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Platform/GFX/WebGPU: Difference between revisions
Describe presentation
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WebGPU is the new API for compute and graphics on the Web. It's developed by the [https://www.w3.org/community/gpu/ GPU for the Web] community group at W3C. | WebGPU is the new API for compute and graphics on the Web. It's developed by the [https://www.w3.org/community/gpu/ GPU for the Web] community group at W3C. | ||
=Architecture= | |||
TODO | TODO | ||
==Presentation== | |||
===Content side=== | |||
''CanvasContext'' creates a new ''wr::ExternalImageId''. | |||
It then sends a ''DeviceCreateSwapChain'' message to the GPU process to associate | |||
this external image with the swapchain ID (via ''Device::InitSwapChain''). It also | |||
provides the size/format of the swapchain, and generates the buffer IDs for | |||
reading back the data. | |||
There is a ''Texture object'' created with matching dimensions. It's communicated | |||
with the other pieces via ''WebRenderLocalCanvasData''. | |||
The ''nsDisplayCanvas::CreateWebRenderCommands'', which runs on a display list | |||
build, checks if the image key exists and matches the display list. Otherwise, | |||
it creates a new key and associates it with the external image via | |||
''AddPrivateExternalImage''. It then pushes the image ID into the display list. | |||
The info about the swapchain is put into ''WebRenderLocalCanvasData'', | |||
which can be accessed by ''CreateOrRecycleWebRenderUserData''. Part of that logic | |||
is done in ''UpdateWebRenderLocalCanvasData'', and another part is at the end of | |||
the ''CanvasContextType::WebGPU'' case. Finally, we send the ''SwapChainPresent'' | |||
message to the GPU. | |||
===GPU side=== | |||
There is ''mCanvasMap'' - a map of "external Id" to associated ''PresentationData''. | |||
It contains the device, the queue, and the pool of buffers used to read back the | |||
data. | |||
On ''RecvDeviceCreateSwapChain'', the new ''PresentationData'' is created and | |||
associated with the external ID. We also create a ''MemoryTextureHost'' object | |||
associated with this external ID. | |||
On ''RecvSwapChainPresent'', we find an available buffer to read the data into, or | |||
create it. We then record a new command buffer to read back the data into this | |||
buffer, and submit it right away. Finally, we request the buffer for mapping, | |||
specifying ''PresentCallback''. | |||
The callback just copies the data (from the mapped buffer) into the | |||
''MemoryTextureHost'' storage. When WebRender builds a frame, it gets | |||
''TextureUpdateSource::External'' update, which is resolved by locking the | |||
external texture handler in ''upload_to_texture_cache'', and getting the | |||
''ExternalImageSource::RawData'' for the data we read back from ''wgpu''. | |||
=Links= | |||
==Bug tracking== | ==Bug tracking== | ||
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"webgpu-mvp" meta-bug [https://bugzilla.mozilla.org/showdependencytree.cgi?id=1602129&hide_resolved=1 dependencies] | "webgpu-mvp" meta-bug [https://bugzilla.mozilla.org/showdependencytree.cgi?id=1602129&hide_resolved=1 dependencies] | ||
[https://github.com/gpuweb/gpuweb/wiki/Implementation-Status#firefox-and-servo Implementation Status] | |||
Demos: | |||
*[https://hello-webgpu-compute.glitch.me/ hello-webgpu-compute] | *[https://hello-webgpu-compute.glitch.me/ hello-webgpu-compute] | ||
General information: | |||
*[https://gpuweb.github.io/gpuweb/ API Specification] | *[https://gpuweb.github.io/gpuweb/ API Specification] | ||
*[https://github.com/kvark/slides/raw/master/IntroductionToWebGPU_BerlinAllHands.pdf Introduction to WebGPU] (Berlin All Hands) | *[https://github.com/kvark/slides/raw/master/IntroductionToWebGPU_BerlinAllHands.pdf Introduction to WebGPU] (Berlin All Hands) | ||