Vulkan-Docs/doc/specs/vulkan/chapters/renderpass.txt

// Copyright (c) 2015-2017 The Khronos Group Inc.
// Copyright notice at https://www.khronos.org/registry/speccopyright.html

[[renderpass]]
= Render Pass

// refBegin VkRenderPass Opaque handle to a render pass object

A _render pass_ represents a collection of attachments, subpasses, and
dependencies between the subpasses, and describes how the attachments are
used over the course of the subpasses.
The use of a render pass in a command buffer is a _render pass instance_.

Render passes are represented by sname:VkRenderPass handles:

include::../api/handles/VkRenderPass.txt[]

// refEnd VkRenderPass

An _attachment description_ describes the properties of an attachment
including its format, sample count, and how its contents are treated at the
beginning and end of each render pass instance.

[[renderpass-subpass]]
A _subpass_ represents a phase of rendering that reads and writes a subset
of the attachments in a render pass.
Rendering commands are recorded into a particular subpass of a render pass
instance.

A _subpass description_ describes the subset of attachments that is involved
in the execution of a subpass.
Each subpass can: read from some attachments as _input attachments_, write
to some as _color attachments_ or _depth/stencil attachments_, and perform
_multisample resolve operations_ to _resolve attachments_.
A subpass description can: also include a set of _preserve attachments_,
which are attachments that are not read or written by the subpass but whose
contents must: be preserved throughout the subpass.

A subpass _uses an attachment_ if the attachment is a color, depth/stencil,
resolve, or input attachment for that subpass (as determined by the
pname:pColorAttachments, pname:pDepthStencilAttachment,
pname:pResolveAttachments, and pname:pInputAttachments members of
slink:VkSubpassDescription, respectively).
A subpass does not use an attachment if that attachment is preserved by the
subpass.
The _first use of an attachment_ is in the lowest numbered subpass that uses
that attachment.
Similarly, the _last use of an attachment_ is in the highest numbered
subpass that uses that attachment.

The subpasses in a render pass all render to the same dimensions, and
fragments for pixel (x,y,layer) in one subpass can: only read attachment
contents written by previous subpasses at that same (x,y,layer) location.

[NOTE]
.Note
====
By describing a complete set of subpasses in advance, render passes provide
the implementation an opportunity to optimize the storage and transfer of
attachment data between subpasses.

In practice, this means that subpasses with a simple framebuffer-space
dependency may: be merged into a single tiled rendering pass, keeping the
attachment data on-chip for the duration of a render pass instance.
However, it is also quite common for a render pass to only contain a single
subpass.
====

_Subpass dependencies_ describe <<synchronization-dependencies, execution
and memory dependencies>> between subpasses.

A _subpass dependency chain_ is a sequence of subpass dependencies in a
render pass, where the source subpass of each subpass dependency (after the
first) equals the destination subpass of the previous dependency.

Execution of subpasses may: overlap or execute out of order with regards to
other subpasses, unless otherwise enforced by an execution dependency.
Each subpass only respects <<synchronization-submission-order, submission
order>> for commands recorded in the same subpass, and the
flink:vkCmdBeginRenderPass and flink:vkCmdEndRenderPass commands that
delimit the render pass - commands within other subpasses are not included.
This affects most other <<synchronization-implicit, implicit ordering
guarantees>>.

A render pass describes the structure of subpasses and attachments
independent of any specific image views for the attachments.
The specific image views that will be used for the attachments, and their
dimensions, are specified in sname:VkFramebuffer objects.
Framebuffers are created with respect to a specific render pass that the
framebuffer is compatible with (see <<renderpass-compatibility,Render Pass
Compatibility>>).
Collectively, a render pass and a framebuffer define the complete render
target state for one or more subpasses as well as the algorithmic
dependencies between the subpasses.

The various pipeline stages of the drawing commands for a given subpass may:
execute concurrently and/or out of order, both within and across drawing
commands, whilst still respecting <<synchronization-pipeline-stages-order,
pipeline order>>.
However for a given (x,y,layer,sample) sample location, certain per-sample
operations are performed in <<primrast-order,rasterization order>>.


[[renderpass-creation]]
== Render Pass Creation

// refBegin vkCreateRenderPass Create a new render pass object

To create a render pass, call:

include::../api/protos/vkCreateRenderPass.txt[]

  * pname:device is the logical device that creates the render pass.
  * pname:pCreateInfo is a pointer to an instance of the
    slink:VkRenderPassCreateInfo structure that describes the parameters of
    the render pass.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pRenderPass points to a sname:VkRenderPass handle in which the
    resulting render pass object is returned.

include::../validity/protos/vkCreateRenderPass.txt[]

// refBegin VkRenderPassCreateInfo Structure specifying parameters of a newly created render pass

The sname:VkRenderPassCreateInfo structure is defined as:

include::../api/structs/VkRenderPassCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:flags is reserved for future use.
  * pname:attachmentCount is the number of attachments used by this render
    pass, or zero indicating no attachments.
    Attachments are referred to by zero-based indices in the range
    [0,pname:attachmentCount).
  * pname:pAttachments points to an array of pname:attachmentCount number of
    slink:VkAttachmentDescription structures describing properties of the
    attachments, or `NULL` if pname:attachmentCount is zero.
  * pname:subpassCount is the number of subpasses to create for this render
    pass.
    Subpasses are referred to by zero-based indices in the range
    [0,pname:subpassCount).
    A render pass must: have at least one subpass.
  * pname:pSubpasses points to an array of pname:subpassCount number of
    slink:VkSubpassDescription structures describing properties of the
    subpasses.
  * pname:dependencyCount is the number of dependencies between pairs of
    subpasses, or zero indicating no dependencies.
  * pname:pDependencies points to an array of pname:dependencyCount number
    of slink:VkSubpassDependency structures describing dependencies between
    pairs of subpasses, or `NULL` if pname:dependencyCount is zero.

.Valid Usage
****
  * If any two subpasses operate on attachments with overlapping ranges of
    the same sname:VkDeviceMemory object, and at least one subpass writes to
    that area of sname:VkDeviceMemory, a subpass dependency must: be
    included (either directly or via some intermediate subpasses) between
    them
  * If the pname:attachment member of any element of
    pname:pInputAttachments, pname:pColorAttachments,
    pname:pResolveAttachments or pname:pDepthStencilAttachment, or the
    attachment indexed by any element of pname:pPreserveAttachments in any
    given element of pname:pSubpasses is bound to a range of a
    sname:VkDeviceMemory object that overlaps with any other attachment in
    any subpass (including the same subpass), the
    sname:VkAttachmentDescription structures describing them must: include
    ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT in pname:flags
  * If the pname:attachment member of any element of
    pname:pInputAttachments, pname:pColorAttachments,
    pname:pResolveAttachments or pname:pDepthStencilAttachment, or any
    element of pname:pPreserveAttachments in any given element of
    pname:pSubpasses is not ename:VK_ATTACHMENT_UNUSED, it must: be less
    than pname:attachmentCount
  * The value of any element of the pname:pPreserveAttachments member in any
    given element of pname:pSubpasses must: not be
    ename:VK_ATTACHMENT_UNUSED
  * For any member of pname:pAttachments with a pname:loadOp equal to
    ename:VK_ATTACHMENT_LOAD_OP_CLEAR, the first use of that attachment
    must: not specify a pname:layout equal to
    pname:VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL or
    pname:VK_IMAGE_LAYOUT_DEPTH_STENCIL_READ_ONLY_OPTIMAL.
  * For any element of pname:pDependencies, if the pname:srcSubpass is not
    ename:VK_SUBPASS_EXTERNAL, all stage flags included in the
    pname:srcStageMask member of that dependency must: be a pipeline stage
    supported by the <<synchronization-pipeline-stages-types, pipeline>>
    identified by the pname:pipelineBindPoint member of the source subpass.
  * For any element of pname:pDependencies, if the pname:dstSubpass is not
    ename:VK_SUBPASS_EXTERNAL, all stage flags included in the
    pname:dstStageMask member of that dependency must: be a pipeline stage
    supported by the <<synchronization-pipeline-stages-types, pipeline>>
    identified by the pname:pipelineBindPoint member of the source subpass.
****

include::../validity/structs/VkRenderPassCreateInfo.txt[]

ifdef::VK_KHX_multiview[]

[[renderpass-multiview]]
// refBegin VkRenderPassMultiviewCreateInfoKHX Structure containing multiview info for all subpasses

If the sname:VkRenderPassCreateInfo::pname:pNext list includes a
sname:VkRenderPassMultiviewCreateInfoKHX structure, then that structure
includes an array of view masks, view offsets, and correlation masks for the
render pass.

