the proper criteria?
RESOLVED: Yes. The difficulty is not immediately obvious here. Naively, if at least 3 images are requested, mailbox mode should always have an image available for the application if the application does not own any images when the call to vkAcquireNextImageKHR() was made. However, some presentation engines may have more than one "current" image, and would still need to block in some cases. The right requirement appears to be that if the application allocates the surface's minimum number of images + 1 then it is guaranteed non- blocking behavior when it does not currently own any images.
13) Is there a way to create and initialize a new swapchain for a surface that has generated a VK_SUBOPTIMAL_KHR return code while still using the old swapchain?
RESOLVED: Not as part of this specification. This could be useful to allow the application to create an "optimal" replacement swapchain and rebuild all its command buffers using it in a background thread at a low priority while continuing to use the "suboptimal" swapchain in the main thread. It could probably use the same "atomic replace" semantics proposed for recreating direct-to-device swapchains without incuring a mode switch. However, after discussion, it was determined some platforms probably could not support concurrent swapchains for the same surface though, so this will be left out of the base KHR extensions. A future extension could add this for platfroms where it is supported.
14) Should there be a special value for VkSurfacePropertiesKHR::maxImageCount to indicate there are no practical limits on the number of images in a swapchain?
RESOLVED: Yes. There where often be cases where there is no practical limit to the number of images in a swapchain other than the amount of available resources (I.e., memory) in the system. Trying to derive a hard limit from things like memory size is prone to failure. It is better in such cases to leave it to applications to figure such soft limits out via trial/failure iterations.
15) Should there be a special value for VkSurfacePropertiesKHR::currentExtent to indicate the size of the platform surface is undefined?
RESOLVED: Yes. On some platforms (Wayland, for example), the surface size is defined by the images presented to it rather than the other way around.
16) Should there be a special value for VkSurfacePropertiesKHR::maxImageExtent to indicate there is no practical limit on the surface size?
RESOLVED: No. It seems unlikely such a system would exist. 0 could be used to indicate the platform places no limits on the extents beyond those imposed by Vulkan for normal images, but this query could just as easily return those same limits, so a special "unlimited" value doesn't seem useful for this field.
17) How should surface rotation and mirroring be exposed to applications? How do they specify rotation and mirroring transforms applied prior to presentation?
RESOLVED: Applications can query both the supported and current transforms of a surface. Both are specified relative to the device's "natural" display rotation and direction. The supported transforms indicates which orientations the presentation engine accepts images in. For example, a presentation engine that does not support transforming surfaces as part of presentation, and which is presenting to a surface that is displayed with a 90-degree rotation, would return only one supported transform bit: VK_SURFACE_TRANSFORM_ROT90_BIT_KHR. Applications must transform their rendering by the transform they specify when creating the swapchain in preTransform field.
18) Can surfaces ever not support VK_MIRROR_NONE? Can they support vertical and horizontal mirroring simultaneously? Relatedly, should VK_MIRROR_NONE[_BIT] be zero, or bit one, and should applications be allowed to specify multiple pre and current mirror transform bits, or exactly one?
RESOLVED: Since some platforms may not support presenting with a transform other than the native window's current transform, and pre-rotation/mirroring are specified relative to the device's natural rotation and direction, rather than relative to the surface's current rotation and direction, it is necessary to express lack of support for no mirroring. To allow this, the MIRROR_NONE enum must occupy a bit in the flags. Since MIRROR_NONE must be a bit in the bitfield rather than a bitfield with no values set, allowing more than one bit to be set in the bitfield would make it possible to describe undefined transforms such as VK_MIRROR_NONE_BIT | VK_MIRROR_HORIZONTAL_BIT, or a transform that includes both "no mirroring" and "horizontal mirroring simultaneously. Therefore, it is desireable to allow specifying all supported mirroring transforms using only one bit. The question then becomes, should there be a VK_MIRROR_HORIZONTAL_AND_VERTICAL_BIT to represent a simultaneous horizontal and vertical mirror transform? However, such a transform is equivalent to a 180 degree rotation, so presentation engines and applications that wish to support or use such a transform can express it through rotation instead. Therefore, 3 exclusive bits are sufficient to express all needed mirroring transforms.
19) Should support for sRGB be required?
