Although we cached hashes of `MeshVertexBufferLayout`, we were paying
the cost of `PartialEq` on `InnerMeshVertexBufferLayout` for every
entity, every frame. This patch changes that logic to place
`MeshVertexBufferLayout`s in `Arc`s so that they can be compared and
hashed by pointer. This results in a 28% speedup in the
`queue_material_meshes` phase of `many_cubes`, with frustum culling
disabled.
Additionally, this patch contains two minor changes:
1. This commit flattens the specialized mesh pipeline cache to one level
of hash tables instead of two. This saves a hash lookup.
2. The example `many_cubes` has been given a `--no-frustum-culling`
flag, to aid in benchmarking.
See the Tracy profile:
<img width="1064" alt="Screenshot 2024-02-29 144406"
src="https://github.com/bevyengine/bevy/assets/157897/18632f1d-1fdd-4ac7-90ed-2d10306b2a1e">
## Migration guide
* Duplicate `MeshVertexBufferLayout`s are now combined into a single
object, `MeshVertexBufferLayoutRef`, which contains an
atomically-reference-counted pointer to the layout. Code that was using
`MeshVertexBufferLayout` may need to be updated to use
`MeshVertexBufferLayoutRef` instead.
# Objective
Reduce the size of `bevy_utils`
(https://github.com/bevyengine/bevy/issues/11478)
## Solution
Move `EntityHash` related types into `bevy_ecs`. This also allows us
access to `Entity`, which means we no longer need `EntityHashMap`'s
first generic argument.
---
## Changelog
- Moved `bevy::utils::{EntityHash, EntityHasher, EntityHashMap,
EntityHashSet}` into `bevy::ecs::entity::hash` .
- Removed `EntityHashMap`'s first generic argument. It is now hardcoded
to always be `Entity`.
## Migration Guide
- Uses of `bevy::utils::{EntityHash, EntityHasher, EntityHashMap,
EntityHashSet}` now have to be imported from `bevy::ecs::entity::hash`.
- Uses of `EntityHashMap` no longer have to specify the first generic
parameter. It is now hardcoded to always be `Entity`.
# Objective
Lightmaps, textures that store baked global illumination, have been a
mainstay of real-time graphics for decades. Bevy currently has no
support for them, so this pull request implements them.
## Solution
The new `Lightmap` component can be attached to any entity that contains
a `Handle<Mesh>` and a `StandardMaterial`. When present, it will be
applied in the PBR shader. Because multiple lightmaps are frequently
packed into atlases, each lightmap may have its own UV boundaries within
its texture. An `exposure` field is also provided, to control the
brightness of the lightmap.
Note that this PR doesn't provide any way to bake the lightmaps. That
can be done with [The Lightmapper] or another solution, such as Unity's
Bakery.
---
## Changelog
### Added
* A new component, `Lightmap`, is available, for baked global
illumination. If your mesh has a second UV channel (UV1), and you attach
this component to the entity with that mesh, Bevy will apply the texture
referenced in the lightmap.
[The Lightmapper]: https://github.com/Naxela/The_Lightmapper
---------
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
