The moon has gimbal lock near the horizon

[sci-comp]

The relevant line of code would be: https://github.com/TokisanGames/Sky3D/blob/40c3490f8d9ae7f34aab076421c264db59936f42/addons/sky_3d/src/Skydome.gd#L443C1-L444C1

Demo of the issue, notice that the moon is rotating around it's forward-looking axis

2025-01-09.23-16-19.mp4

[TokisanGames]

I've noticed that. Do you have a fix?

[sci-comp]

Edit: this comment is no longer relevant. This class has had a major rewrite since I last looked at it.

---

I think we simply can't use looking_at, we'll need to rewrite something or another.

In Skydome.gd, for func update_moon_coords: here are two unrelated things that I think can be cleaned up,

• moon_instance_transform isn't used as far as I can tell
• if not __finish_set_moon_pos: and __finish_set_moon_pos I don't think these if statement makes sense.. there's nothing async here to wait on.

For fixing looking_at, my first thought would be something like this: we could add this method to TOD_Math.gd

static func to_orbit_with_rotation(altitude: float, azimuth: float, radius: float = 1.0) -> Transform3D:
	var rotation_transform: Transform3D = Transform3D()
	rotation_transform = rotation_transform.rotated(Vector3.FORWARD, azimuth)
	rotation_transform = rotation_transform.rotated(Vector3.LEFT, altitude)
	var final_transform: Transform3D = Transform3D()
	final_transform.origin = to_orbit(altitude, azimuth, radius)
	final_transform.basis = rotation_transform.basis
	return final_transform

Back in update_moon_coords, we would have a simplified,

func update_moon_coords() -> void:
	if !is_scene_built:
		return
		
	var azimuth: float = moon_azimuth * TOD_Math.DEG_TO_RAD
	var altitude: float = moon_altitude * TOD_Math.DEG_TO_RAD
	
	__moon_transform = TOD_Math.to_orbit_with_rotation(altitude, azimuth)
	
	emit_signal("moon_transform_changed", __moon_transform)
	emit_signal("moon_direction_changed", moon_direction())
	
	# ... rest of the function

However, I've run into a snag here-- altitude is always positive, so the moon will bounce off the horizon in one quadrant of the sky,

• Rising from 0 to 90 degrees,
• Setting from 90 to 180 degrees (back in the direction we came from)
• Then again rising and setting for 180-360

I see that altitude is set by set_moon_altitude, but I've run out of time for now to chase it down. I hope this helps! I might come back and try to finish this, but I'll need to take a break for now.

[j-c7]

This method of rendering the moon is very hacky, you can change it with this and skip the lookat using quaternions.

https://github.com/sourceonfire/time-of-day/blob/main/src/sky/celestials/tod_moon.gd (line 76)
https://github.com/sourceonfire/time-of-day/blob/main/src/sky/shaders/celestials/tod_moon.gdshaderinc

I didn't recommend v1 of this plugin for production because it was all experimental and the code was messy and hacky(required a complete rewrite for production).

-Regards.

[sci-comp]

I agree, quats would be a better approach! A lot does look like it could be simplified and rewritten, which I think would be a great idea to do.

I definitely don't have time to spearhead the effort, but I can always test and try to follow along!

[TokisanGames]

Fixed by #36

Scratch that, it's still an issue. It's likely unrelated to the shader and has to do with coordinates being passed to the shader as J pointed out above.

[j-c7]

It's possible that the roll problem for looking_at can be solved by multiplying the world direction with the rotation of outer space. Example: tilt * rot * Vector3.RIGHT or tilt * rot * -Vector3.RIGHT
Regards.