> Follow up to #11600 and #10588
@mockersf expressed some [valid
concerns](https://github.com/bevyengine/bevy/pull/11600#issuecomment-1932796498)
about the current system this PR attempts to fix:
The `ComputedTextureSlices` reacts to asset change in both `bevy_sprite`
and `bevy_ui`, meaning that if the `ImageScaleMode` is inserted by
default in the bundles, we will iterate through most 2d items every time
an asset is updated.
# Solution
- `ImageScaleMode` only has two variants: `Sliced` and `Tiled`. I
removed the `Stretched` default
- `ImageScaleMode` is no longer part of any bundle, but the relevant
bundles explain that this additional component can be inserted
This way, the *absence* of `ImageScaleMode` means the image will be
stretched, and its *presence* will include the entity to the various
slicing systems
Optional components in bundles would make this more straigthfoward
# Additional work
Should I add new bundles with the `ImageScaleMode` component ?
> Follow up to #10588
> Closes#11749 (Supersedes #11756)
Enable Texture slicing for the following UI nodes:
- `ImageBundle`
- `ButtonBundle`
<img width="739" alt="Screenshot 2024-01-29 at 13 57 43"
src="https://github.com/bevyengine/bevy/assets/26703856/37675681-74eb-4689-ab42-024310cf3134">
I also added a collection of `fantazy-ui-borders` from
[Kenney's](www.kenney.nl) assets, with the appropriate license (CC).
If it's a problem I can use the same textures as the `sprite_slice`
example
# Work done
Added the `ImageScaleMode` component to the targetted bundles, most of
the logic is directly reused from `bevy_sprite`.
The only additional internal component is the UI specific
`ComputedSlices`, which does the same thing as its spritee equivalent
but adapted to UI code.
Again the slicing is not compatible with `TextureAtlas`, it's something
I need to tackle more deeply in the future
# Fixes
* [x] I noticed that `TextureSlicer::compute_slices` could infinitely
loop if the border was larger that the image half extents, now an error
is triggered and the texture will fallback to being stretched
* [x] I noticed that when using small textures with very small *tiling*
options we could generate hundred of thousands of slices. Now I set a
minimum size of 1 pixel per slice, which is already ridiculously small,
and a warning will be sent at runtime when slice count goes above 1000
* [x] Sprite slicing with `flip_x` or `flip_y` would give incorrect
results, correct flipping is now supported to both sprites and ui image
nodes thanks to @odecay observation
# GPU Alternative
I create a separate branch attempting to implementing 9 slicing and
tiling directly through the `ui.wgsl` fragment shader. It works but
requires sending more data to the GPU:
- slice border
- tiling factors
And more importantly, the actual quad *scale* which is hard to put in
the shader with the current code, so that would be for a later iteration
