Ignore inactive cameras

[torsteingrindvik]

Objective

Currently, if a large amount of inactive cameras are spawned, they will immensely slow down performance.

This can be reproduced by adding

    let default_image = images.add(default());
    for _ in 0..10000 {
        commands.spawn(Camera3dBundle {
            camera: Camera {
                is_active: false,
                target: RenderTarget::Image(default_image.clone()),
                ..default()
            },
            ..default()
        });
    }

to for example 3d_shapes.

Using tracy, it's clear that preparing view bind groups for all cameras is still happening.
Also, visibility checks on the extracted views from inactive cameras also take place.

Performance gains

The following tracy comparisons show the effect of skipping this unneeded work.
Yellow is Bevy main, red is with the fix.

Visibility checks

Bind group preparation

Solution

• Check if the cameras are inactive in the appropriate places, and if so skip them

Changelog

Changed

• Do not extract views from inactive cameras or check visiblity from their extracted views