Split OrthographicProjection::default into 2d & 3d (Adopted) (#15073)

Adopted PR from dmlary, all credit to them!
#9915

Original description:

# Objective

The default value for `near` in `OrthographicProjection` should be
different for 2d & 3d.

For 2d using `near = -1000` allows bevy users to build up scenes using
background `z = 0`, and foreground elements `z > 0` similar to css.
However in 3d `near = -1000` results in objects behind the camera being
rendered. Using `near = 0` works for 3d, but forces 2d users to assign
`z <= 0` for rendered elements, putting the background at some arbitrary
negative value.

There is no common value for `near` that doesn't result in a footgun or
usability issue for either 2d or 3d, so they should have separate
values.

There was discussion about other options in the discord
[0](https://discord.com/channels/691052431525675048/1154114310042292325),
but splitting `default()` into `default_2d()` and `default_3d()` seemed
like the lowest cost approach.

Related/past work #9138,
#9214,
#9310,
#9537 (thanks to @Selene-Amanita
for the list)

## Solution

This commit splits `OrthographicProjection::default` into `default_2d`
and `default_3d`.

## Migration Guide

- In initialization of `OrthographicProjection`, change `..default()` to
`..OrthographicProjection::default_2d()` or
`..OrthographicProjection::default_3d()`

Example:
```diff
--- a/examples/3d/orthographic.rs
+++ b/examples/3d/orthographic.rs
@@ -20,7 +20,7 @@ fn setup(
         projection: OrthographicProjection {
             scale: 3.0,
             scaling_mode: ScalingMode::FixedVertical(2.0),
-            ..default()
+            ..OrthographicProjection::default_3d()
         }
         .into(),
         transform: Transform::from_xyz(5.0, 5.0, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
```

---------

Co-authored-by: David M. Lary <dmlary@gmail.com>
Co-authored-by: Jan Hohenheim <jan@hohenheim.ch>

Author: 3 people

crates/bevy_core_pipeline/src/core_2d/camera_2d.rs

@@ -23,10 +23,6 @@ pub struct Camera2d;
 pub struct Camera2dBundle {
     pub camera: Camera,
     pub camera_render_graph: CameraRenderGraph,
-    /// Note: default value for `OrthographicProjection.near` is `0.0`
-    /// which makes objects on the screen plane invisible to 2D camera.
-    /// `Camera2dBundle::default()` sets `near` to negative value,
-    /// so be careful when initializing this field manually.
     pub projection: OrthographicProjection,
     pub visible_entities: VisibleEntities,
     pub frustum: Frustum,
@@ -41,11 +37,7 @@ pub struct Camera2dBundle {
 
 impl Default for Camera2dBundle {
     fn default() -> Self {
-        let projection = OrthographicProjection {
-            far: 1000.,
-            near: -1000.,
-            ..Default::default()
-        };
+        let projection = OrthographicProjection::default_2d();
         let transform = Transform::default();
         let frustum = projection.compute_frustum(&GlobalTransform::from(transform));
         Self {
@@ -77,7 +69,7 @@ impl Camera2dBundle {
         // the camera's translation by far and use a right handed coordinate system
         let projection = OrthographicProjection {
             far,
-            ..Default::default()
+            ..OrthographicProjection::default_2d()
         };
         let transform = Transform::from_xyz(0.0, 0.0, far - 0.1);
         let frustum = projection.compute_frustum(&GlobalTransform::from(transform));

crates/bevy_dev_tools/src/ui_debug_overlay/mod.rs

@@ -92,7 +92,7 @@ fn update_debug_camera(
                     projection: OrthographicProjection {
                         far: 1000.0,
                         viewport_origin: Vec2::new(0.0, 0.0),
-                        ..default()
+                        ..OrthographicProjection::default_3d()
                     },
                     camera: Camera {
                         order: LAYOUT_DEBUG_CAMERA_ORDER,

crates/bevy_gltf/src/loader.rs

@@ -1256,7 +1256,7 @@ fn load_node(
                         far: orthographic.zfar(),
                         scaling_mode: ScalingMode::FixedHorizontal(1.0),
                         scale: xmag,
-                        ..Default::default()
+                        ..OrthographicProjection::default_3d()
                     };
 
                     Projection::Orthographic(orthographic_projection)

crates/bevy_render/src/camera/projection.rs

@@ -237,7 +237,7 @@ impl Default for PerspectiveProjection {
 /// # use bevy_render::camera::{OrthographicProjection, Projection, ScalingMode};
 /// let projection = Projection::Orthographic(OrthographicProjection {
 ///    scaling_mode: ScalingMode::FixedVertical(2.0),
-///    ..OrthographicProjection::default()
+///    ..OrthographicProjection::default_2d()
 /// });
 /// ```
 #[derive(Debug, Clone, Copy, Reflect, Serialize, Deserialize)]
@@ -334,11 +334,11 @@ impl DivAssign<f32> for ScalingMode {
 /// # use bevy_render::camera::{OrthographicProjection, Projection, ScalingMode};
 /// let projection = Projection::Orthographic(OrthographicProjection {
 ///     scaling_mode: ScalingMode::WindowSize(100.0),
-///     ..OrthographicProjection::default()
+///     ..OrthographicProjection::default_2d()
 /// });
 /// ```
 #[derive(Component, Debug, Clone, Reflect)]
-#[reflect(Component, Default)]
+#[reflect(Component)]
 pub struct OrthographicProjection {
     /// The distance of the near clipping plane in world units.
     ///
@@ -479,8 +479,29 @@ impl CameraProjection for OrthographicProjection {
     }
 }
 
-impl Default for OrthographicProjection {
-    fn default() -> Self {
+impl FromWorld for OrthographicProjection {
+    fn from_world(_world: &mut World) -> Self {
+        OrthographicProjection::default_3d()
+    }
+}
+
+impl OrthographicProjection {
+    /// Returns the default orthographic projection for a 2D context.
+    ///
+    /// The near plane is set to a negative value so that the camera can still
+    /// render the scene when using positive z coordinates to order foreground elements.
+    pub fn default_2d() -> Self {
+        OrthographicProjection {
+            near: -1000.0,
+            ..OrthographicProjection::default_3d()
+        }
+    }
+
+    /// Returns the default orthographic projection for a 3D context.
+    ///
+    /// The near plane is set to 0.0 so that the camera doesn't render
+    /// objects that are behind it.
+    pub fn default_3d() -> Self {
         OrthographicProjection {
             scale: 1.0,
             near: 0.0,

examples/3d/orthographic.rs

@@ -20,7 +20,7 @@ fn setup(
         projection: OrthographicProjection {
             // 6 world units per window height.
             scaling_mode: ScalingMode::FixedVertical(6.0),
-            ..default()
+            ..OrthographicProjection::default_3d()
         }
         .into(),
         transform: Transform::from_xyz(5.0, 5.0, 5.0).looking_at(Vec3::ZERO, Vec3::Y),

examples/3d/pbr.rs

@@ -121,7 +121,7 @@ fn setup(
             transform: Transform::from_xyz(0.0, 0.0, 8.0).looking_at(Vec3::default(), Vec3::Y),
             projection: OrthographicProjection {
                 scale: 0.01,
-                ..default()
+                ..OrthographicProjection::default_3d()
             }
             .into(),
             ..default()

examples/stress_tests/many_lights.rs

@@ -96,7 +96,7 @@ fn setup(
             projection: OrthographicProjection {
                 scale: 20.0,
                 scaling_mode: ScalingMode::FixedHorizontal(1.0),
-                ..default()
+                ..OrthographicProjection::default_3d()
             }
             .into(),
             ..default()