# Objective
- Implement `Meshable` for `Extrusion<T>`
## Solution
- `Meshable` requires `Meshable::Output: MeshBuilder` now. This means
that all `some_primitive.mesh()` calls now return a `MeshBuilder`. These
were added for primitives that did not have one prior to this.
- A new trait `Extrudable: MeshBuilder` has been added. This trait
allows you to specify the indices of the perimeter of the mesh created
by this `MeshBuilder` and whether they are to be shaded smooth or flat.
- `Extrusion<P: Primitive2d + Meshable>` is now `Meshable` aswell. The
associated `MeshBuilder` is `ExtrusionMeshBuilder` which is generic over
`P` and uses the `MeshBuilder` of its baseshape internally.
- `ExtrusionMeshBuilder` exposes the configuration functions of its
base-shapes builder.
- Updated the `3d_shapes` example to include `Extrusion`s
## Migration Guide
- Depending on the context, you may need to explicitly call
`.mesh().build()` on primitives where you have previously called
`.mesh()`
- The `Output` type of custom `Meshable` implementations must now derive
`MeshBuilder`.
## Additional information
- The extrusions UVs are done so that
- the front face (`+Z`) is in the area between `(0, 0)` and `(0.5,
0.5)`,
- the back face (`-Z`) is in the area between `(0.5, 0)` and `(1, 0.5)`
- the mantle is in the area between `(0, 0.5)` and `(1, 1)`. Each
`PerimeterSegment` you specified in the `Extrudable` implementation will
be allocated an equal portion of this area.
- The UVs of the base shape are scaled to be in the front/back area so
whatever method of filling the full UV-space the base shape used is how
these areas will be filled.
Here is an example of what that looks like on a capsule:
https://github.com/bevyengine/bevy/assets/62256001/425ad288-fbbc-4634-9d3f-5e846cdce85f
This is the texture used:
The `3d_shapes` example now looks like this:
---------
Co-authored-by: Lynn Büttgenbach <62256001+solis-lumine-vorago@users.noreply.github.com>
Co-authored-by: Matty <weatherleymatthew@gmail.com>
Co-authored-by: Matty <2975848+mweatherley@users.noreply.github.com>
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