Of course instead of actually working on my cool Casilda-powered app with its epic design that I was so eager to share last weekend, I just had to dive into the internals and make Casilda do things "properly". That is, with this patch it would import dmabufs and shared memory directly into GTK instead of going through wlroots' GLES renderer just for the import operation.

In the past, it was actually used for compositing, but then compositing was moved into GTK/GSK, but getting textures per-surface was simply done exactly how it was done for the composited output texture i.e. via GL. So unless you were using the GL backend in GTK, everything would go through a very silly path: dmabuf imported to GL (by wlroots), shared with GTK as a GL texture, exported by GTK from GL as a dmabuf again and finally imported into Vulkan. :D With the new setup GTK could even offload the entire compositing of our scene graph to the host compositor, if they decide to expose a GSK-level subsurface API or make the GraphicsOffload work with nested scenes and not just single subsurfaces.