libretro_vulkan.h

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/* Copyright (C) 2010-2018 The RetroArch team
 *
 * ---------------------------------------------------------------------------------------------
 * The following license statement only applies to this libretro API header (libretro_vulkan.h)
 * ---------------------------------------------------------------------------------------------
 *
 * Permission is hereby granted, free of charge,
 * to any person obtaining a copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef LIBRETRO_VULKAN_H__
#define LIBRETRO_VULKAN_H__

#include <libretro.h>
#include <vulkan/vulkan.h>

#define RETRO_HW_RENDER_INTERFACE_VULKAN_VERSION 5
#define RETRO_HW_RENDER_CONTEXT_NEGOTIATION_INTERFACE_VULKAN_VERSION 1

struct retro_vulkan_image
{
 VkImageView image_view;
 VkImageLayout image_layout;
 VkImageViewCreateInfo create_info;
};

typedef void (*retro_vulkan_set_image_t)(void *handle,
 const struct retro_vulkan_image *image,
 uint32_t num_semaphores,
 const VkSemaphore *semaphores,
 uint32_t src_queue_family);

typedef uint32_t (*retro_vulkan_get_sync_index_t)(void *handle);
typedef uint32_t (*retro_vulkan_get_sync_index_mask_t)(void *handle);
typedef void (*retro_vulkan_set_command_buffers_t)(void *handle,
 uint32_t num_cmd,
 const VkCommandBuffer *cmd);
typedef void (*retro_vulkan_wait_sync_index_t)(void *handle);
typedef void (*retro_vulkan_lock_queue_t)(void *handle);
typedef void (*retro_vulkan_unlock_queue_t)(void *handle);
typedef void (*retro_vulkan_set_signal_semaphore_t)(void *handle, VkSemaphore semaphore);

typedef const VkApplicationInfo *(*retro_vulkan_get_application_info_t)(void);

struct retro_vulkan_context
{
 VkPhysicalDevice gpu;
 VkDevice device;
 VkQueue queue;
 uint32_t queue_family_index;
 VkQueue presentation_queue;
 uint32_t presentation_queue_family_index;
};

typedef bool (*retro_vulkan_create_device_t)(
 struct retro_vulkan_context *context,
 VkInstance instance,
 VkPhysicalDevice gpu,
 VkSurfaceKHR surface,
 PFN_vkGetInstanceProcAddr get_instance_proc_addr,
 const char **required_device_extensions,
 unsigned num_required_device_extensions,
 const char **required_device_layers,
 unsigned num_required_device_layers,
 const VkPhysicalDeviceFeatures *required_features);

typedef void (*retro_vulkan_destroy_device_t)(void);

/* Note on thread safety:
 * The Vulkan API is heavily designed around multi-threading, and
 * the libretro interface for it should also be threading friendly.
 * A core should be able to build command buffers and submit
 * command buffers to the GPU from any thread.
 */

struct retro_hw_render_context_negotiation_interface_vulkan
{
 /* Must be set to RETRO_HW_RENDER_CONTEXT_NEGOTIATION_INTERFACE_VULKAN. */
 enum retro_hw_render_context_negotiation_interface_type interface_type;
 /* Must be set to RETRO_HW_RENDER_CONTEXT_NEGOTIATION_INTERFACE_VULKAN_VERSION. */
 unsigned interface_version;

 /* If non-NULL, returns a VkApplicationInfo struct that the frontend can use instead of
 * its "default" application info.
 */
 retro_vulkan_get_application_info_t get_application_info;

