Fix ClearColor in 2d pipelines

[pietrosophya]

Objective

• Fixes Setting ClearColor doesn't work #13377
• Fixes Gizmos drawing despawned entities #13383

Solution

• Even if the number of renderables is empty, the transparent phase need to run to set the clear color.

Testing

• Tested on the clear_color example

[JMS55]

Why transparent, and not opaque? This is also unfortunate because render passes cost a good amount of performance, although for 2d it shouldn't matter too much.

[IceSentry]

Why transparent, and not opaque?

Because not enough people have reviewed my opaque 2d work yet #13069

[alice-i-cecile]

This appears to have the same root cause as #13383. @IceSentry is working on a fix.

[IceSentry]

@alice-i-cecile this is the only fix needed, so this can be merged

[IceSentry]

The real fix will be to have an opaque pass, but that's a lot more work since my PR I shared above needs a ton more work on top of it.

[IceSentry]

Actually, @pietrosophya could you add the if !transparent_phase.items.is_empty() check around the transparent_phase.render(&mut render_pass, world, view_entity); line? That would be more correct.

Like this:

if !transparent_phase.items.is_empty() {
	transparent_phase.render(&mut render_pass, world, view_entity);
}

Realistically, it doesn't really matter because that means it's just running an empty scene anyway, but it still makes a bit more sense.

[pietrosophya]

Done! 😉

[alice-i-cecile]

Awesome, thank you all very much! Nice to clean up one of the larger open bugs in the milestone.