Bug#857718: blender: enable GPU rendering with openCL

[Ian Bruce]

Package: blender
Version: 2.78.a+dfsg0-4
Severity: important

As many people are aware, GPU rendering in Blender with Mesa/openCL is
currently broken. HOWEVER, it appears that all the outstanding problems
are now fixable, if the appropriate patches and updates are applied to
the relevant Debian packages. Therefore, this bug report does not
describe a problem with Blender itself, but what changes must be made
elsewhere to get GPU rendering working.

This is what currently happens when GPU rendering is attempted:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=848258

https://developer.blender.org/T50522

There are three separate problems visible here; I have filed a Debian
bug report, with solution, for each of them:



*** implicit declaration of function {lgamma,native_tan} is invalid in C99 ***

This results from using an insufficiently up-to-date version of libclc.
see here:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=857710



*** invalid argument type 'X *' to unary expression ***

This results from a known bug in LLVM; a patch is available upstream.
see here:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=857623



*** unsupported call to function get_local_size ***

This results from a known bug in libclc-amdgcn; a patch is available
upstream. see here:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=857591



All three of these problems are fixable NOW. Once having done that, it
might happen that other problems would become evident, but then they
could be worked on, too. Or it might happen that GPU rendering would
finally just start working.

Can these updates be applied to the Debian archive, in the near future?


-- Ian Bruce