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 implementationdependent
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
where (x_{f}, y_{f}, z_{f}) is a point on the triangle. m may be approximated as
The minimum resolvable difference r is an implementationdependent
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 fixedpoint depth buffer representations, r is constant throughout the range of the entire depth buffer. For floatingpoint 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 floatingpoint mantissa, the minimum resolvable difference, r, for the given primitive is defined as

r = 2^{en}
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
m is computed as described above. If the depth buffer uses a fixedpoint 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 fixedpoint 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/1.2extensions/html/vkspec.html#VK_EXT_depth_range_unrestricted
extension is enabled,
fragment depth values are clamped even when the depth buffer uses a
floatingpoint representation.
See Also
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) 20142020 Khronos Group. This work is licensed under a Creative Commons Attribution 4.0 International License.