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# Objective - Implement the foundations of automatic batching/instancing of draw commands as the next step from #89 - NOTE: More performance improvements will come when more data is managed and bound in ways that do not require rebinding such as mesh, material, and texture data. ## Solution - The core idea for batching of draw commands is to check whether any of the information that has to be passed when encoding a draw command changes between two things that are being drawn according to the sorted render phase order. These should be things like the pipeline, bind groups and their dynamic offsets, index/vertex buffers, and so on. - The following assumptions have been made: - Only entities with prepared assets (pipelines, materials, meshes) are queued to phases - View bindings are constant across a phase for a given draw function as phases are per-view - `batch_and_prepare_render_phase` is the only system that performs this batching and has sole responsibility for preparing the per-object data. As such the mesh binding and dynamic offsets are assumed to only vary as a result of the `batch_and_prepare_render_phase` system, e.g. due to having to split data across separate uniform bindings within the same buffer due to the maximum uniform buffer binding size. - Implement `GpuArrayBuffer` for `Mesh2dUniform` to store Mesh2dUniform in arrays in GPU buffers rather than each one being at a dynamic offset in a uniform buffer. This is the same optimisation that was made for 3D not long ago. - Change batch size for a range in `PhaseItem`, adding API for getting or mutating the range. This is more flexible than a size as the length of the range can be used in place of the size, but the start and end can be otherwise whatever is needed. - Add an optional mesh bind group dynamic offset to `PhaseItem`. This avoids having to do a massive table move just to insert `GpuArrayBufferIndex` components. ## Benchmarks All tests have been run on an M1 Max on AC power. `bevymark` and `many_cubes` were modified to use 1920x1080 with a scale factor of 1. I run a script that runs a separate Tracy capture process, and then runs the bevy example with `--features bevy_ci_testing,trace_tracy` and `CI_TESTING_CONFIG=../benchmark.ron` with the contents of `../benchmark.ron`: ```rust ( exit_after: Some(1500) ) ``` ...in order to run each test for 1500 frames. The recent changes to `many_cubes` and `bevymark` added reproducible random number generation so that with the same settings, the same rng will occur. They also added benchmark modes that use a fixed delta time for animations. Combined this means that the same frames should be rendered both on main and on the branch. The graphs compare main (yellow) to this PR (red). ### 3D Mesh `many_cubes --benchmark` <img width="1411" alt="Screenshot 2023-09-03 at 23 42 10" src="https://github.com/bevyengine/bevy/assets/302146/2088716a-c918-486c-8129-090b26fd2bc4"> The mesh and material are the same for all instances. This is basically the best case for the initial batching implementation as it results in 1 draw for the ~11.7k visible meshes. It gives a ~30% reduction in median frame time. The 1000th frame is identical using the flip tool:  ``` Mean: 0.000000 Weighted median: 0.000000 1st weighted quartile: 0.000000 3rd weighted quartile: 0.000000 Min: 0.000000 Max: 0.000000 Evaluation time: 0.4615 seconds ``` ### 3D Mesh `many_cubes --benchmark --material-texture-count 10` <img width="1404" alt="Screenshot 2023-09-03 at 23 45 18" src="https://github.com/bevyengine/bevy/assets/302146/5ee9c447-5bd2-45c6-9706-ac5ff8916daf"> This run uses 10 different materials by varying their textures. The materials are randomly selected, and there is no sorting by material bind group for opaque 3D so any batching is 'random'. The PR produces a ~5% reduction in median frame time. If we were to sort the opaque phase by the material bind group, then this should be a lot faster. This produces about 10.5k draws for the 11.7k visible entities. This makes sense as randomly selecting from 10 materials gives a chance that two adjacent entities randomly select the same material and can be batched. The 1000th frame is identical in flip:  ``` Mean: 0.000000 Weighted median: 0.000000 1st weighted quartile: 0.000000 3rd weighted quartile: 0.000000 Min: 0.000000 Max: 0.000000 Evaluation time: 0.4537 seconds ``` ### 3D Mesh `many_cubes --benchmark --vary-per-instance` <img width="1394" alt="Screenshot 2023-09-03 at 23 48 44" src="https://github.com/bevyengine/bevy/assets/302146/f02a816b-a444-4c18-a96a-63b5436f3b7f"> This run varies the material data per instance by randomly-generating its colour. This is the worst case for batching and that