524 lines
23 KiB
Plaintext
524 lines
23 KiB
Plaintext
// Copyright (c) 2015-2016 The Khronos Group Inc.
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// Copyright notice at https://www.khronos.org/registry/speccopyright.html
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[[drawing]]
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= Drawing Commands
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_Drawing commands_ (commands with ftext:Draw in the name) provoke work in a
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graphics pipeline. Drawing commands are recorded into a command buffer and
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when executed by a queue, will produce work which executes according to the
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currently bound graphics pipeline. A graphics pipeline must: be bound to a
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command buffer before any drawing commands are recorded in that command
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buffer.
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Each draw is made up of zero or more vertices and zero or more instances,
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which are processed by the device and result in the assembly of
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primitives. Primitives are assembled according to the
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pname:pInputAssemblyState member of the sname:VkGraphicsPipelineCreateInfo
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structure, which is of type sname:VkPipelineInputAssemblyStateCreateInfo:
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include::../structs/VkPipelineInputAssemblyStateCreateInfo.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:primitiveRestartEnable controls whether a special vertex index
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value is treated as restarting the assembly of primitives. This enable
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only applies to indexed draws (flink:vkCmdDrawIndexed and
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flink:vkCmdDrawIndexedIndirect), and the special index value is either
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0xFFFFFFFF when the pname:indexType parameter of
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fname:vkCmdBindIndexBuffer is equal to ename:VK_INDEX_TYPE_UINT32, or
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0xFFFF when pname:indexType is equal to ename:VK_INDEX_TYPE_UINT16.
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Primitive restart is not allowed for ``list'' topologies.
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* pname:topology is a elink:VkPrimitiveTopology defining the primitive
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topology, as described below.
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include::../validity/structs/VkPipelineInputAssemblyStateCreateInfo.txt[]
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Restarting the assembly of primitives discards the most recent index values
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if those elements formed an incomplete primitive, and restarts the primitive
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assembly using the subsequent indices, but only assembling the immediately
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following element through the end of the originally specified elements. The
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primitive restart index value comparison is performed before adding the
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pname:vertexOffset value to the index value.
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[[drawing-primitive-topologies]]
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== Primitive Topologies
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_Primitive topology_ determines how consecutive vertices are organized into
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primitives, and determines the type of primitive that is used at the
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beginning of the graphics pipeline. The effective topology for later stages
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of the pipeline is altered by tessellation or geometry shading (if either is
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in use) and depends on the execution modes of those shaders. Supported
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topologies are defined by elink:VkPrimitiveTopology and include:
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include::../enums/VkPrimitiveTopology.txt[]
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Each primitive topology, and its construction from a list of vertices, is
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summarized below.
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=== Points
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A series of individual points are specified with pname:topology
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ename:VK_PRIMITIVE_TOPOLOGY_POINT_LIST. Each vertex defines a separate
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point.
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=== Separate Lines
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Individual line segments, each defined by a pair of vertices, are specified
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with pname:topology ename:VK_PRIMITIVE_TOPOLOGY_LINE_LIST. The first two
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vertices define the first segment, with subsequent pairs of vertices each
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defining one more segment. If the number of vertices is odd, then the last
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vertex is ignored.
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=== Line Strips
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A series of one or more connected line segments are specified with
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pname:topology ename:VK_PRIMITIVE_TOPOLOGY_LINE_STRIP. In this case, the
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first vertex specifies the first segment's start point while the second
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vertex specifies the first segment's endpoint and the second segment's start
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point. In general, the latexmath:[$i$]th vertex (for latexmath:[$i > 0$])
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specifies the beginning of the latexmath:[$i$]th segment and the end of the
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latexmath:[$i-1$]st. The last vertex specifies the end of the last segment.
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If only one vertex is specified, then no primitive is generated.
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=== Triangle Strips
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A triangle strip is a series of triangles connected along shared edges, and
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is specified with pname:topology ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP.
