Geek Blight

This extension builds on last year’s VK_EXT_attachment_feedback_loop_layout, which is used by DXVK 2.0+ to more efficiently support D3D9 games that read from active render targets. The new extension shipped this year adds support for setting attachment feedback loops dynamically on command buffers. As all extensions that add more dynamic state, the goal here is to reduce the number of pipeline objects applications need to create, which makes using the API more flexible. It was created by our beloved super good coder and Valve contractor Mike Blumenkrantz. We reviewed the spec and are listed as contributors, and we wrote dynamic variants of the existing CTS tests.

A new extension proposed by Joshua Ashton that also helps with layering D3D9 on top of Vulkan. The original problem is quite specific. In D3D9 and other APIs, applications can specify what is called a “depth bias” for geometry using an offset that is to be added directly as an exact value to the original depth of each fragment. In Vulkan, however, the depth bias is expressed as a factor of “r”, where “r” is a number that depends on the depth buffer format and, furthermore, may not have a specific fixed value. Implementations can use different values of “r” in an acceptable range. The mechanism provided by Vulkan without this extension is useful to apply small offsets and solve some problems, but it’s not useful to apply large offsets and/or emulate D3D9 by applying a fixed-value bias. The new extension solves these problems by giving apps the chance to control depth bias in a precise way. We reviewed the spec and are listed as contributors, and wrote CTS tests for this extension to help ship it.

This extension was proposed by Piers Daniell from NVIDIA to lift some restrictions in the original VK_KHR_dynamic_rendering extension, which is used in Vulkan to avoid having to create render passes and framebuffer objects. Dynamic rendering is very interesting because it makes the API much easier to use and, in many cases and specially in desktop platforms, it can be shipped without any associated performance loss. The new extension relaxes some restrictions that made pipelines more tightly coupled with render pass instances. Again, the goal here is to be able to reuse the same pipeline object with multiple render pass instances and remove some combinatorial explosions that may occur in some apps. We reviewed the spec and are listed as contributors, and wrote CTS tests for the new extension.

Shipped at the beginning of the year by Mike Blumenkrantz, the extension again helps emulating other APIs on top of Vulkan. Specifically, the extension allows creating 3D views of 3D images such that the views contain a subset of the slices in the image, using a Z offset and range, in the same way D3D12 allows. We reviewed the spec, we’re listed as contributors, and we wrote CTS tests for it.

This one comes from Valve contractor Hans-Kristian Arntzen, who is mostly known for working on Proton projects like VKD3D-Proton. The extension is related to ray tracing and adds more flexibility when creating ray tracing pipelines. Ray tracing pipelines can hold thousands of different shaders and are sometimes built incrementally by combining so-called pipeline libraries that contain subsets of those shaders. However, to properly use those pipelines we need to create a structure called a shader binding table, which is full of shader group handles that have to be retrieved from pipelines. Prior to this extension, shader group handles from pipeline libraries had to be requeried once the final pipeline is linked, as they were not guaranteed to be constant throughout the whole process. With this extension, an implementation can tell apps they will not modify shader group handles in subsequent link steps, which makes it easier for apps to build shader binding tables. More importantly, this also more closely matches functionality in DXR 1.1, making it easier to emulate DirectX Raytracing on top of Vulkan raytracing. We reviewed the spec, we’re listed as contributors and we wrote CTS tests for it.

Shader objects is probably the most notorious extension shipped this year, and we contributed small bits to it. This extension makes every piece of state dynamic and removes the need to use pipelines. It’s always used in combination with dynamic rendering, which also removes render passes and framebuffers as explained above. This results in great flexibility from the application point of view. The extension was created by Daniel Story from Nintendo, and its vast set of CTS tests was created by Žiga Markuš but we added our grain of sand by reviewing the spec and proposing some changes (which is why we’re listed as contributors), as well as fixing some shader object tests and providing some improvements here and there once they had been merged. A good part of this work was done in coordination with Mesa developers which were working on implementing this extension for different drivers.

Fresh out of the oven, these Vulkan Video extensions allow leveraging the hardware to efficiently encode H.264 and H.265 streams. This year we’ve been doing a ton of work related to Vulkan Video in drivers, libraries like GStreamer and CTS/spec, including the two extensions mentioned above. Although not listed as contributors to the spec in those two Vulkan extensions, our work played a major role in advancing the state of Vulkan Video and getting them shipped.

That’s it for this year! I’m looking forward to help ship more extension work the next one and trying to add my part in making Vulkan drivers on Linux (and other platforms!) more stable and feature rich. My Vulkan Video colleagues at Igalia have already started work on future Vulkan Video extensions for AV1 and VP9. Hopefully some of that work is ratified next year. Fingers crossed!