// Copyright (c) 2015-2018 Khronos Group. This work is licensed under a // Creative Commons Attribution 4.0 International License; see // http://creativecommons.org/licenses/by/4.0/ [[vertexpostproc]] = Fixed-Function Vertex Post-Processing After programmable vertex processing, the following fixed-function operations are applied to vertices of the resulting primitives: ifdef::VK_EXT_transform_feedback[] * Transform feedback (see <>) endif::VK_EXT_transform_feedback[] ifdef::VK_NV_viewport_swizzle[] * Viewport swizzle (see <>) endif::VK_NV_viewport_swizzle[] * Flat shading (see <>). * Primitive clipping, including client-defined half-spaces (see <>). * Shader output attribute clipping (see <>). ifdef::VK_NV_clip_space_w_scaling[] * Clip space W scaling (see <>). endif::VK_NV_clip_space_w_scaling[] * Perspective division on clip coordinates (see <>). * Viewport mapping, including depth range scaling (see <>). * Front face determination for polygon primitives (see <>). ifdef::editing-notes[] [NOTE] .editing-note ==== TODO:Odd that this one link to a different chapter is in this list. ==== endif::editing-notes[] Next, rasterization is performed on primitives as described in chapter <>. ifdef::VK_EXT_transform_feedback[] [[vertexpostproc-transform-feedback]] == Transform Feedback Before any other fixed-function vertex post-processing, vertex outputs from the last shader in the vertex processing stage can: be written out to one or more transform feedback buffers bound to the command buffer. To capture vertex outputs the last vertex processing stage shader must: be declared with the code:Xfb execution mode. Outputs decorated with code:XfbBuffer will be written out to the corresponding transform feedback buffers bound to the command buffer when transform feedback is active. Transform feedback buffers are bound to the command buffer by using flink:vkCmdBindTransformFeedbackBuffersEXT. Transform feedback is made active by calling flink:vkCmdBeginTransformFeedbackEXT and made inactive by calling flink:vkCmdEndTransformFeedbackEXT. After vertex data is written it is possible to use flink:vkCmdDrawIndirectByteCountEXT to start a new draw where the pname:vertexCount is derived from the number of bytes written by a previous transform feedback. When an individual point, line, or triangle primitive reaches the transform feedback stage while transform feedback is active, the values of the specified output variables are assembled into primitives and appended to the bound transform feedback buffers. After activating transform feedback, the values of the first assembled primitive are written at the starting offsets of the bound transform feedback buffers, and subsequent primitives are appended to the buffer. If the optional pname:pCounterBuffers and pname:pCounterBufferOffsets parameters are specified, the starting points within the transform feedback buffers are adjusted so data is appended to the previously written values indicated by the value stored by the implementation in the counter buffer. When capturing line and triangle primitives, all values from the first vertex output are written first, followed by values of the subsequent vertex outputs. When capturing vertices, the stride associated with each transform feedback buffer, as indicated by the code:XfbStride decoration, indicates the number of bytes of storage reserved for each vertex in the transform feedback buffer. For every vertex captured, each output attribute with a code:Offset decoration will be written to the storage reserved for the vertex at the associated transform feedback buffer. When writing output variables that are arrays or structures, individual array elements or structure members are written tightly packed in order. For vector types, individual components are written in order. For matrix types, outputs are written as an array of column vectors. If any component of an output with an assigned transform feedback offset was not written to by its shader, the value recorded for that component is undefined. The results of writing an output variable to a transform feedback buffer are undefined if any component of that variable would be written at an offset not aligned to the size of the component, or the component is less than 4 bytes in size. When capturing a vertex, any portion of the reserved storage not associated with an output variable with an assigned transform feedback offset will be unmodified. When transform feedback is inactive, no vertices are recorded. If there is a valid