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In this case, the first three vertices define the first triangle, and their
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order is significant. Each subsequent vertex defines a new triangle using
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that point along with the last two vertices from the previous triangle, as
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shown in figure <<fig-triangles>>. If fewer than three vertices are
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specified, no primitive is produced. The order of vertices in successive
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triangles changes as shown in the figure, so that all triangle faces have
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the same orientation.
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[[fig-triangles]]
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.Triangle strips, fans, and lists
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image:images/triangles.{svgpdf}["Triangle strips, fans, and lists",{fullimagewidth}]
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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: Add full caption:
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* (a) A triangle strip.
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* (b) A triangle fan.
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* (c) Independent triangles.
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The numbers give the sequencing of the vertices in order within the vertex
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arrays. Note that in (a) and (b) triangle edge ordering is determined by the
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first triangle, while in (c) the order of each triangle's edges is
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independent of the other triangles.
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====
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endif::editing-notes[]
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=== Triangle Fans
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A triangle fan is specified with pname:topology
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ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_FAN. It is similar to a triangle strip,
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but changes the vertex replaced from the previous triangle as shown in
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figure <<fig-triangles>>, so that all triangles in the fan share a common
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vertex.
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=== Separate Triangles
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Separate triangles are specified with pname:topology
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ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST, as shown in figure
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<<fig-triangles>>. In this case, vertices latexmath:[$3i$],
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latexmath:[$3i+1$], and latexmath:[$3i+2$] vertices (in that order)
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determine a triangle for each latexmath:[$i=0,1,\ldots,n-1$], where there
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are latexmath:[$3n+k$] vertices drawn. latexmath:[$k$] is either 0, 1, or 2;
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if latexmath:[$k$] is not zero, the final latexmath:[$k$] vertices are
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ignored.
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=== Lines With Adjacency
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Lines with adjacency are specified with pname:topology
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ename:VK_PRIMITIVE_TOPOLOGY_LINE_LIST_WITH_ADJACENCY, and are independent
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line segments where each endpoint has a corresponding _adjacent_ vertex that
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is accessible in a <<geometry,geometry shader>>.
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If a geometry shader is not active, the adjacent vertices are ignored.
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A line segment is drawn from the latexmath:[$4 i+1$]st vertex to the
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latexmath:[$4 i+2$]nd vertex for each latexmath:[$i=0,1,\ldots, n-1$], where
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there are latexmath:[$4 n+k$] vertices. latexmath:[$k$] is either 0,
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1, 2, or 3; if latexmath:[$k$] is not zero, the final latexmath:[$k$]
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vertices are ignored. For line segment latexmath:[$i$], the latexmath:[$4
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i$]th and latexmath:[$4 i+3$]rd vertices are considered adjacent to the
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latexmath:[$4 i+1$]st and latexmath:[$4 i+2$]nd vertices, respectively, as
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shown in figure <<fig-lineadj>>.
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[[fig-lineadj]]
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.Lines with adjacency
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image:images/lineadj.{svgpdf}["Lines with adjacency",{fullimagewidth}]
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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: Add full caption:
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Lines with adjacency (a) and line strips with adjacency (b). The vertices
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connected with solid lines belong to the main primitives; the vertices
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connected by dashed lines are the adjacent vertices that are accessible in a
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geometry shader.
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====
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endif::editing-notes[]
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=== Line Strips With Adjacency
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Line strips with adjacency are specified with pname:topology
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ename:VK_PRIMITIVE_TOPOLOGY_LINE_STRIP_WITH_ADJACENCY and are similar to
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line strips, except that each line segment has a pair of adjacent vertices
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that are accessible in a geometry shader. If a geometry shader is not
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active, the adjacent vertices are ignored.
