Add cone angle control to particle emission ring shape

[Arnklit]

This adds a Cone Angle control to the particles ring emission shape for GPU and CPU particles.

As far as I know there is no way to ensure completely correct distribution when the shape get's more and more cone shaped. I skew the distribution using pow here, but if someone knows of a better way that would be great.

Note: this will require some additions to #86902

EDIT: Existing proposal this might close: godotengine/godot-proposals#6761
I went for adding an angle rather than a second radius control because that made more sense with the inner radius.

[AThousandShips]

Please open a proposal to track the support and details of this feature

[Arnklit]

Please open a proposal to track the support and details of this feature

Linked the existing proposal godotengine/godot-proposals#6761.
Maybe @QbieShay has time to look this over and see if it works well enough.

[Calinou]

Tested locally, it mostly works as expected.

Testing project: test_pr_91973.zip

I suggest adding property hints to the ring properties, as right now, you can drag them towards negative values, which doesn't make sense.

The angle in particular should be clamped between 0.0 and 180.0, and the degrees inspector property hint should be used (see Node2D's rotation property for an example). All properties (except cone angle) should have or_greater, so you can input values as large as you might need.

Emission Height, Radius and Inner Radius should be limited to positive values as well, as strange things can happen if you use negative values:

ring_negative_radius.mp4

ring_negative_2.mp4

The angle property feels a bit strange, as the cone already has a starting angle of 0 degrees when the value is about 45 in the inspector:

ring_negative_3.mp4

[Arnklit]

Thanks @Calinou . I added the property hints and it makes it nicer and I think resolves any strange behaviour.

It did make me wonder whether it might make sense to turn the inner radius and radius into min and max values with the ADD_MIN_MAX_PROPERTY

[Arnklit]

Just realised that the shader crashes on radius 0. Gonna have to max the value with 0.001. Give me a minute. I'll do another commit.

EDIT: hmm found some unexpected behaviour I don't like. I'll mark this as a draft until I can do a good solution later today.

[Arnklit]

OK, so I think I worked out all unexpected behaviour. I ended up doing it by limiting the angle between 0 and 90 instead of 0 and 180. This avoided all the strange behaviour when inner radius was larger than outer radius and you can still create the same shapes, you might just have to change the orientation of the shape to do so.

[Arnklit]

@Calinou if you have time to give this another look I'd appreaciate it :)

[Mickeon]

Documentation itself is fine if that was of any concern.

[Calinou]

Tested locally (rebased on top of 26d1577 with "Accept incoming" chosen during rebase), it works as expected for both CPU and GPU particles. The new behavior (with the effective angle clamped if the end of the cone is reached) makes sense.

Code looks good to me.

[Arnklit]

Rebased and added in the docs as suggested by @Calinou

[akien-mga]

The docs need to be moved so that they are in alphabetical order: https://github.com/godotengine/godot/actions/runs/9942582709/job/27464431529?pr=91973

[Arnklit]

Oh sorry, did not realise that. I will do this when I'm back from vacation, or if I find a free evening soon.

[Arnklit]

@akien-mga rebased and squashed

[akien-mga]

Thanks!