The sname:VkRenderPassMultiviewCreateInfoKHX structure is defined as:

include::../api/structs/VkRenderPassMultiviewCreateInfoKHX.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:subpassCount is zero or is the number of subpasses in the render
    pass.
  * pname:pViewMasks points to an array of pname:subpassCount number of view
    masks, where each mask is a bitfield of view indices describing which
    views rendering is broadcast to in each subpass, when multiview is
    enabled.
    If pname:subpassCount is zero, each view mask is treated as zero.
  * pname:dependencyCount is zero or the number of dependencies in the
    render pass.
  * pname:pViewOffsets points to an array of pname:dependencyCount view
    offsets, one for each dependency.
    If pname:dependencyCount is zero, each dependency's view offset is
    treated as zero.
    Each view offset controls which views in the source subpass the views in
    the destination subpass depend on.
  * pname:correlationMaskCount is zero or a number of correlation masks.
  * pname:pCorrelationMasks is an array of view masks indicating sets of
    views that may: be more efficient to render concurrently.

When a subpass uses a non-zero view mask, _multiview_ functionality is
considered to be enabled.
Multiview is all-or-nothing for a render pass - that is, either all
subpasses must: have a non-zero view mask (though some subpasses may: have
only one view) or all must: be zero.
Multiview causes all drawing and clear commands in the subpass to behave as
if they were broadcast to each view, where a view is represented by one
layer of the framebuffer attachments.
All draws and clears are broadcast to each _view index_ whose bit is set in
the view mask.
The view index is provided in the code:ViewIndex shader input variable, and
color, depth/stencil, and input attachments all read/write the layer of the
framebuffer corresponding to the view index.

If the view mask is zero for all subpasses, multiview is considered to be
disabled and all drawing commands execute normally, without this additional
broadcasting.

Some implementations may: not support multiview in conjunction with
<<features-features-multiview-gs,geometry shaders>> or
<<features-features-multiview-tess,tessellation shaders>>.

[[renderpass-multiview-view-local]]
When multiview is enabled, the ename:VK_DEPENDENCY_VIEW_LOCAL_BIT_KHX bit in
a dependency can: be used to express a view-local dependency, meaning that
each view in the destination subpass depends on a single view in the source
subpass.
Unlike pipeline barriers, a subpass dependency can: potentially have a
different view mask in the source subpass and the destination subpass.
If the dependency is view-local, then each view ([eq]#dstView#) in the
destination subpass depends on the view [eq]#dstView {plus}
pViewOffsets[dependency]# in the source subpass.
If there is not such a view in the source subpass, then this dependency does
not affect that view in the destination subpass.
If the dependency is not view-local, then all views in the destination
subpass depend on all views in the source subpass, and the view offset is
ignored.
A non-zero view offset is not allowed in a self-dependency.

The elements of pname:pCorrelationMasks are a set of masks of views
indicating that views in the same mask may: exhibit spatial coherency
between the views, making it more efficient to render them concurrently.
Correlation masks must: not have a functional effect on the results of the
multiview rendering.

When multiview is enabled, at the beginning of each subpass all non-render
pass state is undefined.
In particular, each time flink:vkCmdBeginRenderPass or
flink:vkCmdNextSubpass is called the graphics pipeline must: be bound, any
relevant descriptor sets or vertex/index buffers must: be bound, and any
relevant dynamic state or push constants must: be set before they are used.

ifdef::VK_NVX_multiview_per_view_attributes[]

A multiview subpass can: declare that its shaders will write per-view
attributes for all views in a single invocation, by setting the
ename:VK_SUBPASS_DESCRIPTION_PER_VIEW_ATTRIBUTES_BIT_NVX bit in the subpass
description.
The only supported per-view attributes are position and viewport mask, and
per-view position and viewport masks are written to output array variables
decorated with code:PositionPerViewNV and code:ViewportMaskPerViewNV,
respectively.
If +VK_NV_viewport_array2+ is not supported and enabled,
code:ViewportMaskPerViewNV must: not be used.
Values written to elements of code:PositionPerViewNV and
code:ViewportMaskPerViewNV must: not depend on the code:ViewIndex.
The shader must: also write to an output variable decorated with
code:Position, and the value written to code:Position must: equal the value
written to code:PositionPerViewNV[code:ViewIndex].
Similarly, if code:ViewportMaskPerViewNV is written to then the shader must:
also write to an output variable decorated with code:ViewportMaskNV, and the
value written to code:ViewportMaskNV must: equal the value written to
code:ViewportMaskPerViewNV[code:ViewIndex].
Implementations will either use values taken from code:Position and
code:ViewportMaskNV and invoke the shader once for each view, or will use
values taken from code:PositionPerViewNV and code:ViewportMaskPerViewNV and
invoke the shader fewer times.
The values written to code:Position and code:ViewportMaskNV must: not depend
on the values written to code:PositionPerViewNV and
code:ViewportMaskPerViewNV, or vice versa (to allow compilers to eliminate
the unused outputs).
All attributes that do not have *PerViewNV counterparts must: not depend on
code:ViewIndex.

Per-view attributes are all-or-nothing for a subpass.
That is, all pipelines compiled against a subpass that includes the
ename:VK_SUBPASS_DESCRIPTION_PER_VIEW_ATTRIBUTES_BIT_NVX bit must: write
per-view attributes to the *PerViewNV[] shader outputs, in addition to the
non-per-view (e.g. code:Position) outputs.
Pipelines compiled against a subpass that does not include this bit must:
not include the *PerViewNV[] outputs in their interfaces.

endif::VK_NVX_multiview_per_view_attributes[]


.Valid Usage
****
  * If pname:subpassCount is not zero, pname:subpassCount must: be equal to
    the pname:subpassCount in the sname:VkRenderPassCreateInfo structure at
    the start of the chain
  * If pname:dependencyCount is not zero, pname:dependencyCount must: be
    equal to the pname:dependencyCount in the sname:VkRenderPassCreateInfo
    structure at the start of the chain
  * Each view index must: not be set in more than one element of
    pname:pCorrelationMasks
  * If an element of pname:pViewOffsets is non-zero, the corresponding
    slink:VkSubpassDependency structure must: have different values of
    pname:srcSubpass and pname:dstSubpass.
****

include::../validity/structs/VkRenderPassMultiviewCreateInfoKHX.txt[]

endif::VK_KHX_multiview[]

// refBegin VkAttachmentDescription Structure specifying an attachment description

The sname:VkAttachmentDescription structure is defined as:

include::../api/structs/VkAttachmentDescription.txt[]