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A line segment is drawn from the latexmath:[$i+1$]st vertex to the
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latexmath:[$i+2$]nd vertex for each latexmath:[$i=0,1,\ldots, n-1$], where
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there are latexmath:[$n+3$] vertices. If there are fewer than four
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vertices, all vertices are ignored. For line segment latexmath:[$i$], the
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latexmath:[$i$]th and latexmath:[$i+3$]rd vertex are considered adjacent
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to the latexmath:[$i+1$]st and latexmath:[$i+2$]nd vertices, respectively,
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as shown in figure <<fig-lineadj>>.
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=== Triangle List With Adjacency
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Triangles with adjacency are specified with pname:topology
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ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST_WITH_ADJACENCY, and are similar to
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separate triangles except that each triangle edge has an adjacent vertex
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that is accessible in a geometry shader. If a geometry shader is not
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active, the adjacent vertices are ignored.
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The latexmath:[$6i$]th, latexmath:[$6i+2$]nd, and latexmath:[$6i+4$]th
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vertices (in that order) determine a triangle for each
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latexmath:[$i=0,1, \ldots, n-1$], where there are latexmath:[$6 n+k$]
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vertices. latexmath:[$k$] is either 0, 1, 2, 3, 4, or 5; if
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latexmath:[$k$] is non-zero, the final latexmath:[$k$] vertices are ignored.
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For triangle latexmath:[$i$], the latexmath:[$6 i+1$]st, latexmath:[$6
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i+3$]rd, and latexmath:[$6 i+5$]th vertices are considered adjacent to edges
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from the latexmath:[$6 i$]th to the latexmath:[$6 i+2$]nd, from the
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latexmath:[$6 i+2$]nd to the latexmath:[$6 i+4$]th, and from the
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latexmath:[$6 i+4$]th to the latexmath:[$6 i$]th vertices, respectively, as
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shown in figure <<fig-triadj>>.
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[[fig-triadj]]
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.Triangles with adjacency
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image:images/triadj.{svgpdf}["Triangles with adjacency",{fullimagewidth}]
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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: Add full caption:
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Triangles with adjacency. The vertices connected with solid lines belong
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to the main primitive; the vertices connected by dashed lines are the
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adjacent vertices that are accessible in a geometry shader.}
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====
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endif::editing-notes[]
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=== Triangle Strips With Adjacency
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Triangle strips with adjacency are specified with pname:topology
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ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP_WITH_ADJACENCY, and are similar
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to triangle strips except that each triangle edge has an adjacent vertex
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that is accessible in a geometry shader. If a geometry shader is not
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active, the adjacent vertices are ignored.
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In triangle strips with adjacency, latexmath:[$n$] triangles are drawn where
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there are latexmath:[$2(n+2)+k$] vertices. latexmath:[$k$] is
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either 0 or 1; if latexmath:[$k$] is 1, the final vertex is ignored. If
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there are fewer than 6 vertices, the entire primitive is ignored. Table
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<<trigenadj>> describes the vertices and order used to draw each triangle,
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and which vertices are considered adjacent to each edge of the triangle, as
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shown in figure <<fig-tstripadj>>.
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[[trigenadj]]
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.Triangles generated by triangle strips with adjacency.