 /* If non-NULL, the libretro core will choose one or more physical devices,
 * create one or more logical devices and create one or more queues.
 * The core must prepare a designated PhysicalDevice, Device, Queue and queue family index
 * which the frontend will use for its internal operation.
 *
 * If gpu is not VK_NULL_HANDLE, the physical device provided to the frontend must be this PhysicalDevice.
 * The core is still free to use other physical devices.
 *
 * The frontend will request certain extensions and layers for a device which is created.
 * The core must ensure that the queue and queue_family_index support GRAPHICS and COMPUTE.
 *
 * If surface is not VK_NULL_HANDLE, the core must consider presentation when creating the queues.
 * If presentation to "surface" is supported on the queue, presentation_queue must be equal to queue.
 * If not, a second queue must be provided in presentation_queue and presentation_queue_index.
 * If surface is not VK_NULL_HANDLE, the instance from frontend will have been created with supported for
 * VK_KHR_surface extension.
 *
 * The core is free to set its own queue priorities.
 * Device provided to frontend is owned by the frontend, but any additional device resources must be freed by core
 * in destroy_device callback.
 *
 * If this function returns true, a PhysicalDevice, Device and Queues are initialized.
 * If false, none of the above have been initialized and the frontend will attempt
 * to fallback to "default" device creation, as if this function was never called.
 */
 retro_vulkan_create_device_t create_device;

 /* If non-NULL, this callback is called similar to context_destroy for HW_RENDER_INTERFACE.
 * However, it will be called even if context_reset was not called.
 * This can happen if the context never succeeds in being created.
 * destroy_device will always be called before the VkInstance
 * of the frontend is destroyed if create_device was called successfully so that the core has a chance of
 * tearing down its own device resources.
 *
 * Only auxillary resources should be freed here, i.e. resources which are not part of retro_vulkan_context.
 */
 retro_vulkan_destroy_device_t destroy_device;
};

struct retro_hw_render_interface_vulkan
{
 /* Must be set to RETRO_HW_RENDER_INTERFACE_VULKAN. */
 enum retro_hw_render_interface_type interface_type;
 /* Must be set to RETRO_HW_RENDER_INTERFACE_VULKAN_VERSION. */
 unsigned interface_version;

 /* Opaque handle to the Vulkan backend in the frontend
 * which must be passed along to all function pointers
 * in this interface.
 *
 * The rationale for including a handle here (which libretro v1
 * doesn't currently do in general) is:
 *
 * - Vulkan cores should be able to be freely threaded without lots of fuzz.
 * This would break frontends which currently rely on TLS
 * to deal with multiple cores loaded at the same time.
 * - Fixing this in general is TODO for an eventual libretro v2.
 */
 void *handle;

 /* The Vulkan instance the context is using. */
 VkInstance instance;
 /* The physical device used. */
 VkPhysicalDevice gpu;
 /* The logical device used. */
 VkDevice device;

 /* Allows a core to fetch all its needed symbols without having to link
 * against the loader itself. */
 PFN_vkGetDeviceProcAddr get_device_proc_addr;
 PFN_vkGetInstanceProcAddr get_instance_proc_addr;

 /* The queue the core must use to submit data.
 * This queue and index must remain constant throughout the lifetime
 * of the context.
 *
 * This queue will be the queue that supports graphics and compute
 * if the device supports compute.
 */
 VkQueue queue;
 unsigned queue_index;

