When a shader stage accesses buffer or image resources, as described in the Resource Descriptors section, the shader resource variables must be matched with the pipeline layout that is provided at pipeline creation time.
The set of shader resources that form the shader resource interface for a
stage are the variables statically used by OpEntryPoint
with the
storage class of Uniform
, UniformConstant
, or PushConstant
.
For the fragment shader, this includes the fragment input attachment interface.
The shader resource interface consists of two sub-interfaces: the push constant interface and the descriptor set interface.
The shader variables defined with a storage class of PushConstant
that
are statically used by the shader entry points for the pipeline define the
push constant interface.
They must be:
OpTypeStruct
,
Block
decoration, and
Offset
, ArrayStride
, and
MatrixStride
decorations as specified in
Offset and Stride Assignment.
There must be no more than one push constant block statically used per shader entry point.
Each variable in a push constant block must be placed at an Offset
such that the entire constant value is entirely contained within the
VkPushConstantRange
for each OpEntryPoint
that uses it, and the
stageFlags
for that range must specify the appropriate
VkShaderStageFlagBits
for that stage.
The Offset
decoration for any variable in a push constant block must
not cause the space required for that variable to extend outside the range
[0, maxPushConstantsSize
).
Any variable in a push constant block that is declared as an array must only be accessed with dynamically uniform indices.
The descriptor set interface is comprised of the shader variables with the
storage class of Uniform
or UniformConstant
(including the
variables in the fragment input attachment interface) that are statically used by the shader entry points for the
pipeline.
These variables must have DescriptorSet
and Binding
decorations
specified, which are assigned and matched with the
VkDescriptorSetLayout
objects in the pipeline layout as described in
DescriptorSet and Binding Assignment.
Variables identified with the UniformConstant
storage class are used
only as handles to refer to opaque resources.
Such variables must be typed as OpTypeImage
, OpTypeSampler
,
OpTypeSampledImage
, or arrays of only these types.
Variables of type OpTypeImage
must have a Sampled
operand of 1
(sampled image) or 2 (storage image).
Any array of these types must only be indexed with constant integral expressions, except under the following conditions:
OpTypeImage
variables with Sampled
operand of 2,
if the shaderStorageImageArrayDynamicIndexing
feature is enabled
and the shader module declares the StorageImageArrayDynamicIndexing
capability, the array must only be indexed by dynamically uniform
expressions.
OpTypeSampler
, OpTypeSampledImage
variables, or
OpTypeImage
variables with Sampled
operand of 1, if the
shaderSampledImageArrayDynamicIndexing
feature is enabled and the
shader module declares the SampledImageArrayDynamicIndexing
capability, the array must only be indexed by dynamically uniform
expressions.
The Sampled
Type
of an OpTypeImage
declaration must match
the same basic data type as the corresponding resource, or the values
obtained by reading or sampling from this image are undefined.
The Image
Format
of an OpTypeImage
declaration must not be
Unknown, for variables which are used for OpImageRead
or
OpImageWrite
operations, except under the following conditions:
OpImageWrite
, if the shaderStorageImageWriteWithoutFormat
feature is enabled and the shader module declares the
StorageImageWriteWithoutFormat
capability.
OpImageRead
, if the shaderStorageImageReadWithoutFormat
feature is enabled and the shader module declares the
StorageImageReadWithoutFormat
capability.
Variables identified with the Uniform
storage class are used to access
transparent buffer backed resources.
Such variables must be:
OpTypeStruct
, or arrays of only this type,
Block
or BufferBlock
decoration, and
Offset
, ArrayStride
, and
MatrixStride
decorations as specified in
Offset and Stride Assignment.
Any array of these types must only be indexed with constant integral expressions, except under the following conditions.
Block
variables, if the
shaderUniformBufferArrayDynamicIndexing
feature is enabled and the
shader module declares the UniformBufferArrayDynamicIndexing
capability, the array must only be indexed by dynamically uniform
expressions.
BufferBlock
variables, if the
shaderStorageBufferArrayDynamicIndexing
feature is enabled and the
shader module declares the StorageBufferArrayDynamicIndexing
capability, the array must only be indexed by dynamically uniform
expressions.
The Offset
decoration for any variable in a Block
must not cause
the space required for that variable to extend outside the range [0,
maxUniformBufferRange
).
The Offset
decoration for any variable in a BufferBlock
must not
cause the space required for that variable to extend outside the range
[0, maxStorageBufferRange
).