  * pname:flags is a bitmask describing additional properties of the
    attachment.
    Bits which can: be set include:
+
--
// refBegin VkAttachmentDescriptionFlagBits Bitmask specifying additional properties of an attachment
include::../api/enums/VkAttachmentDescriptionFlagBits.txt[]
--
  * pname:format is a elink:VkFormat value specifying the format of the
    image that will be used for the attachment.
  * pname:samples is the number of samples of the image as defined in
    elink:VkSampleCountFlagBits.
  * pname:loadOp specifies how the contents of color and depth components of
    the attachment are treated at the beginning of the subpass where it is
    first used:
+
--
// refBegin VkAttachmentLoadOp Specify how contents of an attachment are treated at the beginning of a subpass
include::../api/enums/VkAttachmentLoadOp.txt[]
--
  ** ename:VK_ATTACHMENT_LOAD_OP_LOAD means the previous contents of the
     image within the render area will be preserved.
     For attachments with a depth/stencil format, this uses the access type
     ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT.
     For attachments with a color format, this uses the access type
     ename:VK_ACCESS_COLOR_ATTACHMENT_READ_BIT.
  ** ename:VK_ATTACHMENT_LOAD_OP_CLEAR means the contents within the render
     area will be cleared to a uniform value, which is specified when a
     render pass instance is begun.
     For attachments with a depth/stencil format, this uses the access type
     ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT.
     For attachments with a color format, this uses the access type
     ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT.
  ** ename:VK_ATTACHMENT_LOAD_OP_DONT_CARE means the previous contents
     within the area need not be preserved; the contents of the attachment
     will be undefined inside the render area.
     For attachments with a depth/stencil format, this uses the access type
     ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT.
     For attachments with a color format, this uses the access type
     ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT.
  * pname:storeOp specifies how the contents of color and depth components
    of the attachment are treated at the end of the subpass where it is last
    used:
+
--
// refBegin VkAttachmentStoreOp Specify how contents of an attachment are treated at the end of a subpass
include::../api/enums/VkAttachmentStoreOp.txt[]
--
  ** ename:VK_ATTACHMENT_STORE_OP_STORE means the contents generated during
     the render pass and within the render area are written to memory.
     For attachments with a depth/stencil format, this uses the access type
     ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT.
     For attachments with a color format, this uses the access type
     ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT.
  ** ename:VK_ATTACHMENT_STORE_OP_DONT_CARE means the contents within the
     render area are not needed after rendering, and may: be discarded; the
     contents of the attachment will be undefined inside the render area.
     For attachments with a depth/stencil format, this uses the access type
     ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT.
     For attachments with a color format, this uses the access type
     ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT.
  * pname:stencilLoadOp specifies how the contents of stencil components of
    the attachment are treated at the beginning of the subpass where it is
    first used, and must: be one of the same values allowed for pname:loadOp
    above.
  * pname:stencilStoreOp specifies how the contents of stencil components of
    the attachment are treated at the end of the last subpass where it is
    used, and must: be one of the same values allowed for pname:storeOp
    above.
  * pname:initialLayout is the layout the attachment image subresource will
    be in when a render pass instance begins.
  * pname:finalLayout is the layout the attachment image subresource will be
    transitioned to when a render pass instance ends.
    During a render pass instance, an attachment can: use a different layout
    in each subpass, if desired.

[[renderpass-load-store-ops]]
If the attachment uses a color format, then pname:loadOp and pname:storeOp
are used, and pname:stencilLoadOp and pname:stencilStoreOp are ignored.
If the format has depth and/or stencil components, pname:loadOp and
pname:storeOp apply only to the depth data, while pname:stencilLoadOp and
pname:stencilStoreOp define how the stencil data is handled.
pname:loadOp and pname:stencilLoadOp define the _load operations_ that
execute as part of the first subpass that uses the attachment.
pname:storeOp and pname:stencilStoreOp define the _store operations_ that
execute as part of the last subpass that uses the attachment.

The load operation for each value in an attachment used by a subpass
happens-before any command recorded into that subpass reads from that value.
Load operations for attachments with a depth/stencil format execute in the
ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT pipeline stage.
Load operations for attachments with a color format execute in the
ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT pipeline stage.

Store operations for each value in an attachment used by a subpass
happen-after any command recorded into that subpass writes to that value.
Store operations for attachments with a depth/stencil format execute in the
ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT pipeline stage.
Store operations for attachments with a color format execute in the
ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT pipeline stage.

If an attachment is not used by any subpass, then pname:loadOp,
pname:storeOp, pname:stencilStoreOp, and pname:stencilLoadOp are ignored,
and the attachment's memory contents will not be modified by execution of a
render pass instance.

ifdef::VK_KHX_multiview[]

The load and store operations apply on the first and last use of each view
in the render pass, respectively.
If a view index of an attachment is not included in the view mask in any
subpass that uses it, then the load and store operations are ignored, and
the attachment's memory contents will not be modified by execution of a
render pass instance.

endif::VK_KHX_multiview[]

[[renderpass-precision]]
During a render pass instance, input/color attachments with color formats
that have a component size of 8, 16, or 32 bits must: be represented in the
attachment's format throughout the instance.
Attachments with other floating- or fixed-point color formats, or with depth
components may: be represented in a format with a precision higher than the
attachment format, but must: be represented with the same range.
When such a component is loaded via the pname:loadOp, it will be converted
into an implementation-dependent format used by the render pass.
Such components must: be converted from the render pass format, to the
format of the attachment, before they are resolved or stored at the end of a
render pass instance via pname:storeOp.
Conversions occur as described in <<fundamentals-numerics,Numeric
Representation and Computation>> and <<fundamentals-fixedconv, Fixed-Point
Data Conversions>>.

[[renderpass-aliasing]]
If pname:flags includes ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT, then
the attachment is treated as if it shares physical memory with another
attachment in the same render pass.
This information limits the ability of the implementation to reorder certain
operations (like layout transitions and the pname:loadOp) such that it is
not improperly reordered against other uses of the same physical memory via
a different attachment.
This is described in more detail below.

.Valid Usage
****
  * pname:finalLayout must: not be ename:VK_IMAGE_LAYOUT_UNDEFINED or
    ename:VK_IMAGE_LAYOUT_PREINITIALIZED
****

include::../validity/structs/VkAttachmentDescription.txt[]

ifdef::editing-notes[]
[NOTE]
.editing-note
====
TODO (Jon) - the following text may need to be moved back to combine with
flink:vkCreateRenderPass above for automatic ref page generation.
====
endif::editing-notes[]

If a render pass uses multiple attachments that alias the same device
memory, those attachments must: each include the
ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT bit in their attachment
description flags.
Attachments aliasing the same memory occurs in multiple ways:

  * Multiple attachments being assigned the same image view as part of
    framebuffer creation.
  * Attachments using distinct image views that correspond to the same image
    subresource of an image.
  * Attachments using views of distinct image subresources which are bound
    to overlapping memory ranges.

.Note
[NOTE]
====
Render passes must: include subpass dependencies (either directly or via a
subpass dependency chain) between any two subpasses that operate on the same
attachment or aliasing attachments and those subpass dependencies must:
include execution and memory dependencies separating uses of the aliases, if
at least one of those subpasses writes to one of the aliases.
These dependencies must: not include the ename:VK_DEPENDENCY_BY_REGION_BIT
if the aliases are views of distinct image subresources which overlap in
memory.
====

Multiple attachments that alias the same memory must: not be used in a
single subpass.
A given attachment index must: not be used multiple times in a single
subpass, with one exception: two subpass attachments can: use the same
attachment index if at least one use is as an input attachment and neither
use is as a resolve or preserve attachment.
In other words, the same view can: be used simultaneously as an input and
color or depth/stencil attachment, but must: not be used as multiple color
or depth/stencil attachments nor as resolve or preserve attachments.
The precise set of valid scenarios is described in more detail
<<renderpass-feedbackloop, below>>.

If a set of attachments alias each other, then all except the first to be
used in the render pass must: use an pname:initialLayout of
ename:VK_IMAGE_LAYOUT_UNDEFINED, since the earlier uses of the other aliases
make their contents undefined.
Once an alias has been used and a different alias has been used after it,
the first alias must: not be used in any later subpasses.
However, an application can: assign the same image view to multiple aliasing
attachment indices, which allows that image view to be used multiple times
even if other aliases are used in between.

[NOTE]
.Note
====
Once an attachment needs the ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT
bit, there should: be no additional cost of introducing additional aliases,
and using these additional aliases may: allow more efficient clearing of the
attachments on multiple uses via ename:VK_ATTACHMENT_LOAD_OP_CLEAR.
====

// refBegin VkSubpassDescription Structure specifying a subpass description

The sname:VkSubpassDescription structure is defined as:

include::../api/structs/VkSubpassDescription.txt[]

