ClearColorConfig not honored with multiple cameras

[viridia]

Bevy version and features

0.20.0-dev (mainline)

[Optional] Relevant system information

• MacOS 15.7.4

AdapterInfo { name: "Apple M1 Pro", vendor: 0, device: 0, device_type: IntegratedGpu, device_pci_bus_id: "", driver: "", driver_info: "", backend: Metal, subgroup_min_size: 4, subgroup_max_size: 64, transient_saves_memory: Some(true), limit_bucket: None }

What you did

Three Camera2ds sharing a window.

What went wrong

Only the last one's ClearColorConfig honored and it clears the whole window instead of its own Viewport

Additional information

Example reproduction:

repro_camera_bug.rs.zip

[beicause]

This is because in wgpu LoadOp::Clear clears the entire texture rather than the viewport region. I think this can be resolved by #25226, which makes the main texture correspond to the viewport.

The current rendering process is:

1. Camera 1 clears the main texture to red and blits it to viewport 1.
2. Camera 2 clears the main texture to blue and blits it to viewport 2.
3. Camera 3 does not clear the main texture and blits the main texture to the full viewport, so the screen is entirely blue.