456 lines
22 KiB
Plaintext
456 lines
22 KiB
Plaintext
// Copyright (c) 2015-2016 The Khronos Group Inc.
|
|
// Copyright notice at https://www.khronos.org/registry/speccopyright.html
|
|
|
|
[[fxvertex]]
|
|
= Fixed-Function Vertex Processing
|
|
|
|
Some implementations have specialized fixed-function hardware for fetching
|
|
and format-converting vertex input data from buffers, rather than performing
|
|
the fetch as part of the vertex shader. {apiname} includes a vertex
|
|
attribute fetch stage in the graphics pipeline in order to take advantage of
|
|
this.
|
|
|
|
|
|
[[fxvertex-attrib]]
|
|
== Vertex Attributes
|
|
|
|
Vertex shaders can: define input variables, which receive _vertex attribute_
|
|
data transferred from one or more sname:VkBuffer(s) by drawing commands.
|
|
Vertex shader input variables are bound to buffers via an indirect binding
|
|
where the vertex shader associates a _vertex input attribute_ number with
|
|
each variable, vertex input attributes are associated to _vertex input
|
|
bindings_ on a per-pipeline basis, and vertex input bindings are associated
|
|
with specific buffers on a per-draw basis via the
|
|
fname:vkCmdBindVertexBuffers command. Vertex input attribute and vertex
|
|
input binding descriptions also contain format information controlling how
|
|
data is extracted from buffer memory and converted to the format expected by
|
|
the vertex shader.
|
|
|
|
There are sname:VkPhysicalDeviceLimits::pname:maxVertexInputAttributes
|
|
number of vertex input attributes and
|
|
sname:VkPhysicalDeviceLimits::pname:maxVertexInputBindings number of
|
|
vertex input bindings (each referred to
|
|
by zero-based indices), where there are at least as many vertex input
|
|
attributes as there are vertex input bindings. Applications can: store
|
|
multiple vertex input attributes interleaved in a single buffer, and use a
|
|
single vertex input binding to access those attributes.
|
|
|
|
In GLSL, vertex shaders associate input variables with a vertex input
|
|
attribute number using the code:location layout qualifier. The
|
|
code:component layout qualifier associates components of a vertex shader
|
|
input variable with components of a vertex input attribute.
|
|
|
|
.GLSL example
|
|
[source,{basebackend@docbook:c:glsl}]
|
|
---------------------------------------------------
|
|
// Assign location M to variableName
|
|
layout (location=M, component=2) in vec2 variableName;
|
|
|
|
// Assign locations [N,N+L) to the array elements of variableNameArray
|
|
layout (location=N) in vec4 variableNameArray[L];
|
|
---------------------------------------------------
|
|
|
|
In SPIR-V, vertex shaders associate input variables with a vertex input
|
|
attribute number using the code:Location decoration. The code:Component
|
|
decoration associates components of a vertex shader input variable with
|
|
components of a vertex input attribute. The code:Location and code:Component
|
|
decorations are specified via the code:OpDecorate instruction.
|
|
|
|
.SPIR-V example
|
|
---------------------------------------------------
|
|
...
|
|
%1 = OpExtInstImport "GLSL.std.450"
|
|
...
|
|
OpName %9 "variableName"
|
|
OpName %15 "variableNameArray"
|
|
OpName %18 "gl_VertexID"
|
|
OpName %19 "gl_InstanceID"
|
|
OpDecorate %9 Location M
|
|
OpDecorate %9 Component 2
|
|
OpDecorate %15 Location N
|
|
...
|
|
%2 = OpTypeVoid
|
|
%3 = OpTypeFunction %2
|
|
%6 = OpTypeFloat 32
|
|
%7 = OpTypeVector %6 2
|
|
%8 = OpTypePointer Input %7
|
|
%9 = OpVariable %8 Input
|
|
%10 = OpTypeVector %6 4
|
|
%11 = OpTypeInt 32 0
|
|
%12 = OpConstant %11 L
|
|
%13 = OpTypeArray %10 %12
|
|
%14 = OpTypePointer Input %13
|
|
%15 = OpVariable %14 Input
|
|
...