  * pname:flags is a bitmask indicating usage of the subpass.
    Bits which can: be set include:
+
--
// refBegin VkSubpassDescriptionFlagBits Bitmask specifying usage of a subpass
include::../api/enums/VkSubpassDescriptionFlagBits.txt[]
--
ifdef::VK_NVX_multiview_per_view_attributes[]
+
  ** ename:VK_SUBPASS_DESCRIPTION_PER_VIEW_ATTRIBUTES_BIT_NVX indicates that
     shaders compiled for this subpass write the attributes for all views in
     a single invocation of each vertex processing stage.
     All pipelines compiled against a subpass that includes this bit must:
     write per-view attributes to the *PerViewNV[] shader outputs, in
     addition to the non-per-view (e.g. code:Position) outputs.
  ** ename:VK_SUBPASS_DESCRIPTION_PER_VIEW_POSITION_X_ONLY_BIT_NVX indicates
     that shaders compiled for this subpass use per-view positions which
     only differ in value in the x component.
     Per-view viewport mask can: also be used.
endif::VK_NVX_multiview_per_view_attributes[]
  * pname:pipelineBindPoint is a elink:VkPipelineBindPoint value specifying
    whether this is a compute or graphics subpass.
    Currently, only graphics subpasses are supported.
  * pname:inputAttachmentCount is the number of input attachments.
  * pname:pInputAttachments is an array of slink:VkAttachmentReference
    structures (defined below) that lists which of the render pass's
    attachments can: be read in the shader during the subpass, and what
    layout each attachment will be in during the subpass.
    Each element of the array corresponds to an input attachment unit number
    in the shader, i.e. if the shader declares an input variable
    `layout(input_attachment_index=X, set=Y, binding=Z)` then it uses the
    attachment provided in pname:pInputAttachments[X].
    Input attachments must: also be bound to the pipeline with a descriptor
    set, with the input attachment descriptor written in the location
    (set=Y, binding=Z).
  * pname:colorAttachmentCount is the number of color attachments.
  * pname:pColorAttachments is an array of pname:colorAttachmentCount
    slink:VkAttachmentReference structures that lists which of the render
    pass's attachments will be used as color attachments in the subpass, and
    what layout each attachment will be in during the subpass.
    Each element of the array corresponds to a fragment shader output
    location, i.e. if the shader declared an output variable
    `layout(location=X)` then it uses the attachment provided in
    pname:pColorAttachments[X].
  * pname:pResolveAttachments is `NULL` or an array of
    pname:colorAttachmentCount slink:VkAttachmentReference structures that
    lists which of the render pass's attachments are resolved to at the end
    of the subpass, and what layout each attachment will be in during the
    multisample resolve operation.
    If pname:pResolveAttachments is not `NULL`, each of its elements
    corresponds to a color attachment (the element in
    pname:pColorAttachments at the same index), and a multisample resolve
    operation is defined for each attachment.
    At the end of each subpass, multisample resolve operations read the
    subpass's color attachments, and resolve the samples for each pixel to
    the same pixel location in the corresponding resolve attachments, unless
    the resolve attachment index is ename:VK_ATTACHMENT_UNUSED.
    If the first use of an attachment in a render pass is as a resolve
    attachment, then the pname:loadOp is effectively ignored as the resolve
    is guaranteed to overwrite all pixels in the render area.
  * pname:pDepthStencilAttachment is a pointer to a
    slink:VkAttachmentReference specifying which attachment will be used for
    depth/stencil data and the layout it will be in during the subpass.
    Setting the attachment index to ename:VK_ATTACHMENT_UNUSED or leaving
    this pointer as `NULL` indicates that no depth/stencil attachment will
    be used in the subpass.
  * pname:preserveAttachmentCount is the number of preserved attachments.
  * pname:pPreserveAttachments is an array of pname:preserveAttachmentCount
    render pass attachment indices describing the attachments that are not
    used by a subpass, but whose contents must: be preserved throughout the
    subpass.

The contents of an attachment within the render area become undefined at the
start of a subpass *S* if all of the following conditions are true:

  * The attachment is used as a color, depth/stencil, or resolve attachment
    in any subpass in the render pass.
  * There is a subpass *S~1~* that uses or preserves the attachment, and a
    subpass dependency from *S~1~* to *S*.
  * The attachment is not used or preserved in subpass *S*.

Once the contents of an attachment become undefined in subpass *S*, they
remain undefined for subpasses in subpass dependency chains starting with
subpass *S* until they are written again.
However, they remain valid for subpasses in other subpass dependency chains
starting with subpass *S~1~* if those subpasses use or preserve the
attachment.

.Valid Usage
****
  * pname:pipelineBindPoint must: be ename:VK_PIPELINE_BIND_POINT_GRAPHICS
  * pname:colorAttachmentCount must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxColorAttachments
  * If the first use of an attachment in this render pass is as an input
    attachment, and the attachment is not also used as a color or
    depth/stencil attachment in the same subpass, then pname:loadOp must:
    not be ename:VK_ATTACHMENT_LOAD_OP_CLEAR
  * If pname:pResolveAttachments is not `NULL`, for each resolve attachment
    that does not have the value ename:VK_ATTACHMENT_UNUSED, the
    corresponding color attachment must: not have the value
    ename:VK_ATTACHMENT_UNUSED
  * If pname:pResolveAttachments is not `NULL`, the sample count of each
    element of pname:pColorAttachments must: be anything other than
    ename:VK_SAMPLE_COUNT_1_BIT
  * Any given element of pname:pResolveAttachments must: have a sample count
    of ename:VK_SAMPLE_COUNT_1_BIT
  * Any given element of pname:pResolveAttachments must: have the same
    elink:VkFormat as its corresponding color attachment
  * All attachments in pname:pColorAttachments and
    pname:pDepthStencilAttachment that are not ename:VK_ATTACHMENT_UNUSED
    must: have the same sample count
  * If any input attachments are ename:VK_ATTACHMENT_UNUSED, then any
    pipelines bound during the subpass must: not access those input
    attachments from the fragment shader
  * The pname:attachment member of any element of pname:pPreserveAttachments
    must: not be ename:VK_ATTACHMENT_UNUSED
  * Any given element of pname:pPreserveAttachments must: not also be an
    element of any other member of the subpass description
  * If any attachment is used as both an input attachment and a color or
    depth/stencil attachment, then each use must: use the same pname:layout
ifdef::VK_NVX_multiview_per_view_attributes[]
  * If pname:flags includes
    ename:VK_SUBPASS_DESCRIPTION_PER_VIEW_POSITION_X_ONLY_BIT_NVX, it must:
    also include ename:VK_SUBPASS_DESCRIPTION_PER_VIEW_ATTRIBUTES_BIT_NVX.
endif::VK_NVX_multiview_per_view_attributes[]
****

include::../validity/structs/VkSubpassDescription.txt[]

// refBegin VkAttachmentReference Structure specifying an attachment reference

The sname:VkAttachmentReference structure is defined as:

include::../api/structs/VkAttachmentReference.txt[]

  * pname:attachment is the index of the attachment of the render pass, and
    corresponds to the index of the corresponding element in the
    pname:pAttachments array of the sname:VkRenderPassCreateInfo structure.
    If any color or depth/stencil attachments are
    ename:VK_ATTACHMENT_UNUSED, then no writes occur for those attachments.
  * pname:layout is a elink:VkImageLayout value specifying the layout the
    attachment uses during the subpass.

.Valid Usage
****
  * pname:layout must: not be ename:VK_IMAGE_LAYOUT_UNDEFINED or
    ename:VK_IMAGE_LAYOUT_PREINITIALIZED
****

include::../validity/structs/VkAttachmentReference.txt[]

// refBegin VkSubpassDependency Structure specifying a subpass dependency

The sname:VkSubpassDependency structure is defined as:

include::../api/structs/VkSubpassDependency.txt[]

  * pname:srcSubpass is the subpass index of the first subpass in the
    dependency, or ename:VK_SUBPASS_EXTERNAL.
  * pname:dstSubpass is the subpass index of the second subpass in the
    dependency, or ename:VK_SUBPASS_EXTERNAL.
  * pname:srcStageMask defines a <<synchronization-pipeline-stages-masks,
    source stage mask>>.
  * pname:dstStageMask defines a <<synchronization-pipeline-stages-masks,
    destination stage mask>>.
  * pname:srcAccessMask defines a <<synchronization-access-masks, source
    access mask>>.
  * pname:dstAccessMask defines a <<synchronization-access-masks,
    destination access mask>>.
  * pname:dependencyFlags is a bitmask of elink:VkDependencyFlagBits.

If pname:srcSubpass is equal to pname:dstSubpass then the
slink:VkSubpassDependency describes a
<<synchronization-pipeline-barriers-subpass-self-dependencies, subpass
self-dependency>>, and only constrains the pipeline barriers allowed within
a subpass instance.
Otherwise, when a render pass instance which includes a subpass dependency
is submitted to a queue, it defines a memory dependency between the
subpasses identified by pname:srcSubpass and pname:dstSubpass.

If pname:srcSubpass is equal to ename:VK_SUBPASS_EXTERNAL, the first
<<synchronization-dependencies-scopes, synchronization scope>> includes
commands submitted to the queue before the render pass instance began.
Otherwise, the first set of commands includes all commands submitted as part
of the subpass instance identified by pname:srcSubpass and any load, store
or multisample resolve operations on attachments used in pname:srcSubpass.
In either case, the first synchronization scope is limited to operations on
the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, source stage mask>> specified by
pname:srcStageMask.

