Vulkan

Startup

VkInstance -> VkPhysicalDevice -> VKDevice

VkInstance for validation layers, extensions, and loggers. Usually only one will suffice for most applications. Extensions can slow down the driver so only enable neccessary ones.

VkPhysicalDevice represents GPUs queried by VkInstance. No communication is allowed yet.

VKDevice is gained from VkPhysicalDevice and is used to communicate with the GPU. Most Vulkan commands require this.

Vulkan allows manual multi-GPU configuration, multiple VKDevice can be made and assigned commands.

Swapchain is optional (headless applications) and is the main way to present an image to the screen. They are internally lists of images but typically 2 or 3 are used for double or triple buffering. Present modes: * VK_PRESENT_MODE_IMMEDIATE_KHR * VK_PRESENT_MODE_FIFO_KHR * VK_PRESENT_MODE_FIFO_RELAXED_KHR * VK_PRESENT_MODE_MAILBOX_KHR

Commands and Queues

VkCommandBuffer is created from VkCommandPool Record VkCmds into the VkCommandBuffer. Then submit the buffer into a VkQueue.

Command records are cheaps while submitting them are not (VkQueueSubmit). Multithreaded code will have a VkCommandPool and VkCommandBuffer each thread and submit commands one at a time (VkQueueSubmit is not threadsafe)

Queues can have a different family, dictating the type of queue and supported commands.

NOTE: Transfer-only queues are great for loading assets. Lifecycle: https://registry.khronos.org/vulkan/specs/1.2-extensions/html/chap6.html#commandbuffers-lifecycle

Renderpass

Renderpasses are the main ways, besides compute commands to render to the screen. Renderpassees are made of subpasses, which are useful on mobile GPUs to optimize work out. On desktop, this is not much of an advantage, but there must be at least one subpass in a renderpass.

Renderpasses will render into a framebuffer, which links the images to be rendered to.

Image layouts dictate the state of images, as we have no control over how GPUs manipulate image layouts during processing. There are four layouts: * VK_IMAGE_LAYOUT_UNDEFINED * VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL (rendering commands) * VK_IMAGE_LAYOUT_PRESENT_SRC_KHR (rendering to screen) * VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL (reading from shaders)