 /* Before calling retro_video_refresh_t with RETRO_HW_FRAME_BUFFER_VALID,
 * set which image to use for this frame.
 *
 * If num_semaphores is non-zero, the frontend will wait for the
 * semaphores provided to be signaled before using the results further
 * in the pipeline.
 *
 * Semaphores provided by a single call to set_image will only be
 * waited for once (waiting for a semaphore resets it).
 * E.g. set_image, video_refresh, and then another
 * video_refresh without set_image,
 * but same image will only wait for semaphores once.
 *
 * For this reason, ownership transfer will only occur if semaphores
 * are waited on for a particular frame in the frontend.
 *
 * Using semaphores is optional for synchronization purposes,
 * but if not using
 * semaphores, an image memory barrier in vkCmdPipelineBarrier
 * should be used in the graphics_queue.
 * Example:
 *
 * vkCmdPipelineBarrier(cmd,
 * srcStageMask = VK_PIPELINE_STAGE_ALL_GRAPHICS_BIT,
 * dstStageMask = VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT,
 * image_memory_barrier = {
 * srcAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT,
 * dstAccessMask = VK_ACCESS_SHADER_READ_BIT,
 * });
 *
 * The use of pipeline barriers instead of semaphores is encouraged
 * as it is simpler and more fine-grained. A layout transition
 * must generally happen anyways which requires a
 * pipeline barrier.
 *
 * The image passed to set_image must have imageUsage flags set to at least
 * VK_IMAGE_USAGE_TRANSFER_SRC_BIT and VK_IMAGE_USAGE_SAMPLED_BIT.
 * The core will naturally want to use flags such as
 * VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT and/or
 * VK_IMAGE_USAGE_TRANSFER_DST_BIT depending
 * on how the final image is created.
 *
 * The image must also have been created with MUTABLE_FORMAT bit set if
 * 8-bit formats are used, so that the frontend can reinterpret sRGB
 * formats as it sees fit.
 *
 * Images passed to set_image should be created with TILING_OPTIMAL.
 * The image layout should be transitioned to either
 * VK_IMAGE_LAYOUT_GENERIC or VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL.
 * The actual image layout used must be set in image_layout.
 *
 * The image must be a 2D texture which may or not be layered
 * and/or mipmapped.
 *
 * The image must be suitable for linear sampling.
 * While the image_view is typically the only field used,
 * the frontend may want to reinterpret the texture as sRGB vs.
 * non-sRGB for example so the VkImageViewCreateInfo used to
 * create the image view must also be passed in.
 *
 * The data in the pointer to the image struct will not be copied
 * as the pNext field in create_info cannot be reliably deep-copied.
 * The image pointer passed to set_image must be valid until
 * retro_video_refresh_t has returned.
 *
 * If frame duping is used when passing NULL to retro_video_refresh_t,
 * the frontend is free to either use the latest image passed to
 * set_image or reuse the older pointer passed to set_image the
 * frame RETRO_HW_FRAME_BUFFER_VALID was last used.
 *
 * Essentially, the lifetime of the pointer passed to
 * retro_video_refresh_t should be extended if frame duping is used
 * so that the frontend can reuse the older pointer.
 *
 * The image itself however, must not be touched by the core until
 * wait_sync_index has been completed later. The frontend may perform
 * layout transitions on the image, so even read-only access is not defined.
 * The exception to read-only rule is if GENERAL layout is used for the image.
 * In this case, the frontend is not allowed to perform any layout transitions,
 * so concurrent reads from core and frontend are allowed.
 *
 * If frame duping is used, or if set_command_buffers is used,
 * the frontend will not wait for any semaphores.
 *
 * The src_queue_family is used to specify which queue family
 * the image is currently owned by. If using multiple queue families
 * (e.g. async compute), the frontend will need to acquire ownership of the
 * image before rendering with it and release the image afterwards.
 *
 * If src_queue_family is equal to the queue family (queue_index),
 * no ownership transfer will occur.
 * Similarly, if src_queue_family is VK_QUEUE_FAMILY_IGNORED,
 * no ownership transfer will occur.
 *
 * The frontend will always release ownership back to src_queue_family.
 * Waiting for frontend to complete with wait_sync_index() ensures that
 * the frontend has released ownership back to the application.
 * Note that in Vulkan, transfering ownership is a two-part process.
 *
 * Example frame:
 * - core releases ownership from src_queue_index to queue_index with VkImageMemoryBarrier.
 * - core calls set_image with src_queue_index.
 * - Frontend will acquire the image with src_queue_index -> queue_index as well, completing the ownership transfer.
 * - Frontend renders the frame.
 * - Frontend releases ownership with queue_index -> src_queue_index.
 * - Next time image is used, core must acquire ownership from queue_index ...
 *
 * Since the frontend releases ownership, we cannot necessarily dupe the frame because
 * the core needs to make the roundtrip of ownership transfer.
 */
 retro_vulkan_set_image_t set_image;