If pname:dstSubpass is equal to ename:VK_SUBPASS_EXTERNAL, the second
<<synchronization-dependencies-scopes, synchronization scope>> includes
commands submitted after the render pass instance is ended.
Otherwise, the second set of commands includes all commands submitted as
part of the subpass instance identified by pname:dstSubpass and any load,
store or multisample resolve operations on attachments used in
pname:dstSubpass.
In either case, the second synchronization scope is limited to operations on
the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, destination stage mask>> specified
by pname:dstStageMask.

The first <<synchronization-dependencies-access-scopes, access scope>> is
limited to access in the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, source stage mask>> specified by
pname:srcStageMask.
It is also limited to access types in the <<synchronization-access-masks,
source access mask>> specified by pname:srcAccessMask.

The second <<synchronization-dependencies-access-scopes, access scope>> is
limited to access in the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, destination stage mask>> specified
by pname:dstStageMask.
It is also limited to access types in the <<synchronization-access-masks,
destination access mask>> specified by pname:dstAccessMask.

The <<synchronization-dependencies-available-and-visible, availability and
visibility operations>> defined by a subpass dependency affect the execution
of <<renderpass-layout-transitions, image layout transitions>> within the
render pass.

.Valid Usage
****
  * If pname:srcSubpass is not ename:VK_SUBPASS_EXTERNAL, pname:srcStageMask
    must: not include ename:VK_PIPELINE_STAGE_HOST_BIT
  * If pname:dstSubpass is not ename:VK_SUBPASS_EXTERNAL, pname:dstStageMask
    must: not include ename:VK_PIPELINE_STAGE_HOST_BIT
  * If the <<features-features-geometryShader,geometry shaders>> feature is
    not enabled, pname:srcStageMask must: not contain
    ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT
  * If the <<features-features-geometryShader,geometry shaders>> feature is
    not enabled, pname:dstStageMask must: not contain
    ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT
  * If the <<features-features-tessellationShader,tessellation shaders>>
    feature is not enabled, pname:srcStageMask must: not contain
    ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT or
    ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT
  * If the <<features-features-tessellationShader,tessellation shaders>>
    feature is not enabled, pname:dstStageMask must: not contain
    ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT or
    ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT
  * pname:srcSubpass must: be less than or equal to pname:dstSubpass, unless
    one of them is ename:VK_SUBPASS_EXTERNAL, to avoid cyclic dependencies
    and ensure a valid execution order
  * pname:srcSubpass and pname:dstSubpass must: not both be equal to
    ename:VK_SUBPASS_EXTERNAL
  * If pname:srcSubpass is equal to pname:dstSubpass, pname:srcStageMask and
    pname:dstStageMask must: only contain one of
    ename:VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT,
    ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT,
    ename:VK_PIPELINE_STAGE_VERTEX_INPUT_BIT,
    ename:VK_PIPELINE_STAGE_VERTEX_SHADER_BIT,
    ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT,
    ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT,
    ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT,
    ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT,
    ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT,
    ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT,
    ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT,
    ename:VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT, or
    ename:VK_PIPELINE_STAGE_ALL_GRAPHICS_BIT
  * If pname:srcSubpass is equal to pname:dstSubpass, the
    <<synchronization-pipeline-stages-order, logically latest>> pipeline
    stage in pname:srcStageMask must: be
    <<synchronization-pipeline-stages-order, logically earlier>> than or
    equal to the <<synchronization-pipeline-stages-order, logically
    earliest>> pipeline stage in pname:dstStageMask
  * Any access flag included in pname:srcAccessMask must: be supported by
    one of the pipeline stages in pname:srcStageMask, as specified in the
    <<synchronization-access-types-supported, table of supported access
    types>>.
  * Any access flag included in pname:dstAccessMask must: be supported by
    one of the pipeline stages in pname:dstStageMask, as specified in the
    <<synchronization-access-types-supported, table of supported access
    types>>.
ifdef::VK_KHX_multiview[]
  * If pname:dependencyFlags includes
    ename:VK_DEPENDENCY_VIEW_LOCAL_BIT_KHX, then both pname:srcSubpass and
    pname:dstSubpass must: not equal ename:VK_SUBPASS_EXTERNAL
  * If pname:dependencyFlags includes
    ename:VK_DEPENDENCY_VIEW_LOCAL_BIT_KHX, then the render pass must: have
    multiview enabled
  * If pname:srcSubpass equals pname:dstSubpass and that subpass has more
    than one bit set in the view mask, then pname:dependencyFlags must:
    include ename:VK_DEPENDENCY_VIEW_LOCAL_BIT_KHX
endif::VK_KHX_multiview[]
****

include::../validity/structs/VkSubpassDependency.txt[]

ifdef::VK_KHX_multiview[]

When multiview is enabled, the execution of the multiple views of one
subpass may: not occur simultaneously or even back-to-back, and rather may:
be interleaved with the execution of other subpasses.
The load and store operations apply to attachments on a per-view basis.
For example, an attachment using ename:VK_ATTACHMENT_LOAD_OP_CLEAR will have
each view cleared on first use, but the first use of one view may be
temporally distant from the first use of another view.

[NOTE]
.Note
====
A good mental model for multiview is to think of a multiview subpass as if
it were a collection of individual (per-view) subpasses that are logically
grouped together and described as a single multiview subpass in the API.
Similarly, a multiview attachment can be thought of like several individual
attachments that happen to be layers in a single image.
A view-local dependency between two multiview subpasses acts like a set of
one-to-one dependencies between corresponding pairs of per-view subpasses.
A view-global dependency between two multiview subpasses acts like a set of
[eq]#N {times} M# dependencies between all pairs of per-view subpasses in
the source and destination.
Thus, it is a more compact representation which also makes clear the
commonality and reuse that is present between views in a subpass.
This interpretation motivates the answers to questions like "when does the
load op apply" - it is on the first use of each view of an attachment, as if
each view were a separate attachment.
====

endif::VK_KHX_multiview[]

ifdef::editing-notes[]
[NOTE]
.editing-note
====
The following two alleged implicit dependencies are practically no-ops, as
the operations they describe are already guaranteed by semaphores and
submission order (so they're almost entirely no-ops on their own).
The *only* reason they exist is because it simplifies reasoning about where
<<renderpass-layout-transitions, automatic layout transitions>> happen.
Further rewrites of this chapter could potentially remove the need for
these.
====
endif::editing-notes[]

If there is no subpass dependency from ename:VK_SUBPASS_EXTERNAL to the
first subpass that uses an attachment, then an implicit subpass dependency
exists from ename:VK_SUBPASS_EXTERNAL to the first subpass it is used in.
The subpass dependency operates as if defined with the following parameters:

[source,c]
----
VkSubpassDependency implicitDependency = {
    .srcSubpass = VK_SUBPASS_EXTERNAL;
    .dstSubpass = firstSubpass; // First subpass attachment is used in
    .srcStageMask = VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT;
    .dstStageMask = VK_PIPELINE_STAGE_ALL_COMMANDS_BIT;
    .srcAccessMask = 0;
    .dstAccessMask = VK_ACCESS_INPUT_ATTACHMENT_READ_BIT |
                     VK_ACCESS_COLOR_ATTACHMENT_READ_BIT |
                     VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT |
                     VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT |
                     VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT;
    .dependencyFlags = 0;
};
----

Similarly, if there is no subpass dependency from the last subpass that uses
an attachment to ename:VK_SUBPASS_EXTERNAL, then an implicit subpass
dependency exists from the last subpass it is used in to
ename:VK_SUBPASS_EXTERNAL.
The subpass dependency operates as if defined with the following parameters:

[source,c]
----
VkSubpassDependency implicitDependency = {
    .srcSubpass = lastSubpass; // Last subpass attachment is used in
    .dstSubpass = VK_SUBPASS_EXTERNAL;
    .srcStageMask = VK_PIPELINE_STAGE_ALL_COMMANDS_BIT;
    .dstStageMask = VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT;
    .srcAccessMask = VK_ACCESS_INPUT_ATTACHMENT_READ_BIT |
                     VK_ACCESS_COLOR_ATTACHMENT_READ_BIT |
                     VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT |
                     VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT |
                     VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT;
    .dstAccessMask = 0;
    .dependencyFlags = 0;
};
----

[[renderpass-layout-transitions]]
As subpasses may: overlap or execute out of order with regards to other
subpasses unless a subpass dependency chain describes otherwise, the layout
transitions required between subpasses cannot: be known to an application.
Instead, an application provides the layout that each attachment must: be in
at the start and end of a renderpass, and the layout it must: be in during
each subpass it is used in.
The implementation then must: execute layout transitions between subpasses
in order to guarantee that the images are in the layouts required by each
subpass, and in the final layout at the end of the render pass.

