Add a true "Once" ReflectionProbe update mode, rename current "Once" to "When Moved"

[Calinou]

See also #2784.

Describe the project you are working on

The Godot editor 🙂

Describe the problem or limitation you are having in your project

ReflectionProbes can currently be told to update only when they move using the default Once update mode, but there is no way to tell them to never update once they've been generated.

On low-end platforms, the mere act of updating a reflection probe is expensive, so it may be desired to never update a reflection probe even if its parent moves.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Having a way to make reflection probes truly update only once would help improve performance on low-end platforms, while still keeping acceptable visuals.

In my experience, having an old/inaccurate probe is often better than no reflection probe at all. It provides better specular occlusion in reflections since the sky won't shine through reflections.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

• Rename the current Once update move to When Moved to better reflect is behavior. It will remain the default mode.
• Add a new Once update move that only updates when one of the ReflectionProbe's parameters is changed (such as extents). The probe will not update when its transform changes (e.g. by moving the node itself or its parent).

If this enhancement will not be used often, can it be worked around with a few lines of script?

No, as this is handled by the renderer itself.

Is there a reason why this should be core and not an add-on in the asset library?

See above.

[clayjohn]

When would you want to move a ReflectionProbe but not have it update?

And alternatively, why would you want to update when extents are changed but not when the probe is moved? To me it seems inconsistent to update when the extents are changed, but not the position.

[Calinou]

When would you want to move a ReflectionProbe but not have it update?

This is for low-end configurations, so that we can avoid spending any frame budget in updating reflection probes. While probes placed in a level generally have no reason to move, probes that are parented to a dynamic object will definitely be moving at some point.

And alternatively, why would you want to update when extents are changed but not when the probe is moved? To me it seems inconsistent to update when the extents are changed, but not the position.

Changing a probe's extents is a conscious decision. It doesn't happen just because you moved one of the ReflectionProbe's parents. In contrast, changing a probe's position will happen whenever one of its parents moves. When you have a dynamic object such as a car with a reflection probe, it will move constantly, which means its reflection probe child will constantly queue for updates. This means it will take away valuable GPU time from the main viewport's frame budget. This is fine on decent dedicated GPUs, but not really on integrated graphics.

[VantaGhost]

Reflection probes really need a way to manually update them, I have a project where large parts of the level are constantly moving, but the contents of the probes don't change enough to warrant re-render. This just causes the "once" mode to update constantly. I know there's an argument against having baked probes for Godot 4, but I'm quite surprised there isn't at least a manual update mode.