bevy/crates/bevy_ui
Carter Anderson 5e2cfb2f19 Camera Driven Viewports (#4898)
# Objective

Users should be able to render cameras to specific areas of a render target, which enables scenarios like split screen, minimaps, etc.

Builds on the new Camera Driven Rendering added here: #4745 
Fixes: #202
Alternative to #1389 and #3626 (which are incompatible with the new Camera Driven Rendering)

## Solution

![image](https://user-images.githubusercontent.com/2694663/171560044-f0694f67-0cd9-4598-83e2-a9658c4fed57.png)


Cameras can now configure an optional "viewport", which defines a rectangle within their render target to draw to. If a `Viewport` is defined, the camera's `CameraProjection`, `View`, and visibility calculations will use the viewport configuration instead of the full render target. 

```rust
// This camera will render to the first half of the primary window (on the left side).
commands.spawn_bundle(Camera3dBundle {
    camera: Camera {
        viewport: Some(Viewport {
            physical_position: UVec2::new(0, 0),
            physical_size: UVec2::new(window.physical_width() / 2, window.physical_height()),
            depth: 0.0..1.0,
        }),
        ..default()
    },
    ..default()
});
```

To account for this, the `Camera` component has received a few adjustments:

* `Camera` now has some new getter functions:
  * `logical_viewport_size`, `physical_viewport_size`, `logical_target_size`, `physical_target_size`, `projection_matrix`
*  All computed camera values are now private and live on the `ComputedCameraValues` field (logical/physical width/height, the projection matrix). They are now exposed on `Camera` via getters/setters  This wasn't _needed_ for viewports, but it was long overdue.

---

## Changelog

### Added

* `Camera` components now have a `viewport` field, which can be set to draw to a portion of a render target instead of the full target.
* `Camera` component has some new functions: `logical_viewport_size`, `physical_viewport_size`, `logical_target_size`, `physical_target_size`, and `projection_matrix`
* Added a new split_screen example illustrating how to render two cameras to the same scene

## Migration Guide

`Camera::projection_matrix` is no longer a public field. Use the new `Camera::projection_matrix()` method instead:

```rust

// Bevy 0.7
let projection = camera.projection_matrix;

// Bevy 0.8
let projection = camera.projection_matrix();
```
2022-06-05 00:27:49 +00:00
..
src Camera Driven Viewports (#4898) 2022-06-05 00:27:49 +00:00
Cargo.toml Enforce type safe usage of Handle::get (#4794) 2022-05-30 16:59:44 +00:00