Automatic layout transitions away from the layout used in a subpass
happen-after the availability operations for all dependencies with that
subpass as the pname:srcSubpass.

Automatic layout transitions into the layout used in a subpass happen-before
the visibility operations for all dependencies with that subpass as the
pname:dstSubpass.

Automatic layout transitions away from pname:initialLayout happens-after the
availability operations for all dependencies with a pname:srcSubpass equal
to ename:VK_SUBPASS_EXTERNAL, where pname:dstSubpass uses the attachment
that will be transitioned.
For attachments created with ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT,
automatic layout transitions away from pname:initialLayout happen-after the
availability operations for all dependencies with a pname:srcSubpass equal
to ename:VK_SUBPASS_EXTERNAL, where pname:dstSubpass uses any aliased
attachment.

Automatic layout transitions into pname:finalLayout happens-before the
visibility operations for all dependencies with a pname:dstSubpass equal to
ename:VK_SUBPASS_EXTERNAL, where pname:srcSubpass uses the attachment that
will be transitioned.
For attachments created with ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT,
automatic layout transitions into pname:finalLayout happen-before the
visibility operations for all dependencies with a pname:dstSubpass equal to
ename:VK_SUBPASS_EXTERNAL, where pname:srcSubpass uses any aliased
attachment.

If two subpasses use the same attachment in different layouts, and both
layouts are read-only, no subpass dependency needs to be specified between
those subpasses.
If an implementation treats those layouts separately, it must: insert an
implicit subpass dependency between those subpasses to separate the uses in
each layout.
The subpass dependency operates as if defined with the following parameters:

[source,c]
----
// Used for input attachments
VkPipelineStageFlags inputAttachmentStages = VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT;
VkAccessFlags inputAttachmentAccess = VK_ACCESS_INPUT_ATTACHMENT_READ_BIT;

// Used for depth/stencil attachments
VkPipelineStageFlags depthStencilAttachmentStages = VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT | VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT;
VkAccessFlags depthStencilAttachmentAccess = VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT;

VkSubpassDependency implicitDependency = {
    .srcSubpass = firstSubpass;
    .dstSubpass = secondSubpass;
    .srcStageMask = inputAttachmentStages | depthStencilAttachmentStages;
    .dstStageMask = inputAttachmentStages | depthStencilAttachmentStages;
    .srcAccessMask = inputAttachmentAccess | depthStencilAttachmentAccess;
    .dstAccessMask = inputAttachmentAccess | depthStencilAttachmentAccess;
    .dependencyFlags = 0;
};
----

[[renderpass-feedbackloop]]
If a subpass uses the same attachment as both an input attachment and either
a color attachment or a depth/stencil attachment, writes via the color or
depth/stencil attachment are not automatically made visible to reads via the
input attachment, causing a _feedback loop_, except in any of the following
conditions:

  * If the color components or depth/stencil components read by the input
    attachment are mutually exclusive with the components written by the
    color or depth/stencil attachments, then there is no feedback loop.
    This requires the graphics pipelines used by the subpass to disable
    writes to color components that are read as inputs via the
    pname:colorWriteMask, and to disable writes to depth/stencil components
    that are read as inputs via pname:depthWriteEnable or
    pname:stencilTestEnable.
  * If the attachment is used as an input attachment and depth/stencil
    attachment only, and the depth/stencil attachment is not written to.
  * If a memory dependency is inserted between when the attachment is
    written and when it is subsequently read by later fragments.
    <<synchronization-pipeline-barriers, Pipeline barriers>> expressing a
    <<synchronization-pipeline-barriers-subpass-self-dependencies, subpass
    self-dependency>> are the only way to achieve this, and one must: be
    inserted every time a fragment will read values at a particular sample
    (x, y, layer, sample) coordinate, if those values have been written
    since the most recent pipeline barrier; or the since start of the
    subpass if there have been no pipeline barriers since the start of the
    subpass.

An attachment used as both an input attachment and a color attachment must:
be in the ename:VK_IMAGE_LAYOUT_GENERAL layout.
An attachment used as an input attachment and depth/stencil attachment must:
be in either ename:VK_IMAGE_LAYOUT_GENERAL or
ename:VK_IMAGE_LAYOUT_DEPTH_STENCIL_READ_ONLY_OPTIMAL.
An attachment must: not be used as both a depth/stencil attachment and a
color attachment.

// refBegin vkDestroyRenderPass Destroy a render pass object

To destroy a render pass, call:

include::../api/protos/vkDestroyRenderPass.txt[]

  * pname:device is the logical device that destroys the render pass.
  * pname:renderPass is the handle of the render pass to destroy.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.

.Valid Usage
****
  * All submitted commands that refer to pname:renderPass must: have
    completed execution
  * If sname:VkAllocationCallbacks were provided when pname:renderPass was
    created, a compatible set of callbacks must: be provided here
  * If no sname:VkAllocationCallbacks were provided when pname:renderPass
    was created, pname:pAllocator must: be `NULL`
****

include::../validity/protos/vkDestroyRenderPass.txt[]


[[renderpass-compatibility]]
== Render Pass Compatibility

Framebuffers and graphics pipelines are created based on a specific render
pass object.
They must: only be used with that render pass object, or one compatible with
it.

Two attachment references are compatible if they have matching format and
sample count, or are both ename:VK_ATTACHMENT_UNUSED or the pointer that
would contain the reference is `NULL`.

Two arrays of attachment references are compatible if all corresponding
pairs of attachments are compatible.
If the arrays are of different lengths, attachment references not present in
the smaller array are treated as ename:VK_ATTACHMENT_UNUSED.

Two render passes are compatible if their corresponding color, input,
resolve, and depth/stencil attachment references are compatible and if they
are otherwise identical except for:

  * Initial and final image layout in attachment descriptions
  * Load and store operations in attachment descriptions
  * Image layout in attachment references

A framebuffer is compatible with a render pass if it was created using the
same render pass or a compatible render pass.


== Framebuffers

// refBegin VkFramebuffer Opaque handle to a framebuffer object

Render passes operate in conjunction with _framebuffers_.
Framebuffers represent a collection of specific memory attachments that a
render pass instance uses.

Framebuffers are represented by sname:VkFramebuffer handles:

include::../api/handles/VkFramebuffer.txt[]

// refEnd VkFramebuffer

// refBegin vkCreateFramebuffer Create a new framebuffer object

To create a framebuffer, call:

include::../api/protos/vkCreateFramebuffer.txt[]

  * pname:device is the logical device that creates the framebuffer.
  * pname:pCreateInfo points to a slink:VkFramebufferCreateInfo structure
    which describes additional information about framebuffer creation.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pFramebuffer points to a sname:VkFramebuffer handle in which the
    resulting framebuffer object is returned.

include::../validity/protos/vkCreateFramebuffer.txt[]

// refBegin VkFramebufferCreateInfo Structure specifying parameters of a newly created framebuffer

The sname:VkFramebufferCreateInfo structure is defined as:

include::../api/structs/VkFramebufferCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:flags is reserved for future use.
  * pname:renderPass is a render pass that defines what render passes the
    framebuffer will be compatible with.
    See <<renderpass-compatibility,Render Pass Compatibility>> for details.
  * pname:attachmentCount is the number of attachments.
  * pname:pAttachments is an array of sname:VkImageView handles, each of
    which will be used as the corresponding attachment in a render pass
    instance.
  * pname:width, pname:height and pname:layers define the dimensions of the
    framebuffer.
ifdef::VK_KHX_multiview[]
    If the render pass uses multiview, then pname:layers must: be one and
    each attachment requires a number of layers that is greater than the
    maximum bit index set in the view mask in the subpasses in which it is
    used.
endif::VK_KHX_multiview[]

Image subresources used as attachments must: not be used via any
non-attachment usage for the duration of a render pass instance.