RESOLVED: In the advent of UHD and HDR display devices, proper colorspace information is vital to the display pipeline represented by the swapchain. The app can discover the supported format/colorspace pairs and select a pair most suited to its rendering needs. Currently only the sRGB colorspace is supported, future extensions may provide support for more colorspaces. See issues 23) and 24).
20) Is there a mechanism to modify or replace an existing swapchain with one targeting the same surface?
RESOLVED: Yes. This is described above in the text.
21) Should there be a way to set pre-rotation and mirroring using native APIs when presenting using a Vulkan swapchain?
RESOLVED: Yes. The transforms that can be expressed in this extension are a subset of those possible on native platforms. If a platform exposes a method to specify the transform of presented images for a given surface using native methods and exposes more transforms or other properties for surfaces than Vulkan supports, it might be impossible, difficult, or inconvenient to set some of those properties using Vulkan KHR extensions and some using the native interfaces. To avoid overwriting properties set using native commands when presenting using a Vulkan swapchain, the application can set the pre-transform to "inherit", in which case the current native properties will be used, or if none are available, a platform-specific default will be used. Platforms that do not specify a reasonable default or do not provide native mechanisms to specify such transforms should not include the inherit bits in the supportedTransform field they return in VkSurfacePropertiesKHR.
22) Should the content of presentable images be clipped by objects obscuring their target surface?
RESOLVED: Applications can choose which behavior they prefer. Allowing the content to be clipped could enable more optimal presentation methods on some platforms, but some applications might rely on the content of presentable images to perform techniques such as partial updates or motion blurs.
23) What is the purpose of specifying a VkColorspaceKHR along with VkFormat when creating a swapchain?
RESOLVED: While Vulkan itself is colorspace agnostic (e.g. even the meaning of R, G, B and A can be freely defined by the rendering application), the swapchain eventually will have to present the images on a display device with specific color reproduction characteristics. If any colorspace transformations are necessary before an image can be displayed, the colorspace of the presented image must be known to the swapchain. A swapchain will only support a restricted set of color format and -space pairs. This set can be discovered via vkGetSurfaceInfoKHR. As it can be expected that most display devices support the sRGB colorspace, at least one format/colorspace pair has to be exposed, where colorspace is VK_COLOR_SPACE_SRGB_NONLINEAR.
24) How are sRGB formats and the sRGB colorspace related?
RESOLVED: While Vulkan exposes a number of SRGB texture formats, using such formats does not guarantee working in a specific colorspace. It merely means that the hardware can directly support applying the non-linear transfer functions defined by the sRGB standard colorspace when reading from or writing to images of that these formats. Still, it is unlikely that a swapchain will expose a _SRGB format along with any colorspace other than VK_COLOR_SPACE_SRGB_NONLINEAR.
On the other hand, non-_SRGB formats will be very likely exposed in pair with a SRGB colorspace. This means, the hardware will not apply any transfer function when reading from or writing to such images, yet they will still be presented on a device with sRGB display characteristics. In this case the application is responsible for applying the transfer function, for instance by using shader math.
25) How are the lifetime of surfaces and swapchains targeting them related?
RESOLVED: A surface must outlive any swapchains targeting it. A VkSurfaceKHR owns the binding of the native window to the Vulkan driver.
26) How can the client control the way the alpha channel of swap chain images is treated by the presentation engine during compositing?
RESOLVED: We should add new enum values to allow the client to negotiate with the presentation engine on how to treat image alpha values during the compositing process. Since not all platforms can practically control this through the Vulkan driver, a value of INHERIT is provided like for surface transforms.
27) Is vkCreateSwapchainKHR() the right function to return VK_ERROR_NATIVE_WINDOW_IN_USE_KHR, or should the various platform- specific VkSurface factory functions catch this error earlier?
RESOLVED: For most platforms, the VkSurface structure is a simple container holding the data that identifies a native window or other object representing a surface on a particular platform. For the surface factory functions to return this error, they would likely need to register a reference on the native objects with the native display server some how, and ensure no other such references exist. Surfaces were not intended to be that heavy- weight.
Swapchains are intended to be the objects that directly manipulate native windows and communicate with the native presentation mechanisms. Swapchains will already need to communicate with the native display server to negotiate allocation and/or presentation of presentable images for a native surface. Therefore, it makes more sense for swapchain creation to be the point at which native object exclusivity is enforced. Platforms may choose to enforce further restrictions on the number of VkSurface objects that may be created for the same native window if such a requirement makes sense on a particular platform, but a global requirement is only sensible at the swapchain level.
