154 lines
5.5 KiB
Plaintext
154 lines
5.5 KiB
Plaintext
// Copyright (c) 2014-2016 Khronos Group. This work is licensed under a
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// Creative Commons Attribution 4.0 International License; see
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// http://creativecommons.org/licenses/by/4.0/
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vkCmdSetDepthBias(3)
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====================
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Name
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----
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vkCmdSetDepthBias - Set the depth bias dynamic state.
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C Specification
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---------------
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// refBegin vkCmdSetDepthBias Set the depth bias dynamic state.
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The depth values of all fragments generated by the rasterization of a
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polygon can: be offset by a single value that is computed for that polygon.
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This behavior is controlled by the pname:depthBiasEnable,
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pname:depthBiasConstantFactor, pname:depthBiasClamp, and
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pname:depthBiasSlopeFactor members of
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slink:VkPipelineRasterizationStateCreateInfo, or by the corresponding
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parameters to the fname:vkCmdSetDepthBias command if depth bias state is
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dynamic.
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include::../api/protos/vkCmdSetDepthBias.txt[]
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Parameters
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----------
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* pname:commandBuffer is the command buffer into which the command will be
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recorded.
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* pname:depthBiasConstantFactor is a scalar factor controlling the
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constant depth value added to each fragment.
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* pname:depthBiasClamp is the maximum (or minimum) depth bias of a
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fragment.
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* pname:depthBiasSlopeFactor is a scalar factor applied to a fragment's
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slope in depth bias calculations.
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Description
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-----------
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If pname:depthBiasEnable is ename:VK_FALSE, no depth bias is applied and the
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fragment's depth values are unchanged.
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pname:depthBiasSlopeFactor scales the maximum depth slope of the polygon,
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and pname:depthBiasConstantFactor scales an implementation-dependent
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constant that relates to the usable resolution of the depth buffer. The
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resulting values are summed to produce the depth bias value which is then
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clamped to a minimum or maximum value specified by pname:depthBiasClamp.
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pname:depthBiasSlopeFactor, pname:depthBiasConstantFactor, and
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pname:depthBiasClamp can: each be positive, negative, or zero.
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The maximum depth slope latexmath:[$m$] of a triangle is
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[latexmath]
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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\begin{equation}
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m = \sqrt{ \left({\partial z_f \over \partial x_f}\right)^2
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+ \left({\partial z_f \over \partial y_f}\right)^2}
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\end{equation}
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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where latexmath:[$(x_f, y_f, z_f)$] is a point on the triangle.
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latexmath:[$m$] may: be approximated as
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[latexmath]
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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\begin{equation}
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m = \max( \left |{\partial z_f \over \partial x_f} \right |,
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\left |{\partial z_f \over \partial y_f} \right | ).
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\end{equation}
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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The minimum resolvable difference latexmath:[$r$] is an
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implementation-dependent parameter that depends on the depth buffer
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representation. It is the smallest difference in framebuffer coordinate
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latexmath:[$z$] values that is guaranteed to remain distinct throughout
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polygon rasterization and in the depth buffer. All pairs of fragments
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generated by the rasterization of two polygons with otherwise identical
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vertices, but latexmath:[$z_f$] values that differ by $r$, will have
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distinct depth values.
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For fixed-point depth buffer representations, latexmath:[$r$] is constant
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throughout the range of the entire depth buffer. For floating-point depth
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buffers, there is no single minimum resolvable difference. In this case, the
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minimum resolvable difference for a given polygon is dependent on the
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maximum exponent, latexmath:[$e$], in the range of latexmath:[$z$] values
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spanned by the primitive. If latexmath:[$n$] is the number of bits in the
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floating-point mantissa, the minimum resolvable difference, latexmath:[$r$],
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for the given primitive is defined as
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[latexmath]
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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\begin{equation}
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r = 2^{e - n}
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\end{equation}
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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If no depth buffer is present, latexmath:[$r$] is undefined.
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The bias value latexmath:[$o$] for a polygon is
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[latexmath]
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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\begin{equation}
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o =
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\begin{cases}
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m \times depthBiasSlopeFactor +
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r \times depthBiasConstantFactor & depthBiasClamp = 0\ or\ NaN \\
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\min(m \times depthBiasSlopeFactor +
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r \times depthBiasConstantFactor,
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depthBiasClamp) & depthBiasClamp > 0 \\
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\max(m \times depthBiasSlopeFactor +
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r \times depthBiasConstantFactor,
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depthBiasClamp) & depthBiasClamp < 0 \\
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\end{cases}
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\end{equation}
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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latexmath:[$m$] is computed as described above. If the depth buffer uses a
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fixed-point representation, latexmath:[$m$] is a function of depth values in
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the range latexmath:[$[0,1\]$], and latexmath:[$o$] is applied to depth
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values in the same range.
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For fixed-point depth buffers, fragment depth values are always limited to
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the range latexmath:[$[0,1\]$] by clamping after depth bias addition is
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performed. Fragment depth values are clamped even when the depth buffer uses
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a floating-point representation.
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include::../validity/protos/vkCmdSetDepthBias.txt[]
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See Also
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--------
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slink:VkCommandBuffer
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Document Notes
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--------------
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For more information, see the Vulkan Specification at URL
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https://www.khronos.org/registry/vulkan/specs/1.0/xhtml/vkspec.html#vkCmdSetDepthBias
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This page is extracted from the Vulkan Specification.
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Fixes and changes should be made to the Specification,not directly.
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include::footer.txt[]
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