# Cold Specialization
## Objective
An ongoing part of our quest to retain everything in the render world,
cold-specialization aims to cache pipeline specialization so that
pipeline IDs can be recomputed only when necessary, rather than every
frame. This approach reduces redundant work in stable scenes, while
still accommodating scenarios in which materials, views, or visibility
might change, as well as unlocking future optimization work like
retaining render bins.
## Solution
Queue systems are split into a specialization system and queue system,
the former of which only runs when necessary to compute a new pipeline
id. Pipelines are invalidated using a combination of change detection
and ECS ticks.
### The difficulty with change detection
Detecting “what changed” can be tricky because pipeline specialization
depends not only on the entity’s components (e.g., mesh, material, etc.)
but also on which view (camera) it is rendering in. In other words, the
cache key for a given pipeline id is a view entity/render entity pair.
As such, it's not sufficient simply to react to change detection in
order to specialize -- an entity could currently be out of view or could
be rendered in the future in camera that is currently disabled or hasn't
spawned yet.
### Why ticks?
Ticks allow us to ensure correctness by allowing us to compare the last
time a view or entity was updated compared to the cached pipeline id.
This ensures that even if an entity was out of view or has never been
seen in a given camera before we can still correctly determine whether
it needs to be re-specialized or not.
## Testing
TODO: Tested a bunch of different examples, need to test more.
## Migration Guide
TODO
- `AssetEvents` has been moved into the `PostUpdate` schedule.
---------
Co-authored-by: Patrick Walton <pcwalton@mimiga.net>
# Objective
Closes#15799.
Many rendering people and maintainers are in favor of reverting default
mesh materials added in #15524, especially as the migration to required
component is already large and heavily breaking.
## Solution
Revert default mesh materials, and adjust docs accordingly.
- Remove `extract_default_materials`
- Remove `clear_material_instances`, and move the logic back into
`extract_mesh_materials`
- Remove `HasMaterial2d` and `HasMaterial3d`
- Change default material handles back to pink instead of white
- 2D uses `Color::srgb(1.0, 0.0, 1.0)`, while 3D uses `Color::srgb(1.0,
0.0, 0.5)`. Not sure if this is intended.
There is now no indication at all about missing materials for `Mesh2d`
and `Mesh3d`. Having a mesh without a material renders nothing.
## Testing
I ran `2d_shapes`, `mesh2d_manual`, and `3d_shapes`, with and without
mesh material components.
# Objective
A big step in the migration to required components: meshes and
materials!
## Solution
As per the [selected
proposal](https://hackmd.io/@bevy/required_components/%2Fj9-PnF-2QKK0on1KQ29UWQ):
- Deprecate `MaterialMesh2dBundle`, `MaterialMeshBundle`, and
`PbrBundle`.
- Add `Mesh2d` and `Mesh3d` components, which wrap a `Handle<Mesh>`.
- Add `MeshMaterial2d<M: Material2d>` and `MeshMaterial3d<M: Material>`,
which wrap a `Handle<M>`.
- Meshes *without* a mesh material should be rendered with a default
material. The existence of a material is determined by
`HasMaterial2d`/`HasMaterial3d`, which is required by
`MeshMaterial2d`/`MeshMaterial3d`. This gets around problems with the
generics.
Previously:
```rust
commands.spawn(MaterialMesh2dBundle {
mesh: meshes.add(Circle::new(100.0)).into(),
material: materials.add(Color::srgb(7.5, 0.0, 7.5)),
transform: Transform::from_translation(Vec3::new(-200., 0., 0.)),
..default()
});
```
Now:
```rust
commands.spawn((
Mesh2d(meshes.add(Circle::new(100.0))),
MeshMaterial2d(materials.add(Color::srgb(7.5, 0.0, 7.5))),
Transform::from_translation(Vec3::new(-200., 0., 0.)),
));
```
If the mesh material is missing, previously nothing was rendered. Now,
it renders a white default `ColorMaterial` in 2D and a
`StandardMaterial` in 3D (this can be overridden). Below, only every
other entity has a material:
Why white? This is still open for discussion, but I think white makes
sense for a *default* material, while *invalid* asset handles pointing
to nothing should have something like a pink material to indicate that
something is broken (I don't handle that in this PR yet). This is kind
of a mix of Godot and Unity: Godot just renders a white material for
non-existent materials, while Unity renders nothing when no materials
exist, but renders pink for invalid materials. I can also change the
default material to pink if that is preferable though.
## Testing
I ran some 2D and 3D examples to test if anything changed visually. I
have not tested all examples or features yet however. If anyone wants to
test more extensively, it would be appreciated!
## Implementation Notes
- The relationship between `bevy_render` and `bevy_pbr` is weird here.
`bevy_render` needs `Mesh3d` for its own systems, but `bevy_pbr` has all
of the material logic, and `bevy_render` doesn't depend on it. I feel
like the two crates should be refactored in some way, but I think that's
out of scope for this PR.
- I didn't migrate meshlets to required components yet. That can
probably be done in a follow-up, as this is already a huge PR.
- It is becoming increasingly clear to me that we really, *really* want
to disallow raw asset handles as components. They caused me a *ton* of
headache here already, and it took me a long time to find every place
that queried for them or inserted them directly on entities, since there
were no compiler errors for it. If we don't remove the `Component`
derive, I expect raw asset handles to be a *huge* footgun for users as
we transition to wrapper components, especially as handles as components
have been the norm so far. I personally consider this to be a blocker
for 0.15: we need to migrate to wrapper components for asset handles
everywhere, and remove the `Component` derive. Also see
https://github.com/bevyengine/bevy/issues/14124.
---
## Migration Guide
Asset handles for meshes and mesh materials must now be wrapped in the
`Mesh2d` and `MeshMaterial2d` or `Mesh3d` and `MeshMaterial3d`
components for 2D and 3D respectively. Raw handles as components no
longer render meshes.
Additionally, `MaterialMesh2dBundle`, `MaterialMeshBundle`, and
`PbrBundle` have been deprecated. Instead, use the mesh and material
components directly.
Previously:
```rust
commands.spawn(MaterialMesh2dBundle {
mesh: meshes.add(Circle::new(100.0)).into(),
material: materials.add(Color::srgb(7.5, 0.0, 7.5)),
transform: Transform::from_translation(Vec3::new(-200., 0., 0.)),
..default()
});
```
Now:
```rust
commands.spawn((
Mesh2d(meshes.add(Circle::new(100.0))),
MeshMaterial2d(materials.add(Color::srgb(7.5, 0.0, 7.5))),
Transform::from_translation(Vec3::new(-200., 0., 0.)),
));
```
If the mesh material is missing, a white default material is now used.
Previously, nothing was rendered if the material was missing.
The `WithMesh2d` and `WithMesh3d` query filter type aliases have also
been removed. Simply use `With<Mesh2d>` or `With<Mesh3d>`.
---------
Co-authored-by: Tim Blackbird <justthecooldude@gmail.com>
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