|
|
---------------------------------------------------
|
|
|
|
|
|
[[fxvertex-attrib-location]]
|
|
=== Attribute Location and Component Assignment
|
|
|
|
Vertex shaders allow code:Location and code:Component decorations on
|
|
input variable declarations. The code:Location decoration specifies which
|
|
vertex input attribute is used to read and interpret the data that
|
|
a variable will consume. The code:Component decoration allows the location
|
|
to be more finely specified for scalars and vectors, down to the
|
|
individual components within a location that are consumed. The
|
|
components within a location are 0, 1, 2, and 3. A variable starting
|
|
at component N will consume components N, N+1, N+2, ... up through
|
|
its size. For single precision types, it is invalid if the sequence
|
|
of components gets larger than 3.
|
|
|
|
When a vertex shader input variable declared using a scalar or vector
|
|
32-bit data type is assigned a location, its value(s) are taken from
|
|
the components of the input attribute specified with the corresponding
|
|
sname:VkVertexInputAttributeDescription::pname:location.
|
|
The components used depend on the type of variable and the
|
|
code:Component decoration specified in the variable declaration,
|
|
as identified in <<fxvertex-attrib-components>>. Any 32-bit scalar
|
|
or vector input will consume a single location. For 32-bit data types,
|
|
missing components are filled in with default values as described
|
|
<<fxvertex-input-extraction,below>>.
|
|
|
|
|
|
[[fxvertex-attrib-components]]
|
|
.Input attribute components accessed by 32-bit input variables
|
|
[width="65%",cols="<5,<3,<3",options="header"]
|
|
|=============================================
|
|
| 32-bit data type | code:Component decoration | Components consumed
|
|
| scalar | 0 or unspecified | (x, o, o, o)
|
|
| scalar | 1 | (o, y, o, o)
|
|
| scalar | 2 | (o, o, z, o)
|
|
| scalar | 3 | (o, o, o, w)
|
|
| two-component vector | 0 or unspecified | (x, y, o, o)
|
|
| two-component vector | 1 | (o, y, z, o)
|
|
| two-component vector | 2 | (o, o, z, w)
|
|
| three-component vector| 0 or unspecified | (x, y, z, o)
|
|
| three-component vector| 1 | (o, y, z, w)
|
|
| four-component vector | 0 or unspecified | (x, y, z, w)
|
|
|=============================================
|
|
|
|
Components indicated by `o' are available for use by other input variables
|
|
which are sourced from the same attribute, and if used, are either filled
|
|
with the corresponding component from the input format (if present), or
|
|
the default value.
|
|
|
|
When a vertex shader input variable declared using a 32-bit floating point
|
|
matrix type is assigned a location _i_, its values are taken from
|
|
consecutive input attributes starting with the corresponding
|
|
sname:VkVertexInputAttributeDescription::pname:location. Such matrices are
|
|
treated as an array of column vectors with values taken from the input
|
|
attributes identified in <<fxvertex-attrib-matrix>>. The
|
|
sname:VkVertexInputAttributeDescription::pname:format must: be specified
|
|
with a elink:VkFormat that corresponds to the appropriate type of column
|
|
vector. The code:Component decoration mustnot: be used with matrix types.
