714 lines
30 KiB
Plaintext
714 lines
30 KiB
Plaintext
// Copyright (c) 2015-2017 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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[[vertexpostproc]]
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= Fixed-Function Vertex Post-Processing
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After programmable vertex processing, the following fixed-function
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operations are applied to vertices of the resulting primitives:
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ifdef::VK_NV_viewport_swizzle[]
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* Viewport swizzle (see <<vertexpostproc-viewport-swizzle,Viewport
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Swizzle>>)
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endif::VK_NV_viewport_swizzle[]
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* Flatshading (see <<vertexpostproc-flatshading,Flatshading>>).
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* Primitive clipping, including client-defined half-spaces (see
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<<vertexpostproc-clipping,Primitive Clipping>>).
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* Shader output attribute clipping (see
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<<vertexpostproc-clipping-shader-outputs,Clipping Shader Outputs>>).
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ifdef::VK_NV_clip_space_w_scaling[]
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* Clip space W scaling (see <<vertexpostproc-viewportwscaling,Controlling
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Viewport W Scaling>>).
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endif::VK_NV_clip_space_w_scaling[]
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* Perspective division on clip coordinates (see
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<<vertexpostproc-coord-transform,Coordinate Transformations>>).
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* Viewport mapping, including depth range scaling (see
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<<vertexpostproc-viewport,Controlling the Viewport>>).
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* Front face determination for polygon primitives (see
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<<primsrast-polygons-basic,Basic Polygon Rasterization>>).
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ifdef::editing-notes[]
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[NOTE]
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.editing-note
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====
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TODO:Odd that this one link to a different chapter is in this list.
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====
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endif::editing-notes[]
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Next, rasterization is performed on primitives as described in chapter
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<<primsrast,Rasterization>>.
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ifdef::VK_NV_viewport_swizzle[]
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[[vertexpostproc-viewport-swizzle]]
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== Viewport Swizzle
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[open,refpage='VkPipelineViewportSwizzleStateCreateInfoNV',desc='Structure specifying swizzle applied to primitive clip coordinates',type='structs']
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--
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Each primitive sent to a given viewport has a swizzle and optional: negation
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applied to its clip coordinates.
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The swizzle that is applied depends on the viewport index, and is controlled
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by the sname:VkPipelineViewportSwizzleStateCreateInfoNV pipeline state:
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include::../api/structs/VkPipelineViewportSwizzleStateCreateInfoNV.txt[]
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* pname:sType is the type of this structure.
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* pname:pNext is `NULL` or a pointer to an extension-specific structure.
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* pname:flags is reserved for future use.
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* pname:viewportCount is the number of viewport swizzles used by the
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pipeline.
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* pname:pViewportSwizzles is a pointer to an array of
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slink:VkViewportSwizzleNV structures, defining the viewport swizzles.
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.Valid Usage
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****
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* [[VUID-VkPipelineViewportSwizzleStateCreateInfoNV-viewportCount-01215]]
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pname:viewportCount must: match the pname:viewportCount set in
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sname:VkPipelineViewportStateCreateInfo
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****
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include::../validity/structs/VkPipelineViewportSwizzleStateCreateInfoNV.txt[]
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--
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The sname:VkPipelineViewportSwizzleStateCreateInfoNV state is set by adding
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an instance of this structure to the pname:pNext chain of an instance of the
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sname:VkPipelineViewportStateCreateInfo structure and setting the graphics
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pipeline state with flink:vkCreateGraphicsPipelines.
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Each viewport specified from 0 to pname:viewportCount - 1 has its x,y,z,w
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swizzle state set to the corresponding pname:x, pname:y, pname:z and pname:w
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in the slink:VkViewportSwizzleNV structure.
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Each component is of type elink:VkViewportCoordinateSwizzleNV, which
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determines the type of swizzle for that component.
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The value of pname:x computes the new x component of the position as:
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if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_X_NV) x' = x; if (x ==
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VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_X_NV) x' = -x; if (x ==
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VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Y_NV) x' = y; if (x ==
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VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_Y_NV) x' = -y; if (x ==
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VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Z_NV) x' = z; if (x ==
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VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_Z_NV) x' = -z; if (x ==
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VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_W_NV) x' = w; if (x ==
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VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_W_NV) x' = -w;
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Similar selections are performed for the pname:y, pname:z, and pname:w
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coordinates.