Example 1
Create a swapchain for a surface on a particular instance of a native platform.
extern VkDevice device; extern VkSurfaceKHR surface; // Must call extension functions through a function pointer: PFN_vkGetSurfacePropertiesKHR pfnGetSurfacePropertiesKHR = (PFN_vkGetSurfacePropertiesKHR)vkGetDeviceProcAddr(device, "vkGetSurfaceInfoKHR"); PFN_vkGetSurfaceFormatsKHR pfnGetSurfaceFormatsKHR = (PFN_vkGetSurfaceFormatsKHR)vkGetDeviceProcAddr(device, "vkGetSurfaceFormatsKHR"); PFN_vkGetSurfacePresentModesKHR pfnGetSurfacePresentModesKHR = (PFN_vkGetSurfacePresentModesKHR)vkGetDeviceProcAddr(device, "vkGetSurfacePresentModesKHR"); PFN_vkCreateSwapchainKHR pfnCreateSwapchainKHR = (PFN_vkCreateSwapchainKHR)vkGetDeviceProcAddr(device, "vkCreateSwapchainKHR"); // Check the surface properties and formats VkSurfacePropertiesKHR surfaceProperties; pfnGetSurfacePropertiesKHR(device, surface, &surfaceProperties); uint32_t formatCount; pfnGetSurfaceFormatsKHR(device, surface, &formatCount, NULL); VkSurfaceFormatKHR* pSurfFormats = (VkSurfaceFormatKHR*)malloc(formatCount * sizeof(VkSurfaceFormatKHR)); pfnGetSurfaceFormatsKHR(device, surface, &formatCount, pSurfFormats); uint32_t presentModeCount; pfnGetSurfacePresentModesKHR(device, surface, &presentModeCount, NULL); VkPresentModeKHR* pPresentModes = (VkPresentModeKHR*)malloc(presentModeCount * sizeof(VkPresentModeKHR)); pfnGetSurfacePresentModesKHR(device, surface, &presentModeCount, pPresentModes); VkExtent2D swapchainExtent; // width and height are either both -1, or both not -1. if (surfaceProperties.currentExtent.width == -1) { // If the surface size is undefined, the size is set to // the size of the images requested, which must fit within the minimum // and maximum values. swapchainExtent.width = 320; swapchainExtent.height = 320; if (swapchainExtent.width < surfaceProperties.minImageExtent.width) swapchainExtent.width = surfaceProperties.minImageExtent.width; else if (swapchainExtent.width > surfaceProperties.maxImageExtent.width) swapchainExtent.width = surfaceProperties.maxImageExtent.width; if (swapchainExtent.height < surfaceProperties.minImageExtent.height) swapchainExtent.height = surfaceProperties.minImageExtent.height; else if (swapchainExtent.height > surfaceProperties.maxImageExtent.height) swapchainExtent.height = surfaceProperties.maxImageExtent.height; } else { // If the surface size is defined, the swapchain size must match swapchainExtent = surfaceProperties.currentExtent; } // Application desires to own 2 images at a time (still allowing // 'minImageCount' images to be owned by the presentation engine). uint32_t desiredNumberOfSwapchainImages = surfaceProperties.minImageCount + 2; if ((surfaceProperties.maxImageCount > 0) && (desiredNumberOfSwapchainImages > surfaceProperties.maxImageCount)) { // Application must settle for fewer images than desired: desiredNumberOfSwapchainImages = surfaceProperties.maxImageCount; } VkFormat swapchainFormat; // 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 (assuming that the // vkGetPhysicalDeviceSurfaceSupportKHR function, in the // VK_KHR_surface extension returned support for the surface). if ((formatCount == 1) && (pSurfFormats[0].format == VK_FORMAT_UNDEFINED)) swapchainFormat = VK_FORMAT_R8G8B8_UNORM; else { assert(formatCount >= 1); swapchainFormat = pSurfFormats[0].format; } VkColorSpaceKHR swapchainColorSpace = pSurfFormats[0].colorSpace; // If mailbox mode is available, use it, as it is the lowest-latency non- // tearing mode. If not, fall back to FIFO which is always available. VkPresentModeKHR swapchainPresentMode = VK_PRESENT_MODE_FIFO_KHR; for (size_t i = 0; i < presentModeCount; ++i) if (pPresentModes[i] == VK_PRESENT_MODE_MAILBOX_KHR) { swapchainPresentMode = VK_PRESENT_MODE_MAILBOX_KHR; break; } const VkSwapchainCreateInfoKHR createInfo = { VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR, // sType NULL, // pNext 0, // flags