|
|
|
|
[[fxvertex-attrib-matrix]]
|
|
.Input attributes accessed by 32-bit input matrix variables
|
|
[width="100%",cols="<10%,<24%,<21%,<45%",options="header"]
|
|
|=============================================
|
|
| Data type | Column vector type | Locations consumed | Components consumed
|
|
| mat2 | two-component vector | i, i+1 | (x, y, o, o), (x, y, o, o)
|
|
| mat2x3 | three-component vector | i, i+1 | (x, y, z, o), (x, y, z, o)
|
|
| mat2x4 | four-component vector | i, i+1 | (x, y, z, w), (x, y, z, w)
|
|
| mat3x2 | two-component vector | i, i+1, i+2 | (x, y, o, o), (x, y, o, o), (x, y, o, o)
|
|
| mat3 | three-component vector | i, i+1, i+2 | (x, y, z, o), (x, y, z, o), (x, y, z, o)
|
|
| mat3x4 | four-component vector | i, i+1, i+2 | (x, y, z, w), (x, y, z, w), (x, y, z, w)
|
|
| mat4x2 | two-component vector | i, i+1, i+2, i+3 | (x, y, o, o), (x, y, o, o), (x, y, o, o), (x, y, o, o)
|
|
| mat4x3 | three-component vector | i, i+1, i+2, i+3 | (x, y, z, o), (x, y, z, o), (x, y, z, o), (x, y, z, o)
|
|
| mat4 | four-component vector | i, i+1, i+2, i+3 | (x, y, z, w), (x, y, z, w), (x, y, z, w), (x, y, z, w)
|
|
|=============================================
|
|
|
|
Components indicated by `o' are available for use by other input variables
|
|
which are sourced from the same attribute, and if used, are either filled
|
|
with the corresponding component from the input (if present), or
|
|
the default value.
|
|
|
|
When a vertex shader input variable declared using a scalar or vector
|
|
64-bit data type is assigned a location _i_, its values are taken from
|
|
consecutive input attributes starting with the corresponding
|
|
sname:VkVertexInputAttributeDescription::pname:location. The locations
|
|
and components used depend on the type of variable and the code:Component
|
|
decoration specified in the variable declaration, as identified in
|
|
<<fxvertex-attrib-double>>. For 64-bit data types, no default
|
|
attribute values are provided. Input variables mustnot: use more
|
|
components than provided by the attribute. Input attributes which have
|
|
one- or two-component 64-bit formats will consume a single location.
|
|
Input attributes which have three- or four-component 64-bit formats
|
|
will consume two consecutive locations. A 64-bit scalar
|
|
data type will consume two components, and a 64-bit two-component
|
|
vector data type will consume all four components available within
|
|
a location. A three- or four-component 64-bit data type mustnot:
|
|
specify a component. A three-component 64-bit data type will consume
|
|
all four components of the first location and components 0 and 1 of
|
|
the second location. This leaves components 2 and 3 available for
|
|
other component-qualified declarations. A four-component 64-bit
|
|
data type will consume all four components of the first location
|
|
and all four components of the second location. It is invalid for
|
|
a scalar or two-component 64-bit data type to specify a component
|
|
of 1 or 3.
|
|
|
|
[[fxvertex-attrib-double]]
|
|
.Input attribute locations and components accessed by 64-bit input variables
|
|
[width="100%",cols="<18%,^12%,<25%,^14%,^18%,<13%",options="header"]
|
|
|=============================================
|
|
^.^| Input format | Locations consumed
|
|
^.^| 64-bit data type |code:Location decoration |code:Component decoration ^| 32-bit components consumed
|
|
| R64 | i
|
|
| scalar | i | 0 or unspecified | (x, y, -, -)
|
|
.3+<.^| R64G64 .3+^.^| i
|
|
| scalar | i | 0 or unspecified | (x, y, o, o)
|
|
| scalar | i | 2 | (o, o, z, w)
|
|
| two-component vector | i | 0 or unspecified | (x, y, z, w)
|
|
.5+<.^| R64G64B64 .5+^.^| i, i+1
|
|
| scalar | i | 0 or unspecified | (x, y, o, o), (o, o, -, -)
|
|
| scalar | i | 2 | (o, o, z, w), (o, o, -, -)
|
|
| scalar | i+1 | 0 or unspecified | (o, o, o, o), (x, y, -, -)
|
|
| two-component vector | i | 0 or unspecified | (x, y, z, w), (o, o, -, -)
|
|
| three-component vector | i | unspecified | (x, y, z, w), (x, y, -, -)
|
|
.8+<.^| R64G64B64A64 .8+^.^| i, i+1
|
|
| scalar | i | 0 or unspecified | (x, y, o, o), (o, o, o, o)
|
|
| scalar | i | 2 | (o, o, z, w), (o, o, o, o)
|
|
| scalar | i+1 | 0 or unspecified | (o, o, o, o), (x, y, o, o)
|
|
| scalar | i+1 | 2 | (o, o, o, o), (o, o, z, w)
|
|
| two-component vector | i | 0 or unspecified | (x, y, z, w), (o, o, o, o)
|
|
| two-component vector | i+1 | 0 or unspecified | (o, o, o, o), (x, y, z, w)
|
|
| three-component vector | i | unspecified | (x, y, z, w), (x, y, o, o)
|
|
| four-component vector | i | unspecified | (x, y, z, w), (x, y, z, w)
|
|
|=============================================
|
|
|
|
Components indicated by `o' are available for use by other input variables
|
|
which are sourced from the same attribute.
