# VkSubpassDescription(3) Manual Page

## Name

VkSubpassDescription - Structure specifying a subpass description

## C Specification

The `VkSubpassDescription` structure is defined as:

    typedef struct VkSubpassDescription {
        VkSubpassDescriptionFlags       flags;
        VkPipelineBindPoint             pipelineBindPoint;
        uint32_t                        inputAttachmentCount;
        const VkAttachmentReference*    pInputAttachments;
        uint32_t                        colorAttachmentCount;
        const VkAttachmentReference*    pColorAttachments;
        const VkAttachmentReference*    pResolveAttachments;
        const VkAttachmentReference*    pDepthStencilAttachment;
        uint32_t                        preserveAttachmentCount;
        const uint32_t*                 pPreserveAttachments;
    } VkSubpassDescription;

## Members

- `flags` is a bitmask of VkSubpassDescriptionFlagBits specifying usage of the subpass.

- `pipelineBindPoint` is a VkPipelineBindPoint value specifying the pipeline type supported for this subpass.

- `inputAttachmentCount` is the number of input attachments.

- `pInputAttachments` is a pointer to an array of VkAttachmentReference structures defining the input attachments for this subpass and their layouts.

- `colorAttachmentCount` is the number of color attachments.

- `pColorAttachments` is a pointer to an array of VkAttachmentReference structures defining the color attachments for this subpass and their layouts.

- `pResolveAttachments` is an optional array of `colorAttachmentCount` VkAttachmentReference structures defining the resolve attachments for this subpass and their layouts.

- `pDepthStencilAttachment` is a pointer to a VkAttachmentReference structure specifying the depth/stencil attachment for this subpass and its layout.

- `preserveAttachmentCount` is the number of preserved attachments.

- `pPreserveAttachments` is a pointer to an array of `preserveAttachmentCount` render pass attachment indices identifying attachments that are not used by this subpass, but whose contents must be preserved throughout the subpass.

## Description

Each element of the `pInputAttachments` array corresponds to an input attachment index in a fragment shader, i.e. if a shader declares an image variable decorated with a `InputAttachmentIndex` value of X, then it uses the attachment provided in `pInputAttachments`[X]. Input attachments must also be bound to the pipeline in a descriptor set. If the `attachment` member of any element of `pInputAttachments` is `VK_ATTACHMENT_UNUSED`, the application must not read from the corresponding input attachment index. Fragment shaders can use subpass input variables to access the contents of an input attachment at the fragment’s (x, y, layer) framebuffer coordinates. Input attachments must not be used by any subpasses within a renderpass that enables render pass transform.

Each element of the `pColorAttachments` array corresponds to an output location in the shader, i.e. if the shader declares an output variable decorated with a `Location` value of X, then it uses the attachment provided in `pColorAttachments`[X]. If the `attachment` member of any element of `pColorAttachments` is `VK_ATTACHMENT_UNUSED`, writes to the corresponding location by a fragment are discarded.

If `pResolveAttachments` is not `NULL`, each of its elements corresponds to a color attachment (the element in `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 within the render area to the same pixel location in the corresponding resolve attachments, unless the resolve attachment index is `VK_ATTACHMENT_UNUSED`.

Similarly, if VkSubpassDescriptionDepthStencilResolve::`pDepthStencilResolveAttachment` is not `NULL` and does not have the value `VK_ATTACHMENT_UNUSED`, it corresponds to the depth/stencil attachment in `pDepthStencilAttachment`, and multisample resolve operations for depth and stencil are defined by VkSubpassDescriptionDepthStencilResolve::`depthResolveMode` and VkSubpassDescriptionDepthStencilResolve::`stencilResolveMode`, respectively. At the end of each subpass, multisample resolve operations read the subpass’s depth/stencil attachment, and resolve the samples for each pixel to the same pixel location in the corresponding resolve attachment. If VkSubpassDescriptionDepthStencilResolve::`depthResolveMode` is `VK_RESOLVE_MODE_NONE`, then the depth component of the resolve attachment is not written to and its contents are preserved. Similarly, if VkSubpassDescriptionDepthStencilResolve::`stencilResolveMode` is `VK_RESOLVE_MODE_NONE`, then the stencil component of the resolve attachment is not written to and its contents are preserved. VkSubpassDescriptionDepthStencilResolve::`depthResolveMode` is ignored if the VkFormat of the `pDepthStencilResolveAttachment` does not have a depth component. Similarly, VkSubpassDescriptionDepthStencilResolve::`stencilResolveMode` is ignored if the VkFormat of the `pDepthStencilResolveAttachment` does not have a stencil component.

If the image subresource range referenced by the depth/stencil attachment is created with `VK_IMAGE_CREATE_SAMPLE_LOCATIONS_COMPATIBLE_DEPTH_BIT_EXT`, then the multisample resolve operation uses the sample locations state specified in the `sampleLocationsInfo` member of the element of the `VkRenderPassSampleLocationsBeginInfoEXT`::`pPostSubpassSampleLocations` for the subpass.

