VKMEMORYPROPERTYHOSTVISIBLEBIT

VKMEMORYPROPERTYHOSTVISIBLEBIT refers to the HOST_VISIBLE bit in the Vulkan API, represented as VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT. This flag is part of VkMemoryPropertyFlags and indicates that a memory type can be mapped into the host (CPU) address space. Memory that has this property can be accessed by the application via vkMapMemory, enabling read and write operations from the CPU.

In practice, the HOST_VISIBLE_BIT is used when selecting a memory type for allocation. During physical device memory property queries, such as VkPhysicalDeviceMemoryProperties, developers choose a memoryTypeIndex from memoryTypes whose propertyFlags include VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT. If a memory type lacks this flag, its memory cannot be mapped by the host.

The HOST_VISIBLE_BIT is commonly considered alongside other host-related flags, such as HOST_COHERENT_BIT and HOST_CACHED_BIT, which influence how host and device memory accesses are synchronized and cached. If a memory type is host-visible but not host-coherent, the application may need to flush or invalidate mapped memory ranges using vkFlushMappedMemoryRanges and vkInvalidateMappedMemoryRanges to maintain correctness.

Notes for developers include the performance implications: host-visible memory may be slower for device-access patterns compared to device-local memory, but it is essential for buffers and resources that require CPU access. The availability and combinations of memory type property flags depend on the hardware and driver, so queries of VkPhysicalDeviceMemoryProperties guide memory allocation decisions.