Zink: Fall Update
I recently went to XDC 2019, where I gave yet another talk about Zink. I kinda forgot to write a blog-post about it, so here’s me trying to make up for it… or something like that. I’ll also go into some more recent developments as well.
My presentation was somewhat similar to the talk I did at SIGGRAPH this year, but with a bit more emphasis on the technical aspect, as the XDC audience is more familiar with Mesa internals.
If you’re interested, you can find the slides for the talk here. The talk goes through the motivation and basic approach. I don’t think I need to go through this again, as I’ve already covered that before.
As for the status, Zink currently supports OpenGL 2.1 and OpenGL ES 2.0. And there’s no immediate plans on working on OpenGL 3.0 and OpenGL ES 3.0 until Zink is upstream.
Which gets us to the more interesting bit; that I started working on upstreaming Zink. So let’s talk about that for a bit.
Upstreaming Zink
So, my current goal is to get Zink upstream in Mesa. The plan outline in my XDC talk is slightly outdated by now, so here I’ll instead say what’s actually happened so far, and what I hope will follow.
Before I could add the driver itself, I decided to send all changes outside of the driver as a set of merge-requests:
- glBitmap R8 textures
- loader/dri3: do not blit outside old/new buffers
- gallium/u_blitter: set a more sane viewport-state
- nir: initialize uses_discard to false
- lowering passes from Zink
The last one is probably the most interesting one, as it moves a lot of fixed-function operations into the state-tracker, so individual drivers won’t have to deal with them. Unless they choose to, of course.
But all of these has already been merged, and there’s just one final merge-request left:
This merge-request adds the driver in its current state. It consists of 163 commits at the time of writing, so it’s not a thing of beauty. But new drivers usually aren’t, so I’m not too worried.
When this is merged, Zink will finally be a “normal” part of Mesa… Well,
sort of anyway. I don’t think we’ll enable Zink to be built by default for a
while. But that’ll just be a matter of adding zink to the
-Dgallium-drivers meson-option.
Testing on CI
The current branch only adds building of Zink to the CI. There’s no testing being done yet. The reasons for this is two-fold:
- We need to get a running environment on CI. Rather of bringing up some hardware-enabled test-runner, I intend to try to set up SwiftShader as a software rasterizer instead, as that supports Vulkan 1.1 these days.
- We need some tests to run. Zink currently only supports OpenGL 2.1, and sadly the conformance test suite doesn’t have any tests for OpenGL versions older than 3.0. Piglit has some, but a full piglit-run takes significantly more time, which makes it tricky for CI. So right now, it seems the OpenGL ES 2.0 conformance tests are our best bet. We’ll of course add more test-suites as we add more features.
So, there’s some work to be done here, but it seems like we should be able to get something working without too much hassle.
Next steps
After Zink is upstream, it will be maintained similarly to other Mesa drivers. Practically speaking, this means that patches are sent to the upstream repo rather than my fork. It shouldn’t make a huge difference for most users.
The good thing is that if I go away on vacation, or are for some other reason unavailable, other people can still merge patches, so we’d slightly reduce the technical bus-factor.
I’m not stopping developing Zink at all, but I have other things going on in my life that means I might be busy with other things at times. As is the case for everyone! 😉
In fact, I’m very excited to start working on OpenGL 3.x and 4.x level features; we still have a few patches for some 3.x features in some older branches.
The future is bright! ☀️