bevy/crates/bevy_core_pipeline/Cargo.toml
James Liu 7e6dd3f03e Allow unbatched render phases to use unstable sorts (#5049)
# Objective

Partially addresses #4291.

Speed up the sort phase for unbatched render phases.

## Solution
Split out one of the optimizations in #4899 and allow implementors of `PhaseItem` to change what kind of sort is used when sorting the items in the phase. This currently includes Stable, Unstable, and Unsorted. Each of these corresponds to `Vec::sort_by_key`, `Vec::sort_unstable_by_key`, and no sorting at all. The default is `Unstable`. The last one can be used as a default if users introduce a preliminary depth prepass.

## Performance
This will not impact the performance of any batched phases, as it is still using a stable sort. 2D's only phase is unchanged. All 3D phases are unbatched currently, and will benefit from this change.

On `many_cubes`, where the primary phase is opaque, this change sees a speed up from 907.02us -> 477.62us, a 47.35% reduction.

![image](https://user-images.githubusercontent.com/3137680/174471253-22424874-30d5-4db5-b5b4-65fb2c612a9c.png)

## Future Work
There were prior discussions to add support for faster radix sorts in #4291, which in theory should be a `O(n)` instead of a `O(nlog(n))` time. [`voracious`](https://crates.io/crates/voracious_radix_sort) has been proposed, but it seems to be optimize for use cases with more than 30,000 items, which may be atypical for most systems.

Another optimization included in #4899 is to reduce the size of a few of the IDs commonly used in `PhaseItem` implementations to shrink the types to make swapping/sorting faster. Both `CachedPipelineId` and `DrawFunctionId` could be reduced to `u32` instead of `usize`.

Ideally, this should automatically change to use stable sorts when `BatchedPhaseItem` is implemented on the same phase item type, but this requires specialization, which may not land in stable Rust for a short while.

---

## Changelog
Added: `PhaseItem::sort`

## Migration Guide
RenderPhases now default to a unstable sort (via `slice::sort_unstable_by_key`). This can typically improve sort phase performance, but may produce incorrect batching results when implementing `BatchedPhaseItem`. To revert to the older stable sort, manually implement `PhaseItem::sort` to implement a stable sort (i.e. via `slice::sort_by_key`).

Co-authored-by: Federico Rinaldi <gisquerin@gmail.com>
Co-authored-by: Robert Swain <robert.swain@gmail.com>
Co-authored-by: colepoirier <colepoirier@gmail.com>
2022-06-23 10:52:49 +00:00

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TOML

[package]
name = "bevy_core_pipeline"
version = "0.8.0-dev"
edition = "2021"
authors = [
"Bevy Contributors <bevyengine@gmail.com>",
"Carter Anderson <mcanders1@gmail.com>",
]
description = "Provides a core render pipeline for Bevy Engine."
homepage = "https://bevyengine.org"
repository = "https://github.com/bevyengine/bevy"
license = "MIT OR Apache-2.0"
keywords = ["bevy"]
[features]
trace = []
webgl = []
[dependencies]
# bevy
bevy_app = { path = "../bevy_app", version = "0.8.0-dev" }
bevy_asset = { path = "../bevy_asset", version = "0.8.0-dev" }
bevy_derive = { path = "../bevy_derive", version = "0.8.0-dev" }
bevy_ecs = { path = "../bevy_ecs", version = "0.8.0-dev" }
bevy_reflect = { path = "../bevy_reflect", version = "0.8.0-dev" }
bevy_render = { path = "../bevy_render", version = "0.8.0-dev" }
bevy_transform = { path = "../bevy_transform", version = "0.8.0-dev" }
bevy_utils = { path = "../bevy_utils", version = "0.8.0-dev" }
serde = { version = "1", features = ["derive"] }
radsort = "0.1"