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 capabilities of the Vulkan driver.

The feature-levels implemented by Zink are exposed by Vulkan Profiles in the VP_ZINK_requirements.json profiles file.

Used with the Vulkan Profiles tools, we can compare the ZINK profiles with Vulkan devices profiles generated with Vulkaninfo or downloaded from GPUinfo.org to establish the feature-levels supported by these drivers.

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:

In addition to this, VK_KHR_external_memory is required to support the DRI code-path.

We also require either the VK_EXT_scalar_block_layout extension or Vulkan 1.2, with the scalarBlockLayout feature.

OpenGL 3.0

For OpenGL 3.0 support, the following additional requirements must be 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 requirements must be supported, although some of these might not actually get verified:

  • VkPhysicalDeviceFeatures:

    • depthClamp

    • geometryShader

    • shaderTessellationAndGeometryPointSize

  • Device extensions:

OpenGL 3.3

For OpenGL 3.3 support, the following additional requirements must be supported, although some of these might not actually get verified:

OpenGL 4.0

For OpenGL 4.0 support, the following additional requirements must be supported:

  • VkPhysicalDeviceFeatures:

    • sampleRateShading

    • tessellationShader

    • imageCubeArray

  • Device extensions:

  • Formats requiring VK_FORMAT_FEATURE_UNIFORM_TEXEL_BUFFER_BIT:

    • VK_FORMAT_R32G32B32_SFLOAT

    • VK_FORMAT_R32G32B32_SINT

    • VK_FORMAT_R32G32B32_UINT

OpenGL 4.1

For OpenGL 4.1 support, the following additional requirements must be supported:

  • VkPhysicalDeviceFeatures:

    • multiViewport

  • VkPhysicalDeviceLimits

    • maxImageDimension1D ≥ 16384

    • maxImageDimension2D ≥ 16384

    • maxImageDimension3D ≥ 2048

    • maxImageDimensionCube ≥ 16384

    • maxImageArrayLayers ≥ 2048

    • maxViewports ≥ 16

OpenGL 4.2

For OpenGL 4.2 support, the following additional requirements must be supported:

  • Device extensions:
  • VkPhysicalDeviceLimits:

    • shaderStorageImageExtendedFormats

    • shaderStorageImageWriteWithoutFormat

    • vertexPipelineStoresAndAtomics

    • fragmentStoresAndAtomics

  • For Vulkan 1.2 and above:

    • VkPhysicalDeviceVulkan11Features:

      • shaderDrawParameters

  • For Vulkan 1.1 and below:

OpenGL 4.3

For OpenGL 4.3 support, the following additional requirements must be supported:

  • VkPhysicalDeviceFeatures:

    • robustBufferAccess

  • Formats requiring VK_FORMAT_FEATURE_SAMPLED_IMAGE_BIT:

    • VK_FORMAT_R8G8B8A8_UNORM

    • VK_FORMAT_R8G8B8A8_SRGB

    • VK_FORMAT_R16_UNORM

    • VK_FORMAT_R16G16_UNORM

    • VK_FORMAT_R16_SNORM

    • VK_FORMAT_R16G16_SNORM

    • VK_FORMAT_D32_SFLOAT_S8_UINT

OpenGL 4.4

For OpenGL 4.4 support, the following additional requirements must be supported:

OpenGL 4.5

For OpenGL 4.5 support, the following additional VkPhysicalDeviceFeatures are required to be supported

  • shaderCullDistance

OpenGL 4.6

For OpenGL 4.6 support, the following additional VkPhysicalDeviceFeatures are required to be supported

Debugging

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

ZINK_DEBUG

Accepts the following comma-separated list of flags:

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.

sync

Emit full synchronization barriers before every draw and dispatch.

compact

Use a maximum of 4 descriptor sets

noreorder

Do not reorder or optimize GL command streams

gpl

Force using Graphics Pipeline Library for all shaders

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 OFTC and say hi!