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[options="header", cols="2,1,1,1,1,1,1"]
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|====
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| 3+| Primitive Vertices 3+| Adjacent Vertices
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| Primitive | 1st | 2nd | 3rd | 1/2 | 2/3 | 3/1
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| only (latexmath:[$i=0$], latexmath:[$n=1$]) | 0 | 2 | 4 | 1 | 5 | 3
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| first (latexmath:[$i=0$]) | 0 | 2 | 4 | 1 | 6 | 3
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| middle (latexmath:[$i$] odd) | latexmath:[$2 i+2$] | latexmath:[$2 i $] | latexmath:[$2 i+4$] | latexmath:[$2 i-2$] | latexmath:[$2 i+3$] | latexmath:[$2 i+6$]
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| middle (latexmath:[$i$] even) | latexmath:[$2 i $] | latexmath:[$2 i+2$] | latexmath:[$2 i+4$] | latexmath:[$2 i-2$] | latexmath:[$2 i+6$] | latexmath:[$2 i+3$]
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| last (latexmath:[$i=n-1$], latexmath:[$i$] odd) | latexmath:[$2 i+2$] | latexmath:[$2 i $] | latexmath:[$2 i+4$] | latexmath:[$2 i-2$] | latexmath:[$2 i+3$] | latexmath:[$2 i+5$]
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| last (latexmath:[$i=n-1$], latexmath:[$i$] even)| latexmath:[$2 i $] | latexmath:[$2 i+2$] | latexmath:[$2 i+4$] | latexmath:[$2 i-2$] | latexmath:[$2 i+5$] | latexmath:[$2 i+3$]
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|====
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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: Add full caption:
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Triangles generated by triangle strips with adjacency. Each triangle is
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drawn using the vertices whose numbers are in the *1st*, *2nd*, and *3rd*
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columns under *primitive vertices*, in that order. The vertices in the 1/2,
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2/3, and 3/1 columns under *adjacent vertices* are considered adjacent to
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the edges from the first to the second, from the second to the third, and
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from the third to the first vertex of the triangle, respectively. The six
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rows correspond to six cases: the first and only triangle latexmath:[$(i=0,
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n=1)$], the first triangle of several latexmath:[$(i=0, n>0)$], ``odd''
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middle triangles latexmath:[$(i=1,3,5 \ldots)$], ``even'' middle triangles
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latexmath:[$(i=2,4,6,\ldots)$], and special cases for the last triangle,
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when latexmath:[$i$] is either even or odd. For the purposes of this table,
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both the first vertex and first triangle are numbered latexmath:[$0$].
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====
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endif::editing-notes[]
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[[fig-tstripadj]]
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.Triangle strips with adjacency
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image:images/tstripadj.{svgpdf}["Triangle strips with adjacency",width="{svgpdf@pdf:400:800}"]
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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: Add full caption:
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Triangle strips with adjacency. The vertices connected with solid lines
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belong to the main primitives; the vertices connected by dashed lines are
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the adjacent vertices that are accessible in a geometry shader.
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====
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endif::editing-notes[]
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[[drawing-primitive-topologies-patches]]
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=== Separate Patches
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Separate patches are specified with pname:topology
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ename:VK_PRIMITIVE_TOPOLOGY_PATCH_LIST. A patch is an ordered collection of
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vertices used for <<tessellation,primitive tessellation>>. The
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vertices comprising a patch have no implied geometric ordering, and are used
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by tessellation shaders and the fixed-function tessellator to generate new
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point, line, or triangle primitives.
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Each patch in the series has a fixed number of vertices, specified by the
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pname:patchControlPoints member of the
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slink:VkPipelineTessellationStateCreateInfo structure passed to
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flink:vkCreateGraphicsPipelines. Once assembled and vertex shaded, these
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patches are provided as input to the tessellation control shader stage.
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If the number of vertices in a patch is given by latexmath:[$v$], the
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latexmath:[$v i$]th through latexmath:[$v i+v-1$]st vertices (in that
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order) determine a patch for each
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latexmath:[$i=0,1,\dots n-1$],
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where there are latexmath:[$v n+k$] vertices. latexmath:[$k$] is in the
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range latexmath:[$[0,v-1\]$]; if latexmath:[$k$] is not zero, the final
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latexmath:[$k$] vertices are ignored.
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=== General Considerations For Polygon Primitives
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Depending on the <<primsrast-polygonmode,polygon mode>>, a _polygon
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primitive_ generated from a drawing command with pname:topology
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ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_FAN,
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ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP,
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ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST,
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ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST_WITH_ADJACENCY, or
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ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP_WITH_ADJACENCY is rendered in
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one of several ways, such as outlining its border or filling its interior.
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The order of vertices in such a primitive is significant during
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<<primsrast-polygons-basic,polygon rasterization>> and
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<<shaders-fragment,fragment shading>>.