counter buffer handle and counter buffer offset in the pname:pCounterBuffers and pname:pCounterBufferOffsets arrays, writes to the corresponding transform feedback buffer will start at the byte offset represented by the value stored in the counter buffer location. Individual lines or triangles of a strip or fan primitive will be extracted and recorded separately. Incomplete primitives are not recorded. When using a geometry shader that emits vertices to multiple vertex streams, a primitive will be assembled and output for each stream when there are enough vertices emitted for the output primitive type. All outputs assigned to a given transform feedback buffer are required to come from a single vertex stream. The sizes of the transform feedback buffers are defined by the flink:vkCmdBindTransformFeedbackBuffersEXT pname:pSizes parameter for each of the bound buffers, or the size of the bound buffer, whichever is the lesser. If there is less space remaining in any of the transform feedback buffers than the size of the all the vertex data for that primitive based on the code:XfbStride for that code:XfbBuffer then no vertex data of that primitive is recorded in any transform feedback buffer, and the value for the number of primitives written in the corresponding ename:VK_QUERY_TYPE_TRANSFORM_FEEDBACK_STREAM_EXT query for all transform feedback buffers is no longer incremented. Any outputs made to a code:XfbBuffer that is not bound to a transform feedback buffer is ignored. [open,refpage='vkCmdBindTransformFeedbackBuffersEXT',desc='Bind transform feedback buffers to a command buffer',type='protos'] -- To bind transform feedback buffers to a command buffer for use in subsequent draw commands, call: include::../api/protos/vkCmdBindTransformFeedbackBuffersEXT.txt[] * pname:commandBuffer is the command buffer into which the command is recorded. * pname:firstBinding is the index of the first transform feedback binding whose state is updated by the command. * pname:bindingCount is the number of transform feedback bindings whose state is updated by the command. * pname:pBuffers is a pointer to an array of buffer handles. * pname:pOffsets is a pointer to an array of buffer offsets. * pname:pSizes is an optional array of buffer sizes, which specifies the maximum number of bytes to capture to the corresponding transform feedback buffer. If pname:pSizes is `NULL`, or the value of the pname:pSizes array element is ename:VK_WHOLE_SIZE, then the maximum bytes captured will be the size of the corresponding buffer minus the buffer offset. The values taken from elements [eq]#i# of pname:pBuffers, pname:pOffsets and pname:pSizes replace the current state for the transform feedback binding [eq]#pname:firstBinding {plus} i#, for [eq]#i# in [eq]#[0, pname:bindingCount)#. The transform feedback binding is updated to start at the offset indicated by pname:pOffsets[i] from the start of the buffer pname:pBuffers[i]. .Valid Usage **** * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-transformFeedback-02355]] sname:VkPhysicalDeviceTransformFeedbackFeaturesEXT::pname:transformFeedback must: be enabled * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-firstBinding-02356]] pname:firstBinding must: be less than sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-firstBinding-02357]] The sum of pname:firstBinding and pname:bindingCount must: be less than or equal to sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pOffsets-02358]] All elements of pname:pOffsets must: be less than the size of the corresponding element in pname:pBuffers * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pOffsets-02359]] All elements of pname:pOffsets must: be a multiple of 4 * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pBuffers-02360]] All elements of pname:pBuffers must: have been created with the ename:VK_BUFFER_USAGE_TRANSFORM_FEEDBACK_BUFFER_BIT_EXT flag * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pSize-02361]] If the optional pname:pSize array is specified, each element of pname:pSizes must: either be ename:VK_WHOLE_SIZE, or be less than or equal to sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBufferSize * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pSizes-02362]] All elements of pname:pSizes must: be less than or equal to the size of the corresponding buffer in pname:pBuffers * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pOffsets-02363]] All elements of pname:pOffsets plus pname:pSizes, where the pname:pSizes, element is