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This swizzling is applied before clipping and perspective divide.
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If the swizzle for an active viewport index is not specified, the swizzle
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for pname:x is ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_X_NV, pname:y
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is ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Y_NV, pname:z is
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ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Z_NV and pname:w is
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ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_W_NV.
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Viewport swizzle parameters are specified by setting the pname:pNext pointer
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of sname:VkGraphicsPipelineCreateInfo to point to an instance of
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sname:VkPipelineViewportSwizzleStateCreateInfoNV.
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slink:VkPipelineViewportSwizzleStateCreateInfoNV uses
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sname:VkViewportSwizzleNV to set the viewport swizzle parameters.
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[open,refpage='VkViewportSwizzleNV',desc='Structure specifying a viewport swizzle',type='structs']
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--
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The sname:VkViewportSwizzleNV structure is defined as:
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include::../api/structs/VkViewportSwizzleNV.txt[]
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* pname:x is a elink:VkViewportCoordinateSwizzleNV value specifying the
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swizzle operation to apply to the x component of the primitive
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* pname:y is a elink:VkViewportCoordinateSwizzleNV value specifying the
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swizzle operation to apply to the y component of the primitive
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* pname:z is a elink:VkViewportCoordinateSwizzleNV value specifying the
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swizzle operation to apply to the z component of the primitive
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* pname:w is a elink:VkViewportCoordinateSwizzleNV value specifying the
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swizzle operation to apply to the w component of the primitive
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include::../validity/structs/VkViewportSwizzleNV.txt[]
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--
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[open,refpage='VkViewportCoordinateSwizzleNV',desc='Specify how a viewport coordinate is swizzled',type='enums']
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--
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Possible values of the elink:VkViewportSwizzleNV::pname:x, pname:y, pname:z,
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and pname:w members, specifying swizzling of the corresponding components of
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primitives, are:
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include::../api/enums/VkViewportCoordinateSwizzleNV.txt[]
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These values are described in detail in <<vertexpostproc-viewport-swizzle,
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Viewport Swizzle>>.
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--
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endif::VK_NV_viewport_swizzle[]
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[[vertexpostproc-flatshading]]
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== Flat Shading
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_Flat shading_ a vertex output attribute means to assign all vertices of the
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primitive the same value for that output.
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The output values assigned are those of the _provoking vertex_ of the
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primitive.
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The provoking vertex depends on the primitive topology, and is generally the
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"`first`" vertex of the primitive.
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For primitives not processed by tessellation or geometry shaders, the
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provoking vertex is selected from the input vertices according to the
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following table.
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<<<
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[[provoking-vertex-selection]]
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.Provoking vertex selection
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[align="center",cols="75%,25%"]
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|====
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| Primitive type of primitive [eq]#i# | Provoking vertex number
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| ename:VK_PRIMITIVE_TOPOLOGY_POINT_LIST | [eq]#i#
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| ename:VK_PRIMITIVE_TOPOLOGY_LINE_LIST | [eq]#2 i#
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| ename:VK_PRIMITIVE_TOPOLOGY_LINE_STRIP | [eq]#i#
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| ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST | [eq]#3 i#
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| ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP | [eq]#i#
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| ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_FAN | [eq]#i {plus} 1#
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| ename:VK_PRIMITIVE_TOPOLOGY_LINE_LIST_WITH_ADJACENCY | [eq]#4 i {plus} 1#
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| ename:VK_PRIMITIVE_TOPOLOGY_LINE_STRIP_WITH_ADJACENCY | [eq]#i {plus} 1#
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| ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST_WITH_ADJACENCY | [eq]#6 i#
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| ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP_WITH_ADJACENCY | [eq]#2 i#
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|====
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.Caption
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****
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The <<provoking-vertex-selection,Provoking vertex selection>> table defines
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the output values used for flat shading the i^th^ primitive generated by
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drawing commands with the indicated primitive type, derived from the
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corresponding values of the vertex whose index is shown in the table.
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Primitives and vertices are numbered starting from zero.
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****
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Flat shading is applied to those vertex attributes that
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<<interfaces-iointerfaces-matching,match>> fragment input attributes which
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are decorated as code:Flat.
