Zink

Overview

The Zink driver is a Gallium driver that emits Vulkan API calls instead of targeting a specific GPU architecture. This can be used to get full desktop OpenGL support on devices that only support Vulkan.

Features

The feature-level of Zink depends on two things; what’s implemented in Zink, as well as the features of the Vulkan driver.

OpenGL 2.1

OpenGL 2.1 is the minimum version Zink can support, and will always be exposed, given Vulkan support. There’s a few features that are required for correct behavior, but not all of these are validated; instead you’ll see rendering-issues and likely validation error, or even crashes.

Here’s a list of those requirements:

OpenGL 3.0

For OpenGL 3.0 support, the following additional device extensions are required to be exposed and fully supported:

OpenGL 3.1

For OpenGL 3.1 support, the following additional VkPhysicalDeviceLimits are required:

  • maxPerStageDescriptorSamplers ≥ 16

OpenGL 3.2

For OpenGL 3.2 support, the following additional VkPhysicalDeviceFeatures are required to be supported, although some of these might not actually get verified:

  • depthClamp

  • geometryShader

  • shaderTessellationAndGeometryPointSize

OpenGL 3.3

For OpenGL 3.3 support, the following additional VkPhysicalDeviceFeatures are required to be supported, although some of these might not actually get verified:

Debugging

There’s a few tools that are useful for debugging Zink, like this environment variable:

ZINK_DEBUG Type: flags, Default: ""
nir

Print the NIR form of all shaders to stderr.

spirv

Write the binary SPIR-V form of all compiled shaders to a file in the current directory, and print a message with the filename to stderr.

tgsi

Print the TGSI form of TGSI shaders to stderr.

validation

Dump Validation layer output.

Vulkan Validation Layers

Another useful tool for debugging is the Vulkan Validation Layers.

The validation layers effectively insert extra checking between Zink and the Vulkan driver, pointing out incorrect usage of the Vulkan API. The layers can be enabled by setting the environment variable VK_INSTANCE_LAYERS to “VK_LAYER_KHRONOS_validation”. You can read more about the Validation Layers in the link above.

IRC

In order to make things a bit easier to follow, we have decided to create our own IRC channel. If you’re interested in contributing, or have any technical questions, don’t hesitate to visit #zink on FreeNode and say hi!