|
|
Components indicated by `-' are not available for input variables
|
|
as there are no default values provided for 64-bit data types, and
|
|
there is no data provided by the input format.
|
|
|
|
When a vertex shader input variable declared using a 64-bit floating-point
|
|
matrix type is assigned a location _i_, its values are taken from
|
|
consecutive input attribute locations. Such matrices are treated as an array
|
|
of column vectors with values taken from the input attributes as shown in
|
|
<<fxvertex-attrib-double>>. Each column vector starts at the location
|
|
immediately following the last location of the previous column vector. The
|
|
number of attributes and components assigned to each matrix is determined by
|
|
the matrix dimensions and ranges from two to eight locations.
|
|
|
|
When a vertex shader input variable declared using an array type
|
|
is assigned a location, its values are taken from consecutive
|
|
input attributes starting with the corresponding
|
|
sname:VkVertexInputAttributeDescription::pname:location. The number
|
|
of attributes and components assigned to each element are determined
|
|
according to the data type of the array elements and code:Component
|
|
decoration (if any) specified in the declaration of the array, as described
|
|
above. Each element of the array, in order, is assigned to consecutive
|
|
locations, but all at the same specified component within each location.
|
|
|
|
Only input variables declared with the data types and component decorations
|
|
as specified above are supported. _Location aliasing_ is
|
|
causing two variables to have the same location number. _Component aliasing_
|
|
is assigning the same (or overlapping) component number for
|
|
two location aliases. Location aliasing is allowed only if it does
|
|
not cause component aliasing. Further, when location aliasing, the
|
|
aliases sharing the location must: have the same underlying numerical
|
|
type (floating-point or integer). Failure to meet these requirements
|
|
will result in an invalid pipeline.
|
|
|
|
|
|
|
|
[[fxvertex-input]]
|
|
== Vertex Input Description
|
|
|
|
Applications specify vertex input attribute and vertex input binding
|
|
descriptions as part of graphics pipeline creation, via the
|
|
pname:pVertexInputState member of sname:VkGraphicsPipelineCreateInfo, which
|
|
is of type sname:VkPipelineVertexInputStateCreateInfo:
|
|
|
|
include::../structs/VkPipelineVertexInputStateCreateInfo.txt[]
|
|
|
|
The members of sname:VkPipelineVertexInputStateCreateInfo have the following
|
|
meanings:
|
|
|
|
* 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:vertexBindingDescriptionCount is the number of vertex binding
|
|
descriptions provided in pname:pVertexBindingDescriptions.
|
|
* pname:pVertexBindingDescriptions is a pointer to an array of
|
|
sname:VkVertexInputBindingDescription structures.
|
|
* pname:vertexAttributeDescriptionCount is the number of vertex attribute
|
|
descriptions provided in pname:pVertexAttributeDescriptions.
|
|
* pname:pVertexAttributeDescriptions is a pointer to an array of
|
|
sname:VkVertexInputAttributeDescription structures.