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If a geometry shader is active, the output primitive topology is either
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points, line strips, or triangle strips, and the selection of the provoking
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vertex behaves according to the corresponding row of the table.
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If a tessellation evaluation shader is active and a geometry shader is not
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active, the provoking vertex is undefined but must: be one of the vertices
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of the primitive.
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[[vertexpostproc-clipping]]
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== Primitive Clipping
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Primitives are culled against the _cull volume_ and then clipped to the
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_clip volume_.
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In clip coordinates, the _view volume_ is defined by:
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[latexmath]
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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\begin{array}{c}
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-w_c \leq x_c \leq w_c \\
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-w_c \leq y_c \leq w_c \\
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0 \leq z_c \leq w_c
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\end{array}
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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This view volume can: be further restricted by as many as
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sname:VkPhysicalDeviceLimits::pname:maxClipDistances client-defined
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half-spaces.
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The cull volume is the intersection of up to
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sname:VkPhysicalDeviceLimits::pname:maxCullDistances client-defined
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half-spaces (if no client-defined cull half-spaces are enabled, culling
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against the cull volume is skipped).
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A shader must: write a single cull distance for each enabled cull half-space
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to elements of the code:CullDistance array.
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If the cull distance for any enabled cull half-space is negative for all of
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the vertices of the primitive under consideration, the primitive is
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discarded.
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Otherwise the primitive is clipped against the clip volume as defined below.
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The clip volume is the intersection of up to
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sname:VkPhysicalDeviceLimits::pname:maxClipDistances client-defined
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half-spaces with the view volume (if no client-defined clip half-spaces are
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enabled, the clip volume is the view volume).
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A shader must: write a single clip distance for each enabled clip half-space
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to elements of the code:ClipDistance array.
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Clip half-space [eq]#i# is then given by the set of points satisfying the
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inequality
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:: [eq]#c~i~(**P**) {geq} 0#
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where [eq]#c~i~(**P**)# is the clip distance [eq]#i# at point [eq]#**P**#.
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For point primitives, [eq]#c~i~(**P**)# is simply the clip distance for the
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vertex in question.
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For line and triangle primitives, per-vertex clip distances are interpolated
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using a weighted mean, with weights derived according to the algorithms
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described in sections <<primsrast-lines-basic,Basic Line Segment
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Rasterization>> and <<primsrast-polygons-basic,Basic Polygon
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Rasterization>>, using the perspective interpolation equations.
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The number of client-defined clip and cull half-spaces that are enabled is
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determined by the explicit size of the built-in arrays code:ClipDistance and
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code:CullDistance, respectively, declared as an output in the interface of
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the entry point of the final shader stage before clipping.
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Depth clamping is enabled or disabled via the pname:depthClampEnable enable
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of the sname:VkPipelineRasterizationStateCreateInfo structure.
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If depth clamping is enabled, the plane equation
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:: [eq]#0 {leq} z~c~ {leq} w~c~#
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(see the clip volume definition above) is ignored by view volume clipping
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(effectively, there is no near or far plane clipping).
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If the primitive under consideration is a point or line segment, then
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clipping passes it unchanged if its vertices lie entirely within the clip
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volume.
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ifndef::VK_KHR_maintenance2[]
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If a point's vertex lies outside of the clip volume, the entire primitive
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may: be discarded.
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endif::VK_KHR_maintenance2[]
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ifdef::VK_KHR_maintenance2[]
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[open,refpage='VkPointClippingBehaviorKHR',desc='Enum specifying the point clipping behaviour',type='enums']
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--
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Possible values of
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slink:VkPhysicalDevicePointClippingPropertiesKHR::pname:pointClippingBehavior,
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specifying clipping behavior of a point primitive whose vertex lies outside
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the clip volume, are:
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include::../api/enums/VkPointClippingBehaviorKHR.txt[]
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* ename:VK_POINT_CLIPPING_BEHAVIOR_ALL_CLIP_PLANES_KHR specifies that the
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primitive is discarded if the vertex lies outside any clip plane,
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including the planes bounding the view volume.
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* ename:VK_POINT_CLIPPING_BEHAVIOR_USER_CLIP_PLANES_ONLY_KHR specifies that
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the primitive is discarded only if the vertex lies outside any user clip
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plane.
