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# Objective - Encoding many GPU commands (such as in a renderpass with many draws, such as the main opaque pass) onto a `wgpu::CommandEncoder` is very expensive, and takes a long time. - To improve performance, we want to perform the command encoding for these heavy passes in parallel. ## Solution - `RenderContext` can now queue up "command buffer generation tasks" which are closures that will generate a command buffer when called. - When finalizing the render context to produce the final list of command buffers, these tasks are run in parallel on the `ComputeTaskPool` to produce their corresponding command buffers. - The general idea is that the node graph will run in serial, but in a node, instead of doing rendering work, you can add tasks to do render work in parallel with other node's tasks that get ran at the end of the graph execution. ## Nodes Parallelized - `MainOpaquePass3dNode` - `PrepassNode` - `DeferredGBufferPrepassNode` - `ShadowPassNode` (One task per view) ## Future Work - For large number of draws calls, might be worth further subdividing passes into 2+ tasks. - Extend this to UI, 2d, transparent, and transmissive nodes? - Needs testing - small command buffers are inefficient - it may be worth reverting to the serial command encoder usage for render phases with few items. - All "serial" (traditional) rendering work must finish before parallel rendering tasks (the new stuff) can start to run. - There is still only one submission to the graphics queue at the end of the graph execution. There is still no ability to submit work earlier. ## Performance Improvement Thanks to @Elabajaba for testing on Bistro. ![image](https://github.com/bevyengine/bevy/assets/47158642/be50dafa-85eb-4da5-a5cd-c0a044f1e76f) TLDR: Without shadow mapping, this PR has no impact. _With_ shadow mapping, this PR gives **~40 more fps** than main. --- ## Changelog - `MainOpaquePass3dNode`, `PrepassNode`, `DeferredGBufferPrepassNode`, and each shadow map within `ShadowPassNode` are now encoded in parallel, giving _greatly_ increased CPU performance, mainly when shadow mapping is enabled. - Does not work on WASM or AMD+Windows+Vulkan. - Added `RenderContext::add_command_buffer_generation_task()`. - `RenderContext::new()` now takes adapter info - Some render graph and Node related types and methods now have additional lifetime constraints. ## Migration Guide `RenderContext::new()` now takes adapter info - Some render graph and Node related types and methods now have additional lifetime constraints. --------- Co-authored-by: Elabajaba <Elabajaba@users.noreply.github.com> Co-authored-by: François <mockersf@gmail.com> |
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