The cause for this policy was due to dynamic linker behavior which could have
resulted in the wrong symbols being used. However, this didn't occur in
practical usage of the dynamic linker. Also drivers exporting Vulkan
entrypoints was a useful behavior to enable testing and more flexible usage
that this policy actively interfered with.
Modify the loader to only use VK_ADD_DRIVER_FILES if
VK_DRIVER_FILES or VK_ICD_FILENAMES is not used.
This could have caused weird issues with systems where VK_DRIVER_FILES
was used to force drivers in a specific order/location for testing.
Resolves issue #871
Add "additive" environment variables for adding additional layer
paths or driver JSON files instead of replacing default ones.
Also, rename VK_ICD_FILENAMES to VK_DRIVER_FILES since we're trying
to remove references to ICDs because software driver implementations
of Vulkan aren't ICDs (but continue to support the old name as well).
Added documentation around these changes to reflect the new name and
the new variables.
Define expected behavior for a well-behaved loader, layers, and drivers.
This has been reviewed with other companies so that when issues arise,
it is easy to clearly communicate where one of the components has failed
to properly behave.
Add warnings/errors in the loader output when cases of policy that can
be detected are noticed.
Feedback from Khronos was that "Implementation" was for the entire
set of Vulkan components underlying the application (including the
loader, layers, and drivers). Instead, what I had been calling
implementation should be called "Driver" including software
implementations of Vulkan at that level.
Also update the LOADER_DEBUG option "implem" to take "driver" as well.
All images also updated.
Charles Giessen