surface, // surface desiredNumberOfSwapchainImages, // minImageCount swapchainFormat, // imageFormat swapchainColorSpace, // imageColorSpace swapchainExtent, // imageExtent 1, // imageArrayLayers VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT, // imageUsage VK_SHARING_MODE_EXCLUSIVE, // imageSharingMode 0, // queueFamilyIndexCount NULL, // pQueueFamilyIndices surfaceProperties.currentTransform, // preTransform VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR, // compositeAlpha swapchainPresentMode, // presentMode VK_TRUE, // clipped VK_NULL_HANDLE // oldSwapchain }; VkSwapchainKHR swapchain; pfnCreateSwapchainKHR(device, &createInfo, NULL, &swapchain);
Example 2
Obtaining the persistent images of a swapchain
// Must call extension functions through a function pointer: PFN_vkGetSwapchainImagesKHR pfnGetSwapchainImagesKHR = (PFN_vkGetSwapchainImagesKHR)vkGetDeviceProcAddr(device, "vkGetSwapchainImagesKHR"); uint32_t swapchainImageCount; pfnGetSwapchainImagesKHR(device, swapchain, &swapchainImageCount, NULL); VkImage* pSwapchainImages = (VkImage*)malloc(swapchainImageCount * sizeof(VkImage)); pfnGetSwapchainImagesKHR(device, swapchain, &swapchainImageCount, pSwapchainImages);
Example 3
Simple rendering and presenting using separate graphics and present queues.
// Must call extension functions through a function pointer: PFN_vkAcquireNextImageKHR pfnAcquireNextImageKHR = (PFN_vkAcquireNextImageKHR)vkGetDeviceProcAddr(device, "vkAcquireNextImageKHR"); PFN_vkQueuePresentKHR pfnQueuePresentKHR = (PFN_vkQueuePresentKHR)vkGetDeviceProcAddr(device, "vkQueuePresentKHR"); // Construct command buffers rendering to the presentable images VkCmdBuffer cmdBuffers[swapchainImageCount]; VkImageView views[swapchainImageCount]; extern VkCmdBufferBeginInfo beginInfo; extern uint32_t graphicsQueueFamilyIndex, presentQueueFamilyIndex; for (size_t i = 0; i < swapchainImageCount; ++i) { const VkImageViewCreateInfo viewInfo = { VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO, // sType NULL, // pNext 0, // flags pSwapchainImages[i], // image VK_IMAGE_VIEW_TYPE_2D, // viewType swapchainFormat, // format ... }; vkCreateImageView(device, &viewInfo, &views[i]); ... vkBeginCommandBuffer(cmdBuffers[i], &beginInfo); // Need to transition image from presentable state before being able to render const VkImageMemoryBarrier acquireImageBarrier = { VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER, // sType NULL, // pNext VK_ACCESS_MEMORY_READ_BIT, // srcAccessMask VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT, // dstAccessMask VK_IMAGE_LAYOUT_PRESENT_SRC_KHR, // oldLayout VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, // newLayout presentQueueFamilyIndex, // srcQueueFamilyIndex graphicsQueueFamilyIndex, // dstQueueFamilyIndex pSwapchainImages[i].image, // image ... }; vkCmdPipelineBarrier( cmdBuffers[i], VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT, VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT, VK_FALSE, 1, &acquireImageBarrier) // ... Render to views[i] ... // Need to transition image into presentable state before being able to present const VkImageMemoryBarrier presentImageBarrier = { VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER, // sType NULL, // pNext VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT, // srcAccessMask VK_ACCESS_MEMORY_READ_BIT, // dstAccessMask VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, // oldLayout VK_IMAGE_LAYOUT_PRESENT_SRC_KHR, // newLayout graphicsQueueFamilyIndex, // srcQueueFamilyIndex presentQueueFamilyIndex, // dstQueueFamilyIndex pSwapchainImages[i].image, // image ... }; vkCmdPipelineBarrier( cmdBuffers[i], VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT, VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT, VK_FALSE, 1, &presentImageBarrier); ... vkEndCommandBuffer(cmdBuffers[i]); } const VkSemaphoreCreateInfo semaphoreCreateInfo = { VK_STRUCTURE_TYPE_SEMAPHORE_CREATE_INFO, // sType NULL, // pNext 0 // flags }; VkSemaphore imageAcquiredSemaphore; vkCreateSemaphore(device, &semaphoreCreateInfo, &imageAcquiredSemaphore); VkSemaphore renderingCompleteSemaphore; vkCreateSemaphore(device, &semaphoreCreateInfo, &renderingCompleteSemaphore); VkResult result; do { uint32_t imageIndex = UINT32_MAX; // Get the next available swapchain image result = pfnAcquireNextImageKHR( device, swapchain, UINT64_MAX, imageAcquiredSemaphore, VK_NULL_HANDLE, &imageIndex); // Swapchain cannot be used for presentation if failed to acquired new image. if (result < 0) break; // Submit rendering work to the graphics queue const VkPipelineStageFlags waitDstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT; const VkSubmitInfo submitInfo = { VK_STRUCTURE_TYPE_SUBMIT_INFO, // sType NULL, // pNext 1, // waitSemaphoreCount &imageAcquiredSemaphore, // pWaitSemaphores &waitDstStageMask, // pWaitDstStageMasks 1, // commandBufferCount &cmdBuffers[imageIndex], // pCommandBuffers 1, // signalSemaphoreCount &renderingCompleteSemaphore // pSignalSemaphores }; vkQueueSubmit(graphicsQueue, 1, &submitInfo, VK_NULL_HANDLE); // Submit present operation to present queue const VkPresentInfoKHR presentInfo = { VK_STRUCTURE_TYPE_PRESENT_INFO_KHR, // sType NULL, // pNext 1, // waitSemaphoreCount &renderingCompleteSemaphore, // pWaitSemaphores 1, // swapchainCount &swapchain, // pSwapchains &imageIndex, // pImageIndices NULL // pResults }; result = pfnQueuePresentKHR(presentQueue, &presentInfo); } while (result >= 0);
Example 4
Handle VK_ERROR_OUT_OF_DATE_KHR by recreating the swapchain and VK_SUBOPTIMAL_KHR by checking whether recreation is needed.
extern VkDevice device; extern VkQueue presentQueue; extern VkSurfaceKHR surface; // Contains code to build the application's reusable command buffers. extern void CreateCommandBuffers(VkDevice device, const VkImage* swapchainImages); // Returns non-zero if the application considers the swapchain out // of date even though it is still compatible with the platform // surface it is targeting. extern int MustRecreateSwapchain(VkDevice device, VkSwapchainKHR swapchain, VkSurfaceKHR surface); PFN_vkGetSurfacePropertiesKHR pfnGetSurfacePropertiesKHR; PFN_vkGetSurfaceFormatsKHR pfnGetSurfaceFormatsKHR; PFN_vkGetSurfacePresentModesKHR pfnGetSurfacePresentModesKHR; PFN_vkCreateSwapchainKHR pfnCreateSwapchainKHR; PFN_vkGetSwapchainImagesKHR pfnGetSwapchainImagesKHR; PFN_vkAcquireNextImageKHR pfnAcquireNextImageKHR; PFN_vkDestroySwapchainKHR pfnDestroySwapchainKHR; PFN_vkQueuePresentKHR pfnQueuePresentKHR; void initFuncs(void) { // Must call extension functions through a function pointer: pfnGetSurfacePropertiesKHR = (PFN_vkGetSurfacePropertiesKHR)vkGetDeviceProcAddr(device, "vkGetSurfaceInfoKHR"); pfnGetSurfaceFormatsKHR = (PFN_vkGetSurfaceFormatsKHR)vkGetDeviceProcAddr(device, "vkGetSurfaceFormatsKHR"); pfnGetSurfacePresentModesKHR = (PFN_vkGetSurfacePresentModesKHR)vkGetDeviceProcAddr(device, "vkGetSurfacePresentModesKHR"); pfnCreateSwapchainKHR = (PFN_vkCreateSwapchainKHR)vkGetDeviceProcAddr(device, "vkCreateSwapchainKHR"); pfnGetSwapchainImagesKHR = (PFN_vkGetSwapchainImagesKHR)vkGetDeviceProcAddr(device, "vkGetSwapchainImagesKHR"); pfnAcquireNextImageKHR = (PFN_vkAcquireNextImageKHR)vkGetDeviceProcAddr(device, "vkAcquireNextImageKHR"); pfnDestroySwapchainKHR = (PFN_vkDestroySwapchainKHR)vkGetDeviceProcAddr(device, "vkDestroySwapchainKHR"); pfnQueuePresentKHR = (PFN_vkQueuePresentKHR)vkGetDeviceProcAddr(device, "vkQueuePresentKHR"); } void CreateSwapchain(VkDevice device, VkSurfaceKHR surface, VkSwapchainKHR oldSwapchain, VkSwapchainKHR* pSwapchain) { // Check the surface properties and formats VkSurfacePropertiesKHR surfaceProperties; pfnGetSurfacePropertiesKHR(device, surface, &surfaceProperties); uint32_t formatCount; pfnGetSurfaceFormatsKHR(device, surface, &formatCount, NULL); VkSurfaceFormatKHR* pSurfFormats = (VkSurfaceFormatKHR*)malloc(formatCount * sizeof(VkSurfaceFormatKHR)); pfnGetSurfaceFormatsKHR(device, surface, &formatCount, pSurfFormats); uint32_t presentModeCount; pfnGetSurfacePresentModesKHR(device, surface, &presentModeCount, NULL); VkPresentModeKHR* pPresentModes = (VkPresentModeKHR*)malloc(presentModeCount * sizeof(VkPresentModeKHR)); pfnGetSurfacePresentModesKHR(device, surface, &presentModeCount, pPresentModes); VkExtent2D swapchainExtent; // width and height are either both -1, or both not -1. if (surfaceProperties.currentExtent.width == -1) { // If the surface size is undefined, the size is set to // the size of the images requested, which must fit within the minimum // and maximum values. swapchainExtent.width = 320; swapchainExtent.height = 320; if (swapchainExtent.width < surfaceProperties.minImageExtent.width) swapchainExtent.width = surfaceProperties.minImageExtent.width; else if (swapchainExtent.width > surfaceProperties.maxImageExtent.width) swapchainExtent.width = surfaceProperties.maxImageExtent.width; if (swapchainExtent.height < surfaceProperties.minImageExtent.height) swapchainExtent.height = surfaceProperties.minImageExtent.height; else if (swapchainExtent.height > surfaceProperties.maxImageExtent.height) swapchainExtent.height = surfaceProperties.maxImageExtent.height; } else { // If the surface size is defined, the swapchain size must match swapchainExtent = surfaceProperties.currentExtent; } // Application desires to own 2 images at a time (still allowing // 'minImageCount' images to be owned by the presentation engine). uint32_t desiredNumberOfSwapchainImages = surfaceProperties.minImageCount + 2; if ((surfaceProperties.maxImageCount > 0) && (desiredNumberOfSwapchainImages > surfaceProperties.maxImageCount)) { // Application must settle for fewer images than desired: desiredNumberOfSwapchainImages = surfaceProperties.maxImageCount; } VkFormat swapchainFormat; // 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 (assuming that the // vkGetPhysicalDeviceSurfaceSupportKHR function, in the // VK_KHR_surface extension returned support for the surface). if ((formatCount == 1) && (pSurfFormats[0].format == VK_FORMAT_UNDEFINED)) swapchainFormat = VK_FORMAT_R8G8B8_UNORM; else { assert(formatCount >= 1); swapchainFormat = pSurfFormats[0].format; } VkColorSpaceKHR swapchainColorSpace = pSurfFormats[0].colorSpace; // If mailbox mode is available, use it, as it is the lowest-latency non- // tearing mode. If not, fall back to FIFO which is always available. VkPresentModeKHR swapchainPresentMode = VK_PRESENT_MODE_FIFO_KHR; for (size_t i = 0; i < presentModeCount; ++i) if (pPresentModes[i] == VK_PRESENT_MODE_MAILBOX_KHR) { swapchainPresentMode = VK_PRESENT_MODE_MAILBOX_KHR; break; } const VkSwapchainCreateInfoKHR createInfo = { VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR, // sType NULL, // pNext 0, // flags surface, // surface desiredNumberOfSwapchainImages, // minImageCount swapchainFormat, // imageFormat swapchainColorSpace, // imageColorSpace swapchainExtent, // imageExtent 1, // imageArrayLayers VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT, // imageUsage VK_SHARING_MODE_EXCLUSIVE, // imageSharingMode 0, // queueFamilyIndexCount NULL, // pQueueFamilyIndices surfaceProperties.currentTransform, // preTransform VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR, // compositeAlpha swapchainPresentMode, // presentMode VK_TRUE, // clipped // If the caller specified an existing swapchain, replace it with the // new swapchain being created here. This will allow a seamless // transition between the old and new swapchains on platforms that // support it. oldSwapchain // oldSwapchain }; pfnCreateSwapchainKHR(device, &createInfo, NULL, pSwapchain); // Clean up the old swapchain, if it exists. // Note: destroying the swapchain also cleans up all its associated // presentable images once the platform is done with