Hash :
5921a040
Author :
Date :
2020-08-06T17:39:56
Vulkan: Refactor image dependency commands. Uses commands similar to the Buffer APIs. Also updates docs. Bug: angleproject:4911 Change-Id: I1f2ec9bdd1d725d4ec3d6601e63bcb0c045e2121 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2342287 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Charlie Lao <cclao@google.com>
ANGLE’s Vulkan back-end implementation lives in this folder.
Vulkan is an explicit graphics API. It has a lot in common with other explicit APIs such as Microsoft’s D3D12 and Apple’s Metal. Compared to APIs like OpenGL or D3D11 explicit APIs can offer a number of significant benefits:
The RendererVk class represents an EGLDisplay. RendererVk 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.
The back-end records commands into command buffers via the the following ContextVk APIs:
getOutsideRenderPassCommandBuffer: returns a secondary command buffer outside a RenderPass instance. flushAndBeginRenderPass: returns a secondary command buffer inside a RenderPass instance.
Note: All of these commands may write out (aka flush) prior pending commands into a primary
command buffer. When a RenderPass is open getOutsideRenderPassCommandBuffer will flush the
pending RenderPass commands. flushAndBeginRenderPass will flush out pending commands outside a
RenderPass to a primary buffer. On submit ANGLE submits the primary command buffer to a VkQueue.
If you need to record inside a RenderPass, use flushAndBeginRenderPass. Otherwise, use
getOutsideRenderPassCommandBuffer.
The back-end (mostly) records Image and Buffer barriers through additional ContextVk APIs:
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 we flush (e.g. on swap) or when we call
ContextVk::finishToSerial.
See the code for more details.
In this example we’ll be recording a buffer copy command:
# Ensure that ANGLE sets proper read and write barriers for the Buffers.
ANGLE_TRY(contextVk->onBufferTransferWrite(destBuffer));
ANGLE_TRY(contextVk->onBufferTransferRead(srcBuffer));
# Get a pointer to a secondary command buffer for command recording. May "flush" the RP.
vk::CommandBuffer *commandBuffer;
ANGLE_TRY(contextVk->getOutsideRenderPassCommandBuffer(&commandBuffer));
# Record the copy command into the secondary buffer. We're done!
commandBuffer->copyBuffer(srcBuffer->getBuffer(), destBuffer->getBuffer(), copyCount, copies);
More implementation details can be found in the doc directory:
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# 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. It has a lot in common with
other explicit APIs such as Microsoft's [D3D12][D3D12 Guide] and Apple's
[Metal](https://developer.apple.com/metal/). 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.
[D3D12 Guide]: https://docs.microsoft.com/en-us/windows/desktop/direct3d12/directx-12-programming-guide
## Back-end Design
The [`RendererVk`](RendererVk.cpp) class represents an `EGLDisplay`. `RendererVk` 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
The back-end records commands into command buffers via the the following `ContextVk` APIs:
* `getOutsideRenderPassCommandBuffer`: returns a secondary command buffer *outside* a RenderPass instance.
* `flushAndBeginRenderPass`: returns a secondary command buffer *inside* a RenderPass instance.
*Note*: All of these commands may write out (aka flush) prior pending commands into a primary
command buffer. When a RenderPass is open `getOutsideRenderPassCommandBuffer` will flush the
pending RenderPass commands. `flushAndBeginRenderPass` will flush out pending commands outside a
RenderPass to a primary buffer. On submit ANGLE submits the primary command buffer to a `VkQueue`.
If you need to record inside a RenderPass, use `flushAndBeginRenderPass`. Otherwise, use
`getOutsideRenderPassCommandBuffer`.
The back-end (mostly) records Image and Buffer barriers through additional `ContextVk` APIs:
* `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 we flush (e.g. on swap) or when we call
`ContextVk::finishToSerial`.
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.
ANGLE_TRY(contextVk->onBufferTransferWrite(destBuffer));
ANGLE_TRY(contextVk->onBufferTransferRead(srcBuffer));
# Get a pointer to a secondary command buffer for command recording. May "flush" the RP.
vk::CommandBuffer *commandBuffer;
ANGLE_TRY(contextVk->getOutsideRenderPassCommandBuffer(&commandBuffer));
# Record the copy command into the secondary buffer. We're done!
commandBuffer->copyBuffer(srcBuffer->getBuffer(), destBuffer->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)
- [OpenGL Line Segment Rasterization](doc/OpenGLLineSegmentRasterization.md)
- [Format Tables and Emulation](doc/FormatTablesAndEmulation.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