 /* Get the current sync index for this frame which is obtained in
 * frontend by calling e.g. vkAcquireNextImageKHR before calling
 * retro_run().
 *
 * This index will correspond to which swapchain buffer is currently
 * the active one.
 *
 * Knowing this index is very useful for maintaining safe asynchronous CPU
 * and GPU operation without stalling.
 *
 * The common pattern for synchronization is to receive fences when
 * submitting command buffers to Vulkan (vkQueueSubmit) and add this fence
 * to a list of fences for frame number get_sync_index().
 *
 * Next time we receive the same get_sync_index(), we can wait for the
 * fences from before, which will usually return immediately as the
 * frontend will generally also avoid letting the GPU run ahead too much.
 *
 * After the fence has signaled, we know that the GPU has completed all
 * GPU work related to work submitted in the frame we last saw get_sync_index().
 *
 * This means we can safely reuse or free resources allocated in this frame.
 *
 * In theory, even if we wait for the fences correctly, it is not technically
 * safe to write to the image we earlier passed to the frontend since we're
 * not waiting for the frontend GPU jobs to complete.
 *
 * The frontend will guarantee that the appropriate pipeline barrier
 * in graphics_queue has been used such that
 * VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT cannot
 * start until the frontend is done with the image.
 */
 retro_vulkan_get_sync_index_t get_sync_index;

 /* Returns a bitmask of how many swapchain images we currently have
 * in the frontend.
 *
 * If bit #N is set in the return value, get_sync_index can return N.
 * Knowing this value is useful for preallocating per-frame management
 * structures ahead of time.
 *
 * While this value will typically remain constant throughout the
 * applications lifecycle, it may for example change if the frontend
 * suddently changes fullscreen state and/or latency.
 *
 * If this value ever changes, it is safe to assume that the device
 * is completely idle and all synchronization objects can be deleted
 * right away as desired.
 */
 retro_vulkan_get_sync_index_mask_t get_sync_index_mask;

 /* Instead of submitting the command buffer to the queue first, the core
 * can pass along its command buffer to the frontend, and the frontend
 * will submit the command buffer together with the frontends command buffers.
 *
 * This has the advantage that the overhead of vkQueueSubmit can be
 * amortized into a single call. For this mode, semaphores in set_image
 * will be ignored, so vkCmdPipelineBarrier must be used to synchronize
 * the core and frontend.
 *
 * The command buffers in set_command_buffers are only executed once,
 * even if frame duping is used.
 *
 * If frame duping is used, set_image should be used for the frames
 * which should be duped instead.
 *
 * Command buffers passed to the frontend with set_command_buffers
 * must not actually be submitted to the GPU until retro_video_refresh_t
 * is called.
 *
 * The frontend must submit the command buffer before submitting any
 * other command buffers provided by set_command_buffers. */
 retro_vulkan_set_command_buffers_t set_command_buffers;

 /* Waits on CPU for device activity for the current sync index to complete.
 * This is useful since the core will not have a relevant fence to sync with
 * when the frontend is submitting the command buffers. */
 retro_vulkan_wait_sync_index_t wait_sync_index;

 /* If the core submits command buffers itself to any of the queues provided
 * in this interface, the core must lock and unlock the frontend from
 * racing on the VkQueue.
 *
 * Queue submission can happen on any thread.
 * Even if queue submission happens on the same thread as retro_run(),
 * the lock/unlock functions must still be called.
 *
 * NOTE: Queue submissions are heavy-weight. */
 retro_vulkan_lock_queue_t lock_queue;
 retro_vulkan_unlock_queue_t unlock_queue;

 /* Sets a semaphore which is signaled when the image in set_image can safely be reused.
 * The semaphore is consumed next call to retro_video_refresh_t.
 * The semaphore will be signalled even for duped frames.
 * The semaphore will be signalled only once, so set_signal_semaphore should be called every frame.
 * The semaphore may be VK_NULL_HANDLE, which disables semaphore signalling for next call to retro_video_refresh_t.
 *
 * This is mostly useful to support use cases where you're rendering to a single image that
 * is recycled in a ping-pong fashion with the frontend to save memory (but potentially less throughput).
 */
 retro_vulkan_set_signal_semaphore_t set_signal_semaphore;
};

#endif