VkDrmFormatModifierPropertiesEXT

The VkDrmFormatModifierPropertiesEXT structure describes properties of a VkFormat when that format is combined with a Linux DRM format modifier. These properties, like those of VkFormatProperties2, are independent of any particular image.

The VkDrmFormatModifierPropertiesEXT structure is defined as:

typedef struct VkDrmFormatModifierPropertiesEXT {
    uint64_t drmFormatModifier;
    uint32_t drmFormatModifierPlaneCount;
    VkFormatFeatureFlags drmFormatModifierTilingFeatures;
} VkDrmFormatModifierPropertiesEXT;

• drmFormatModifier is a Linux DRM format modifier.
• drmFormatModifierPlaneCount is the number of memory planes in any image created with format and drmFormatModifier. An image’s memory planecount is distinct from its format planecount, as explained below.
• drmFormatModifierTilingFeatures is a bitmask of VkFormatFeatureFlagBits that are supported by any image created with format and drmFormatModifier.

The returned drmFormatModifierTilingFeatures must contain at least one bit.

The implementation must not return DRM_FORMAT_MOD_INVALID in drmFormatModifier.

An image’s memory planecount (as returned by drmFormatModifierPlaneCount) is distinct from its format planecount (in the sense of multi-planar Y′C_BC_R formats). In VkImageAspectFlags, each VK_IMAGE_ASPECT_MEMORY_PLANE*_i_BIT_EXT represents a memory plane and each VK_IMAGE_ASPECT_PLANE_i_*BIT a format plane.

An image’s set of format planes is an ordered partition of the image’s content into separable groups of format components. The ordered partition is encoded in the name of each VkFormat. For example, VK_FORMAT_G8_B8R8_2PLANE_420_UNORM contains two format planes; the first plane contains the green component and the second plane contains the blue component and red component. If the format name does not contain PLANE, then the format contains a single plane; for example, VK_FORMAT_R8G8B8A8_UNORM. Some commands, such as vkCmdCopyBufferToImage, do not operate on all format components in the image, but instead operate only on the format planes explicitly chosen by the application and operate on each format plane independently.

An image’s set of memory planes is an ordered partition of the image’s memory rather than the image’s content. Each memory plane is a contiguous range of memory. The union of an image’s memory planes is not necessarily contiguous.

If an image is linear, then the partition is the same for memory planes and for format planes. Therefore, if the returned drmFormatModifier is DRM_FORMAT_MOD_LINEAR, then drmFormatModifierPlaneCount must equal the format planecount, and drmFormatModifierTilingFeaturesmust be identical to the VkFormatProperties2::linearTilingFeatures returned in the same pNext chain.

If an image is non-linear, then the partition of the image’s memory into memory planes is implementation-specific and may be unrelated to the partition of the image’s content into format planes. For example, consider an image whose format is VK_FORMAT_G8_B8_R8_3PLANE_420_UNORM, tiling is VK_IMAGE_TILING_DRM_FORMAT_MODIFIER_EXT, whose drmFormatModifier is not DRM_FORMAT_MOD_LINEAR, and flags lacks VK_IMAGE_CREATE_DISJOINT_BIT. The image has 3 format planes, and commands such vkCmdCopyBufferToImage act on each format plane independently as if the data of each format plane were separable from the data of the other planes. In a straightforward implementation, the implementation may store the image’s content in 3 adjacent memory planes where each memory plane corresponds exactly to a format plane. However, the implementation may also store the image’s content in a single memory plane where all format components are combined using an implementation-private block-compressed format; or the implementation may store the image’s content in a collection of 7 adjacent memory planes using an implementation-private sharding technique. Because the image is non-linear and non-disjoint, the implementation has much freedom when choosing the image’s placement in memory.

The memory planecount applies to function parameters and structures only when the API specifies an explicit requirement on drmFormatModifierPlaneCount. In all other cases, the memory planecount is ignored.