not ename:VK_WHOLE_SIZE, must: be less than or equal to the size of the corresponding element in pname:pBuffers * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pBuffers-02364]] Each element of pname:pBuffers that is non-sparse must: be bound completely and contiguously to a single sname:VkDeviceMemory object * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-None-02365]] Transform feedback must: not be active when the fname:vkCmdBindTransformFeedbackBuffersEXT command is recorded **** include::../validity/protos/vkCmdBindTransformFeedbackBuffersEXT.txt[] -- [open,refpage='vkCmdBeginTransformFeedbackEXT',desc='Make transform feedback active in the command buffer',type='protos'] -- Transform feedback for specific transform feedback buffers is made active by calling: include::../api/protos/vkCmdBeginTransformFeedbackEXT.txt[] * pname:commandBuffer is the command buffer into which the command is recorded. * pname:firstCounterBuffer is the index of the first transform feedback buffer corresponding to pname:pCounterBuffers[0] and pname:pCounterBufferOffsets[0]. * pname:counterBufferCount is the size of the pname:pCounterBuffers and pname:pCounterBufferOffsets arrays. * pname:pCounterBuffers is an optional array of buffer handles to the counter buffers which contain a 4 byte integer value representing the byte offset from the start of the corresponding transform feedback buffer from where to start capturing vertex data. If the byte offset stored to the counter buffer location was done using flink:vkCmdEndTransformFeedbackEXT it can be used to resume transform feedback from the previous location. If pname:pCounterBuffers is `NULL`, then transform feedback will start capturing vertex data to byte offset zero in all bound transform feedback buffers. For each element of pname:pCounterBuffers that is dlink:VK_NULL_HANDLE, transform feedback will start capturing vertex data to byte zero in the corresponding bound transform feedback buffer. * pname:pCounterBufferOffsets is an optional array of offsets within each of the pname:pCounterBuffers where the counter values were previously written. The location in each counter buffer at these offsets must: be large enough to contain 4 bytes of data. This data is the number of bytes captured by the previous transform feedback to this buffer. If pname:pCounterBufferOffsets is `NULL`, then it is assumed the offsets are zero. The active transform feedback buffers will capture primitives emitted from the corresponding code:XfbBuffer in the bound graphics pipeline. Any code:XfbBuffer emitted that does not output to an active transform feedback buffer will not be captured. .Valid Usage **** * [[VUID-vkCmdBeginTransformFeedbackEXT-transformFeedback-02366]] sname:VkPhysicalDeviceTransformFeedbackFeaturesEXT::pname:transformFeedback must: be enabled * [[VUID-vkCmdBeginTransformFeedbackEXT-None-02367]] Transform feedback must: not be active * [[VUID-vkCmdBeginTransformFeedbackEXT-firstCounterBuffer-02368]] pname:firstCounterBuffer must: be less than sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers * [[VUID-vkCmdBeginTransformFeedbackEXT-firstCounterBuffer-02369]] The sum of pname:firstCounterBuffer and pname:counterBufferCount must: be less than or equal to sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers * [[VUID-vkCmdBeginTransformFeedbackEXT-pCounterBufferOffsets-02370]] For each buffer handle in the array, if it is not dlink:VK_NULL_HANDLE it must: reference a buffer large enough to hold 4 bytes at the corresponding offset from the pname:pCounterBufferOffsets array * [[VUID-vkCmdBeginTransformFeedbackEXT-pCounterBuffer-02371]] If pname:pCounterBuffer is `NULL`, then pname:pCounterBufferOffsets must: also be `NULL` * [[VUID-vkCmdBeginTransformFeedbackEXT-pCounterBuffers-02372]] For each buffer handle in the pname:pCounterBuffers array that is not dlink:VK_NULL_HANDLE it must: have been created with a pname:usage value containing ename:VK_BUFFER_USAGE_TRANSFORM_FEEDBACK_COUNTER_BUFFER_BIT_EXT ifdef::VK_VERSION_1_1,VK_KHR_multiview[] * [[VUID-vkCmdBeginTransformFeedbackEXT-None-02373]] Transform feedback must: not be made active in a render pass instance with multiview enabled endif::VK_VERSION_1_1,VK_KHR_multiview[] **** include::../validity/protos/vkCmdBeginTransformFeedbackEXT.txt[] -- [open,refpage='vkCmdEndTransformFeedbackEXT',desc='Make transform feedback inactive in the command buffer',type='protos'] -- Transform feedback for specific transform feedback buffers is made inactive by