# VkAccessFlagBits(3) Manual Page

## Name

VkAccessFlagBits - Bitmask specifying memory access types that will participate in a memory dependency

## C Specification

Memory in Vulkan can be accessed from within shader invocations and via some fixed-function stages of the pipeline. The access type is a function of the descriptor type used, or how a fixed-function stage accesses memory. Each access type corresponds to a bit flag in VkAccessFlagBits.

Some synchronization commands take sets of access types as parameters to define the access scopes of a memory dependency. If a synchronization command includes a source access mask, its first access scope only includes accesses via the access types specified in that mask. Similarly, if a synchronization command includes a destination access mask, its second access scope only includes accesses via the access types specified in that mask.

Access types that can be set in an access mask include:

    typedef enum VkAccessFlagBits {
        VK_ACCESS_INDIRECT_COMMAND_READ_BIT = 0x00000001,
        VK_ACCESS_INDEX_READ_BIT = 0x00000002,
        VK_ACCESS_VERTEX_ATTRIBUTE_READ_BIT = 0x00000004,
        VK_ACCESS_UNIFORM_READ_BIT = 0x00000008,
        VK_ACCESS_INPUT_ATTACHMENT_READ_BIT = 0x00000010,
        VK_ACCESS_SHADER_READ_BIT = 0x00000020,
        VK_ACCESS_SHADER_WRITE_BIT = 0x00000040,
        VK_ACCESS_COLOR_ATTACHMENT_READ_BIT = 0x00000080,
        VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT = 0x00000100,
        VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT = 0x00000200,
        VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT = 0x00000400,
        VK_ACCESS_TRANSFER_READ_BIT = 0x00000800,
        VK_ACCESS_TRANSFER_WRITE_BIT = 0x00001000,
        VK_ACCESS_HOST_READ_BIT = 0x00002000,
        VK_ACCESS_HOST_WRITE_BIT = 0x00004000,
        VK_ACCESS_MEMORY_READ_BIT = 0x00008000,
        VK_ACCESS_MEMORY_WRITE_BIT = 0x00010000,
        VK_ACCESS_TRANSFORM_FEEDBACK_WRITE_BIT_EXT = 0x02000000,
        VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_READ_BIT_EXT = 0x04000000,
        VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_WRITE_BIT_EXT = 0x08000000,
        VK_ACCESS_CONDITIONAL_RENDERING_READ_BIT_EXT = 0x00100000,
        VK_ACCESS_COLOR_ATTACHMENT_READ_NONCOHERENT_BIT_EXT = 0x00080000,
        VK_ACCESS_ACCELERATION_STRUCTURE_READ_BIT_KHR = 0x00200000,
        VK_ACCESS_ACCELERATION_STRUCTURE_WRITE_BIT_KHR = 0x00400000,
        VK_ACCESS_SHADING_RATE_IMAGE_READ_BIT_NV = 0x00800000,
        VK_ACCESS_FRAGMENT_DENSITY_MAP_READ_BIT_EXT = 0x01000000,
        VK_ACCESS_COMMAND_PREPROCESS_READ_BIT_NV = 0x00020000,
        VK_ACCESS_COMMAND_PREPROCESS_WRITE_BIT_NV = 0x00040000,
        VK_ACCESS_ACCELERATION_STRUCTURE_READ_BIT_NV = VK_ACCESS_ACCELERATION_STRUCTURE_READ_BIT_KHR,
        VK_ACCESS_ACCELERATION_STRUCTURE_WRITE_BIT_NV = VK_ACCESS_ACCELERATION_STRUCTURE_WRITE_BIT_KHR,
        VK_ACCESS_FLAG_BITS_MAX_ENUM = 0x7FFFFFFF
    } VkAccessFlagBits;

## Description

- `VK_ACCESS_INDIRECT_COMMAND_READ_BIT` specifies read access to indirect command data read as part of an indirect drawing or dispatch command.

- `VK_ACCESS_INDEX_READ_BIT` specifies read access to an index buffer as part of an indexed drawing command, bound by vkCmdBindIndexBuffer.

- `VK_ACCESS_VERTEX_ATTRIBUTE_READ_BIT` specifies read access to a vertex buffer as part of a drawing command, bound by vkCmdBindVertexBuffers.

- `VK_ACCESS_UNIFORM_READ_BIT` specifies read access to a uniform buffer.

- `VK_ACCESS_INPUT_ATTACHMENT_READ_BIT` specifies read access to an input attachment within a render pass during fragment shading.

