Gizmos Billboards

[lynn-lumen]

Objective

• Most game engines like Unity and Unreal Engine have the ability to draw sprites as gizmos. This may be useful for drawing "nodes" for paths, lights and much more.
• This PR adds flat coloured billboards for bevy. Since this PR already is pretty big, I would like to add drawing textures on the billboards in a future PR.

Solution

• Moved the rendering code of line gizmos into its own module.
• Added rendering code for billboard gizmos.
• Added gizmos.billboard(position_3d, color) and gizmos.billboard_2d(position_2d, color) to actually draw gizmos.
• GizmoConfignow includes two additional properties:
  • .billboard_size to configure the visual size (length along the edge) of billboards. This behaves very similar to .line_width
  • .billboard_perspectiveto apply perspective scaling to billboards.
• The GizmoConfig.depth_bias applies to billboards aswell.

Showcase

You can draw billboards like this:

gizmos.billboard(Vec3::ZERO, RED);

Which produces results like these...

in 3D:

https://github.com/user-attachments/assets/6643d993-76d4-4acb-99f9-bd4a8b01c0d3

and in 2D:

[alice-i-cecile]

Very nice: thanks for the polished video!

[alice-i-cecile]

@lynn-lumen what needs to be done here to take this out of draft?

[lynn-lumen]

I don' really understand the ambiguity error🥲 Any help would be much appreciated:)

[alice-i-cecile]

It looks like you've added some ambiguous systems. The diff of "what new systems are conflicting" is frustratingly annoying to get at though: I'm going to be spending some time today driving the count down to zero, which should make this much clearer.

[alice-i-cecile]

#15031 should solve your pain here: particularly https://github.com/bevyengine/bevy/pull/15031/commits/5b157e98ac4728074ab0fe24282db973c70aa5b3

[lynn-lumen]

Thanks, I will have another try tomorrow :)

[lynn-lumen]

#15031 should solve your pain here: particularly 5b157e9

Thanks again, that really was very helpful :D

[lynn-lumen]

@alice-i-cecile This is ready for review now :)

[TimJentzsch]

@lynn-lumen @tychedelia what is required to move this PR forward?

[lynn-lumen]

@lynn-lumen @tychedelia what is required to move this PR forward?

This PR probably needs updating to the current version. Apart from that, I am not aware of anything blocking this PR. I believe @tychedelia requested format changes to some of the shader code though, but I was unable to determine what exactly they meant.

[tychedelia]

@lynn-lumen @tychedelia what is required to move this PR forward?

This PR probably needs updating to the current version. Apart from that, I am not aware of anything blocking this PR. I believe @tychedelia requested format changes to some of the shader code though, but I was unable to determine what exactly they meant.

Line 43 and 76-79 aren't formatted. The conflicts might be complex to resolve. We've moved towards retaining gizmos which may be worth evaluating if you want to revive this.

[lynn-lumen]

Ahh OK, thank you for clarifying :) If there still is interest, I will take a look at updating this next week.