Fix sprite picking viewport

[jannik4]

Objective

Fixes sprite picking when using a viewport. Related to #19744.

Solution

• Do not substract viewport.min as Camera::viewport_to_world already does that.
• Skip pointers outside the viewport.

Testing

Tested with the following example:

Click to expand code

use bevy::{
    prelude::*, render::camera::Viewport, window::SystemCursorIcon, winit::cursor::CursorIcon,
};

fn main() -> AppExit {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .insert_resource(ClearColor(Color::BLACK))
        .run()
}

fn setup(mut commands: Commands, window: Single<&Window>) {
    commands.spawn((
        Camera2d,
        Camera {
            clear_color: ClearColorConfig::Custom(Color::WHITE),
            viewport: Some(Viewport {
                physical_position: UVec2::new(
                    window.physical_width() / 4,
                    window.physical_height() / 4,
                ),
                physical_size: UVec2::new(
                    window.physical_width() / 2,
                    window.physical_height() / 2,
                ),
                ..default()
            }),
            ..default()
        },
    ));

    commands
        .spawn((
            Transform::from_xyz(100.0, 100.0, 0.0),
            Sprite::from_color(Color::srgb(0.0, 1.0, 0.0), Vec2::new(200.0, 200.0)),
            Pickable::default(),
        ))
        .observe(
            |trigger: On<Pointer<Drag>>, mut transform: Query<&mut Transform>| {
                let mut transform = transform.get_mut(trigger.target()).unwrap();
                transform.translation.x += trigger.delta.x;
                transform.translation.y -= trigger.delta.y;
            },
        )
        .observe(
            |_: On<Pointer<DragStart>>,
             window: Single<Entity, With<Window>>,
             mut commands: Commands| {
                commands
                    .entity(*window)
                    .insert(CursorIcon::from(SystemCursorIcon::Grabbing));
            },
        )
        .observe(
            |_: On<Pointer<DragEnd>>,
             window: Single<Entity, With<Window>>,
             mut commands: Commands| {
                commands.entity(*window).remove::<CursorIcon>();
            },
        );
}