them. if (oldSwapchain != VK_NULL_HANDLE) { pfnDestroySwapchainKHR(device, oldSwapchain, NULL); } } void mainLoop(void) { VkSwapchainKHR swapchain = VK_NULL_HANDLE; const VkSemaphoreCreateInfo semaphoreCreateInfo = { VK_STRUCTURE_TYPE_SEMAPHORE_CREATE_INFO, // sType NULL, // pNext 0 // flags }; VkSemaphore imageAcquiredSemaphore; vkCreateSemaphore(device, &semaphoreCreateInfo, &imageAcquiredSemaphore); VkSemaphore renderingCompleteSemaphore; vkCreateSemaphore(device, &semaphoreCreateInfo, &renderingCompleteSemaphore); while (1) { VkResult result; CreateSwapchain(device, surface, swapchain, &swapchain); uint32_t swapchainImageCount; pfnGetSwapchainImagesKHR(device, swapchain, &swapchainImageCount, NULL); VkImage* pSwapchainImages = (VkImage*)malloc(swapchainImageCount * sizeof(VkImage)); pfnGetSwapchainImagesKHR(device, swapchain, &swapchainImageCount, pSwapchainImages); CreateCommandBuffers(device, pSwapchainImages); free(pSwapchainImages); while (1) { uint32_t imageIndex; // Get the next available swapchain image result = pfnAcquireNextImageKHR( device, swapchain, UINT64_MAX, imageAcquiredSemaphore, VK_NULL_HANDLE, &imageIndex); if (result == VK_ERROR_OUT_OF_DATE_KHR) { // swapchain is out of date. Needs to be recreated for // defined results. break; } else if (result == VK_SUBOPTIMAL_KHR) { // Ignore this result here. If any expensive pre-processing // work has already been done for this frame, it is likely // in the application's interest to continue processing this // frame with the current swapchain rather than recreate it // and waste the pre-processing work. } else if (result < 0) { // Unhandled error. Abort. return; } // Submit rendering work to the graphics queue const VkPipelineStageFlags waitDstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT; const VkSubmitInfo submitInfo = { VK_STRUCTURE_TYPE_SUBMIT_INFO, // sType NULL, // pNext 1, // waitSemaphoreCount &imageAcquiredSemaphore, // pWaitSemaphores &waitDstStageMask, // pWaitDstStageMasks 1, // commandBufferCount &cmdBuffers[imageIndex], // pCommandBuffers 1, // signalSemaphoreCount &renderingCompleteSemaphore // pSignalSemaphores }; vkQueueSubmit(graphicsQueue, 1, &submitInfo, VK_NULL_HANDLE); // Submit present operation to present queue const VkPresentInfoKHR presentInfo = { VK_STRUCTURE_TYPE_PRESENT_INFO_KHR, // sType NULL, // pNext 1, // waitSemaphoreCount &renderingCompleteSemaphore, // pWaitSemaphores 1, // swapchainCount &swapchain, // pSwapchains &imageIndex, // pImageIndices NULL // pResults }; result = pfnQueuePresentKHR(presentQueue, &presentInfo); if (result == VK_ERROR_OUT_OF_DATE_KHR) { // The swapchain is out of date, and must be recreated for // defined results. break; } else if (result == VK_SUBOPTIMAL_KHR) { // Something has changed about the native surface since the // swapchain was created, but it is still compatible with the // swapchain. The app must choose whether it wants to create // a more up to date swapchain before it begins processing // the next frame. if (MustRecreateSwapchain(device, swapchain, surface)) break; } else if (result < 0) { // Unhandled error. Abort. return; } } } }
Example 5
Meter a CPU thread based on presentation rate. Note this will only limit the thread to the actual presentation rate when using VK_PRESENT_MODE_FIFO_KHR. When using VK_PRESENT_MODE_IMMEDIATE_KHR, presentation rate will be limited only by rendering rate, so this example will be equivalent to waiting on a command buffer fence. When using VK_PRESENT_MODE_MAILBOX_KHR, some presented images may be skipped if a newer image is available by the time the presentation target is ready to process a new frame, so this code would again be limited only by the rendering rate. Applications using mailbox mode should use some other mechanism to meter their rendering, and it is assumed applications using immediate mode have no desire to limit the rate of their rendering based on presentation rate.
