Zink — The Mesa 3D Graphics Library latest documentation

# 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`:

  - logicOp

  - fillModeNonSolid

  - alphaToOne

  - shaderClipDistance

- 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`:

    - rectangularLines

    - bresenhamLines

    - smoothLines

    - stippledRectangularLines

    - stippledBresenhamLines

    - stippledSmoothLines

  - 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`:

  - depthClamp

  - geometryShader

  - shaderTessellationAndGeometryPointSize

- 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`:

  - sampleRateShading

  - tessellationShader

  - imageCubeArray

- 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 render pass optimizations (for tiling GPUs)

  `norp`

    Disable render pass 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!