VK_IMAGE_LAYOUT_DEPTH_ATTACHMENT_OPTIMAL

Undocumented in source but is binding to an external library. You might be able to learn more by searching the web for its name.
nothrow @nogc extern (System)
enum VK_IMAGE_LAYOUT_DEPTH_ATTACHMENT_OPTIMAL = VkImageLayout.VK_IMAGE_LAYOUT_DEPTH_ATTACHMENT_OPTIMAL;

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