8.2. Host Access to Device Memory Objects

Memory objects created with vkAllocateMemory are not directly host accessible.

由 vkAllocateMemory 创建的 Memory object 并不是直接 host accessiable 。

Memory objects created with the memory property VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT are considered mappable. Memory objects must be mappable in order to be successfully mapped on the host.

创建 Memory objects 时指定了 memory 属性 VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT 被认为是可映射的（ mappable ）。要能够成功映射到 host ， Memory object 必须是可映射的。

To retrieve a host virtual address pointer to a region of a mappable memory object, call

要获取一个指向可映射 memory object 的 host 虚拟地址指针，调用：

VkResult vkMapMemory(
    VkDevice          device,
    VkDeviceMemory    memory,
    VkDeviceSize      offset,
    VkDeviceSize        size,
    VkMemoryMapFlags   flags,
    void**           ppData);

vkMapMemory does not check whether the device memory is currently in use before returning the host-accessible pointer. The application must guarantee that any previously submitted command that writes to this range has completed before the host reads from or writes to that range, and that any previously submitted command that reads from that range has completed before the host writes to that region (see here for details on fulfilling such a guarantee). If the device memory was allocated without the VK_MEMORY_PROPERTY_HOST_COHERENT_BIT set, these guarantees must be made for an extended range: the application must round down the start of the range to the nearest multiple of VkPhysicalDeviceLimits::nonCoherentAtomSize, and round the end of the range up to the nearest multiple of VkPhysicalDeviceLimits::nonCoherentAtomSize.

While a range of device memory is mapped for host access, the application is responsible for synchronizing both device and host access to that memory range.

void vkGetImageSubresourceLayout(
    VkDevice                        device,
    VkImage                          image,
    const VkImageSubresource* pSubresource,
    VkSubresourceLayout*           pLayout);

typedef struct VkImageSubresource {
    VkImageAspectFlags aspectMask;
    uint32_t             mipLevel;
    uint32_t           arrayLayer;
} VkImageSubresource;

typedef struct VkSubresourceLayout {
    VkDeviceSize     offset;
    VkDeviceSize       size;
    VkDeviceSize   rowPitch;
    VkDeviceSize arrayPitch;
    VkDeviceSize depthPitch;
} VkSubresourceLayout;