// Copyright (c) 2014-2016 Khronos Group. This work is licensed under a
// Creative Commons Attribution 4.0 International License; see
// http://creativecommons.org/licenses/by/4.0/

VkFrontFace(3)
==============

Name
----
VkFrontFace - interpret polygon front-facing orientation

C Specification
---------------

// refBegin VkFrontFace interpret polygon front-facing orientation

The first step of polygon rasterization is to determine whether the triangle
is _back-facing_ or _front-facing_. This determination is made based on the
sign of the (clipped or unclipped) polygon's area computed in framebuffer
coordinates. One way to compute this area is:

[latexmath]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
\[
  a = -{1 \over 2}\sum_{i=0}^{n-1}
        x_f^i y_f^{i \oplus 1} -
        x_f^{i \oplus 1} y_f^i
\]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

where latexmath:[$x_f^i$] and latexmath:[$y_f^i$] are the latexmath:[$x$]
and latexmath:[$y$] framebuffer coordinates of the latexmath:[$i$]th vertex
of the latexmath:[$n$]-vertex polygon (vertices are numbered starting at
zero for the purposes of this computation) and latexmath:[$i \oplus 1$] is
latexmath:[$(i + 1)~ \textrm{mod}~ n$].

The interpretation of the sign of latexmath:[$a$]
is determined by the
slink:VkPipelineRasterizationStateCreateInfo::pname:frontFace property of
the currently active pipeline, which takes the following values:

include::../api/enums/VkFrontFace.txt[]


Description
-----------

If pname:frontFace is set to ename:VK_FRONT_FACE_COUNTER_CLOCKWISE, a triangle with
positive area is considered front-facing. If it is set to
ename:VK_FRONT_FACE_CLOCKWISE, a triangle with negative area is considered
front-facing. Any triangle which is not front-facing is back-facing,
including zero-area triangles.

// refEnd VkFrontFace


See Also
--------

slink:VkPipelineRasterizationStateCreateInfo


Document Notes
--------------

For more information, see the Vulkan Specification at URL

https://www.khronos.org/registry/vulkan/specs/1.0/xhtml/vkspec.html#VkFrontFace

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

include::footer.txt[]