extern void CreateSemAndFences(VkDevice device, VkSemaphore sem, VkFence *fences, const int maxOutstandingPresents); extern void GenFrameCmdBuffer(VkCmdbuffer cmdBuffer); extern VkDevice device; extern VkQueue queue; extern VkCmdBuffer cmdBuffer; extern VkSwapchain fifoModeSwapchain; extern numSwapchainImages; // Must call extension functions through a function pointer: PFN_vkAcquireNextImageKHR pfnAcquireNextImageKHR = (PFN_vkAcquireNextImageKHR)vkGetDeviceProcAddr(device, "vkAcquireNextImageKHR"); PFN_vkQueuePresentKHR pfnQueuePresentKHR = (PFN_vkQueuePresentKHR)vkGetDeviceProcAddr(device, "vkQueuePresentKHR"); // Allow a maximum of two outstanding presentation operations. static const int FRAME_LAG = 2 VkPresentInfoKHR presentInfo; const VkSemaphoreCreateInfo semaphoreCreateInfo = { VK_STRUCTURE_TYPE_SEMAPHORE_CREATE_INFO, // sType NULL, // pNext 0 // flags }; VkSemaphore imageAcquiredSemaphore; vkCreateSemaphore(device, &semaphoreCreateInfo, &imageAcquiredSemaphore); VkSemaphore renderingCompleteSemaphore; vkCreateSemaphore(device, &semaphoreCreateInfo, &renderingCompleteSemaphore); VkFence fences[FRAME_LAG]; bool fencesInited[FRAME_LAG]; int frameIdx = 0; int imageIdx = 0; int waitFrame; CreateFences(device, fences, FRAME_LAG); for (int i = 0; i < FRAME_LAG; ++i) fencesInited[i] = false; while (1) { if (fencesInited[frameIdx]) { // Ensure no more than FRAME_LAG presentations are outstanding vkWaitForFences(device, 1, &fences[frameIdx], VK_TRUE, UINT64_MAX); vkResetFences(device, 1, &fences[frameIdx]); } pfnAcquireNextImageKHR( device, fifoSwapchain, UINT64_MAX, imageAcquiredSemaphore, fences[frameIdx], &imageIdx); fencesInited[frameIdx] = true; // Generate a command buffer for the current frame. GenFrameCmdBuffer(cmdBuffer); // Submit rendering work to the graphics queue const VkPipelineStageFlags waitDstStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT; const VkSubmitInfo submitInfo = { VK_STRUCTURE_TYPE_SUBMIT_INFO, // sType NULL, // pNext 1, // waitSemaphoreCount &imageAcquiredSemaphore, // pWaitSemaphores &waitDstStageMask, // pWaitDstStageMasks 1, // commandBufferCount &cmdBuffer, // pCommandBuffers 1, // signalSemaphoreCount &renderingCompleteSemaphore // pSignalSemaphores }; vkQueueSubmit(queue, 1, &submitInfo, VK_NULL_HANDLE); // Submit present operation to present queue const VkPresentInfoKHR presentInfo = { VK_STRUCTURE_TYPE_PRESENT_INFO_KHR, // sType NULL, // pNext 1, // waitSemaphoreCount &renderingCompleteSemaphore, // pWaitSemaphores 1, // swapchainCount &fifoSwapchain, // pSwapchains &imageIdx, // pImageIndices NULL // pResults }; result = pfnQueuePresentKHR(queue, &presentInfo); frameIdx += 1; frameIdx %= FRAME_LAG; }
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