bevy/examples/2d/texture_atlas.rs

use bevy::prelude::*;
use bevy_asset::{HandleId, LoadState};
use bevy_sprite::TextureAtlasBuilder;

fn main() {
    App::build()
        .init_resource::<RpgSpriteHandles>()
        .init_resource::<State>()
        .add_default_plugins()
        .add_startup_system(setup.system())
        .add_system(load_atlas.system())
        .run();
}

#[derive(Default)]
pub struct RpgSpriteHandles {
    handles: Vec<HandleId>,
}

fn setup(
    command_buffer: &mut CommandBuffer,
    mut rpg_sprite_handles: ResMut<RpgSpriteHandles>,
    asset_server: Res<AssetServer>,
) {
    rpg_sprite_handles.handles = asset_server
        .load_asset_folder("assets/textures/rpg")
        .unwrap();
    command_buffer
        .build()
        .add_entity(OrthographicCameraEntity::default());
}

#[derive(Default)]
struct State {
    atlas_loaded: bool,
}

fn load_atlas(
    command_buffer: &mut CommandBuffer,
    mut state: ResMut<State>,
    rpg_sprite_handles: Res<RpgSpriteHandles>,
    asset_server: Res<AssetServer>,
    mut texture_atlases: ResMut<Assets<TextureAtlas>>,
    mut textures: ResMut<Assets<Texture>>,
    mut materials: ResMut<Assets<ColorMaterial>>,
) {
    if state.atlas_loaded {
        return;
    }

    let mut texture_atlas_builder = TextureAtlasBuilder::default();
    if let Some(LoadState::Loaded(_)) =
        asset_server.get_group_load_state(&rpg_sprite_handles.handles)
    {
        // TODO: sort by size (within atlas builder)
        for texture_id in rpg_sprite_handles.handles.iter() {
            let handle = Handle::from_id(*texture_id);
            texture_atlas_builder.add_texture(handle, &textures);
        }

        let texture_atlas = texture_atlas_builder.finish(&mut textures);
        let texture_atlas_texture= texture_atlas.texture;
        let vendor_handle = asset_server
            .get_handle("assets/textures/rpg/chars/vendor/generic-rpg-vendor.png")
            .unwrap();
        let vendor_index = texture_atlas.get_texture_index(vendor_handle).unwrap();
        let atlas_handle = texture_atlases.add(texture_atlas);
        command_buffer
            .build()
            // draw a sprite from the atlas
            .add_entity(SpriteSheetEntity {
                sprite: TextureAtlasSprite {
                    index: vendor_index as u32,
                    scale: 4.0,
                    position: Vec3::new(150.0, 0.0, 0.0),
                    ..Default::default()
                },
                texture_atlas: atlas_handle,
                ..Default::default()
            })
            // draw the atlas itself
            .add_entity(SpriteEntity {
                material: materials.add(texture_atlas_texture.into()),
                quad: Quad {
                    position: Vec2::new(-300.0, 0.),
                    ..Default::default()
                },
                sprite: Sprite { scale: 0.65 },
                ..Default::default()
            });

        state.atlas_loaded = true;
    }
}