Built-in skybox

[JMS55]

Objective

• Closes First-party skybox support #8008

Solution

• Add a skybox plugin that renders a fullscreen triangle, and then modifies the vertices in a vertex shader to enforce that it renders as a skybox background.
• Skybox is run at the end of MainOpaquePass3dNode.
• In the future, it would be nice to get something like bevy_atmosphere built-in, and have a default skybox+environment map light.

---

Changelog

• Added Skybox.
• EnvironmentMapLight now renders in the correct orientation.

Migration Guide

• Flip EnvironmentMapLight maps if needed to match how they previously rendered (which was backwards).

[JMS55]

Currently this is not used in any examples. Should it be? Also, what should we do about the existing skybox example?

[alice-i-cecile]

I'm happy that this exists! Unsure if this is the right crate for it: I really wish the rendering crate structure was better split up so users could more easily pull in only the things they need for their games.

[alice-i-cecile]

Currently this is not used in any examples. Should it be? Also, what should we do about the existing skybox example?

This should be used to replace the existing skybox example please.

[superdump]

Part of the value of the current skybox example is to show use of cubemaps with some different compressed texture types. So, I would say, update the current skybox example to use this plugin.

[superdump]

This isn't a full review but there are some significant things to address.

[JonahPlusPlus]

Looks good to me. I liked how you used the vertex shader to put the vertices on the far plane.

I was going to ask whether it handles split screen, but I see it adds the mesh during the pipeline, so that works. You could probably remove that match statement for drawing indexed/unindexed since you know the mesh before hand.

Other than that, there was some talk about using a fullscreen triangle? Did that not work out, or is it planned for a future PR? Either way, this works fine and probably makes the math for sampling easier.

[JMS55]

A fullscreen triangle is probably possible, but I couldn't figure out the math myself. This seems simpler, and works. Someone else could try and get the triangle working if they want.

[superdump]

For other reviewers, I added this documentation as part of figuring out how to do the fullscreen triangle approach.

[robtfm]

looks good.

it's not this pr's fault i think, but it doesn't line up with environment mapping.

on the example i added a box mesh and an environment map with the skybox cubemap texture to check it looked right. it looks correct (i.e. reflects the skybox) from above and below, and looking at +/- x, but when i look at +z or -z the reflection is the same as the skybox behind so i suspect we need the same handedness switch for environment maps.

[robtfm]

Suggested change

	let clip_position = vec4(
	f32(vertex_index & 1u),
	f32((vertex_index >> 1u) & 1u),
	0.25,
	0.5
	) * 4.0 - vec4(1.0);
	let clip_xy = vec2<f32>(f32(vertex_index & 1u), f32(vertex_index >> 1u)) * 4.0 - 1.0;
	let clip_position = vec4<f32>(clip_xy, 0.0, 1.0);

just to keep the logic closer to fullscreen.wgsl and reduce cognitive load a bit.

[superdump]

I would agree but I remember it being argued by industry peeps that my version is faster. I don’t see how though.

[JMS55]

@robtfm is the environment map sampling now correct?

[superdump]

@robtfm is the environment map sampling now correct?

I checked, it is now correct! :)