README.md

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Hash : 26926a8b
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Date : 2025-09-08T13:07:49

Vulkan: Rename CommandBufferAccess to CommandResources

CommandBufferAccess was named as such to indicate "what the command
buffer is going to access". The new name indicates "what resources are
the following command going to use".

The rename is happening to reduce usages of "access", in preparation for
introducing another "access" which can be confused with this.

Bug: angleproject:422982681
Change-Id: Ib072cde8533515ba76734b6426b4d673cb07cc45
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6923331
Reviewed-by: Charlie Lao <cclao@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>

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ANGLE: Vulkan Back-end

ANGLE’s Vulkan back-end implementation lives in this folder.

Vulkan is an explicit graphics API. Compared to APIs like OpenGL or D3D11 explicit APIs can offer a number of significant benefits:

Lower API call CPU overhead.
A smaller API surface with more direct hardware control.
Better support for multi-core programming.
Vulkan in particular has open-source tooling and tests.

Back-end Design

The vk::Renderer class represents an EGLDisplay. vk::Renderer owns shared global resources like the VkDevice, VkQueue, the Vulkan format tables and internal Vulkan shaders. The ContextVk class implements the back-end of a front-end OpenGL Context. ContextVk processes state changes and handles action commands like glDrawArrays and glDrawElements.

Command recording

A render pass has three states: unstarted, started and active (we call it active in short), started but inactive (we call it inactive in short). The back-end records commands into command buffers via the following ContextVk APIs:

beginNewRenderPass: Writes out (aka flushes) prior pending commands into a primary command buffer, then starts a new render pass. Returns a secondary command buffer inside a render pass instance.
getOutsideRenderPassCommandBuffer: May flush prior command buffers and close the render pass if necessary, in addition to issuing the appropriate barriers. Returns a secondary command buffer outside a render pass instance.
getStartedRenderPassCommands: Returns a reference to the currently open render pass’ commands buffer.
onRenderPassFinished: Puts render pass into inactive state where you can not record more commands into secondary command buffer, except in some special cases where ANGLE does some optimization internally.
flushCommandsAndEndRenderPassWithoutSubmit: Marks the end of render pass. It flushes secondary command buffer into vulkan’s primary command buffer, puts secondary command buffer back to unstarted state and then goes into recycler for reuse.

The back-end (mostly) records Image and Buffer barriers through additional CommandResources APIs, the result of which is passed to getOutsideRenderPassCommandBuffer. Note that the barriers are not actually recorded until getOutsideRenderPassCommandBuffer is called:

onBufferTransferRead and onBufferComputeShaderRead accumulate VkBuffer read barriers.
onBufferTransferWrite and onBufferComputeShaderWrite accumulate VkBuffer write barriers.
onBuffferSelfCopy is a special case for VkBuffer self copies. It behaves the same as write.
onImageTransferRead and onImageComputerShadeRead accumulate VkImage read barriers.
onImageTransferWrite and onImageComputerShadeWrite accumulate VkImage write barriers.
onImageRenderPassRead and onImageRenderPassWrite accumulate VkImage barriers inside a started RenderPass.

After the back-end records commands to the primary buffer and we flush (e.g. on swap) or when we call vk::Renderer::finishQueueSerial, ANGLE submits the primary command buffer to a VkQueue.

See the code for more details.

Simple command recording example

In this example we’ll be recording a buffer copy command:

    // Ensure that ANGLE sets proper read and write barriers for the Buffers.
    vk::CommandResources resources;
    resources.onBufferTransferWrite(dstBuffer);
    resources.onBufferTransferRead(srcBuffer);

    // Get a pointer to a secondary command buffer for command recording.
    vk::OutsideRenderPassCommandBuffer *commandBuffer;
    ANGLE_TRY(contextVk->getOutsideRenderPassCommandBuffer(resources, &commandBuffer));

    // Record the copy command into the secondary buffer. We're done!
    commandBuffer->copyBuffer(srcBuffer->getBuffer(), dstBuffer->getBuffer(), copyCount, copies);

Additional Reading

More implementation details can be found in the doc directory:

Source

src/libANGLE/renderer/vulkan/README.md

# ANGLE: Vulkan Back-end

ANGLE's Vulkan back-end implementation lives in this folder.

[Vulkan](https://www.khronos.org/vulkan/) is an explicit graphics API. Compared to APIs like OpenGL
or D3D11 explicit APIs can offer a number of significant benefits:

 * Lower API call CPU overhead.
 * A smaller API surface with more direct hardware control.
 * Better support for multi-core programming.
 * Vulkan in particular has open-source tooling and tests.