calling: include::../api/protos/vkCmdEndTransformFeedbackEXT.txt[] * pname:commandBuffer is the command buffer into which the command is recorded. * pname:firstCounterBuffer is the index of the first transform feedback buffer corresponding to pname:pCounterBuffers[0] and pname:pCounterBufferOffsets[0]. * pname:counterBufferCount is the size of the pname:pCounterBuffers and pname:pCounterBufferOffsets arrays. * pname:pCounterBuffers is an optional array of buffer handles to the counter buffers used to record the current byte positions of each transform feedback buffer where the next vertex output data would be captured. This can: be used by a subsequent flink:vkCmdBeginTransformFeedbackEXT call to resume transform feedback capture from this position. It can also be used by flink:vkCmdDrawIndirectByteCountEXT to determine the vertex count of the draw call. * pname:pCounterBufferOffsets is an optional array of offsets within each of the pname:pCounterBuffers where the counter values can be written. The location in each counter buffer at these offsets must: be large enough to contain 4 bytes of data. The data stored at this location is the byte offset from the start of the transform feedback buffer binding where the next vertex data would be written. If pname:pCounterBufferOffsets is `NULL`, then it is assumed the offsets are zero. .Valid Usage **** * [[VUID-vkCmdEndTransformFeedbackEXT-transformFeedback-02374]] sname:VkPhysicalDeviceTransformFeedbackFeaturesEXT::pname:transformFeedback must: be enabled * [[VUID-vkCmdEndTransformFeedbackEXT-None-02375]] Transform feedback must: be active * [[VUID-vkCmdEndTransformFeedbackEXT-firstCounterBuffer-02376]] pname:firstCounterBuffer must: be less than sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers * [[VUID-vkCmdEndTransformFeedbackEXT-firstCounterBuffer-02377]] The sum of pname:firstCounterBuffer and pname:counterBufferCount must: be less than or equal to sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers * [[VUID-vkCmdEndTransformFeedbackEXT-pCounterBufferOffsets-02378]] For each buffer handle in the array, if it is not dlink:VK_NULL_HANDLE it must: reference a buffer large enough to hold 4 bytes at the corresponding offset from the pname:pCounterBufferOffsets array * [[VUID-vkCmdEndTransformFeedbackEXT-pCounterBuffer-02379]] If pname:pCounterBuffer is `NULL`, then pname:pCounterBufferOffsets must: also be `NULL` * [[VUID-vkCmdEndTransformFeedbackEXT-pCounterBuffers-02380]] For each buffer handle in the pname:pCounterBuffers array that is not dlink:VK_NULL_HANDLE it must: have been created with a pname:usage value containing ename:VK_BUFFER_USAGE_TRANSFORM_FEEDBACK_COUNTER_BUFFER_BIT_EXT **** include::../validity/protos/vkCmdEndTransformFeedbackEXT.txt[] -- endif::VK_EXT_transform_feedback[] ifdef::VK_NV_viewport_swizzle[] [[vertexpostproc-viewport-swizzle]] == Viewport Swizzle [open,refpage='VkPipelineViewportSwizzleStateCreateInfoNV',desc='Structure specifying swizzle applied to primitive clip coordinates',type='structs'] -- Each primitive sent to a given viewport has a swizzle and optional: negation applied to its clip coordinates. The swizzle that is applied depends on the viewport index, and is controlled by the sname:VkPipelineViewportSwizzleStateCreateInfoNV pipeline state: include::../api/structs/VkPipelineViewportSwizzleStateCreateInfoNV.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 viewport swizzles used by the pipeline. * pname:pViewportSwizzles is a pointer to an array of slink:VkViewportSwizzleNV structures, defining the viewport swizzles. .Valid Usage **** * [[VUID-VkPipelineViewportSwizzleStateCreateInfoNV-viewportCount-01215]] pname:viewportCount must: match the pname:viewportCount set in sname:VkPipelineViewportStateCreateInfo **** include::../validity/structs/VkPipelineViewportSwizzleStateCreateInfoNV.txt[] -- [open,refpage='VkPipelineViewportSwizzleStateCreateFlagsNV',desc='Reserved for future use',type='enums'] -- include::../api/flags/VkPipelineViewportSwizzleStateCreateFlagsNV.txt[] tname:VkPipelineViewportSwizzleStateCreateFlagsNV is a bitmask type for setting a mask, but is currently reserved for future use. -- The sname:VkPipelineViewportSwizzleStateCreateInfoNV state is set by adding an instance of this structure to the pname:pNext chain of an instance of the sname:VkPipelineViewportStateCreateInfo structure and setting the graphics pipeline state with flink:vkCreateGraphicsPipelines. Each viewport specified from 0 to pname:viewportCount - 1 has