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--
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endif::VK_KHR_maintenance2[]
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If either of a line segment's vertices lie outside of the clip volume, the
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line segment may: be clipped, with new vertex coordinates computed for each
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vertex that lies outside the clip volume.
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A clipped line segment endpoint lies on both the original line segment and
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the boundary of the clip volume.
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This clipping produces a value, [eq]#0 {leq} t {leq} 1#, for each clipped
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vertex.
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If the coordinates of a clipped vertex are [eq]#**P**# and the original
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vertices' coordinates are [eq]#**P**~1~# and [eq]#**P**~2~#, then [eq]#t# is
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given by
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:: [eq]#**P** = t **P**~1~ {plus} (1-t) **P**~2~#.
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ifdef::editing-notes[]
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[NOTE]
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.editing-note
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====
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This is weird - it gives **P**, not t.
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====
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endif::editing-notes[]
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[eq]#t# is used to clip vertex output attributes as described in
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<<vertexpostproc-clipping-shader-outputs,Clipping Shader Outputs>>.
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If the primitive is a polygon, it passes unchanged if every one of its edges
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lie entirely inside the clip volume, and it is discarded if every one of its
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edges lie entirely outside the clip volume.
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If the edges of the polygon intersect the boundary of the clip volume, the
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intersecting edges are reconnected by new edges that lie along the boundary
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of the clip volume - in some cases requiring the introduction of new
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vertices into a polygon.
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If a polygon intersects an edge of the clip volume's boundary, the clipped
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polygon must: include a point on this boundary edge.
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Primitives rendered with user-defined half-spaces must: satisfy a
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complementarity criterion.
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Suppose a series of primitives is drawn where each vertex [eq]#i# has a
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single specified clip distance [eq]#d~i~# (or a number of similarly
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specified clip distances, if multiple half-spaces are enabled).
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Next, suppose that the same series of primitives are drawn again with each
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such clip distance replaced by [eq]#-d~i~# (and the graphics pipeline is
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otherwise the same).
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In this case, primitives must: not be missing any pixels, and pixels must:
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not be drawn twice in regions where those primitives are cut by the clip
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planes.
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[[vertexpostproc-clipping-shader-outputs]]
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== Clipping Shader Outputs
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Next, vertex output attributes are clipped.
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The output values associated with a vertex that lies within the clip volume
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are unaffected by clipping.
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If a primitive is clipped, however, the output values assigned to vertices
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produced by clipping are clipped.
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Let the output values assigned to the two vertices [eq]#**P**~1~# and
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[eq]#**P**~2~# of an unclipped edge be [eq]#**c**~1~# and [eq]#**c**~2~#.
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The value of [eq]#t# (see <<vertexpostproc-clipping,Primitive Clipping>>)
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for a clipped point [eq]#**P**# is used to obtain the output value
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associated with [eq]#**P**# as
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:: [eq]#**c** = t **c**~1~ {plus} (1-t) **c**~2~#.
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(Multiplying an output value by a scalar means multiplying each of _x_, _y_,
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_z_, and _w_ by the scalar.)
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Since this computation is performed in clip space before division by
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[eq]#w~c~#, clipped output values are perspective-correct.
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Polygon clipping creates a clipped vertex along an edge of the clip volume's
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boundary.
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This situation is handled by noting that polygon clipping proceeds by
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clipping against one half-space at a time.
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Output value clipping is done in the same way, so that clipped points always
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occur at the intersection of polygon edges (possibly already clipped) with
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the clip volume's boundary.
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For vertex output attributes whose matching fragment input attributes are
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decorated with code:NoPerspective, the value of [eq]#t# used to obtain the
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output value associated with [eq]#**P**# will be adjusted to produce results
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that vary linearly in framebuffer space.
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Output attributes of integer or unsigned integer type must: always be flat
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shaded.
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Flat shaded attributes are constant over the primitive being rasterized (see
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<<primsrast-lines-basic,Basic Line Segment Rasterization>> and
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<<primsrast-polygons-basic,Basic Polygon Rasterization>>), and no
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interpolation is performed.
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The output value [eq]#**c**# is taken from either [eq]#**c**~1~# or
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[eq]#**c**~2~#, since flat shading has already occurred and the two values
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are identical.