## Back-end Design

The [`vk::Renderer`](Renderer.cpp) class represents an `EGLDisplay`. `vk::Renderer` owns shared global
resources like the [VkDevice][VkDevice], [VkQueue][VkQueue], the [Vulkan format tables](vk_format_utils.h)
and [internal Vulkan shaders](shaders). The [ContextVk](ContextVk.cpp) class implements the back-end
of a front-end OpenGL Context. ContextVk processes state changes and handles action commands like
`glDrawArrays` and `glDrawElements`.

## Command recording

A render pass has three states: `unstarted`, started and active (we call it `active` in short),
started but inactive (we call it `inactive` in short). The back-end records commands into command
buffers via the following `ContextVk` APIs:

 * `beginNewRenderPass`: Writes out (aka flushes) prior pending commands into a primary command
   buffer, then starts a new render pass. Returns a secondary command buffer *inside* a render pass
instance.
 * `getOutsideRenderPassCommandBuffer`: May flush prior command buffers and close the render pass if
   necessary, in addition to issuing the appropriate barriers. Returns a secondary command buffer
*outside* a render pass instance.
 * `getStartedRenderPassCommands`: Returns a reference to the currently open render pass' commands
   buffer.
 * `onRenderPassFinished`: Puts render pass into inactive state where you can not record more
   commands into secondary command buffer, except in some special cases where ANGLE does some
optimization internally.
 * `flushCommandsAndEndRenderPassWithoutSubmit`: Marks the end of render pass. It flushes secondary
   command buffer into vulkan's primary command buffer, puts secondary command buffer back to
unstarted state and then goes into recycler for reuse.

The back-end (mostly) records Image and Buffer barriers through additional `CommandResources`
APIs, the result of which is passed to `getOutsideRenderPassCommandBuffer`.  Note that the barriers
are not actually recorded until `getOutsideRenderPassCommandBuffer` is called:

 * `onBufferTransferRead` and `onBufferComputeShaderRead` accumulate `VkBuffer` read barriers.
 * `onBufferTransferWrite` and `onBufferComputeShaderWrite` accumulate `VkBuffer` write barriers.
 * `onBuffferSelfCopy` is a special case for `VkBuffer` self copies. It behaves the same as write.
 * `onImageTransferRead` and `onImageComputerShadeRead` accumulate `VkImage` read barriers.
 * `onImageTransferWrite` and `onImageComputerShadeWrite` accumulate `VkImage` write barriers.
 * `onImageRenderPassRead` and `onImageRenderPassWrite` accumulate `VkImage` barriers inside a
   started RenderPass.

After the back-end records commands to the primary buffer and we flush (e.g. on swap) or when we call
`vk::Renderer::finishQueueSerial`, ANGLE submits the primary command buffer to a `VkQueue`.

See the [code][CommandAPIs] for more details.

### Simple command recording example

In this example we'll be recording a buffer copy command:

```
    // Ensure that ANGLE sets proper read and write barriers for the Buffers.
    vk::CommandResources resources;
    resources.onBufferTransferWrite(dstBuffer);
    resources.onBufferTransferRead(srcBuffer);

    // Get a pointer to a secondary command buffer for command recording.
    vk::OutsideRenderPassCommandBuffer *commandBuffer;
    ANGLE_TRY(contextVk->getOutsideRenderPassCommandBuffer(resources, &commandBuffer));

    // Record the copy command into the secondary buffer. We're done!
    commandBuffer->copyBuffer(srcBuffer->getBuffer(), dstBuffer->getBuffer(), copyCount, copies);
```

## Additional Reading

More implementation details can be found in the `doc` directory:

- [Fast OpenGL State Transitions](doc/FastOpenGLStateTransitions.md)
- [Shader Module Compilation](doc/ShaderModuleCompilation.md)
- [Format Tables and Emulation](doc/FormatTablesAndEmulation.md)
- [Deferred Clears](doc/DeferredClears.md)
- [Queries](doc/Queries.md)
- [Present Semaphores](doc/PresentSemaphores.md)

[VkDevice]: https://www.khronos.org/registry/vulkan/specs/1.1-extensions/man/html/VkDevice.html
[VkQueue]: https://www.khronos.org/registry/vulkan/specs/1.1-extensions/man/html/VkQueue.html
[CommandAPIs]: https://chromium.googlesource.com/angle/angle/+/df31624eaf3df986a0bdf3f58a87b79b0cc8db5c/src/libANGLE/renderer/vulkan/ContextVk.h#620

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