Add emission shape gizmos to Particles2D

[Arnklit]

This adds emission gizmos to CPU and GPU Particles2D. In combination with #100113 this would complete godotengine/godot-proposals#7826

godot.windows.editor.dev.x86_64_IFseWBzJ1M.mp4

I'd like some feedback or suggestion on what the best solution is for the gizmo color and look as it can look weird that there is another gizmo for the Visibility Rect on the GPU version.

Note: The Ring gizmo for GPUParticles will only display when the ring_axis is (1, 0, 0), (0, 1, 0) or (0, 0, 1) as it's not feasible to render gizmos for arbitrary axis in 2D.

[KoBeWi]

I think the gizmos should only draw when the node is selected, or at least there should be an option to hide them.

[Calinou]

I think the gizmos should only draw when the node is selected, or at least there should be an option to hide them.

As I mentioned in #102198 (comment), the consensus nowadays is to show visual-oriented gizmos only when the node is selected, so I'd do that first.

If there's still a need to add a dedicated property to toggle gizmo visibility, we can do that later.

[Arnklit]

Thanks @KoBeWi for the review. Looking at the code I feel like it might make the most sense to use the show_visibility_rect bool for both the visibility rect and the emission gizmo, obviously it should then be renamed to show_gizmos instead or something along those lines. That bool gets set to true when selecting particle systems, so they would only show when selected and that would also remove them from runtime without having to add the is_editor_hint() guard

[Arnklit]

@KoBeWi it should be much improved now if you have time to look it over again at some point :)

[KoBeWi]

Functionality-wise looks fine.

[Calinou]

Tested locally (rebased on top of master), it mostly works as expected.

Testing project: test_particles2d_gizmos.zip

I noticed an issue with GPUParticles2D that has a box emitter. Its gizmo isn't at the correct position:

This doesn't occur with other emission shape types and occurs regardless of whether the scene root is transformed.

However, with CPUParticles2D, it occurs with all emission shape types when the scene root is transformed (like in the testing project):

Also, Ring emission shape in GPUParticles2D is only drawn if the axis is (0.0, 0.0, 1.0), but it should also draw when it's (0.0, 0.0, 0.0) with the same orientation:

There's a special behavior that makes the zero axis (which is not a valid unit vector) act like (0.0, 0.0, 1.0), so that it's easier to configure for 2D users.

[Arnklit]

Rebased. And I think all the issues mentioned above are addressed now.

@Calinou thanks so much for the thorough testing, it made me realise there were a few more errors. I think they should all align now no matter how offset, rotated, scaled and skewed the particle nodes and their parents are :). Could you test again?

[Calinou]

Works great now 🙂

[Arnklit]

Realised I'd missed submitting one file for the typo correction. Should be all good now.

[Repiteo]

Thanks!