A variation is a #define/specialization constant that every shader can
use to specialize itself as it sees fit.
This commit adds the infrastrcture, future commits will add
implementations.
Let the objects track the number of samplers or buffers needed.
This is a required step for making Vulkan work with less featureful
(read: mobile) implementations.
This now uses all the previously added features to allow displaying YUV
images.
Also add a utility function that turns an image into a toggle ref for a
texture. This makes sure that reffing the image also refs the texture
and that ensures that textures stay alive as long as the image is in
use.
This allows having different layouts sothat we can support immutable
samplers, whcih are required for multiplane and YUV formats.
We don't use them yet.
use it to collect the optional features we are interested in and turn
them on only if available.
For now we add the dmabuf features, but we don't use them yet.
This heaves over an inital chunk of code from the Vulkan renderer to
execute shaders.
The only shader that exists for now is a shader that draws a single
texture.
We use that to replace the blit op we were doing before.
For now, it just renders using cairo, uploads the result to the GPU,
blits it onto the framebuffer and then is happy.
But it can do that using Vulkan and using GL (no idea which version).
The most important thing still missing is shaders.
It also has a bunch of copy/paste from the Vulkan renderer that isn't
used yet.
But I didn't want to rip it out and then try to copy it back later
