Updating Image::data does not change how the image is displayed in StandardMaterial.

[mintlu8]

Bevy version

0.15

What you did

Update an existing Image's data after it has been created and rendered at least once.

What went wrong

StandardMaterial did not update its render, despite the content of the Image asset has changed.

Additional information

Reproduction:
https://github.com/mintlu8/bevy_bug

[thebluefish]

See #15595 (and the related issue mention there).

Basically, you need to mutably touch the materials for it to "see" the changes in their dependent assets.

AsyncWorld.run_cached_system(
    move |mut assets: ResMut<Assets<Image>>, mut materials: ResMut<Assets<StandardMaterial>>, mut query: Query<&mut MeshMaterial3d<StandardMaterial>>| {
        let mat = query.single_mut();
        let mat_asset = materials.get_mut(mat.id()).unwrap(); // remove the `_mut` part here and observe how it breaks, due to no change detection on the underlying asset
        if let Some(img) = assets.get_mut(mat_asset.base_color_texture.as_ref().unwrap().id()) {
            for x in 0..128 {
                for y in 0..128 {
                    // Make fourth quadrant blue.
                    img.data[((y + 128) * 256 + x + 128) * 4 + 2] = 255;
                }
            }
            println!("Changed fourth quadrant to blue!");
        }
    }
)?;

[BenjaminBrienen]

I'm leaving this open because I'd like to know whether the API can be improved to make this more obvious.