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== Programmable Primitive Shading
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Once primitives are assembled, they proceed to the vertex shading stage of
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the pipeline. If the draw includes multiple instances, then the set of
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primitives is sent to the vertex shading stage multiple times, once for each
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instance.
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It is undefined whether vertex shading occurs on vertices that are discarded
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as part of incomplete primitives, but if it does occur then it operates as
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if they were vertices in complete primitives and such invocations can: have
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side effects.
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Vertex shading receives two per-vertex inputs from the primitive assembly
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stage - the code:vertexIndex and the code:instanceIndex. How these values
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are generated is defined below, with each command.
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Drawing commands fall roughly into two categories:
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* Non-indexed drawing (fname:vkCmdDraw and fname:vkCmdDrawIndirect)
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commands present a sequential code:vertexIndex to the vertex shader. The
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sequential index is generated automatically by the device (see
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<<fxvertex,Fixed-Function Vertex Processing>> for details on both
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specifying the vertex attributes indexed by code:vertexIndex, as well as
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binding vertex buffers containing those attributes to a command buffer).
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* Indexed drawing commands (fname:vkCmdDrawIndexed and
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fname:vkCmdDrawIndexedIndirect) read index values from an _index buffer_ and use
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this to compute the code:vertexIndex value for the vertex shader.
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An index buffer is bound to a command buffer by calling:
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include::../protos/vkCmdBindIndexBuffer.txt[]
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* pname:commandBuffer is the command buffer into which the command is
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recorded.
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* pname:buffer is the buffer being bound.
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* pname:offset is the starting offset in bytes within pname:buffer used in
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index buffer address calculations.
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* pname:indexType selects whether indices are treated as 16 bits or 32
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bits. Possible values include:
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+
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include::../enums/VkIndexType.txt[]
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include::../validity/protos/vkCmdBindIndexBuffer.txt[]
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The parameters for each drawing command are specified directly in the
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command or read from buffer memory, depending on the command. Drawing
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commands that source their parameters from buffer memory are known as
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_indirect_ drawing commands.
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All drawing commands interact with the
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<<features-features-robustBufferAccess, Robust Buffer Access>> feature.
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[[drawing-primitive-assembly-apiorder]]
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Primitives assembled by draw commands are considered to have an
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<<fundamentals-queueoperation-apiorder,API order>>, which defines the order
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their fragments affect the framebuffer. When a draw command includes
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multiple instances, the lower numbered instances are earlier in API order.
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For non-indexed draws, primitives with lower numbered code:vertexIndex
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values are earlier in API order. For indexed draws, primitives assembled
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from lower index buffer addresses are earlier in API order.
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To record a non-indexed draw, call:
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include::../protos/vkCmdDraw.txt[]
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* pname:commandBuffer is the command buffer into which the command is
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recorded.
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* pname:vertexCount is the number of vertices to draw.
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* pname:instanceCount is the number of instances to draw.
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* pname:firstVertex is the index of the first vertex to draw.
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* pname:firstInstance is the instance ID of the first instance to draw.
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When the command is executed, primitives are assembled using the current
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primitive topology and pname:vertexCount consecutive vertex indices with the
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first code:vertexIndex value equal to pname:firstVertex. The primitives are
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drawn pname:instanceCount times with code:instanceIndex starting with
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pname:firstInstance and increasing sequentially for each instance. The
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assembled primitives execute the currently bound graphics pipeline.
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include::../validity/protos/vkCmdDraw.txt[]
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To record an indexed draw, call:
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include::../protos/vkCmdDrawIndexed.txt[]
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* pname:commandBuffer is the command buffer into which the command is
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recorded.
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* pname:indexCount is the number of vertices to draw.
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* pname:instanceCount is the number of instances to draw.
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* pname:firstIndex is the base index within the index buffer.
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* pname:vertexOffset is the value added to the vertex index before indexing
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into the vertex buffer.
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* pname:firstInstance is the instance ID of the first instance to draw.
