Collider scale (#189)

# Objective

Depends on #154, which needs to be merged first.

Currently, modifying the transform scale of an entity has no effect on its collider. This means that people need to set the collider size to match the size of the scaled mesh, which is often inconvenient. Colliders should get scaled by their transforms like in other game engines such as Godot, Unity and so on.

## Solution

Extend `Collider` to support scaling:

```rust
pub struct Collider {
    /// The raw unscaled collider shape.
    shape: SharedShape,
    /// The scaled version of the collider shape.
    ///
    /// If the scale is `Vector::ONE`, this will be `None` and `unscaled_shape`
    /// will be used instead.
    scaled_shape: SharedShape,
    /// The global scale used for the collider shape.
    scale: Vector,
}
```

Transform scale works in hierarchies the same way as it does for meshes, so scale is propagated to children.

---

## Migration Guide

This:

```rust
let mesh = meshes.add(Mesh::from(shape::Cube { size: 1.0 }));
commands.spawn((
    PbrBundle {
        mesh,
        transform: Transform::from_scale(Vec3::new(10.0, 1.0, 10.0)),
        ..default()
    },
    Collider::cuboid(10.0, 1.0, 10.0),
    RigidBody::Static,
));
```

becomes this: (collider size matches unscaled mesh size)

```rust
let mesh = meshes.add(Mesh::from(shape::Cube { size: 1.0 }));
commands.spawn((
    PbrBundle {
        mesh,
        transform: Transform::from_scale(Vec3::new(10.0, 1.0, 10.0)),
        ..default()
    },
    Collider::cuboid(1.0, 1.0, 1.0),
    RigidBody::Static,
));
```

crates/bevy_xpbd_2d/Cargo.toml

@@ -41,12 +41,12 @@ glam = { version = "0.24", features = ["approx"] }
 derive_more = "0.99"
 indexmap = "2.0.0"
 fxhash = "0.2.1"
+itertools = "0.11"
 
 [dev-dependencies]
 examples_common_2d = { path = "../examples_common_2d" }
 approx = "0.5"
 insta = "1.0"
-itertools = "0.10"
 
 [[example]]
 name = "chain_2d"

crates/bevy_xpbd_2d/examples/chain_2d.rs

@@ -72,15 +72,11 @@ fn follow_mouse(
         let (camera, camera_transform) = camera.single();
         let mut follower_position = follower.single_mut();
 
-        // Set position of follower to cursor position in world coordinates
-        // https://bevy-cheatbook.github.io/cookbook/cursor2world.html
-        if let Some(pos) = window.cursor_position() {
-            let window_size = Vec2::new(window.width(), window.height());
-            let ndc = (pos / window_size) * 2.0 - Vec2::ONE;
-            let ndc_to_world =
-                camera_transform.compute_matrix() * camera.projection_matrix().inverse();
-            let world_pos = ndc_to_world.project_point3(ndc.extend(-1.0));
-            follower_position.0 = world_pos.truncate().adjust_precision();
+        if let Some(cursor_world_pos) = window
+            .cursor_position()
+            .and_then(|cursor| camera.viewport_to_world_2d(camera_transform, cursor))
+        {
+            follower_position.0 = cursor_world_pos.adjust_precision();
         }
     }
 }

crates/bevy_xpbd_2d/examples/many_shapes.rs

@@ -40,7 +40,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::Y * 50.0 * 6.0),
-        Collider::cuboid(50.0 * 20.0, 50.0),
+        Collider::cuboid(50.0, 50.0),
     ));
     // Floor
     commands.spawn((
@@ -51,7 +51,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::NEG_Y * 50.0 * 6.0),
-        Collider::cuboid(50.0 * 20.0, 50.0),
+        Collider::cuboid(50.0, 50.0),
     ));
     // Left wall
     commands.spawn((
@@ -62,7 +62,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::NEG_X * 50.0 * 9.5),
-        Collider::cuboid(50.0, 50.0 * 11.0),
+        Collider::cuboid(50.0, 50.0),
     ));
     // Right wall
     commands.spawn((
@@ -73,7 +73,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::X * 50.0 * 9.5),
-        Collider::cuboid(50.0, 50.0 * 11.0),
+        Collider::cuboid(50.0, 50.0),
     ));
 