its x,y,z,w swizzle state set to the corresponding pname:x, pname:y, pname:z and pname:w in the slink:VkViewportSwizzleNV structure. Each component is of type elink:VkViewportCoordinateSwizzleNV, which determines the type of swizzle for that component. The value of pname:x computes the new x component of the position as: [source,c] --------------------------------------------------- if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_X_NV) x' = x; if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_X_NV) x' = -x; if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Y_NV) x' = y; if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_Y_NV) x' = -y; if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Z_NV) x' = z; if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_Z_NV) x' = -z; if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_W_NV) x' = w; if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_W_NV) x' = -w; --------------------------------------------------- Similar selections are performed for the pname:y, pname:z, and pname:w coordinates. This swizzling is applied before clipping and perspective divide. If the swizzle for an active viewport index is not specified, the swizzle for pname:x is ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_X_NV, pname:y is ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Y_NV, pname:z is ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Z_NV and pname:w is ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_W_NV. Viewport swizzle parameters are specified by setting the pname:pNext pointer of sname:VkGraphicsPipelineCreateInfo to point to an instance of sname:VkPipelineViewportSwizzleStateCreateInfoNV. slink:VkPipelineViewportSwizzleStateCreateInfoNV uses sname:VkViewportSwizzleNV to set the viewport swizzle parameters. [open,refpage='VkViewportSwizzleNV',desc='Structure specifying a viewport swizzle',type='structs'] -- The sname:VkViewportSwizzleNV structure is defined as: include::../api/structs/VkViewportSwizzleNV.txt[] * pname:x is a elink:VkViewportCoordinateSwizzleNV value specifying the swizzle operation to apply to the x component of the primitive * pname:y is a elink:VkViewportCoordinateSwizzleNV value specifying the swizzle operation to apply to the y component of the primitive * pname:z is a elink:VkViewportCoordinateSwizzleNV value specifying the swizzle operation to apply to the z component of the primitive * pname:w is a elink:VkViewportCoordinateSwizzleNV value specifying the swizzle operation to apply to the w component of the primitive include::../validity/structs/VkViewportSwizzleNV.txt[] -- [open,refpage='VkViewportCoordinateSwizzleNV',desc='Specify how a viewport coordinate is swizzled',type='enums'] -- Possible values of the slink:VkViewportSwizzleNV::pname:x, pname:y, pname:z, and pname:w members, specifying swizzling of the corresponding components of primitives, are: include::../api/enums/VkViewportCoordinateSwizzleNV.txt[] These values are described in detail in <>. -- endif::VK_NV_viewport_swizzle[] [[vertexpostproc-flatshading]] == Flat Shading _Flat shading_ a vertex output attribute means to assign all vertices of the primitive the same value for that output. The output values assigned are those of the _provoking vertex_ of the primitive. The provoking vertex depends on the primitive topology, and is generally the "`first`" vertex of the primitive. For primitives not processed by tessellation or geometry shaders, the provoking vertex is selected from the input vertices according to the following table. <<< [[provoking-vertex-selection]] .Provoking vertex selection [align="center",cols="75%,25%"] |==== | Primitive type of primitive [eq]#i# | Provoking vertex number | ename:VK_PRIMITIVE_TOPOLOGY_POINT_LIST | [eq]#i# | ename:VK_PRIMITIVE_TOPOLOGY_LINE_LIST | [eq]#2 i# | ename:VK_PRIMITIVE_TOPOLOGY_LINE_STRIP | [eq]#i# | ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST | [eq]#3 i# | ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP | [eq]#i# | ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_FAN | [eq]#i {plus} 1# | ename:VK_PRIMITIVE_TOPOLOGY_LINE_LIST_WITH_ADJACENCY | [eq]#4 i {plus} 1# | ename:VK_PRIMITIVE_TOPOLOGY_LINE_STRIP_WITH_ADJACENCY | [eq]#i {plus} 1# | ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST_WITH_ADJACENCY | [eq]#6 i# | ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP_WITH_ADJACENCY | [eq]#2 i# |==== .Caption **** The <> table defines the output values used for flat shading the i^th^ primitive generated by drawing commands with the indicated primitive type, derived from the corresponding values of the vertex whose index is shown in the table. Primitives and vertices are numbered starting from zero. **** Flat shading is applied to those vertex attributes that <> fragment input attributes which are decorated as code:Flat. If a geometry shader is active, the output primitive topology is either points, line strips, or triangle strips, and the selection of the provoking vertex behaves according to the corresponding row of the table. If a tessellation evaluation shader is active and a geometry shader is not active, the provoking vertex is undefined: but must: be one of the vertices of the primitive. [[vertexpostproc-clipping]] == Primitive Clipping Primitives are culled against the _cull volume_ and then clipped to the _clip volume_. In clip coordinates, the _view volume_ is defined by: [latexmath] ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ \begin{array}{c} -w_c \leq x_c \leq w_c \\ -w_c \leq y_c \leq w_c \\ 0 \leq z_c \leq w_c \end{array} ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ This view volume can: be further restricted by as many as sname:VkPhysicalDeviceLimits::pname:maxClipDistances client-defined half-spaces. The cull volume is the intersection of up to sname:VkPhysicalDeviceLimits::pname:maxCullDistances client-defined half-spaces (if no client-defined cull half-spaces are enabled, culling against the cull volume is skipped). A shader must: write a single cull distance for each enabled cull half-space to elements of the code:CullDistance array. If the cull distance for any enabled cull half-space is negative for all of the vertices of the primitive under consideration, the primitive is discarded. Otherwise the primitive is clipped against the clip volume as defined below. The clip volume is the intersection of up to sname:VkPhysicalDeviceLimits::pname:maxClipDistances client-defined half-spaces with the view volume (if no client-defined clip half-spaces are enabled, the clip volume is the view volume). A shader must: write a single clip distance for each enabled clip half-space to elements of the code:ClipDistance array. Clip half-space [eq]#i# is then given by the set of points satisfying the inequality :: [eq]#c~i~(**P**) {geq} 0# where [eq]#c~i~(**P**)# is the clip distance [eq]#i# at point [eq]#**P**#. For point primitives, [eq]#c~i~(**P**)# is simply the clip distance for the vertex in question. For line and triangle primitives, per-vertex clip distances are interpolated using a weighted mean, with weights derived according to the algorithms described in sections <> and <>, using the perspective interpolation equations. The number of client-defined clip and cull half-spaces that are enabled is determined by the explicit size of the built-in arrays code:ClipDistance and code:CullDistance, respectively, declared as an output in the interface of the entry point of the final shader stage before clipping. Depth clamping is enabled or disabled via the pname:depthClampEnable enable of the sname:VkPipelineRasterizationStateCreateInfo structure. If depth clamping is enabled, the plane equation :: [eq]#0 {leq} z~c~ {leq} w~c~# (see the clip volume definition above) is ignored by view volume clipping (effectively, there is no near or far plane clipping). If the primitive under consideration is a point or line segment, then clipping passes it unchanged if its vertices lie entirely within the clip volume. ifndef::VK_VERSION_1_1,VK_KHR_maintenance2[] If a point's vertex lies outside of the clip volume, the entire primitive may: be discarded. endif::VK_VERSION_1_1,VK_KHR_maintenance2[] ifdef::VK_VERSION_1_1,VK_KHR_maintenance2[] [open,refpage='VkPointClippingBehavior',desc='Enum specifying the point clipping behaviour',type='enums'] -- Possible values of slink:VkPhysicalDevicePointClippingProperties::pname:pointClippingBehavior, specifying clipping behavior of a point primitive whose vertex lies outside the clip volume, are: include::../api/enums/VkPointClippingBehavior.txt[] ifdef::VK_KHR_maintenance2[] or the equivalent include::../api/enums/VkPointClippingBehaviorKHR.txt[] endif::VK_KHR_maintenance2[] * ename:VK_POINT_CLIPPING_BEHAVIOR_ALL_CLIP_PLANES specifies that the primitive is discarded if the vertex lies outside any clip plane, including the planes bounding the view volume. * ename:VK_POINT_CLIPPING_BEHAVIOR_USER_CLIP_PLANES_ONLY specifies that the primitive is discarded only if the vertex lies