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ifdef::VK_NV_clip_space_w_scaling[]
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include::VK_NV_clip_space_w_scaling/vertexpostproc.txt[]
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endif::VK_NV_clip_space_w_scaling[]
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[[vertexpostproc-coord-transform]]
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== Coordinate Transformations
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_Clip coordinates_ for a vertex result from shader execution, which yields a
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vertex coordinate code:Position.
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Perspective division on clip coordinates yields _normalized device
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coordinates_, followed by a _viewport_ transformation (see
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<<vertexpostproc-viewport,Controlling the Viewport>>) to convert these
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coordinates into _framebuffer coordinates_.
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If a vertex in clip coordinates has a position given by
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[latexmath]
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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\left(\begin{array}{c}
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x_c \\
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y_c \\
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z_c \\
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w_c
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\end{array}\right)
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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then the vertex's normalized device coordinates are
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[latexmath]
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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\left(
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\begin{array}{c}
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x_d \\
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y_d \\
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z_d
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\end{array}
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\right) =
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\left(
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\begin{array}{c}
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\frac{x_c}{w_c} \\
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\frac{y_c}{w_c} \\
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\frac{z_c}{w_c}
|
|
\end{array}
|
|
\right)
|
|
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
|
|
|
|
|
|
[[vertexpostproc-viewport]]
|
|
== Controlling the Viewport
|
|
|
|
The viewport transformation is determined by the selected viewport's width
|
|
and height in pixels, [eq]#p~x~# and [eq]#p~y~#, respectively, and its
|
|
center [eq]#(o~x~, o~y~)# (also in pixels), as well as its depth range min
|
|
and max determining a depth range scale value [eq]#p~z~# and a depth range
|
|
bias value [eq]#o~z~# (defined below).
|
|
The vertex's framebuffer coordinates [eq]#(x~f~, y~f~, z~f~)# are given by
|
|
|
|
:: [eq]#x~f~ = (p~x~ / 2) x~d~ {plus} o~x~#
|
|
:: [eq]#y~f~ = (p~y~ / 2) y~d~ {plus} o~y~#
|
|
:: [eq]#z~f~ = p~z~ {times} z~d~ {plus} o~z~#
|
|
|
|
Multiple viewports are available, numbered zero up to
|
|
sname:VkPhysicalDeviceLimits::pname:maxViewports minus one.
|
|
The number of viewports used by a pipeline is controlled by the
|
|
pname:viewportCount member of the sname:VkPipelineViewportStateCreateInfo
|
|
structure used in pipeline creation.
|
|
|
|
[open,refpage='VkPipelineViewportStateCreateInfo',desc='Structure specifying parameters of a newly created pipeline viewport state',type='structs']
|
|
--
|
|
|
|
The sname:VkPipelineViewportStateCreateInfo structure is defined as:
|
|
|
|
include::../api/structs/VkPipelineViewportStateCreateInfo.txt[]
|
|
|
|
* pname:sType is the type of this structure.
|
|
* pname:pNext is `NULL` or a pointer to an extension-specific structure.
|
|
* pname:flags is reserved for future use.
|
|
* pname:viewportCount is the number of viewports used by the pipeline.
|
|
* pname:pViewports is a pointer to an array of slink:VkViewport
|
|
structures, defining the viewport transforms.
|
|
If the viewport state is dynamic, this member is ignored.
|
|
* pname:scissorCount is the number of <<fragops-scissor,scissors>> and
|
|
must: match the number of viewports.
|
|
* pname:pScissors is a pointer to an array of sname:VkRect2D structures
|
|
which define the rectangular bounds of the scissor for the corresponding
|
|
viewport.
|
|
If the scissor state is dynamic, this member is ignored.