     let ball = (

crates/bevy_xpbd_2d/examples/move_marbles.rs

@@ -40,7 +40,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::Y * 50.0 * 6.0),
-        Collider::cuboid(50.0 * 20.0, 50.0),
+        Collider::cuboid(50.0, 50.0),
     ));
     // Floor
     commands.spawn((
@@ -51,7 +51,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::NEG_Y * 50.0 * 6.0),
-        Collider::cuboid(50.0 * 20.0, 50.0),
+        Collider::cuboid(50.0, 50.0),
     ));
     // Left wall
     commands.spawn((
@@ -62,7 +62,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::NEG_X * 50.0 * 9.5),
-        Collider::cuboid(50.0, 50.0 * 11.0),
+        Collider::cuboid(50.0, 50.0),
     ));
     // Right wall
     commands.spawn((
@@ -73,7 +73,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::X * 50.0 * 9.5),
-        Collider::cuboid(50.0, 50.0 * 11.0),
+        Collider::cuboid(50.0, 50.0),
     ));
 
     let marble_radius = 5.0;

crates/bevy_xpbd_2d/examples/one_way_platform_2d.rs

@@ -60,7 +60,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::Y * 50.0 * 6.0),
-        Collider::cuboid(50.0 * 20.0, 50.0),
+        Collider::cuboid(50.0, 50.0),
     ));
     // Floor
     commands.spawn((
@@ -71,7 +71,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::NEG_Y * 50.0 * 6.0),
-        Collider::cuboid(50.0 * 20.0, 50.0),
+        Collider::cuboid(50.0, 50.0),
     ));
     // Left wall
     commands.spawn((
@@ -82,7 +82,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::NEG_X * 50.0 * 9.5),
-        Collider::cuboid(50.0, 50.0 * 11.0),
+        Collider::cuboid(50.0, 50.0),
     ));
     // Right wall
     commands.spawn((
@@ -93,7 +93,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::X * 50.0 * 9.5),
-        Collider::cuboid(50.0, 50.0 * 11.0),
+        Collider::cuboid(50.0, 50.0),
     ));
 
     // For one-way platforms
@@ -113,7 +113,7 @@ fn setup(
             },
             RigidBody::Static,
             Position(Vector::Y * 16.0 * 6.0 * y as Scalar),
-            Collider::cuboid(25.0 * 20.0, 25.0),
+            Collider::cuboid(50.0, 50.0),
             OneWayPlatform::default(),
         ));
     }

crates/bevy_xpbd_3d/Cargo.toml

@@ -41,14 +41,14 @@ glam = { version = "0.24", features = ["approx"] }
 derive_more = "0.99"
 indexmap = "2.0.0"
 fxhash = "0.2.1"
+itertools = "0.11"
 
 [dev-dependencies]
 examples_common_3d = { path = "../examples_common_3d" }
 benches_common_3d = { path = "../benches_common_3d" }
 approx = "0.5"
 criterion = { version = "0.4", features = ["html_reports"] }
 insta = "1.0"
-itertools = "0.10"
 
 [[example]]
 name = "basic_dynamic_character"

crates/bevy_xpbd_3d/examples/cubes.rs

@@ -34,7 +34,7 @@ fn setup(
         },
         RigidBody::Static,
         Position(Vector::NEG_Y * 2.0),
-        Collider::cuboid(100.0, 1.0, 100.0),
+        Collider::cuboid(1.0, 1.0, 1.0),
     ));
 
     let cube_size = 2.0;
@@ -57,7 +57,7 @@ fn setup(
                     },
                     RigidBody::Dynamic,
                     Position(pos + Vector::Y * 5.0),
-                    Collider::cuboid(cube_size, cube_size, cube_size),
+                    Collider::cuboid(1.0, 1.0, 1.0),
                     Cube,
                 ));
             }