|
|
|
|
include::../validity/structs/VkPipelineVertexInputStateCreateInfo.txt[]
|
|
|
|
Each vertex input binding is specified by an instance of the
|
|
sname:VkVertexInputBindingDescription structure:
|
|
|
|
include::../structs/VkVertexInputBindingDescription.txt[]
|
|
|
|
The members of sname:VkVertexInputBindingDescription have the following
|
|
meanings:
|
|
|
|
* pname:binding is the binding number that this structure
|
|
describes.
|
|
* pname:stride is the distance in bytes between two
|
|
consecutive elements within the buffer.
|
|
* pname:inputRate is a elink:VkVertexInputRate value that specifies
|
|
whether vertex attribute addressing is a function of the vertex index or
|
|
of the instance index.
|
|
|
|
include::../validity/structs/VkVertexInputBindingDescription.txt[]
|
|
|
|
The definition of elink:VkVertexInputRate is:
|
|
|
|
include::../enums/VkVertexInputRate.txt[]
|
|
|
|
The values of elink:VkVertexInputRate have the following meanings:
|
|
|
|
* ename:VK_VERTEX_INPUT_RATE_VERTEX indicates that vertex attribute
|
|
addressing is a function of the vertex index.
|
|
* ename:VK_VERTEX_INPUT_RATE_INSTANCE indicates that vertex attribute
|
|
addressing is a function of the instance index.
|
|
|
|
Each vertex input attribute is specified by an instance of the
|
|
sname:VkVertexInputAttributeDescription structure:
|
|
|
|
include::../structs/VkVertexInputAttributeDescription.txt[]
|
|
|
|
The members of sname:VkVertexInputAttributeDescription have the following
|
|
meanings:
|
|
|
|
* pname:location is the shader binding location number for this
|
|
attribute.
|
|
* pname:binding is the binding number which this attribute takes
|
|
its data from.
|
|
* pname:format is the size and type of the vertex attribute data.
|
|
* pname:offset is a byte offset of this attribute relative
|
|
to the start of an element in the vertex input binding.
|
|
|
|
include::../validity/structs/VkVertexInputAttributeDescription.txt[]
|
|
|
|
Vertex buffers are bound to a command buffer for use in subsequent draw
|
|
commands by calling:
|
|
|
|
include::../protos/vkCmdBindVertexBuffers.txt[]
|
|
|
|
* pname:commandBuffer is the command buffer into which the command is
|
|
recorded.
|
|
* pname:firstBinding is the index of the first vertex input binding whose
|
|
state is updated by the command.
|
|
* pname:bindingCount is the number of vertex input 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.
|
|
|
|
The values taken from elements latexmath:[$i$] of pname:pBuffers and
|
|
pname:pOffsets replace the current state for the vertex input binding
|
|
latexmath:[$\mathit{firstBinding}+i$], for latexmath:[$i$] in
|
|
latexmath:[$[0, bindingCount)$]. The vertex input binding is updated to
|
|
start at the offset indicated by pname:pOffsets[i] from the start of the
|
|
buffer pname:pBuffers[i]. All vertex input attributes that use each of these
|
|
bindings will use these updated addresses in their address calculations for
|
|
subsequent draw commands.
|
|
|
|
include::../validity/protos/vkCmdBindVertexBuffers.txt[]
|
|
|
|
The address of each attribute for each code:vertexIndex and
|
|
code:instanceIndex is calculated as follows:
|
|
|
|
- Let attribDesc be the member of
|
|
sname:VkPipelineVertexInputStateCreateInfo::pname:pVertexAttributeDescriptions
|
|
with sname:VkVertexInputAttributeDescription::pname:location equal to
|
|
the vertex input attribute number.
|
|
- Let bindingDesc be the member of
|
|
sname:VkPipelineVertexInputStateCreateInfo::pname:pVertexBindingDescriptions
|
|
with sname:VkVertexInputAttributeDescription::pname:binding equal to
|
|
attribDesc.binding.
