# vkCmdSetDepthBias(3) Manual Page

## Name

vkCmdSetDepthBias - Set the depth bias dynamic state

## C Specification

The depth values of all fragments generated by the rasterization of a polygon can be offset by a single value that is computed for that polygon. This behavior is controlled by the `depthBiasEnable`, `depthBiasConstantFactor`, `depthBiasClamp`, and `depthBiasSlopeFactor` members of VkPipelineRasterizationStateCreateInfo, or by the corresponding parameters to the `vkCmdSetDepthBias` command if depth bias state is dynamic.

    void vkCmdSetDepthBias(
        VkCommandBuffer                             commandBuffer,
        float                                       depthBiasConstantFactor,
        float                                       depthBiasClamp,
        float                                       depthBiasSlopeFactor);

## Parameters

- `commandBuffer` is the command buffer into which the command will be recorded.

- `depthBiasConstantFactor` is a scalar factor controlling the constant depth value added to each fragment.

- `depthBiasClamp` is the maximum (or minimum) depth bias of a fragment.

- `depthBiasSlopeFactor` is a scalar factor applied to a fragment’s slope in depth bias calculations.

## Description

If `depthBiasEnable` is `VK_FALSE`, no depth bias is applied and the fragment’s depth values are unchanged.

`depthBiasSlopeFactor` scales the maximum depth slope of the polygon, and `depthBiasConstantFactor` scales an implementation-dependent constant that relates to the usable resolution of the depth buffer. The resulting values are summed to produce the depth bias value which is then clamped to a minimum or maximum value specified by `depthBiasClamp`. `depthBiasSlopeFactor`, `depthBiasConstantFactor`, and `depthBiasClamp` can each be positive, negative, or zero.

The maximum depth slope m of a triangle is

\[m = \sqrt{ \left({{\partial z_f} \over {\partial x_f}}\right)^2 + \left({{\partial z_f} \over {\partial y_f}}\right)^2}\]

where (xf, yf, zf) is a point on the triangle. m may be approximated as

\[m = \max\left( \left| { {\partial z_f} \over {\partial x_f} } \right|, \left| { {\partial z_f} \over {\partial y_f} } \right| \right).\]

The minimum resolvable difference r is an implementation-dependent parameter that depends on the depth buffer representation. It is the smallest difference in framebuffer coordinate z values that is guaranteed to remain distinct throughout polygon rasterization and in the depth buffer. All pairs of fragments generated by the rasterization of two polygons with otherwise identical vertices, but `z`f values that differ by r, will have distinct depth values.

For fixed-point depth buffer representations, r is constant throughout the range of the entire depth buffer. For floating-point depth buffers, there is no single minimum resolvable difference. In this case, the minimum resolvable difference for a given polygon is dependent on the maximum exponent, e, in the range of z values spanned by the primitive. If n is the number of bits in the floating-point mantissa, the minimum resolvable difference, r, for the given primitive is defined as

  r = 2e-n

If a triangle is rasterized using the `VK_POLYGON_MODE_FILL_RECTANGLE_NV` polygon mode, then this minimum resolvable difference may not be resolvable for samples outside of the triangle, where the depth is extrapolated.

If no depth buffer is present, r is undefined.

The bias value o for a polygon is

\[\begin{aligned} o &= \mathrm{dbclamp}( m \times \mathtt{depthBiasSlopeFactor} + r \times \mathtt{depthBiasConstantFactor} ) \\ \text{where} &\quad \mathrm{dbclamp}(x) = \begin{cases} x & \mathtt{depthBiasClamp} = 0 \ \text{or}\ \texttt{NaN} \\ \min(x, \mathtt{depthBiasClamp}) & \mathtt{depthBiasClamp} > 0 \\ \max(x, \mathtt{depthBiasClamp}) & \mathtt{depthBiasClamp} < 0 \\ \end{cases} \end{aligned}\]

m is computed as described above. If the depth buffer uses a fixed-point representation, m is a function of depth values in the range [0,1], and o is applied to depth values in the same range.

For fixed-point depth buffers, fragment depth values are always limited to the range [0,1] by clamping after depth bias addition is performed. Unless the `https://www.khronos.org/registry/vulkan/specs/1.2-extensions/html/vkspec.html#VK_EXT_depth_range_unrestricted` extension is enabled, fragment depth values are clamped even when the depth buffer uses a floating-point representation.

Valid Usage

- If the depth bias clamping feature is not enabled, `depthBiasClamp` must be `0.0`

Valid Usage (Implicit)

- `commandBuffer` must be a valid VkCommandBuffer handle

- `commandBuffer` must be in the recording state

- The `VkCommandPool` that `commandBuffer` was allocated from must support graphics operations

Host Synchronization

- Host access to `commandBuffer` must be externally synchronized

- Host access to the `VkCommandPool` that `commandBuffer` was allocated from must be externally synchronized

Command Properties

Command Buffer Levels | Render Pass Scope | Supported Queue Types | Pipeline Type
--- | --- | --- | ---
Primary Secondary | Both | Graphics |

## See Also

VkCommandBuffer

## Document Notes

For more information, see the Vulkan Specification

This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.

## Copyright

Copyright (c) 2014-2020 Khronos Group. This work is licensed under a Creative Commons Attribution 4.0 International License.