memoryRequirementsmemoryTypeBits

memoryRequirementsmemoryTypeBits is a field in the Vulkan API that expresses memory compatibility for a resource such as a buffer or image. It is part of VkMemoryRequirements, which also includes the resource’s size and alignment. The memoryTypeBits field is a bitmask where each bit corresponds to a physical device memory type. If bit i is set, memory type i can be used to back the resource; if it is clear, that type is not suitable.

How it is used

To allocate memory for a resource, a developer first retrieves its memory requirements via vkGetBufferMemoryRequirements or vkGetImageMemoryRequirements. The next step is to select a memory type index that satisfies two conditions: the bit corresponding to the index is set in memoryRequirements.memoryTypeBits, and the memory type’s property flags meet the resource’s needs (for example, VK_MEMORY_PROPERTY_HOST_VISIBLE, VK_MEMORY_PROPERTY_HOST_COHERENT, or VK_MEMORY_PROPERTY_DEVICE_LOCAL). The memory types array of the physical device, obtained with vkGetPhysicalDeviceMemoryProperties, provides these property flags. Once a suitable type is found, vkAllocateMemory is called with the chosen type index and the required allocation size.

Notes

Memory type bits reflect static hardware capabilities and do not guarantee current availability beyond initial compatibility. The number of valid memory types is given by the device’s memoryProperties.memoryTypes, and bits outside this range should not be considered valid. In practice, memoryTypeBits is interpreted in conjunction with memory property flags to ensure the allocated memory matches the resource’s usage pattern.