Why is this asset being dropped/removed?

[k9]

Hi, new to bevy, and I'm trying to understand why my asset is being dropped. I created a minimal example to highlight the problem I'm running into. It's basically the bevy Sprite example, except I'm using an image asset created in code. I'm cloneing the handle to try to avoid it being dropped but it still is removed. Thanks!

Code:

use bevy::{
    prelude::*,
    render::{
        render_asset::RenderAssetUsages,
        render_resource::{Extent3d, TextureDimension, TextureFormat},
    },
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, track_assets)
        .run();
}

fn setup(mut commands: Commands, mut images: ResMut<Assets<Image>>) {
    let image = uv_debug_texture();
    let handle = images.add(image);
    println!("The handle: {:?}", handle.clone());

    commands.spawn(Camera2dBundle::default());

    commands.spawn(SpriteBundle {
        texture: handle.clone(),
        ..default()
    });
}

fn track_assets(mut ev_asset: EventReader<AssetEvent<Image>>) {
    for ev in ev_asset.read() {
        println!("{:?}", ev);
    }
}

/// Creates a colorful test pattern
fn uv_debug_texture() -> Image {
    const TEXTURE_SIZE: usize = 8;

    let mut palette: [u8; 32] = [
        255, 102, 159, 255, 255, 159, 102, 255, 236, 255, 102, 255, 121, 255, 102, 255, 102, 255,
        198, 255, 102, 198, 255, 255, 121, 102, 255, 255, 236, 102, 255, 255,
    ];

    let mut texture_data = [0; TEXTURE_SIZE * TEXTURE_SIZE * 4];
    for y in 0..TEXTURE_SIZE {
        let offset = TEXTURE_SIZE * y * 4;
        texture_data[offset..(offset + TEXTURE_SIZE * 4)].copy_from_slice(&palette);
        palette.rotate_right(4);
    }

    Image::new_fill(
        Extent3d {
            width: TEXTURE_SIZE as u32,
            height: TEXTURE_SIZE as u32,
            depth_or_array_layers: 1,
        },
        TextureDimension::D2,
        &texture_data,
        TextureFormat::Rgba8UnormSrgb,
        RenderAssetUsages::RENDER_WORLD,
    )
}

Output:

The handle: StrongHandle<Image>{ id: Index(AssetIndex { generation: 0, index: 3 }), path: None }
Added { id: AssetId<bevy_render::texture::image::Image>{uuid: 97128bb1-2588-480b-bdc6-87b4adbec477} }
Added { id: AssetId<bevy_render::texture::image::Image>{uuid: 7467b61f-c116-4fa5-7a3d-0584a707da20} }
Added { id: AssetId<bevy_render::texture::image::Image>{ index: 0, generation: 0} }
Added { id: AssetId<bevy_render::texture::image::Image>{ index: 1, generation: 0} }
Added { id: AssetId<bevy_render::texture::image::Image>{ index: 2, generation: 0} }
Added { id: AssetId<bevy_render::texture::image::Image>{uuid: 00000000-0000-0000-d41a-1553ad31f8c6} }
Added { id: AssetId<bevy_render::texture::image::Image>{uuid: 00000000-0000-0000-2c3b-9d8679da41ca} }
Added { id: AssetId<bevy_render::texture::image::Image>{ index: 3, generation: 0} }
Removed { id: AssetId<bevy_render::texture::image::Image>{ index: 3, generation: 0} }

[simbleau]

When it comes to manually adding assets like this, as soon as the scope of that system ends, the strong handle is dropped.

If no strong handles exist, the asset is removed.

You can store the handle in a resource or a local and that would prevent the drop!

[k9]

Thanks @simbleau . So here's a version where I try to keep the asset around by adding it as a resource but it still goes away. (The show_resource system prints Some(...) for the asset once, then None on subsequent updates):

use bevy::{
    prelude::*,
    render::{
        render_asset::RenderAssetUsages,
        render_resource::{Extent3d, TextureDimension, TextureFormat},
    },
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, (track_assets, show_image_resource))
        .run();
}

#[derive(Resource, Debug)]
struct MyImageResource {
    image: Handle<Image>,
}

fn setup(mut commands: Commands, mut images: ResMut<Assets<Image>>) {
    let image = uv_debug_texture();
    let handle = images.add(image);
    println!("The handle: {:?}", handle.clone());

    commands.spawn(Camera2dBundle::default());

    commands.spawn(SpriteBundle {
        texture: handle.clone(),
        ..default()
    });

    commands.insert_resource(MyImageResource { image: handle });
}

fn show_image_resource(r: Res<MyImageResource>, images: ResMut<Assets<Image>>) {
    println!("The handle stored in a resource: {:?}", r.image.clone());
    println!("The asset: {:?}", images.get(&r.image.clone()));
}

fn track_assets(mut ev_asset: EventReader<AssetEvent<Image>>) {
    for ev in ev_asset.read() {
        println!("{:?}", ev);
    }
}

/// Creates a colorful test pattern
fn uv_debug_texture() -> Image {
    const TEXTURE_SIZE: usize = 8;

    let mut palette: [u8; 32] = [
        255, 102, 159, 255, 255, 159, 102, 255, 236, 255, 102, 255, 121, 255, 102, 255, 102, 255,
        198, 255, 102, 198, 255, 255, 121, 102, 255, 255, 236, 102, 255, 255,
    ];

    let mut texture_data = [0; TEXTURE_SIZE * TEXTURE_SIZE * 4];
    for y in 0..TEXTURE_SIZE {
        let offset = TEXTURE_SIZE * y * 4;
        texture_data[offset..(offset + TEXTURE_SIZE * 4)].copy_from_slice(&palette);
        palette.rotate_right(4);
    }

    Image::new_fill(
        Extent3d {
            width: TEXTURE_SIZE as u32,
            height: TEXTURE_SIZE as u32,
            depth_or_array_layers: 1,
        },
        TextureDimension::D2,
        &texture_data,
        TextureFormat::Rgba8UnormSrgb,
        RenderAssetUsages::RENDER_WORLD,
    )
}

[simbleau]

In this case, the handle will continue to persist, however the image texture isn't being used and gets removed!

You should continue to see a Strong handle when you print it out.

[k9]

OK I think some debugging showed me the issue. In this case the asset wasn't being removed due to the handle's reference count going to zero, but because the image was being extracted into the Render World.

bevy/crates/bevy_render/src/render_asset.rs

Line 246 in a2fc9de

/// This system extracts all created or modified assets of the corresponding [`RenderAsset::SourceAsset`] type

I tried changing the asset usage from RenderAssetUsages::RENDER_WORLD to RenderAssetUsages::RENDER_WORLD | RenderAssetUsages::MAIN_WORLD and now it's not dropped! Thanks for the help!