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
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VK_ACCESS_INDIRECT_COMMAND_READ_BITspecifies read access to indirect command data read as part of an indirect drawing or dispatch command. -
VK_ACCESS_INDEX_READ_BITspecifies read access to an index buffer as part of an indexed drawing command, bound by vkCmdBindIndexBuffer. -
VK_ACCESS_VERTEX_ATTRIBUTE_READ_BITspecifies read access to a vertex buffer as part of a drawing command, bound by vkCmdBindVertexBuffers. -
VK_ACCESS_UNIFORM_READ_BITspecifies read access to a uniform buffer. -
VK_ACCESS_INPUT_ATTACHMENT_READ_BITspecifies read access to an input attachment within a render pass during fragment shading. -
VK_ACCESS_SHADER_READ_BITspecifies read access to a storage buffer, physical storage buffer, uniform texel buffer, storage texel buffer, sampled image, or storage image. -
VK_ACCESS_SHADER_WRITE_BITspecifies write access to a storage buffer, physical storage buffer, storage texel buffer, or storage image. -
VK_ACCESS_COLOR_ATTACHMENT_READ_BITspecifies 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_BITspecifies 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_BITspecifies read access to a depth/stencil attachment, via depth or stencil operations or via certain subpass load operations. -
VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BITspecifies write access to a depth/stencil attachment, via depth or stencil operations or via certain subpass load and store operations. -
VK_ACCESS_TRANSFER_READ_BITspecifies read access to an image or buffer in a copy operation. -
VK_ACCESS_TRANSFER_WRITE_BITspecifies write access to an image or buffer in a clear or copy operation. -
VK_ACCESS_HOST_READ_BITspecifies read access by a host operation. Accesses of this type are not performed through a resource, but directly on memory. -
VK_ACCESS_HOST_WRITE_BITspecifies write access by a host operation. Accesses of this type are not performed through a resource, but directly on memory. -
VK_ACCESS_MEMORY_READ_BITspecifies all read accesses. It is always valid in any access mask, and is treated as equivalent to setting allREADaccess flags that are valid where it is used. -
VK_ACCESS_MEMORY_WRITE_BITspecifies all write accesses. It is always valid in any access mask, and is treated as equivalent to setting allWRITEaccess flags that are valid where it is used. -
VK_ACCESS_CONDITIONAL_RENDERING_READ_BIT_EXTspecifies read access to a predicate as part of conditional rendering. -
VK_ACCESS_TRANSFORM_FEEDBACK_WRITE_BIT_EXTspecifies write access to a transform feedback buffer made when transform feedback is active. -
VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_READ_BIT_EXTspecifies read access to a transform feedback counter buffer which is read whenvkCmdBeginTransformFeedbackEXTexecutes. -
VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_WRITE_BIT_EXTspecifies write access to a transform feedback counter buffer which is written whenvkCmdEndTransformFeedbackEXTexecutes. -
VK_ACCESS_COMMAND_PREPROCESS_READ_BIT_NVspecifies reads fromVkBufferinputs to vkCmdPreprocessGeneratedCommandsNV. -
VK_ACCESS_COMMAND_PREPROCESS_WRITE_BIT_NVspecifies writes to theVkBufferpreprocess outputs in vkCmdPreprocessGeneratedCommandsNV. -
VK_ACCESS_COLOR_ATTACHMENT_READ_NONCOHERENT_BIT_EXTis similar toVK_ACCESS_COLOR_ATTACHMENT_READ_BIT, but also includes advanced blend operations. -
VK_ACCESS_SHADING_RATE_IMAGE_READ_BIT_NVspecifies read access to a shading rate image as part of a drawing command, as bound by vkCmdBindShadingRateImageNV. -
VK_ACCESS_ACCELERATION_STRUCTURE_READ_BIT_KHRspecifies read access to an acceleration structure as part of a trace or build command. -
VK_ACCESS_ACCELERATION_STRUCTURE_WRITE_BIT_KHRspecifies write access to an acceleration structure as part of a build command. -
VK_ACCESS_FRAGMENT_DENSITY_MAP_READ_BIT_EXTspecifies 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.
| Access flag | Supported pipeline stages |
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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.
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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. |
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.