it performs about the same as `main` is a good thing as it demonstrates that the batching has minimal overhead when dealing with ~11k visible mesh entities. The 1000th frame is identical according to flip:  ``` Mean: 0.000000 Weighted median: 0.000000 1st weighted quartile: 0.000000 3rd weighted quartile: 0.000000 Min: 0.000000 Max: 0.000000 Evaluation time: 0.4568 seconds ``` ### 2D Mesh `bevymark --benchmark --waves 160 --per-wave 1000 --mode mesh2d` <img width="1412" alt="Screenshot 2023-09-03 at 23 59 56" src="https://github.com/bevyengine/bevy/assets/302146/cb02ae07-237b-4646-ae9f-fda4dafcbad4"> This spawns 160 waves of 1000 quad meshes that are shaded with ColorMaterial. Each wave has a different material so 160 waves currently should result in 160 batches. This results in a 50% reduction in median frame time. Capturing a screenshot of the 1000th frame main vs PR gives:  ``` Mean: 0.001222 Weighted median: 0.750432 1st weighted quartile: 0.453494 3rd weighted quartile: 0.969758 Min: 0.000000 Max: 0.990296 Evaluation time: 0.4255 seconds ``` So they seem to produce the same results. I also double-checked the number of draws. `main` does 160000 draws, and the PR does 160, as expected. ### 2D Mesh `bevymark --benchmark --waves 160 --per-wave 1000 --mode mesh2d --material-texture-count 10` <img width="1392" alt="Screenshot 2023-09-04 at 00 09 22" src="https://github.com/bevyengine/bevy/assets/302146/4358da2e-ce32-4134-82df-3ab74c40849c"> This generates 10 textures and generates materials for each of those and then selects one material per wave. The median frame time is reduced by 50%. Similar to the plain run above, this produces 160 draws on the PR and 160000 on `main` and the 1000th frame is identical (ignoring the fps counter text overlay).  ``` Mean: 0.002877 Weighted median: 0.964980 1st weighted quartile: 0.668871 3rd weighted quartile: 0.982749 Min: 0.000000 Max: 0.992377 Evaluation time: 0.4301 seconds ``` ### 2D Mesh `bevymark --benchmark --waves 160 --per-wave 1000 --mode mesh2d --vary-per-instance` <img width="1396" alt="Screenshot 2023-09-04 at 00 13 53" src="https://github.com/bevyengine/bevy/assets/302146/b2198b18-3439-47ad-919a-cdabe190facb"> This creates unique materials per instance by randomly-generating the material's colour. This is the worst case for 2D batching. Somehow, this PR manages a 7% reduction in median frame time. Both main and this PR issue 160000 draws. The 1000th frame is the same:  ``` Mean: 0.001214 Weighted median: 0.937499 1st weighted quartile: 0.635467 3rd weighted quartile: 0.979085 Min: 0.000000 Max: 0.988971 Evaluation time: 0.4462 seconds ``` ### 2D Sprite `bevymark --benchmark --waves 160 --per-wave 1000 --mode sprite` <img width="1396" alt="Screenshot 2023-09-04 at 12 21 12" src="https://github.com/bevyengine/bevy/assets/302146/8b31e915-d6be-4cac-abf5-c6a4da9c3d43"> This just spawns 160 waves of 1000 sprites. There should be and is no notable difference between main and the PR. ### 2D Sprite `bevymark --benchmark --waves 160 --per-wave 1000 --mode sprite --material-texture-count 10` <img width="1389" alt="Screenshot 2023-09-04 at 12 36 08" src="https://github.com/bevyengine/bevy/assets/302146/45fe8d6d-c901-4062-a349-3693dd044413"> This spawns the sprites selecting a texture at random per instance from the 10 generated textures. This has no significant change vs main and shouldn't. ### 2D Sprite `bevymark --benchmark --waves 160 --per-wave 1000 --mode sprite --vary-per-instance` <img width="1401" alt="Screenshot 2023-09-04 at 12 29 52" src="https://github.com/bevyengine/bevy/assets/302146/762c5c60-352e-471f-8dbe-bbf10e24ebd6"> This sets the sprite colour as being unique per instance. This can still all be drawn using one batch. There should be no difference but the PR produces median frame times that are 4% higher. Investigation showed no clear sources of cost, rather a mix of give and take that should not happen. It seems like noise in the results. ### Summary | Benchmark | % change in median frame time | | ------------- | ------------- | | many_cubes | 🟩 -30% | | many_cubes 10 materials | 🟩 -5% | | many_cubes unique materials | 🟩 ~0% | | bevymark mesh2d | 🟩 -50% | | bevymark mesh2d 10 materials | 🟩 -50% | | bevymark mesh2d unique materials | 🟩 -7% | | bevymark sprite | 🟥 2% | | bevymark sprite 10 materials | 🟥 0.6% | | bevymark sprite unique materials | 🟥 4.1% | --- ## Changelog - Added: 2D and 3D mesh entities that share the same mesh and material (same textures, same data) are now batched into the same draw command for better performance. --------- Co-authored-by: robtfm <50659922+robtfm@users.noreply.github.com> Co-authored-by: Nicola Papale <nico@nicopap.ch> |
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