memoryTypeIndex

memoryTypeIndex is an index used in Vulkan to select a specific memory type for a device memory allocation. It refers to an entry in the physical device’s memoryTypes array, where each memory type describes a combination of properties (such as host visibility or device locality) and a memory heap. The memory types are enumerated by the physical device memory properties and identified by their indices.

In Vulkan, memory allocation begins with querying the resource’s memory requirements. This yields a memoryTypeBits bitmask indicating which memory types are compatible with the resource. To allocate memory, you must choose an index i such that the corresponding bit in memoryTypeBits is set and the memory type’s propertyFlags satisfy the desired properties (for example VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT for CPU access or VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT for optimal GPU access). The chosen index is then supplied as memoryTypeIndex in VkMemoryAllocateInfo when calling vkAllocateMemory.

If no memory type satisfies both the compatibility and the desired properties, the allocation cannot proceed. In that case, you may need to adjust the resource usage, select a different property set, or create an intermediate staging buffer in a suitable memory type before transferring data.

MemoryTypeIndex is a required field for vkAllocateMemory and must be a valid, in-range index that matches the resource’s memory requirements. Correct selection is essential for correct operation and performance, and it typically involves querying VkPhysicalDeviceMemoryProperties and evaluating memoryRequirements.memoryTypeBits against the supported memory types.

See also: VkMemoryAllocateInfo, VkPhysicalDeviceMemoryProperties, VkMemoryRequirements, vkAllocateMemory.