[NOTE]
.Note
====
This restriction means that the render pass has full knowledge of all uses
of all of the attachments, so that the implementation is able to make
correct decisions about when and how to perform layout transitions, when to
overlap execution of subpasses, etc.
====

[[renderpass-noattachments]]
It is legal for a subpass to use no color or depth/stencil attachments, and
rather use shader side effects such as image stores and atomics to produce
an output.
In this case, the subpass continues to use the pname:width, pname:height,
and pname:layers of the framebuffer to define the dimensions of the
rendering area, and the pname:rasterizationSamples from each pipeline's
slink:VkPipelineMultisampleStateCreateInfo to define the number of samples
used in rasterization; however, if
slink:VkPhysicalDeviceFeatures::pname:variableMultisampleRate is
code:VK_FALSE, then all pipelines to be bound with a given zero-attachment
subpass must: have the same value for
slink:VkPipelineMultisampleStateCreateInfo::pname:rasterizationSamples.

.Valid Usage
****
  * pname:attachmentCount must: be equal to the attachment count specified
    in pname:renderPass
  * Any given element of pname:pAttachments that is used as a color
    attachment or resolve attachment by pname:renderPass must: have been
    created with a pname:usage value including
    ename:VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT
  * Any given element of pname:pAttachments that is used as a depth/stencil
    attachment by pname:renderPass must: have been created with a
    pname:usage value including
    ename:VK_IMAGE_USAGE_DEPTH_STENCIL_ATTACHMENT_BIT
  * Any given element of pname:pAttachments that is used as an input
    attachment by pname:renderPass must: have been created with a
    pname:usage value including ename:VK_IMAGE_USAGE_INPUT_ATTACHMENT_BIT
  * Any given element of pname:pAttachments must: have been created with an
    elink:VkFormat value that matches the elink:VkFormat specified by the
    corresponding sname:VkAttachmentDescription in pname:renderPass
  * Any given element of pname:pAttachments must: have been created with a
    pname:samples value that matches the pname:samples value specified by
    the corresponding sname:VkAttachmentDescription in pname:renderPass
  * Any given element of pname:pAttachments must: have dimensions at least
    as large as the corresponding framebuffer dimension
  * Any given element of pname:pAttachments must: only specify a single mip
    level
  * Any given element of pname:pAttachments must: have been created with the
    identity swizzle
  * pname:width must: be greater than `0`.
  * pname:width must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxFramebufferWidth
  * pname:height must: be greater than `0`.
  * pname:height must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxFramebufferHeight
  * pname:layers must: be greater than `0`.
  * pname:layers must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxFramebufferLayers
ifdef::VK_KHR_maintenance1[]
  * Any given element of pname:pAttachments that is a 2D or 2D array image
    view taken from a 3D image must: not be a depth/stencil format
endif::VK_KHR_maintenance1[]
****

include::../validity/structs/VkFramebufferCreateInfo.txt[]

// refBegin vkDestroyFramebuffer Destroy a framebuffer object

To destroy a framebuffer, call:

include::../api/protos/vkDestroyFramebuffer.txt[]

  * pname:device is the logical device that destroys the framebuffer.
  * pname:framebuffer is the handle of the framebuffer to destroy.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.

.Valid Usage
****
  * All submitted commands that refer to pname:framebuffer must: have
    completed execution
  * If sname:VkAllocationCallbacks were provided when pname:framebuffer was
    created, a compatible set of callbacks must: be provided here
  * If no sname:VkAllocationCallbacks were provided when pname:framebuffer
    was created, pname:pAllocator must: be `NULL`
****

include::../validity/protos/vkDestroyFramebuffer.txt[]


[[renderpass-commands]]
== Render Pass Commands

An application records the commands for a render pass instance one subpass
at a time, by beginning a render pass instance, iterating over the subpasses
to record commands for that subpass, and then ending the render pass
instance.

// refBegin vkCmdBeginRenderPass Begin a new render pass

To begin a render pass instance, call:

include::../api/protos/vkCmdBeginRenderPass.txt[]

  * pname:commandBuffer is the command buffer in which to record the
    command.
  * pname:pRenderPassBegin is a pointer to a slink:VkRenderPassBeginInfo
    structure (defined below) which indicates the render pass to begin an
    instance of, and the framebuffer the instance uses.
  * pname:contents specifies how the commands in the first subpass will be
    provided, and is one of the values:
+
--
// refBegin VkSubpassContents Specify how commands in the first subpass of a render pass are provided
include::../api/enums/VkSubpassContents.txt[]
--
+
If pname:contents is ename:VK_SUBPASS_CONTENTS_INLINE, the contents of the
subpass will be recorded inline in the primary command buffer, and secondary
command buffers must: not be executed within the subpass.
If pname:contents is ename:VK_SUBPASS_CONTENTS_SECONDARY_COMMAND_BUFFERS,
the contents are recorded in secondary command buffers that will be called
from the primary command buffer, and fname:vkCmdExecuteCommands is the only
valid command on the command buffer until fname:vkCmdNextSubpass or
fname:vkCmdEndRenderPass.

After beginning a render pass instance, the command buffer is ready to
record the commands for the first subpass of that render pass.

.Valid Usage
****
  * If any of the pname:initialLayout or pname:finalLayout member of the
    sname:VkAttachmentDescription structures or the pname:layout member of
    the sname:VkAttachmentReference structures specified when creating the
    render pass specified in the pname:renderPass member of
    pname:pRenderPassBegin is ename:VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL
    then the corresponding attachment image subresource of the framebuffer
    specified in the pname:framebuffer member of pname:pRenderPassBegin
    must: have been created with ename:VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT
    set
****

ifdef::editing-notes[]
[NOTE]
.editing-note
====
Split Valid Usage block into two parts to work around asciidoctor-pdf
problem (internal issue 683).
====
endif::editing-notes[]

.Valid Usage
****
  * If any of the pname:initialLayout or pname:finalLayout member of the
    sname:VkAttachmentDescription structures or the pname:layout member of
    the sname:VkAttachmentReference structures specified when creating the
    render pass specified in the pname:renderPass member of
    pname:pRenderPassBegin is
    ename:VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL or
    ename:VK_IMAGE_LAYOUT_DEPTH_STENCIL_READ_ONLY_OPTIMAL then the
    corresponding attachment image subresource of the framebuffer specified
    in the pname:framebuffer member of pname:pRenderPassBegin must: have
    been created with ename:VK_IMAGE_USAGE_DEPTH_STENCIL_ATTACHMENT_BIT set
  * If any of the pname:initialLayout or pname:finalLayout member of the
    sname:VkAttachmentDescription structures or the pname:layout member of
    the sname:VkAttachmentReference structures specified when creating the
    render pass specified in the pname:renderPass member of
    pname:pRenderPassBegin is ename:VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL
    then the corresponding attachment image subresource of the framebuffer
    specified in the pname:framebuffer member of pname:pRenderPassBegin
    must: have been created with ename:VK_IMAGE_USAGE_SAMPLED_BIT or
    ename:VK_IMAGE_USAGE_INPUT_ATTACHMENT_BIT set
  * If any of the pname:initialLayout or pname:finalLayout member of the
    sname:VkAttachmentDescription structures or the pname:layout member of
    the sname:VkAttachmentReference structures specified when creating the
    render pass specified in the pname:renderPass member of
    pname:pRenderPassBegin is ename:VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL
    then the corresponding attachment image subresource of the framebuffer
    specified in the pname:framebuffer member of pname:pRenderPassBegin
    must: have been created with ename:VK_IMAGE_USAGE_TRANSFER_SRC_BIT set
  * If any of the pname:initialLayout or pname:finalLayout member of the
    sname:VkAttachmentDescription structures or the pname:layout member of
    the sname:VkAttachmentReference structures specified when creating the
    render pass specified in the pname:renderPass member of
    pname:pRenderPassBegin is ename:VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL
    then the corresponding attachment image subresource of the framebuffer
    specified in the pname:framebuffer member of pname:pRenderPassBegin
    must: have been created with ename:VK_IMAGE_USAGE_TRANSFER_DST_BIT set
  * If any of the pname:initialLayout members of the
    sname:VkAttachmentDescription structures specified when creating the
    render pass specified in the pname:renderPass member of
    pname:pRenderPassBegin is not ename:VK_IMAGE_LAYOUT_UNDEFINED, then each
    such pname:initialLayout must: be equal to the current layout of the
    corresponding attachment image subresource of the framebuffer specified
    in the pname:framebuffer member of pname:pRenderPassBegin
  * The pname:srcStageMask and pname:dstStageMask members of any element of
    the pname:pDependencies member of slink:VkRenderPassCreateInfo used to
    create pname:renderpass must: be supported by the capabilities of the
    queue family identified by the pname:queueFamilyIndex member of the
    slink:VkCommandPoolCreateInfo used to create the command pool which
    pname:commandBuffer was allocated from.
****

include::../validity/protos/vkCmdBeginRenderPass.txt[]