outside any user clip plane. -- endif::VK_VERSION_1_1,VK_KHR_maintenance2[] If either of a line segment's vertices lie outside of the clip volume, the line segment may: be clipped, with new vertex coordinates computed for each vertex that lies outside the clip volume. A clipped line segment endpoint lies on both the original line segment and the boundary of the clip volume. This clipping produces a value, [eq]#0 {leq} t {leq} 1#, for each clipped vertex. If the coordinates of a clipped vertex are [eq]#**P**# and the original vertices`' coordinates are [eq]#**P**~1~# and [eq]#**P**~2~#, then [eq]#t# is given by :: [eq]#**P** = t **P**~1~ {plus} (1-t) **P**~2~#. ifdef::editing-notes[] [NOTE] .editing-note ==== This is weird - it gives **P**, not t. ==== endif::editing-notes[] [eq]#t# is used to clip vertex output attributes as described in <>. If the primitive is a polygon, it passes unchanged if every one of its edges lie entirely inside the clip volume, and it is discarded if every one of its edges lie entirely outside the clip volume. If the edges of the polygon intersect the boundary of the clip volume, the intersecting edges are reconnected by new edges that lie along the boundary of the clip volume - in some cases requiring the introduction of new vertices into a polygon. If a polygon intersects an edge of the clip volume's boundary, the clipped polygon must: include a point on this boundary edge. Primitives rendered with user-defined half-spaces must: satisfy a complementarity criterion. Suppose a series of primitives is drawn where each vertex [eq]#i# has a single specified clip distance [eq]#d~i~# (or a number of similarly specified clip distances, if multiple half-spaces are enabled). Next, suppose that the same series of primitives are drawn again with each such clip distance replaced by [eq]#-d~i~# (and the graphics pipeline is otherwise the same). In this case, primitives must: not be missing any pixels, and pixels must: not be drawn twice in regions where those primitives are cut by the clip planes. [[vertexpostproc-clipping-shader-outputs]] == Clipping Shader Outputs Next, vertex output attributes are clipped. The output values associated with a vertex that lies within the clip volume are unaffected by clipping. If a primitive is clipped, however, the output values assigned to vertices produced by clipping are clipped. Let the output values assigned to the two vertices [eq]#**P**~1~# and [eq]#**P**~2~# of an unclipped edge be [eq]#**c**~1~# and [eq]#**c**~2~#. The value of [eq]#t# (see <>) for a clipped point [eq]#**P**# is used to obtain the output value associated with [eq]#**P**# as :: [eq]#**c** = t **c**~1~ {plus} (1-t) **c**~2~#. (Multiplying an output value by a scalar means multiplying each of _x_, _y_, _z_, and _w_ by the scalar.) Since this computation is performed in clip space before division by [eq]#w~c~#, clipped output values are perspective-correct. Polygon clipping creates a clipped vertex along an edge of the clip volume's boundary. This situation is handled by noting that polygon clipping proceeds by clipping against one half-space at a time. Output value clipping is done in the same way, so that clipped points always occur at the intersection of polygon edges (possibly already clipped) with the clip volume's boundary. For vertex output attributes whose matching fragment input attributes are decorated with code:NoPerspective, the value of [eq]#t# used to obtain the output value associated with [eq]#**P**# will be adjusted to produce results that vary linearly in framebuffer space. Output attributes of integer or unsigned integer type must: always be flat shaded. Flat shaded attributes are constant over the primitive being rasterized (see <> and <>), and no interpolation is performed. The output value [eq]#**c**# is taken from either [eq]#**c**~1~# or [eq]#**c**~2~#, since flat shading has already occurred and the two values are identical. ifdef::VK_NV_clip_space_w_scaling[] include::VK_NV_clip_space_w_scaling/vertexpostproc.txt[] endif::VK_NV_clip_space_w_scaling[] [[vertexpostproc-coord-transform]] == Coordinate Transformations _Clip coordinates_ for a vertex result from shader execution, which yields a vertex coordinate code:Position. Perspective division on clip coordinates yields _normalized device coordinates_, followed by a _viewport_ transformation (see <>) to convert these coordinates into _framebuffer coordinates_. If a vertex in clip coordinates has a position given by [latexmath] ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ \left(\begin{array}{c} x_c \\ y_c \\ z_c \\ w_c \end{array}\right) ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ then the vertex's normalized device coordinates are [latexmath] ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ \left( \begin{array}{c} x_d \\ y_d \\ z_d \end{array} \right) = \left( \begin{array}{c} \frac{x_c}{w_c} \\ \frac{y_c}{w_c} \\ \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 <> and must: match the number of viewports. * pname:pScissors is a pointer to an array of slink: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 <> feature is not enabled, pname:viewportCount must: be `1` * [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-01217]] If the <> 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 ifdef::VK_NV_clip_space_w_scaling[] * [[VUID-VkPipelineViewportStateCreateInfo-viewportWScalingEnable-01726]] If the pname:viewportWScalingEnable member of a slink:VkPipelineViewportWScalingStateCreateInfoNV structure chained to the pname:pNext chain is ename:VK_TRUE, the pname:viewportCount member of the slink:VkPipelineViewportWScalingStateCreateInfoNV structure must: be equal to pname:viewportCount endif::VK_NV_clip_space_w_scaling[] **** include::../validity/structs/VkPipelineViewportStateCreateInfo.txt[] -- [open,refpage='VkPipelineViewportStateCreateFlags',desc='Reserved for future use',type='enums'] -- include::../api/flags/VkPipelineViewportStateCreateFlags.txt[] tname:VkPipelineViewportStateCreateFlags is a bitmask type for setting a mask, but is currently reserved for future use. -- 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 values resulting from 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 values resulting from 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 values resulting from 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 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 <> feature is not enabled, pname:firstViewport must: be `0` * [[VUID-vkCmdSetViewport-viewportCount-01225]] If the <> feature is not enabled, pname:viewportCount must: be `1` **** 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_VERSION_1_1,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_VERSION_1_1,VK_KHR_maintenance1[] The width and height of the <> 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 <>. .Valid Usage **** * [[VUID-VkViewport-width-01770]] pname:width must: be greater than `0.0` * [[VUID-VkViewport-width-01771]] pname:width must: be less than or equal to sname:VkPhysicalDeviceLimits::pname:maxViewportDimensions[0] ifndef::VK_VERSION_1_1,VK_KHR_maintenance1,VK_AMD_negative_viewport_height[] * [[VUID-VkViewport-height-01772]] pname:height must: be greater than `0.0` endif::VK_VERSION_1_1,VK_KHR_maintenance1,VK_AMD_negative_viewport_height[] * [[VUID-VkViewport-height-01773]] The absolute value of pname:height must: be less than or equal to sname:VkPhysicalDeviceLimits::pname:maxViewportDimensions[1] * [[VUID-VkViewport-x-01774]] pname:x must: be greater than or equal to pname:viewportBoundsRange[0] * [[VUID-VkViewport-x-01232]] [eq]#(pname:x {plus} pname:width)# must: be less than or equal to pname:viewportBoundsRange[1] * [[VUID-VkViewport-y-01775]] pname:y must: be greater than or equal to pname:viewportBoundsRange[0] ifdef::VK_VERSION_1_1,VK_KHR_maintenance1,VK_AMD_negative_viewport_height[] * [[VUID-VkViewport-y-01776]] pname:y must: be less than or equal to pname:viewportBoundsRange[1] * [[VUID-VkViewport-y-01777]] [eq]#(pname:y {plus} pname:height)# must: be greater than or equal to pname:viewportBoundsRange[0] endif::VK_VERSION_1_1,VK_KHR_maintenance1,VK_AMD_negative_viewport_height[] * [[VUID-VkViewport-y-01233]] [eq]#(pname:y {plus} pname:height)# must: be less than or equal to pname:viewportBoundsRange[1] ifdef::VK_EXT_depth_range_unrestricted[] * [[VUID-VkViewport-minDepth-01234]] Unless `<>` extension is enabled pname:minDepth must: be between `0.0` and `1.0`, inclusive endif::VK_EXT_depth_range_unrestricted[] ifndef::VK_EXT_depth_range_unrestricted[] * [[VUID-VkViewport-minDepth-01234]] pname:minDepth must: be between `0.0` and `1.0`, inclusive endif::VK_EXT_depth_range_unrestricted[] ifdef::VK_EXT_depth_range_unrestricted[] * [[VUID-VkViewport-maxDepth-01235]] Unless `<>` extension is enabled pname:maxDepth must: be between `0.0` and `1.0`, inclusive endif::VK_EXT_depth_range_unrestricted[] ifndef::VK_EXT_depth_range_unrestricted[] * [[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[] --