Add TextureAtlasLoader

[lynn-lumen]

Objective

• Fixes AssetLoader for TextureAtlas #11634

Solution

• Adding an AssetLoader for TextureAtlasLayout The loader has three extensions:
  • atlas.ron: Creates a TextureAtlasLayout with the specified size and texture rectangles.
  • atlas.grid.ron: Creates a TextureAtlasLayout with the specified grid, similar to TextureAtlasLayout::from_grid.
  • atlas.composed.ron: Creates a TextureAtlasLayout from the specified source textures by composing them using TextureAtlasBuilder. The composed image returned by the TextureAtlasBuilder is added as a labeled asset: composed_texture .

The AssetLoader implementation is based on @viridia's code as posted in the original issue

[viridia]

I think this would go a lot better if there was an example showing how to use it. For example, imagine a novice user who wants to spawn an AtlasImageBundle. That accepts a TextureAtlas, not a TextureAtlasLayout, but it won't be obvious to the novice how to get one from the other (it's not obvious to me either).

My original PR assumed that you could spawn an AtlasImageBundle in just two steps:

• Load a TextureAtlas resource and get a handle. This would automatically load the image as a dependency of the atlas, since the texture atlas resource would include a relative path to the image.
• Spawn an AtlasImageBundle using the returned handle.

However, that no longer works due to the changes in the way texture atlases work.

[lynn-lumen]

I think this would go a lot better if there was an example showing how to use it. For example, imagine a novice user who wants to spawn an AtlasImageBundle. That accepts a TextureAtlas, not a TextureAtlasLayout, but it won't be obvious to the novice how to get one from the other (it's not obvious to me either).

There already are some examples demonstrating how to use TextureAtlas and TextureAtlasLayout. However I agree, that an example demonstrating how to load a TextureAtlasLayout is useful.

I have added an example like that now, but I would appreciate someone reading over that since my English is not that good.

[github-actions]

The generated examples/README.md is out of sync with the example metadata in Cargo.toml or the example readme template. Please run cargo run -p build-templated-pages -- update examples to update it, and commit the file change.

[viridia]

Looks like there are some problems with the dependencies. Otherwise looks good.

[lynn-lumen]

Looks like there are some problems with the dependencies.

This is apparently an issue on main. The test will get triggered anytime you modify a Cargo.toml and failing should be non-blocking for merging. I asked on discord because I was confused 😅

There's also a related issue: #11917

[msvbg]

Having a name for each packed sprite here might be useful too.

[msvbg]

Nevermind, this is out of scope for this PR.