// refBegin VkRenderPassBeginInfo Structure specifying render pass begin info

The sname:VkRenderPassBeginInfo structure is defined as:

include::../api/structs/VkRenderPassBeginInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:renderPass is the render pass to begin an instance of.
  * pname:framebuffer is the framebuffer containing the attachments that are
    used with the render pass.
  * pname:renderArea is the render area that is affected by the render pass
    instance, and is described in more detail below.
  * pname:clearValueCount is the number of elements in pname:pClearValues.
  * pname:pClearValues is an array of slink:VkClearValue structures that
    contains clear values for each attachment, if the attachment uses a
    pname:loadOp value of ename:VK_ATTACHMENT_LOAD_OP_CLEAR or if the
    attachment has a depth/stencil format and uses a pname:stencilLoadOp
    value of ename:VK_ATTACHMENT_LOAD_OP_CLEAR.
    The array is indexed by attachment number.
    Only elements corresponding to cleared attachments are used.
    Other elements of pname:pClearValues are ignored.

pname:renderArea is the render area that is affected by the render pass
instance.
The effects of attachment load, store and multisample resolve operations are
restricted to the pixels whose x and y coordinates fall within the render
area on all attachments.
The render area extends to all layers of pname:framebuffer.
The application must: ensure (using scissor if necessary) that all rendering
is contained within the render area, otherwise the pixels outside of the
render area become undefined and shader side effects may: occur for
fragments outside the render area.
The render area must: be contained within the framebuffer dimensions.

ifdef::VK_KHX_multiview[]

When multiview is enabled, the resolve operation at the end of a subpass
applies to all views in the view mask.

endif::VK_KHX_multiview[]

[NOTE]
.Note
====
There may: be a performance cost for using a render area smaller than the
framebuffer, unless it matches the render area granularity for the render
pass.
====

.Valid Usage
****
  * pname:clearValueCount must: be greater than the largest attachment index
    in pname:renderPass that specifies a pname:loadOp (or
    pname:stencilLoadOp, if the attachment has a depth/stencil format) of
    ename:VK_ATTACHMENT_LOAD_OP_CLEAR
  * If pname:clearValueCount is not `0`, pname:pClearValues must: be a
    pointer to an array of pname:clearValueCount valid sname:VkClearValue
    unions
  * pname:renderPass must: be <<renderpass-compatibility,compatible>> with
    the pname:renderPass member of the sname:VkFramebufferCreateInfo
    structure specified when creating pname:framebuffer.
****

include::../validity/structs/VkRenderPassBeginInfo.txt[]

ifdef::VK_KHX_device_group[]

// refBegin VkDeviceGroupRenderPassBeginInfoKHX Set the initial device mask and render areas for a render pass instance

If the pname:pNext list of slink:VkRenderPassBeginInfo includes a
sname:VkDeviceGroupRenderPassBeginInfoKHX structure, then that structure
includes a device mask and set of render areas for the render pass instance.

The sname:VkDeviceGroupRenderPassBeginInfoKHX structure is defined as:

include::../api/structs/VkDeviceGroupRenderPassBeginInfoKHX.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:deviceMask is the device mask for the render pass instance.
  * pname:deviceRenderAreaCount is the number of elements in the
    pname:pDeviceRenderAreas array.
  * pname:pDeviceRenderAreas is an array of structures of type
    slink:VkRect2D defining the render area for each physical device.

The pname:deviceMask serves several purposes.
It is an upper bound on the set of physical devices that can: be used during
the render pass instance, and the initial device mask when the render pass
instance begins.
Render pass attachment load, store, and resolve operations only apply to
physical devices included in the device mask.
Subpass dependencies only apply to the physical devices in the device mask.

If pname:deviceRenderAreaCount is not zero, then the elements of
pname:pDeviceRenderAreas override the value of
slink:VkRenderPassBeginInfo::pname:renderArea, and provide a render area
specific to each physical device.
These render areas serve the same purpose as
slink:VkRenderPassBeginInfo::pname:renderArea, including controlling the
region of attachments that are cleared by ename:VK_ATTACHMENT_LOAD_OP_CLEAR
and that are resolved into resolve attachments.

If this structure is not present, the render pass instance's device mask is
the value of slink:VkDeviceGroupCommandBufferBeginInfoKHX::pname:deviceMask.
If this structure is not present or if pname:deviceRenderAreaCount is zero,
slink:VkRenderPassBeginInfo::pname:renderArea is used for all physical
devices.

.Valid Usage
****
  * pname:deviceMask must: be a valid device mask value
  * pname:deviceMask must: not be zero
  * pname:deviceMask must: be a subset of the command buffer's initial
    device mask
  * pname:deviceRenderAreaCount must: either be zero or equal to the number
    of physical devices in the logical device.
****

include::../validity/structs/VkDeviceGroupRenderPassBeginInfoKHX.txt[]

endif::VK_KHX_device_group[]

// refBegin vkGetRenderAreaGranularity Returns the granularity for optimal render area

To query the render area granularity, call:

include::../api/protos/vkGetRenderAreaGranularity.txt[]

  * pname:device is the logical device that owns the render pass.
  * pname:renderPass is a handle to a render pass.
  * pname:pGranularity points to a slink:VkExtent2D structure in which the
    granularity is returned.

The conditions leading to an optimal pname:renderArea are:

  * the pname:offset.x member in pname:renderArea is a multiple of the
    pname:width member of the returned slink:VkExtent2D (the horizontal
    granularity).
  * the pname:offset.y member in pname:renderArea is a multiple of the
    pname:height of the returned slink:VkExtent2D (the vertical
    granularity).
  * either the pname:offset.width member in pname:renderArea is a multiple
    of the horizontal granularity or pname:offset.x+pname:offset.width is
    equal to the pname:width of the pname:framebuffer in the
    slink:VkRenderPassBeginInfo.
  * either the pname:offset.height member in pname:renderArea is a multiple
    of the vertical granularity or pname:offset.y+pname:offset.height is
    equal to the pname:height of the pname:framebuffer in the
    slink:VkRenderPassBeginInfo.

Subpass dependencies are not affected by the render area, and apply to the
entire image subresources attached to the framebuffer.
Similarly, pipeline barriers are valid even if their effect extends outside
the render area.

include::../validity/protos/vkGetRenderAreaGranularity.txt[]

// refBegin vkCmdNextSubpass Transition to the next subpass of a render pass

To transition to the next subpass in the render pass instance after
recording the commands for a subpass, call:

include::../api/protos/vkCmdNextSubpass.txt[]

  * pname:commandBuffer is the command buffer in which to record the
    command.
  * pname:contents specifies how the commands in the next subpass will be
    provided, in the same fashion as the corresponding parameter of
    flink:vkCmdBeginRenderPass.

The subpass index for a render pass begins at zero when
fname:vkCmdBeginRenderPass is recorded, and increments each time
fname:vkCmdNextSubpass is recorded.

Moving to the next subpass automatically performs any multisample resolve
operations in the subpass being ended.
End-of-subpass multisample resolves are treated as color attachment writes
for the purposes of synchronization.
That is, they are considered to execute in the
ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT pipeline stage and their
writes are synchronized with ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT.
Synchronization between rendering within a subpass and any resolve
operations at the end of the subpass occurs automatically, without need for
explicit dependencies or pipeline barriers.
However, if the resolve attachment is also used in a different subpass, an
explicit dependency is needed.

After transitioning to the next subpass, the application can: record the
commands for that subpass.

.Valid Usage
****
  * The current subpass index must: be less than the number of subpasses in
    the render pass minus one
****

include::../validity/protos/vkCmdNextSubpass.txt[]

// refBegin vkCmdEndRenderPass End the current render pass

To record a command to end a render pass instance after recording the
commands for the last subpass, call:

include::../api/protos/vkCmdEndRenderPass.txt[]

  * pname:commandBuffer is the command buffer in which to end the current
    render pass instance.

Ending a render pass instance performs any multisample resolve operations on
the final subpass.

.Valid Usage
****
  * The current subpass index must: be equal to the number of subpasses in
    the render pass minus one
****

include::../validity/protos/vkCmdEndRenderPass.txt[]