Make Skybox’s image optional so that Skybox::default() is valid.

[kpreid]

Objective

• Partially addresses Skybox::default() causes an internal error #23688.
• Prevents use of Skybox::default() from causing errors.

Solution

Skybox::default() is problematic because it contains an Image that is not a valid skybox. This change removes the Default implementation and instead provides a new() function which takes the image as a parameter (and also the brightness, which is practically required). This change makes the image field optional so that the default None renders nothing.

Things we could do instead of this:

• Make Skybox not implement Default. I am informed this is a bad idea.
• Create a default cubemap image for default() to use.

Testing

Ran the skybox and irradiance_volumes examples.

[IceSentry]

I would prefer the Option<Image> solution. I believe this will work better with bsn. I vaguely remember Default being required for bsn.

[kpreid]

@IceSentry Happy to turn this PR into that instead, if I hear a more confident statement that that is the way to go.

[alice-i-cecile]

@IceSentry Happy to turn this PR into that instead, if I hear a more confident statement that that is the way to go.

Insert more confident statement that this is the way to go.

(I spent a ton of time last week writing docs for the crate and that will play much nicer.)

[kpreid]

I have updated the code to make the image field optional and continue to implement Default. Also, I made prepare_skybox_bind_groups remove the SkyboxBindGroup component again so that if the image value goes from Some to None, the rendering follows.

[kpreid]

This PR is a breaking change. Should I be doing anything regarding the migration guide?

[github-actions]

It looks like your PR is a breaking change, but you didn't provide a migration guide.

Please review the instructions for writing migration guides, then expand or revise the content in the migration guides directory to reflect your changes.

[alice-i-cecile]

Yep: something brief would be good. The bot will be by with advice momentarily <3

[alice-i-cecile]

Sibling to #23689.

[kpreid]

Added migration guide.

[kpreid]

I rebased and, as a consequence, had to add #[template(OptionTemplate<HandleTemplate<Image>>)] to satisfy the new derive(FromTemplate). I hope that’s the right code.

[alice-i-cecile]

You might be able to use the new #[template(builtin)] to clean that up further :)