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When the command is executed, primitives are assembled using the current
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primitive topology and pname:indexCount vertices whose indices are retrieved
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from the index buffer. The index buffer is treated as an array of tightly
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packed unsigned integers of size defined by the
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flink:vkCmdBindIndexBuffer::pname:indexType parameter with which the buffer
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was bound.
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The first vertex index is at an offset of pname:firstIndex * code:indexSize
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+ pname:offset within the currently bound index buffer, where pname:offset
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is the offset specified by fname:vkCmdBindIndexBuffer and code:indexSize is
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the byte size of the type specified by pname:indexType. Subsequent index
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values are retrieved from consecutive locations in the index buffer. Indices
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are first compared to the primitive restart value, then zero extended to 32
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bits (if the code:indexType is ename:VK_INDEX_TYPE_UINT16) and have
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pname:vertexOffset added to them, before being supplied as the
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code:vertexIndex value.
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The primitives are drawn pname:instanceCount times with code:instanceIndex
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starting with pname:firstInstance and increasing sequentially for each
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instance. The assembled primitives execute the currently bound graphics
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pipeline.
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include::../validity/protos/vkCmdDrawIndexed.txt[]
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A non-indexed indirect draw is recorded by calling:
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include::../protos/vkCmdDrawIndirect.txt[]
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* pname:commandBuffer is the command buffer into which the command is
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recorded.
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* pname:buffer is the buffer containing draw parameters.
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* pname:offset is the byte offset into pname:buffer where parameters
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begin.
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* pname:drawCount is the number of draws to execute, and can: be zero.
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* pname:stride is the byte stride between successive sets of draw
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parameters.
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fname:vkCmdDrawIndirect behaves similarly to flink:vkCmdDraw except that the
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parameters are read by the device from a buffer during execution.
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pname:drawCount draws are executed by the command, with parameters taken
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from pname:buffer starting at pname:offset and increasing by pname:stride
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bytes for each successive draw. The parameters of each draw are encoded in
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an array of slink:VkDrawIndirectCommand structures. If pname:drawCount is
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less than or equal to one, pname:stride is ignored.
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include::../validity/protos/vkCmdDrawIndirect.txt[]
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The sname:VkDrawIndirectCommand structure is defined as:
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include::../structs/VkDrawIndirectCommand.txt[]
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The members of sname:VkDrawIndirectCommand have the same meaning as the
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similarly named parameters of flink:vkCmdDraw.
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include::../validity/structs/VkDrawIndirectCommand.txt[]
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An indexed indirect draw is recorded by calling:
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include::../protos/vkCmdDrawIndexedIndirect.txt[]
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* pname:commandBuffer is the command buffer into which the command is
|
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recorded.
|
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* pname:buffer is the buffer containing draw parameters.
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* pname:offset is the byte offset into pname:buffer where parameters
|
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begin.
|
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* pname:drawCount is the number of draws to execute, and can: be zero.
|
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* pname:stride is the byte stride between successive sets of draw
|
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parameters.
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fname:vkCmdDrawIndexedIndirect behaves similarly to flink:vkCmdDrawIndirect
|
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except that the parameters are read by the device from a buffer during
|
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execution. pname:drawCount draws are executed by the command, with
|
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parameters taken from pname:buffer starting at pname:offset and increasing
|
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by pname:stride bytes for each successive draw. The parameters of each draw
|
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are encoded in an array of slink:VkDrawIndexedIndirectCommand structures. If
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pname:drawCount is less than or equal to one, pname:stride is ignored.
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|
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include::../validity/protos/vkCmdDrawIndexedIndirect.txt[]
|
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|
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The sname:VkDrawIndexedIndirectCommand structure is defined as:
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|
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include::../structs/VkDrawIndexedIndirectCommand.txt[]
|
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|
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The members of sname:VkDrawIndexedIndirectCommand have the same meaning as
|
|
the similarly named parameters of flink:vkCmdDrawIndexed.
|
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|
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include::../validity/structs/VkDrawIndexedIndirectCommand.txt[]
|