|
|
- Let code:vertexIndex be the index of the vertex within the draw (a value
|
|
between pname:firstVertex and pname:firstVertex+pname:vertexCount for
|
|
fname:vkCmdDraw, or a value taken from the index buffer for
|
|
fname:vkCmdDrawIndexed), and let code:instanceIndex be the instance
|
|
number of the draw (a value between pname:firstInstance and
|
|
pname:firstInstance+pname:instanceCount).
|
|
|
|
[source,c]
|
|
---------------------------------------------------
|
|
bufferBindingAddress = buffer[binding].baseAddress + offset[binding];
|
|
|
|
if (bindingDesc.inputRate == VK_VERTEX_INPUT_RATE_VERTEX)
|
|
vertexOffset = vertexIndex * bindingDesc.stride;
|
|
else
|
|
vertexOffset = instanceIndex * bindingDesc.stride;
|
|
|
|
attribAddress = bufferBindingAddress + vertexOffset + attribDesc.offset;
|
|
---------------------------------------------------
|
|
|
|
[[fxvertex-input-extraction]]
|
|
For each attribute, raw data is extracted starting at `attribAddress` and is
|
|
converted from the sname:VkVertexInputAttributeDescription's pname:format to
|
|
either to floating-point, unsigned integer, or signed integer based on the
|
|
base type of the format; the base type of the format must: match the base
|
|
type of the input variable in the shader. If pname:format is a packed
|
|
format, `attribAddress` must: be a multiple of the size in bytes of the
|
|
whole attribute data type as described in <<features-formats-packed,Packed
|
|
Formats>>. Otherwise, `attribAddress` must: be a multiple of the size in
|
|
bytes of the component type indicated by pname:format (see
|
|
<<features-formats,Formats>>). If the format does not include G, B, or A
|
|
components, then those are filled with (0,0,1) as needed (using either 1.0f
|
|
or integer 1 based on the format) for attributes that are not 64-bit data
|
|
types. The number of components in the vertex shader input variable need not
|
|
exactly match the number of components in the format. If the vertex shader
|
|
has fewer components, the extra components are discarded.
|
|
|
|
|
|
[[fxvertex-example]]
|
|
== Example
|
|
|
|
To create a graphics pipeline that uses the following vertex description:
|
|
|
|
[source,{basebackend@docbook:c++:cpp}]
|
|
---------------------------------------------------
|
|
struct Vertex
|
|
{
|
|
float x, y, z, w;
|
|
uint8_t u, v;
|
|
};
|
|
---------------------------------------------------
|
|
|
|
The application could use the following set of structures:
|
|
|
|
[source,{basebackend@docbook:c++:cpp}]
|
|
---------------------------------------------------
|
|
const VkVertexInputBindingDescription binding =
|
|
{
|
|
0, // binding
|
|
sizeof(Vertex), // stride
|
|
VK_VERTEX_INPUT_RATE_VERTEX // inputRate
|
|
};
|
|
|
|
const VkVertexInputAttributeDescription attributes[] =
|
|
{
|
|
{
|
|
0, // location
|
|
binding.binding, // binding
|
|
VK_FORMAT_R32G32B32A32_SFLOAT, // format
|
|
0 // offset
|
|
},
|
|
{
|
|
1, // location
|
|
binding.binding, // binding
|
|
VK_FORMAT_R8G8_UNORM, // format
|
|
4 * sizeof(float) // offset
|
|
}
|
|
};
|
|
|
|
const VkPipelineVertexInputStateCreateInfo viInfo =
|
|
{
|
|
VK_STRUCTURE_TYPE_PIPELINE_VERTEX_INPUT_CREATE_INFO, // sType
|
|
NULL, // pNext
|
|
0, // flags
|
|
1, // vertexBindingDescriptionCount
|
|
&binding, // pVertexBindingDescriptions
|
|
2, // vertexAttributeDescriptionCount
|
|
&attributes[0] // pVertexAttributeDescriptions
|
|
};
|
|
---------------------------------------------------
|