VkBaseInStructureVkBaseOutStructure

VkBaseInStructure and VkBaseOutStructure are two Vulkan structures that underpin the API’s extension mechanism via the pNext chain. They are designed to be embedded in other Vulkan structures to enable optional, future-safe extensions without breaking compatibility.

VkBaseInStructure defines a simple input-facing header for extension chains. Its fields are sType, a VkStructureType that identifies the specific structure, and pNext, a const void* that points to the next structure in the input chain. VkBaseOutStructure is the corresponding output-facing header, with sType and pNext, but pNext is a void* rather than a const void*, reflecting its use as a writable part of the chain when Vulkan returns information.

Purpose and usage: The pNext chain allows applications to attach multiple extension structures to a single core structure. Each extension structure typically begins with one of these base headers, which lets the Vulkan implementation walk the chain generically to discover and/or populate extension data. sType must be set to the appropriate enumerant (for example VK_STRUCTURE_TYPE_BASE_IN_STRUCTURE or VK_STRUCTURE_TYPE_BASE_OUT_STRUCTURE) to identify the base type, and the chain must remain valid for the duration of the API call.

Common patterns: When defining your own extension structures, you usually include VkBaseInStructure as the first member (for input chains) or VkBaseOutStructure (for output chains). You then link structures by setting the pNext pointers to form a linked list. The API can then read from or write to the chain as needed, and callers should ensure the entire chain is valid for the duration of the call.

These base structures are a standardized, lightweight mechanism that enables Vulkan’s extensibility while preserving binary and source compatibility.