|
|
|
|
.Valid Usage
|
|
****
|
|
* [[VUID-VkPipelineViewportStateCreateInfo-viewportCount-01216]]
|
|
If the <<features-features-multiViewport,multiple viewports>> feature is
|
|
not enabled, pname:viewportCount must: be `1`
|
|
* [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-01217]]
|
|
If the <<features-features-multiViewport,multiple viewports>> feature is
|
|
not enabled, pname:scissorCount must: be `1`
|
|
* [[VUID-VkPipelineViewportStateCreateInfo-viewportCount-01218]]
|
|
pname:viewportCount must: be between `1` and
|
|
sname:VkPhysicalDeviceLimits::pname:maxViewports, inclusive
|
|
* [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-01219]]
|
|
pname:scissorCount must: be between `1` and
|
|
sname:VkPhysicalDeviceLimits::pname:maxViewports, inclusive
|
|
* [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-01220]]
|
|
pname:scissorCount and pname:viewportCount must: be identical
|
|
****
|
|
|
|
include::../validity/structs/VkPipelineViewportStateCreateInfo.txt[]
|
|
--
|
|
|
|
ifndef::VK_NV_viewport_array2+VK_EXT_shader_viewport_index_layer[]
|
|
If a geometry shader is active and has an output variable decorated with
|
|
code:ViewportIndex, the viewport transformation uses the viewport
|
|
corresponding to the value assigned to code:ViewportIndex taken from an
|
|
implementation-dependent vertex of each primitive.
|
|
If code:ViewportIndex is outside the range zero to pname:viewportCount minus
|
|
one for a primitive, or if the geometry shader did not assign a value to
|
|
code:ViewportIndex for all vertices of a primitive due to flow control, the
|
|
results of the viewport transformation of the vertices of such primitives
|
|
are undefined.
|
|
If no geometry shader is active, or if the geometry shader does not have an
|
|
output decorated with code:ViewportIndex, the viewport numbered zero is used
|
|
by the viewport transformation.
|
|
endif::VK_NV_viewport_array2+VK_EXT_shader_viewport_index_layer[]
|
|
|
|
ifdef::VK_NV_viewport_array2,VK_EXT_shader_viewport_index_layer[]
|
|
ifdef::VK_NV_viewport_array2[]
|
|
A _vertex processing stage_ may direct each primitive to zero or more
|
|
viewports.
|
|
The destination viewports for a primitive are selected by the last active
|
|
vertex processing stage that has an output variable decorated with
|
|
code:ViewportIndex (selecting a single viewport) or code:ViewportMaskNV
|
|
(selecting multiple viewports).
|
|
The viewport transform uses the viewport corresponding to either the value
|
|
assigned to code:ViewportIndex or one of the bits set in
|
|
code:ViewportMaskNV, and taken from an implementation-dependent vertex of
|
|
each primitive.
|
|
If code:ViewportIndex or any of the bits in code:ViewportMaskNV are outside
|
|
the range zero to pname:viewportCount minus one for a primitive, or if the
|
|
last active vertex processing stage did not assign a value to either
|
|
code:ViewportIndex or code:ViewportMaskNV for all vertices of a primitive
|
|
due to flow control, the results of the viewport transformation of the
|
|
vertices of such primitives are undefined.
|
|
If the last vertex processing stage does not have an output decorated with
|
|
code:ViewportIndex or code:ViewportMaskNV, the viewport numbered zero is
|
|
used by the viewport transformation.
|
|
endif::VK_NV_viewport_array2[]
|
|
ifndef::VK_NV_viewport_array2[]
|
|
ifdef::VK_EXT_shader_viewport_index_layer[]
|
|
A _vertex processing stage_ can: direct each primitive to one of several
|
|
viewports.
|
|
The destination viewport for a primitive is selected by the last active
|
|
vertex processing stage that has an output variable decorated with
|
|
code:ViewportIndex.
|
|
The viewport transform uses the viewport corresponding to the value assigned
|
|
to code:ViewportIndex taken from an implementation-dependent vertex of each
|
|
primitive.
|
|
If code:ViewportIndex is outside the range zero to pname:viewportCount minus
|
|
one for a primitive, or if the last active vertex processing stage did not
|
|
assign a value to code:ViewportIndex for all vertices of a primitive due to
|
|
flow control, the results of the viewport transformation of the vertices of
|
|
such primitives are undefined.
|
|
If the last vertex processing stage does not have an output decorated with
|
|
code:ViewportIndex, the viewport numbered zero is used by the viewport
|
|
transformation.
|
|
endif::VK_EXT_shader_viewport_index_layer[]
|
|
endif::VK_NV_viewport_array2[]
|
|
endif::VK_NV_viewport_array2,VK_EXT_shader_viewport_index_layer[]
|
|
|
|
A single vertex can: be used in more than one individual primitive, in
|
|
primitives such as ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP.
