85 lines
4.2 KiB
Markdown
85 lines
4.2 KiB
Markdown
# 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)
|
|
- [Deferred Clears](doc/DeferredClears.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
|
|
|