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:

Vulkan 1.0
VkPhysicalDeviceFeatures:
- logicOp
- fillModeNonSolid
- wideLines
- largePoints
- alphaToOne
- shaderClipDistance
Device extensions:
- VK_KHR_maintenance1
- VK_EXT_custom_border_color
- VK_EXT_provoking_vertex
- VK_EXT_line_rasterization, with the following VkPhysicalDeviceLineRasterizationFeaturesEXT:
  - rectangularLines
  - bresenhamLines
  - smoothLines
  - stippledRectangularLines
  - stippledBresenhamLines
  - stippledSmoothLines

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 needs to be supported:

VkPhysicalDeviceFeatures:
- independentBlend
Device extensions:
- VK_EXT_transform_feedback
- VK_EXT_conditional_rendering

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 requirements needs to be supported, although some of these might not actually get verified:

VkPhysicalDeviceFeatures:
- occlusionQueryPrecise
Device extensions:
- VK_EXT_vertex_attribute_divisor

OpenGL 4.0¶

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

VkPhysicalDeviceFeatures:
- sampleRateShading
- tessellationShader
- imageCubeArray
Device extensions:
- VK_KHR_maintenance2
Formats requiring VK_FORMAT_FEATURE_SAMPLED_IMAGE_BIT:
- VK_FORMAT_R32G32B32_SFLOAT
- VK_FORMAT_R32G32B32_SINT
- VK_FORMAT_R32G32B32_UINT

OpenGL 4.1¶

For OpenGL 4.1 support, the following additional VkPhysicalDeviceLimits are required:

maxImageDimension2D ≥ 16384
maxViewports ≥ 16

OpenGL 4.2¶

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

VkPhysicalDeviceLimits:
- shaderStorageImageExtendedFormats
- shaderStorageImageWriteWithoutFormat
For Vulkan 1.2 and above:
- VkPhysicalDeviceVulkan11Features:
  - shaderDrawParameters
  - vertexPipelineStoresAndAtomics
  - fragmentStoresAndAtomics
  - textureCompressionBC
For Vulkan 1.1 and below:
- Device extensions:
  - VK_KHR_shader_draw_parameters
Formats requiring VK_FORMAT_FEATURE_SAMPLED_IMAGE_BIT:
- VK_FORMAT_BC7_UNORM_BLOCK
- VK_FORMAT_BC7_SRGB_BLOCK
- VK_FORMAT_BC6H_SFLOAT_BLOCK
- VK_FORMAT_BC6H_UFLOAT_BLOCK

OpenGL 4.3¶

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

VkPhysicalDeviceFeatures:
- robustBufferAccess
- multiViewport
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 needs to be supported:

Formats requiring VK_FORMAT_FEATURE_VERTEX_BUFFER_BIT:
- VK_FORMAT_B10G11R11_UFLOAT_PACK32
Device extensions:
- VK_KHR_sampler_mirror_clamp_to_edge

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

VkPhysicalDeviceFeatures:
- samplerAnisotropy
- pipelineStatisticsQuery
- depthBiasClamp
Device extensions:
- VK_KHR_draw_indirect_count

Performance¶

If you notice poor performance and high CPU usage while running an application, changing the descriptor manager may improve performance:

ZINK_DESCRIPTORS Type: mode, Default: "auto"¶

auto: Automatically detect best mode. This is the default.
lazy: Disable caching and attempt to use the least amount of CPU.
nofallback: Always use caching to try reducing GPU churn.
notemplates: The same as auto, but disables the use of VK_KHR_descriptor_templates.

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 OFTC and say hi!