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:

Vulkan 1.0
VkPhysicalDeviceFeatures:
Device extensions:
- VK_KHR_maintenance1
- VK_KHR_create_renderpass2
- VK_KHR_imageless_framebuffer
- VK_KHR_timeline_semaphore
- VK_EXT_custom_border_color with customBorderColorWithoutFormat
- VK_EXT_provoking_vertex
- VK_EXT_line_rasterization, with the following VkPhysicalDeviceLineRasterizationFeaturesEXT:
- VK_KHR_swapchain_mutable_format
- VK_EXT_border_color_swizzle
- VK_KHR_descriptor_update_template

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 met:

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 requirements must be met, although some of these might not actually get verified:

VkPhysicalDeviceFeatures:
Device extensions:
- VK_EXT_depth_clip_enable

OpenGL 3.3¶

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

VkPhysicalDeviceFeatures:
- dualSrcBlend
Device extensions:
- VK_EXT_vertex_attribute_divisor

OpenGL 4.0¶

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

VkPhysicalDeviceFeatures:
Device extensions:
- VK_KHR_maintenance2
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 met:

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 met:

Device extensions:
- VK_EXT_image_2d_view_of_3d
VkPhysicalDeviceLimits:
- shaderStorageImageExtendedFormats
- shaderStorageImageWriteWithoutFormat
- vertexPipelineStoresAndAtomics
- fragmentStoresAndAtomics
For Vulkan 1.2 and above:
- VkPhysicalDeviceVulkan11Features:
  - shaderDrawParameters
For Vulkan 1.1 and below:
- Device extensions:
  - VK_KHR_shader_draw_parameters

OpenGL 4.3¶

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

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 met:

Formats requiring VK_FORMAT_FEATURE_VERTEX_BUFFER_BIT:
- VK_FORMAT_B10G11R11_UFLOAT_PACK32
For Vulkan 1.2 and above:
- VkPhysicalDeviceVulkan12Features:
  - samplerMirrorClampToEdge
For Vulkan 1.1 and below:
- 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 requirements must be met:

VkPhysicalDeviceFeatures:
- samplerAnisotropy
- 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 <mode> ("auto")¶

auto: Automatically detect best mode. This is the default.
lazy: Attempt to use the least amount of CPU by binding descriptors opportunistically.
db: Use EXT_descriptor_buffer when possible.

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
rp: Enable renderpass optimizations (for tiling GPUs)
norp: Disable renderpass optimizations (for tiling GPUs)
map: Print info about mapped VRAM
flushsync: Force synchronous flushes/presents
noshobj: Disable EXT_shader_object
optimal_keys: Debug/use optimal_keys
noopt: Disable async optimized pipeline compiles
nobgc: Disable all async pipeline compiles
mem: Enable memory allocation debugging
quiet: Suppress probably-harmless warnings

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_LOADER_LAYERS_ENABLE to VK_LAYER_KHRONOS_validation. You can read more about the Validation Layers in the link above.

Apple macOS and MoltenVK¶

Zink on macOS is experimental with very limited capabilities. The Vulkan SDK (1.3.250 or newer) is required to build Zink. Set the build option -Dmoltenvk-dir=<directory> to point at your Vulkan SDK install or MoltenVK build. Add Zink to the Gallium drivers build option -Dgallium-drivers=zink. If installed using brew, you can set -D moltenvk-dir=$(brew --prefix molten-vk).

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!