Re: Blender export backend missing

[Théo Maxime Tyburn]

Hi

Ekaitz Zarraga <ekaitz@elenq.tech> writes:

> Make sure the version of alembic we have packaged is the one Blender expects.
>
> Sometimes the APIs change and that may led to that kind of errors.

The version of alembic that blender 3.0.1 requires is the same we
have.

The problem might come from another version mismastch problem. Namely
with OpenEXR. OpenEXR
version 2.x provided Imath inside of its subdirectory Ilmbase, for
which we also have a separate package. From version 3.x of OpenEXR, Imath
became a separate package. The guix blender package still uses openexr
version 2.x. and its subpackage ilmbase. However guix package alembic uses the 
new imath. Blender
upstream actually also expect openexr 3.x and imath.

The quick and dirty fix is to just downgrade alembic. I just tried it
and it works. So at least we can work with alembic files in blender now.

A better fix would be to add openexr 3.x and imath
to blender package’s inputs and remove openexr-2 and ilmbase.

I tried that but it doesn’t work. The error is
--8<---------------cut here---------------start------------->8---
CMake Error: The following variables are used in this project, but they are set 
to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake 
files:
OPENEXR_HALF_LIBRARY (ADVANCED)
    linked by target "cycles_scene" in directory 
/tmp/guix-build-blender-3.0.1.drv-0/blender-3.0.1/intern/cycles/scene
OPENEXR_ILMIMF_LIBRARY (ADVANCED)
    linked by target "cycles_scene" in directory 
/tmp/guix-build-blender-3.0.1.drv-0/blender-3.0.1/intern/cycles/scene
--8<---------------cut here---------------end--------------->8---

It seems this is due to some error in the cmake of blender’s source. Some
other packge maintainers have come across the same issue aparently
https://devtalk.blender.org/t/building-blender-2-93-3-with-the-new-half-implementation-of-openexr-that-uses-half-of-imath/20074.
I guess it has not been fixed in upstream blender yet. There is a patch though
here
https://github.com/bartoszek/AUR-blender-2.83-git/blob/master/openexr3.patch

So this could be the better solution if want to rely on that patch. Do we?
I also have no idea how to apply a patch from another repo in a package
definition though. Any idea?

A general build / packaging question: For testing purposes I sometimes want to 
just try some command in the
build environment. Like applying this patch for example. Is there a
simple way to somehow enter the build env and do things from there
imperatively, just to quickly check some things?

Best,

Théo