Vulkan: FogVolume with volumetric fog temporal reprojection enabled causes the editor to redraw continuously, wasting CPU and GPU resources

[Calinou]

Godot version

4.0.dev (c89061e)

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 470.74)

Issue description

Related to #54892.

If at least one FogVolume node is visible in the scene tree, the editor will redraw continuously when volumetric fog and temporal reprojection are enabled. This wastes CPU and GPU power, which in turn harms the project's performance when run from the editor and decreases battery life on laptops.

We should use the temporal reprojection setting to determine at which point redrawing is no longer necessary. With the default value of 0.9, there is most likely no meaningful visual difference after 20 frames of convergence or so. (At higher values, we need to wait for more frames for volumetric fog to mostly converge.)

Notice the update spinner in the top-right corner:

fog-volume-visible-constant-editor-redrawing.mp4

Steps to reproduce

• Enable Show Update Spinner in the Editor Settings.
• Add a WorldEnvironment node with a Environment resource.
• Enable volumetric fog. Despite temporal reprojection being enabled, the editor will only redraw when needed. (This can cause fog to become outdated like in Vulkan: SDFGI does not make the editor redraw until it has fully converged #54892, but this is what we're aiming to resolve here too.)
• Add a FogVolume node. Notice how the editor starts redrawing constantly, even when nothing on screen has changed.
• Toggle the FogVolume node's visibility. Notice how the editor no longer redraws constantly when the FogVolume node is hidden.

Minimal reproduction project

test_fog_volume.zip

Keywords for easier searching: low processor mode, low-processor mode