|
|
In this case, the viewport transformation is applied separately for each
|
|
primitive.
|
|
|
|
[open,refpage='vkCmdSetViewport',desc='Set the viewport on a command buffer',type='protos']
|
|
--
|
|
|
|
If the bound pipeline state object was not created with the
|
|
ename:VK_DYNAMIC_STATE_VIEWPORT dynamic state enabled, viewport
|
|
transformation parameters are specified using the pname:pViewports member of
|
|
sname:VkPipelineViewportStateCreateInfo in the pipeline state object.
|
|
If the pipeline state object was created with the
|
|
ename:VK_DYNAMIC_STATE_VIEWPORT dynamic state enabled, the viewport
|
|
transformation parameters are dynamically set and changed with the command:
|
|
|
|
include::../api/protos/vkCmdSetViewport.txt[]
|
|
|
|
* pname:commandBuffer is the command buffer into which the command will be
|
|
recorded.
|
|
* pname:firstViewport is the index of the first viewport whose parameters
|
|
are updated by the command.
|
|
* pname:viewportCount is the number of viewports whose parameters are
|
|
updated by the command.
|
|
* pname:pViewports is a pointer to an array of slink:VkViewport structures
|
|
specifying viewport parameters.
|
|
|
|
The viewport parameters taken from element [eq]#i# of pname:pViewports
|
|
replace the current state for the viewport index [eq]#pname:firstViewport
|
|
{plus} i#, for [eq]#i# in [eq]#[0, pname:viewportCount)#.
|
|
|
|
.Valid Usage
|
|
****
|
|
* [[VUID-vkCmdSetViewport-None-01221]]
|
|
The currently bound graphics pipeline must: have been created with the
|
|
ename:VK_DYNAMIC_STATE_VIEWPORT dynamic state enabled
|
|
* [[VUID-vkCmdSetViewport-firstViewport-01222]]
|
|
pname:firstViewport must: be less than
|
|
sname:VkPhysicalDeviceLimits::pname:maxViewports
|
|
* [[VUID-vkCmdSetViewport-firstViewport-01223]]
|
|
The sum of pname:firstViewport and pname:viewportCount must: be between
|
|
`1` and sname:VkPhysicalDeviceLimits::pname:maxViewports, inclusive
|
|
* [[VUID-vkCmdSetViewport-firstViewport-01224]]
|
|
If the <<features-features-multiViewport,multiple viewports>> feature is
|
|
not enabled, pname:firstViewport must: be `0`
|
|
* [[VUID-vkCmdSetViewport-viewportCount-01225]]
|
|
If the <<features-features-multiViewport,multiple viewports>> feature is
|
|
not enabled, pname:viewportCount must: be `1`
|
|
* [[VUID-vkCmdSetViewport-pViewports-01226]]
|
|
pname:pViewports must: be a pointer to an array of pname:viewportCount
|
|
valid sname:VkViewport structures
|
|
****
|
|
|
|
include::../validity/protos/vkCmdSetViewport.txt[]
|
|
--
|
|
|
|
Both slink:VkPipelineViewportStateCreateInfo and flink:vkCmdSetViewport use
|
|
sname:VkViewport to set the viewport transformation parameters.
|
|
|
|
[open,refpage='VkViewport',desc='Structure specifying a viewport',type='structs']
|
|
--
|
|
|
|
The sname:VkViewport structure is defined as:
|
|
|
|
include::../api/structs/VkViewport.txt[]
|
|
|
|
* pname:x and pname:y are the viewport's upper left corner [eq]#(x,y)#.
|
|
* pname:width and pname:height are the viewport's width and height,
|
|
respectively.
|
|
* pname:minDepth and pname:maxDepth are the depth range for the viewport.
|
|
It is valid for pname:minDepth to be greater than or equal to
|
|
pname:maxDepth.
|
|
|
|
The framebuffer depth coordinate [eq]#pname:z~f~# may: be represented using
|
|
either a fixed-point or floating-point representation.
|
|
However, a floating-point representation must: be used if the depth/stencil
|
|
attachment has a floating-point depth component.