If `pDepthStencilAttachment` is `NULL`, or if its attachment index is `VK_ATTACHMENT_UNUSED`, it indicates that no depth/stencil attachment will be used in 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 S1 that uses or preserves the attachment, and a subpass dependency from S1 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 S1 if those subpasses use or preserve the attachment.

Valid Usage

- `pipelineBindPoint` must be `VK_PIPELINE_BIND_POINT_GRAPHICS`

- `colorAttachmentCount` must be less than or equal to `VkPhysicalDeviceLimits`::`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 `loadOp` must not be `VK_ATTACHMENT_LOAD_OP_CLEAR`

- If `pResolveAttachments` is not `NULL`, for each resolve attachment that is not `VK_ATTACHMENT_UNUSED`, the corresponding color attachment must not be `VK_ATTACHMENT_UNUSED`

- If `pResolveAttachments` is not `NULL`, for each resolve attachment that is not `VK_ATTACHMENT_UNUSED`, the corresponding color attachment must not have a sample count of `VK_SAMPLE_COUNT_1_BIT`

- If `pResolveAttachments` is not `NULL`, each resolve attachment that is not `VK_ATTACHMENT_UNUSED` must have a sample count of `VK_SAMPLE_COUNT_1_BIT`

- If `pResolveAttachments` is not `NULL`, each resolve attachment that is not `VK_ATTACHMENT_UNUSED` must have the same VkFormat as its corresponding color attachment

- All attachments in `pColorAttachments` that are not `VK_ATTACHMENT_UNUSED` must have the same sample count

- All attachments in `pInputAttachments` that are not `VK_ATTACHMENT_UNUSED` must have formats whose features contain at least one of `VK_FORMAT_FEATURE_COLOR_ATTACHMENT_BIT` or `VK_FORMAT_FEATURE_DEPTH_STENCIL_ATTACHMENT_BIT`.

- All attachments in `pColorAttachments` that are not `VK_ATTACHMENT_UNUSED` must have formats whose features contain `VK_FORMAT_FEATURE_COLOR_ATTACHMENT_BIT`

- All attachments in `pResolveAttachments` that are not `VK_ATTACHMENT_UNUSED` must have formats whose features contain `VK_FORMAT_FEATURE_COLOR_ATTACHMENT_BIT`

- If `pDepthStencilAttachment` is not `NULL` and the attachment is not `VK_ATTACHMENT_UNUSED` then it must have a format whose features contain `VK_FORMAT_FEATURE_DEPTH_STENCIL_ATTACHMENT_BIT`

- If the `VK_AMD_mixed_attachment_samples` extension is enabled, and all attachments in `pColorAttachments` that are not `VK_ATTACHMENT_UNUSED` must have a sample count that is smaller than or equal to the sample count of `pDepthStencilAttachment` if it is not `VK_ATTACHMENT_UNUSED`

- If neither the `VK_AMD_mixed_attachment_samples` nor the `VK_NV_framebuffer_mixed_samples` extensions are enabled, and if `pDepthStencilAttachment` is not `VK_ATTACHMENT_UNUSED` and any attachments in `pColorAttachments` are not `VK_ATTACHMENT_UNUSED`, they must have the same sample count

- The `attachment` member of each element of `pPreserveAttachments` must not be `VK_ATTACHMENT_UNUSED`

- Each element of `pPreserveAttachments` must not also be an element of any other member of the subpass description

- If any attachment is used by more than one VkAttachmentReference member, then each use must use the same `layout`

- If `flags` includes `VK_SUBPASS_DESCRIPTION_PER_VIEW_POSITION_X_ONLY_BIT_NVX`, it must also include `VK_SUBPASS_DESCRIPTION_PER_VIEW_ATTRIBUTES_BIT_NVX`.

- If the render pass is created with `VK_RENDER_PASS_CREATE_TRANSFORM_BIT_QCOM` each of the elements of `pInputAttachments` must be `VK_ATTACHMENT_UNUSED`.

Valid Usage (Implicit)

- `flags` must be a valid combination of VkSubpassDescriptionFlagBits values

- `pipelineBindPoint` must be a valid VkPipelineBindPoint value

- If `inputAttachmentCount` is not `0`, `pInputAttachments` must be a valid pointer to an array of `inputAttachmentCount` valid VkAttachmentReference structures

- If `colorAttachmentCount` is not `0`, `pColorAttachments` must be a valid pointer to an array of `colorAttachmentCount` valid VkAttachmentReference structures

- If `colorAttachmentCount` is not `0`, and `pResolveAttachments` is not `NULL`, `pResolveAttachments` must be a valid pointer to an array of `colorAttachmentCount` valid VkAttachmentReference structures

- If `pDepthStencilAttachment` is not `NULL`, `pDepthStencilAttachment` must be a valid pointer to a valid VkAttachmentReference structure

- If `preserveAttachmentCount` is not `0`, `pPreserveAttachments` must be a valid pointer to an array of `preserveAttachmentCount` `uint32_t` values

## See Also

VkAttachmentReference, VkPipelineBindPoint, VkRenderPassCreateInfo, VkSubpassDescriptionFlags

## 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.

## Copyright

Copyright (c) 2014-2020 Khronos Group. This work is licensed under a Creative Commons Attribution 4.0 International License.