- `VK_ACCESS_SHADER_READ_BIT` specifies read access to a storage buffer, physical storage buffer, uniform texel buffer, storage texel buffer, sampled image, or storage image.

- `VK_ACCESS_SHADER_WRITE_BIT` specifies write access to a storage buffer, physical storage buffer, storage texel buffer, or storage image.

- `VK_ACCESS_COLOR_ATTACHMENT_READ_BIT` specifies read access to a color attachment, such as via blending, logic operations, or via certain subpass load operations. It does not include advanced blend operations.

- `VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT` specifies write access to a color, resolve, or depth/stencil resolve attachment during a render pass or via certain subpass load and store operations.

- `VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT` specifies read access to a depth/stencil attachment, via depth or stencil operations or via certain subpass load operations.

- `VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT` specifies write access to a depth/stencil attachment, via depth or stencil operations or via certain subpass load and store operations.

- `VK_ACCESS_TRANSFER_READ_BIT` specifies read access to an image or buffer in a copy operation.

- `VK_ACCESS_TRANSFER_WRITE_BIT` specifies write access to an image or buffer in a clear or copy operation.

- `VK_ACCESS_HOST_READ_BIT` specifies read access by a host operation. Accesses of this type are not performed through a resource, but directly on memory.

- `VK_ACCESS_HOST_WRITE_BIT` specifies write access by a host operation. Accesses of this type are not performed through a resource, but directly on memory.

- `VK_ACCESS_MEMORY_READ_BIT` specifies all read accesses. It is always valid in any access mask, and is treated as equivalent to setting all `READ` access flags that are valid where it is used.

- `VK_ACCESS_MEMORY_WRITE_BIT` specifies all write accesses. It is always valid in any access mask, and is treated as equivalent to setting all `WRITE` access flags that are valid where it is used.

- `VK_ACCESS_CONDITIONAL_RENDERING_READ_BIT_EXT` specifies read access to a predicate as part of conditional rendering.

- `VK_ACCESS_TRANSFORM_FEEDBACK_WRITE_BIT_EXT` specifies write access to a transform feedback buffer made when transform feedback is active.

- `VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_READ_BIT_EXT` specifies read access to a transform feedback counter buffer which is read when `vkCmdBeginTransformFeedbackEXT` executes.

- `VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_WRITE_BIT_EXT` specifies write access to a transform feedback counter buffer which is written when `vkCmdEndTransformFeedbackEXT` executes.

- `VK_ACCESS_COMMAND_PREPROCESS_READ_BIT_NV` specifies reads from `VkBuffer` inputs to vkCmdPreprocessGeneratedCommandsNV.

- `VK_ACCESS_COMMAND_PREPROCESS_WRITE_BIT_NV` specifies writes to the `VkBuffer` preprocess outputs in vkCmdPreprocessGeneratedCommandsNV.

- `VK_ACCESS_COLOR_ATTACHMENT_READ_NONCOHERENT_BIT_EXT` is similar to `VK_ACCESS_COLOR_ATTACHMENT_READ_BIT`, but also includes advanced blend operations.

- `VK_ACCESS_SHADING_RATE_IMAGE_READ_BIT_NV` specifies read access to a shading rate image as part of a drawing command, as bound by vkCmdBindShadingRateImageNV.

- `VK_ACCESS_ACCELERATION_STRUCTURE_READ_BIT_KHR` specifies read access to an acceleration structure as part of a trace or build command.

- `VK_ACCESS_ACCELERATION_STRUCTURE_WRITE_BIT_KHR` specifies write access to an acceleration structure as part of a build command.

- `VK_ACCESS_FRAGMENT_DENSITY_MAP_READ_BIT_EXT` specifies read access to a fragment density map attachment during dynamic fragment density map operations

Certain access types are only performed by a subset of pipeline stages. Any synchronization command that takes both stage masks and access masks uses both to define the access scopes - only the specified access types performed by the specified stages are included in the access scope. An application must not specify an access flag in a synchronization command if it does not include a pipeline stage in the corresponding stage mask that is able to perform accesses of that type. The following table lists, for each access flag, which pipeline stages can perform that type of access.

