PFN_vkSignalSemaphore

Undocumented in source but is binding to an external library. You might be able to learn more by searching the web for its name.
extern (System) nothrow @nogc
alias PFN_vkSignalSemaphore = VkResult function
(
VkDevice device
,
const(VkSemaphoreSignalInfo)* pSignalInfo
)

Meta