This allows using opencl as an alternative to opengl compute shaders on
macos, which does not support compute shaders. Now, macos can finally
use the extended draw distance feature of the gpu plugin.
This also includes code for using opencl with Windows and Linux if we
want to enable that in the future. A copy of the existing compute
shaders have been checked in and ported to opencl, keeping support for
opengl compute shaders on Windows and Linux.
Co-authored-by: Paul Norton <napkinorton@gmail.com>
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