|
|
If an [eq]#m#-bit fixed-point representation is used, we assume that it
|
|
represents each value latexmath:[\frac{k}{2^m - 1}], where [eq]#k {elem} {
|
|
0, 1, ..., 2^m^-1 }#, as [eq]#k# (e.g. 1.0 is represented in binary as a
|
|
string of all ones).
|
|
|
|
The viewport parameters shown in the above equations are found from these
|
|
values as
|
|
|
|
:: [eq]#o~x~ = pname:x {plus} pname:width / 2#
|
|
:: [eq]#o~y~ = pname:y {plus} pname:height / 2#
|
|
:: [eq]#o~z~ = pname:minDepth#
|
|
:: [eq]#p~x~ = pname:width#
|
|
:: [eq]#p~y~ = pname:height#
|
|
:: [eq]#p~z~ = pname:maxDepth - pname:minDepth#.
|
|
|
|
ifdef::VK_KHR_maintenance1[]
|
|
The application can: specify a negative term for pname:height, which has the
|
|
effect of negating the y coordinate in clip space before performing the
|
|
transform.
|
|
When using a negative pname:height, the application should: also adjust the
|
|
pname:y value to point to the lower left corner of the viewport instead of
|
|
the upper left corner.
|
|
Using the negative pname:height allows the application to avoid having to
|
|
negate the y component of the code:Position output from the last vertex
|
|
processing stage in shaders that also target other graphics APIs.
|
|
endif::VK_KHR_maintenance1[]
|
|
|
|
The width and height of the <<features-limits-maxViewportDimensions,
|
|
implementation-dependent maximum viewport dimensions>> must: be greater than
|
|
or equal to the width and height of the largest image which can: be created
|
|
and attached to a framebuffer.
|
|
|
|
The floating-point viewport bounds are represented with an
|
|
<<features-limits-viewportSubPixelBits,implementation-dependent precision>>.
|
|
|
|
.Valid Usage
|
|
****
|
|
* [[VUID-VkViewport-width-01227]]
|
|
pname:width must: be greater than `0.0` and less than or equal to
|
|
sname:VkPhysicalDeviceLimits::pname:maxViewportDimensions[0]
|
|
ifndef::VK_KHR_maintenance1[]
|
|
* [[VUID-VkViewport-height-01228]]
|
|
pname:height must: be greater than `0.0` and less than or equal to
|
|
sname:VkPhysicalDeviceLimits::pname:maxViewportDimensions[1]
|
|
endif::VK_KHR_maintenance1[]
|
|
ifdef::VK_KHR_maintenance1[]
|
|
* [[VUID-VkViewport-height-01229]]
|
|
pname:height must: be greater than or equal to
|
|
-sname:VkPhysicalDeviceLimits::pname:maxViewportDimensions[1] and less
|
|
than or equal to
|
|
sname:VkPhysicalDeviceLimits::pname:maxViewportDimensions[1]
|
|
endif::VK_KHR_maintenance1[]
|
|
ifdef::VK_AMD_negative_viewport_height[]
|
|
* [[VUID-VkViewport-height-01230]]
|
|
If the +VK_AMD_negative_viewport_height+ extension is enabled,
|
|
pname:height can: also be negative.
|
|
endif::VK_AMD_negative_viewport_height[]
|
|
* [[VUID-VkViewport-x-01231]]
|
|
pname:x and pname:y must: each be between pname:viewportBoundsRange[0]
|
|
and pname:viewportBoundsRange[1], inclusive
|
|
* [[VUID-VkViewport-x-01232]]
|
|
[eq]#(pname:x {plus} pname:width)# must: be less than or equal to
|
|
pname:viewportBoundsRange[1]
|
|
* [[VUID-VkViewport-y-01233]]
|
|
[eq]#(pname:y {plus} pname:height)# must: be less than or equal to
|
|
pname:viewportBoundsRange[1]
|
|
ifndef::VK_EXT_depth_range_unrestricted[]
|
|
* [[VUID-VkViewport-minDepth-01234]]
|
|
pname:minDepth must: be between `0.0` and `1.0`, inclusive
|
|
* [[VUID-VkViewport-maxDepth-01235]]
|
|
pname:maxDepth must: be between `0.0` and `1.0`, inclusive
|
|
endif::VK_EXT_depth_range_unrestricted[]
|
|
****
|
|
|
|
include::../validity/structs/VkViewport.txt[]
|
|
--
|