Variables identified with a storage class of UniformConstant
and a
decoration of InputAttachmentIndex
must be declared as described in
Fragment Input Attachment Interface.
Each shader variable declaration must refer to the same type of resource as
is indicated by the descriptorType
.
See Shader Resource and Descriptor Type Correspondence for the relationship between shader declarations and
descriptor types.
Table 14.2. Shader Resource and Descriptor Type Correspondence
Resource type | Descriptor Type |
---|---|
sampler |
|
sampled image |
|
storage image |
|
combined image sampler |
|
uniform texel buffer |
|
storage texel buffer |
|
uniform buffer |
|
storage buffer |
|
input attachment |
|
Table 14.3. Shader Resource and Storage Class Correspondence
Resource type | Storage Class | Type | Decoration(s)1 |
---|---|---|---|
sampler |
|
| |
sampled image |
|
| |
storage image |
|
| |
combined image sampler |
|
| |
uniform texel buffer |
|
| |
storage texel buffer |
|
| |
uniform buffer |
|
|
|
storage buffer |
|
|
|
input attachment |
|
|
|
DescriptorSet
and Binding
A variable identified with a DescriptorSet
decoration of s and a
Binding
decoration of b indicates that this variable is
associated with the VkDescriptorSetLayoutBinding
that has a
binding
equal to b in pSetLayouts
[s] that was specified
in VkPipelineLayoutCreateInfo
.
The range of descriptor sets is between zero and
maxBoundDescriptorSets
minus one.
If a descriptor set value is statically used by an entry point there must
be an associated pSetLayout
in the corresponding pipeline layout as
described in Pipeline Layouts consistency.
If the Binding
decoration is used with an array, the entire array is
identified with that binding value.
The size of the array declaration must be no larger than the
descriptorCount
of that VkDescriptorSetLayoutBinding
.
The index of each element of the array is referred to as the arrayElement.
For the purposes of interface matching and descriptor set
operations, if a resource variable is not an
array, it is treated as if it has an arrayElement of zero.
The binding can be any 32-bit unsigned integer value, as described in Section 13.2.1, “Descriptor Set Layout”. Each descriptor set has its own binding name space.
There is a limit on the number of resources of each type that can be accessed by a pipeline stage as shown in Shader Resource Limits. The “Resources Per Stage” column gives the limit on the number each type of resource that can be statically used for an entry point in any given stage in a pipeline. The “Resource Types” column lists which resource types are counted against the limit. Some resource types count against multiple limits.
If multiple entry points in the same pipeline refer to the same set and
binding, all variable definitions with that DescriptorSet
and
Binding
must have the same basic type.
Not all descriptor sets and bindings specified in a pipeline layout need to
be used in a particular shader stage or pipeline, but if a
DescriptorSet
and Binding
decoration is specified for a variable
that is statically used in that shader there must be a pipeline layout
entry identified with that descriptor set and binding
and the
corresponding stageFlags
must specify the appropriate
VkShaderStageFlagBits
for that stage.
Table 14.4. Shader Resource Limits
Resources per Stage | Resource Types |
---|---|
| sampler |
combined image sampler | |
| sampled image |
combined image sampler | |
uniform texel buffer | |
| storage image |
storage texel buffer | |
| uniform buffer |
uniform buffer dynamic | |
| storage buffer |
storage buffer dynamic | |
| input attachment1 |
All variables with a storage class of PushConstant
or Uniform
must be explicitly laid out using the Offset
, ArrayStride
, and
MatrixStride
decorations.
There are two different layouts requirements depending on the specific
resources.
Standard Uniform Buffer Layout
Member variables of an OpTypeStruct
with storage class of Uniform
and a decoration of Block
(uniform buffers) must be laid out according
to the following rules.
The Offset
Decoration must be a multiple of its base alignment,
computed recursively as follows:
ArrayStride
or MatrixStride
decoration must be an integer
multiple of the base alignment of the array or matrix from above.
Offset
Decoration of a member must not place it between the
end of a structure or an array and the next multiple of the base
alignment of that structure or array.
Offset
Decorations need not follow member
declaration order.
![]() | Note |
---|---|
The std140 layout in GLSL satisfies these rules. |
Standard Storage Buffer Layout
Member variables of an OpTypeStruct
with a storage class of
PushConstant
(push constants), or a storage class of Uniform
with
a decoration of BufferBlock
(storage buffers) must be laid out as
above, except for array and structure
base alignment which do not need to be rounded up to a multiple of 16.
![]() | Note |
---|---|
The std430 layout in GLSL satisfies these rules. |