# Objective
- This PR fixes#12488
## Solution
- This PR adds a new property to `Camera` that emulates the
functionality of the
[setViewOffset()](https://threejs.org/docs/#api/en/cameras/PerspectiveCamera.setViewOffset)
API in three.js.
- When set, the perspective and orthographic projections will restrict
the visible area of the camera to a part of the view frustum defined by
`offset` and `size`.
## Testing
- In the new `camera_sub_view` example, a fixed, moving and control sub
view is created for both perspective and orthographic projection
- Run the example with `cargo run --example camera_sub_view`
- The code can be tested by adding a `SubCameraView` to a camera
---
## Showcase
- Left Half: Perspective Projection
- Right Half: Orthographic Projection
- Small boxes in order:
- Sub view of the left half of the full image
- Sub view moving from the top left to the bottom right of the full
image
- Sub view of the full image (acting as a control)
- Large box: No sub view
<details>
<summary>Shortened camera setup of `camera_sub_view` example</summary>
```rust
// Main perspective Camera
commands.spawn(Camera3dBundle {
transform,
..default()
});
// Perspective camera left half
commands.spawn(Camera3dBundle {
camera: Camera {
sub_camera_view: Some(SubCameraView {
// Set the sub view camera to the left half of the full image
full_size: uvec2(500, 500),
offset: ivec2(0, 0),
size: uvec2(250, 500),
}),
order: 1,
..default()
},
transform,
..default()
});
// Perspective camera moving
commands.spawn((
Camera3dBundle {
camera: Camera {
sub_camera_view: Some(SubCameraView {
// Set the sub view camera to a fifth of the full view and
// move it in another system
full_size: uvec2(500, 500),
offset: ivec2(0, 0),
size: uvec2(100, 100),
}),
order: 2,
..default()
},
transform,
..default()
},
MovingCameraMarker,
));
// Perspective camera control
commands.spawn(Camera3dBundle {
camera: Camera {
sub_camera_view: Some(SubCameraView {
// Set the sub view to the full image, to ensure that it matches
// the projection without sub view
full_size: uvec2(450, 450),
offset: ivec2(0, 0),
size: uvec2(450, 450),
}),
order: 3,
..default()
},
transform,
..default()
});
// Main orthographic camera
commands.spawn(Camera3dBundle {
projection: OrthographicProjection {
...
}
.into(),
camera: Camera {
order: 4,
..default()
},
transform,
..default()
});
// Orthographic camera left half
commands.spawn(Camera3dBundle {
projection: OrthographicProjection {
...
}
.into(),
camera: Camera {
sub_camera_view: Some(SubCameraView {
// Set the sub view camera to the left half of the full image
full_size: uvec2(500, 500),
offset: ivec2(0, 0),
size: uvec2(250, 500),
}),
order: 5,
..default()
},
transform,
..default()
});
// Orthographic camera moving
commands.spawn((
Camera3dBundle {
projection: OrthographicProjection {
...
}
.into(),
camera: Camera {
sub_camera_view: Some(SubCameraView {
// Set the sub view camera to a fifth of the full view and
// move it in another system
full_size: uvec2(500, 500),
offset: ivec2(0, 0),
size: uvec2(100, 100),
}),
order: 6,
..default()
},
transform,
..default()
},
MovingCameraMarker,
));
// Orthographic camera control
commands.spawn(Camera3dBundle {
projection: OrthographicProjection {
...
}
.into(),
camera: Camera {
sub_camera_view: Some(SubCameraView {
// Set the sub view to the full image, to ensure that it matches
// the projection without sub view
full_size: uvec2(450, 450),
offset: ivec2(0, 0),
size: uvec2(450, 450),
}),
order: 7,
..default()
},
transform,
..default()
});
```
</details>
c323db02e0