C Specification
The VkAttachmentDescription structure is defined as:
// Provided by VK_VERSION_1_0
typedef struct VkAttachmentDescription {
VkAttachmentDescriptionFlags flags;
VkFormat format;
VkSampleCountFlagBits samples;
VkAttachmentLoadOp loadOp;
VkAttachmentStoreOp storeOp;
VkAttachmentLoadOp stencilLoadOp;
VkAttachmentStoreOp stencilStoreOp;
VkImageLayout initialLayout;
VkImageLayout finalLayout;
} VkAttachmentDescription;Members
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flagsis a bitmask of VkAttachmentDescriptionFlagBits specifying additional properties of the attachment. -
formatis a VkFormat value specifying the format of the image view that will be used for the attachment. -
samplesis a VkSampleCountFlagBits value specifying the number of samples of the image. -
loadOpis a VkAttachmentLoadOp value specifying how the contents of color and depth components of the attachment are treated at the beginning of the subpass where it is first used. -
storeOpis a VkAttachmentStoreOp value specifying how the contents of color and depth components of the attachment are treated at the end of the subpass where it is last used. -
stencilLoadOpis a VkAttachmentLoadOp value specifying how the contents of stencil components of the attachment are treated at the beginning of the subpass where it is first used. -
stencilStoreOpis a VkAttachmentStoreOp value specifying how the contents of stencil components of the attachment are treated at the end of the last subpass where it is used. -
initialLayoutis the layout the attachment image subresource will be in when a render pass instance begins. -
finalLayoutis the layout the attachment image subresource will be transitioned to when a render pass instance ends.
Description
If the attachment uses a color format, then loadOp and storeOp
are used, and stencilLoadOp and stencilStoreOp are ignored.
If the format has depth and/or stencil components, loadOp and
storeOp apply only to the depth data, while stencilLoadOp and
stencilStoreOp define how the stencil data is handled.
loadOp and stencilLoadOp define the load operations that
execute as part of the first subpass that uses the attachment.
storeOp and stencilStoreOp define the store operations that
execute as part of the last subpass that uses the attachment.
The load operation for each sample in an attachment happens-before any
recorded command which accesses the sample in the first subpass where the
attachment is used.
Load operations for attachments with a depth/stencil format execute in the
VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT pipeline stage.
Load operations for attachments with a color format execute in the
VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT pipeline stage.
The store operation for each sample in an attachment happens-after any
recorded command which accesses the sample in the last subpass where the
attachment is used.
Store operations for attachments with a depth/stencil format execute in the
VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT pipeline stage.
Store operations for attachments with a color format execute in the
VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT pipeline stage.
If an attachment is not used by any subpass, loadOp, storeOp,
stencilStoreOp, and stencilLoadOp will be ignored for that
attachment, and no load or store ops will be performed.
However, any transition specified by initialLayout and
finalLayout will still be executed.
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.
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 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 storeOp.
Conversions occur as described in Numeric
Representation and Computation and Fixed-Point
Data Conversions.
If flags includes 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 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.
If a render pass uses multiple attachments that alias the same device
memory, those attachments must each include the
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.
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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 |
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 below.
If a set of attachments alias each other, then all except the first to be
used in the render pass must use an initialLayout of
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.
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Note
Once an attachment needs the |
Document Notes
For more information, see the Vulkan Specification
This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.