qemu: support OpenGL acceleration (VirGL)

[AkihiroSuda]

UTM seems to have been supporting VirGL with forked repos:
https://github.com/utmapp/UTM/blob/62bd84c78c045870c580df34c1ba233d75e02995/patches/sources#L38-L45

I'm not sure we can just use them in Homebrew's QEMU. Maybe we need a custom Tap.

[afbjorklund]

If I understand correctly, you need to configure the QEMU build

--enable-virglrenderer

And then make sure to use the new device, when starting the VM

-device virtio-gpu-gl

---

https://www.qemu.org/docs/master/system/devices/virtio-gpu.html

There should be a virtio-gpu for testing, that uses software rendering.

EDIT: Also need to set gl=on option, for the default display. Otherwise:

qemu-system-x86_64: -device virtio-gpu-gl: opengl is not available

[AkihiroSuda]

Support for Venus was recently merged to QEMU: qemu/qemu@e4bad9c

[AkihiroSuda]

Patches in https://github.com/akihikodaki/virglrenderer/commits/macos/ are still not upstreamed to https://gitlab.freedesktop.org/virgl/virglrenderer
(Where is the merge request?)

[AkihiroSuda]

@akihikodaki May I ask if you are planning to submit your macOS patches in https://github.com/akihikodaki/virglrenderer/commits/macos/ to the upstream repo (https://gitlab.freedesktop.org/virgl/virglrenderer)?
Thanks!

[akihikodaki]

@AkihiroSuda It depends on a libepoxy change which has not landed yet: anholt/libepoxy#239
cc: @ebassi