// 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 value of the code:Component decoration specified in the variable declaration, as identified in <>. 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-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 <>. 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 <>. 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 <>. 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 compenent 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 <>. Otherwise, `attribAddress` must: be a multiple of the size in bytes of the component type indicated by pname:format (see <>). 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 }; ---------------------------------------------------