Table 1. Supported access types
Access flag | Supported pipeline stages
--- | ---
`VK_ACCESS_INDIRECT_COMMAND_READ_BIT` | `VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT`
`VK_ACCESS_INDEX_READ_BIT` | `VK_PIPELINE_STAGE_VERTEX_INPUT_BIT`
`VK_ACCESS_VERTEX_ATTRIBUTE_READ_BIT` | `VK_PIPELINE_STAGE_VERTEX_INPUT_BIT`
`VK_ACCESS_UNIFORM_READ_BIT` | `VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV`, `VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV`, `VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR`, `VK_PIPELINE_STAGE_VERTEX_SHADER_BIT`, `VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT`, `VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT`, `VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT`, `VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT`, or `VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT`
`VK_ACCESS_SHADER_READ_BIT` | `VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV`, `VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV`, `VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR`, `VK_PIPELINE_STAGE_VERTEX_SHADER_BIT`, `VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT`, `VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT`, `VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT`, `VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT`, or `VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT`
`VK_ACCESS_SHADER_WRITE_BIT` | `VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV`, `VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV`, `VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR`, `VK_PIPELINE_STAGE_VERTEX_SHADER_BIT`, `VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT`, `VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT`, `VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT`, `VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT`, or `VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT`
`VK_ACCESS_INPUT_ATTACHMENT_READ_BIT` | `VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT`
`VK_ACCESS_COLOR_ATTACHMENT_READ_BIT` | `VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT`
`VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT` | `VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT`
`VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT` | `VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT`, or `VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT`
`VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT` | `VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT`, or `VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT`
`VK_ACCESS_TRANSFER_READ_BIT` | `VK_PIPELINE_STAGE_TRANSFER_BIT`
`VK_ACCESS_TRANSFER_WRITE_BIT` | `VK_PIPELINE_STAGE_TRANSFER_BIT`
`VK_ACCESS_HOST_READ_BIT` | `VK_PIPELINE_STAGE_HOST_BIT`
`VK_ACCESS_HOST_WRITE_BIT` | `VK_PIPELINE_STAGE_HOST_BIT`
`VK_ACCESS_MEMORY_READ_BIT` | Any
`VK_ACCESS_MEMORY_WRITE_BIT` | Any
`VK_ACCESS_COLOR_ATTACHMENT_READ_NONCOHERENT_BIT_EXT` | `VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT`
`VK_ACCESS_COMMAND_PREPROCESS_READ_BIT_NV` | `VK_PIPELINE_STAGE_COMMAND_PREPROCESS_BIT_NV`
`VK_ACCESS_COMMAND_PREPROCESS_WRITE_BIT_NV` | `VK_PIPELINE_STAGE_COMMAND_PREPROCESS_BIT_NV`
`VK_ACCESS_CONDITIONAL_RENDERING_READ_BIT_EXT` | `VK_PIPELINE_STAGE_CONDITIONAL_RENDERING_BIT_EXT`
`VK_ACCESS_SHADING_RATE_IMAGE_READ_BIT_NV` | `VK_PIPELINE_STAGE_SHADING_RATE_IMAGE_BIT_NV`
`VK_ACCESS_TRANSFORM_FEEDBACK_WRITE_BIT_EXT` | `VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT`
`VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_WRITE_BIT_EXT` | `VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT`
`VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_READ_BIT_EXT` | `VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT`
`VK_ACCESS_ACCELERATION_STRUCTURE_READ_BIT_KHR` | `VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR`, or `VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR`
`VK_ACCESS_ACCELERATION_STRUCTURE_WRITE_BIT_KHR` | `VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR`
`VK_ACCESS_FRAGMENT_DENSITY_MAP_READ_BIT_EXT` | `VK_PIPELINE_STAGE_FRAGMENT_DENSITY_PROCESS_BIT_EXT`

If a memory object does not have the `VK_MEMORY_PROPERTY_HOST_COHERENT_BIT` property, then vkFlushMappedMemoryRanges must be called in order to guarantee that writes to the memory object from the host are made available to the host domain, where they can be further made available to the device domain via a domain operation. Similarly, vkInvalidateMappedMemoryRanges must be called to guarantee that writes which are available to the host domain are made visible to host operations.

If the memory object does have the `VK_MEMORY_PROPERTY_HOST_COHERENT_BIT` property flag, writes to the memory object from the host are automatically made available to the host domain. Similarly, writes made available to the host domain are automatically made visible to the host.

| Note The vkQueueSubmit command automatically performs a domain operation from host to device for all writes performed before the command executes, so in most cases an explicit memory barrier is not needed for this case. In the few circumstances where a submit does not occur between the host write and the device read access, writes can be made available by using an explicit memory barrier.

## See Also

VkAccessFlags

## 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.