# Objective
Add a way to use the gizmo API in a retained manner, for increased
performance.
## Solution
- Move gizmo API from `Gizmos` to `GizmoBuffer`, ~ab~using `Deref` to
keep usage the same as before.
- Merge non-strip and strip variant of `LineGizmo` into one, storing the
data in a `GizmoBuffer` to have the same API for retained `LineGizmo`s.
### Review guide
- The meat of the changes are in `lib.rs`, `retained.rs`, `gizmos.rs`,
`pipeline_3d.rs` and `pipeline_2d.rs`
- The other files contain almost exclusively the churn from moving the
gizmo API from `Gizmos` to `GizmoBuffer`
## Testing
### Performance
Performance compared to the immediate mode API is from 65 to 80 times
better for static lines.
```
7900 XTX, 3700X
1707.9k lines/ms: gizmos_retained (21.3ms)
3488.5k lines/ms: gizmos_retained_continuous_polyline (31.3ms)
0.5k lines/ms: gizmos_retained_separate (97.7ms)
3054.9k lines/ms: bevy_polyline_retained_nan (16.8ms)
3596.3k lines/ms: bevy_polyline_retained_continuous_polyline (14.2ms)
0.6k lines/ms: bevy_polyline_retained_separate (78.9ms)
26.9k lines/ms: gizmos_immediate (14.9ms)
43.8k lines/ms: gizmos_immediate_continuous_polyline (18.3ms)
```
Looks like performance is good enough, being close to par with
`bevy_polyline`.
Benchmarks can be found here:
This branch:
https://github.com/tim-blackbird/line_racing/tree/retained-gizmos
Bevy 0.14: https://github.com/DGriffin91/line_racing
## Showcase
```rust
fn setup(
mut commands: Commands,
mut gizmo_assets: ResMut<Assets<GizmoAsset>>
) {
let mut gizmo = GizmoAsset::default();
// A sphere made out of one million lines!
gizmo
.sphere(default(), 1., CRIMSON)
.resolution(1_000_000 / 3);
commands.spawn(Gizmo {
handle: gizmo_assets.add(gizmo),
..default()
});
}
```
## Follow-up work
- Port over to the retained rendering world proper
- Calculate visibility and cull `Gizmo`s
