Bevy Minesweeper: Assets

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We have great board configuration with our BoardOptions resource but we hard coded every color, texture and fonts.
Let's create a new configuration resource in board_assets.rs for our board_plugin:

// board_assets.rs
use bevy::prelude::*;
use bevy::render::texture::DEFAULT_IMAGE_HANDLE;

/// Material of a `Sprite` with a texture and color
#[derive(Debug, Clone)]
pub struct SpriteMaterial {
    pub color: Color,
    pub texture: Handle<Image>,
}

impl Default for SpriteMaterial {
    fn default() -> Self {
        Self {
            color: Color::WHITE,
            texture: DEFAULT_IMAGE_HANDLE.typed(),
        }
    }
}

/// Assets for the board. Must be used as a resource.
///
/// Use the loader for partial setup
#[derive(Debug, Clone)]
pub struct BoardAssets {
    /// Label
    pub label: String,
    ///
    pub board_material: SpriteMaterial,
    ///
    pub tile_material: SpriteMaterial,
    ///
    pub covered_tile_material: SpriteMaterial,
    ///
    pub bomb_counter_font: Handle<Font>,
    ///
    pub bomb_counter_colors: Vec<Color>,
    ///
    pub flag_material: SpriteMaterial,
    ///
    pub bomb_material: SpriteMaterial,
}

impl BoardAssets {
    /// Default bomb counter color set
    pub fn default_colors() -> Vec<Color> {
        vec![
            Color::WHITE,
            Color::GREEN,
            Color::YELLOW,
            Color::ORANGE,
            Color::PURPLE,
        ]
    }

    /// Safely retrieves the color matching a bomb counter
    pub fn bomb_counter_color(&self, counter: u8) -> Color {
        let counter = counter.saturating_sub(1) as usize;
        match self.bomb_counter_colors.get(counter) {
            Some(c) => *c,
            None => match self.bomb_counter_colors.last() {
                None => Color::WHITE,
                Some(c) => *c,
            },
        }
    }
}

Declare the module in resources/mod.rs:

// mod.rs
// ..
pub use board_assets::*;
mod board_assets;

This new resource will store every visual data we need and allow customization.

We also added a bomb_counter_colors field to customize the bomb neighbor text colors and made a utility bomb_counter_color method to retrieve it.

What is this DEFAULT_IMAGE_HANDLE constant value?

We copy the way SpriteBundle handles its default texture using the same hard coded Handle<Image> for a white texture.
Now that we have the option for custom textures for everything from the tiles to the board background we will enable every texture field we omitted.

Plugin

Let's use our now resource in our create_board system in our board_plugin:

// lib.rs
+ use resources::BoardAssets;
// ..

    pub fn create_board(
        mut commands: Commands,
        board_options: Option<Res<BoardOptions>>,
+       board_assets: Res<BoardAssets>,
        window: Res<WindowDescriptor>,
-       asset_server: Res<AssetServer>,
    ) {
        // ..
-     let font = asset_server.load("fonts/pixeled.ttf");
-     let bomb_image = asset_server.load("sprites/bomb.png");
      // ..

      // Board background sprite:
      parent
                    .spawn_bundle(SpriteBundle {
                        sprite: Sprite {
-                            color: Color::WHITE
+                            color: board_assets.board_material.color,
                            custom_size: Some(board_size),
                            ..Default::default()
                        },
+                       texture: board_assets.board_material.texture.clone(),
                        transform: Transform::from_xyz(board_size.x / 2., board_size.y / 2., 0.),
                        ..Default::default()
                    })
        // ..
        Self::spawn_tiles(
                    parent,
                    &tile_map,
                    tile_size,
                    options.tile_padding,
-                   Color::GRAY,
-                   bomb_image,
-                   font,
-                   Color::DARK_GRAY,
+                   &board_assets,
                    &mut covered_tiles,
                    &mut safe_start,
                );
        // ..
    }

We remove the asset_server argument.

Why is board_assets not optional?

Making it optional is not easy because bevy doesn't provide a default font Handle. It would require advanced engine manipulation like using FromWorld and Assets implementations and using a hard coded font or font path.

But Handle implements Default

Indeed but then either the app will panic when trying to print out text or nothing will show up.

Our spawn_tiles and bomb_count_text_bundle functions should be cleaned up as well:

// lib.rs

fn spawn_tiles(
        parent: &mut ChildBuilder,
        tile_map: &TileMap,
        size: f32,
        padding: f32,
-       color: Color,
-       bomb_image: Handle<Image>,
-       font: Handle<Font>,
-       covered_tile_color: Color,
+       board_assets: &BoardAssets,
        covered_tiles: &mut HashMap<Coordinates, Entity>,
        safe_start_entity: &mut Option<Entity>,
    ) {
        // ..
        // Tile sprite
        cmd.insert_bundle(SpriteBundle {
                    sprite: Sprite {
-                       color
+                       color: board_assets.tile_material.color,
                        custom_size: Some(Vec2::splat(size - padding)),
                        ..Default::default()
                    },
                    transform: Transform::from_xyz(
                        (x as f32 * size) + (size / 2.),
                        (y as f32 * size) + (size / 2.),
                        1.,
                    ),
+                   texture: board_assets.tile_material.texture.clone(),
                    ..Default::default()
                })
                // ..
                // Tile Cover
           let entity = parent
                        .spawn_bundle(SpriteBundle {
                            sprite: Sprite {
                                custom_size: Some(Vec2::splat(size - padding)),
-                               color: covered_tile_color,
+                               color: board_assets.covered_tile_material.color,
                                ..Default::default()
                            },
+                           texture: board_assets.covered_tile_material.texture.clone(),
                            transform: Transform::from_xyz(0., 0., 2.),
                            ..Default::default()
                        })
                        .insert(Name::new("Tile Cover"))
                        .id();
                // ..
                // Bomb neighbor text
                parent.spawn_bundle(Self::bomb_count_text_bundle(
                                *v,
-                               font.clone(),
+                               board_assets,
                                size - padding,
                            ));
}

fn bomb_count_text_bundle(
        count: u8,
-       font: Handle<Font>,        
+       board_assets: &BoardAssets,
        size: f32,
    ) -> Text2dBundle {
        // We retrieve the text and the correct color
-       let (text, color) = (
-           count.to_string(),
-           match count {
-               1 => Color::WHITE,
-               2 => Color::GREEN,
-               3 => Color::YELLOW,
-               4 => Color::ORANGE,
-               _ => Color::PURPLE,
-           },
-       );
+       let color = board_assets.bomb_counter_color(count);
        // We generate a text bundle
        Text2dBundle {
            text: Text {
                sections: vec![TextSection {
-                   value: text,
+                   value: count.to_string(),
                    style: TextStyle {
                        color,
-                       font,
+                       font: board_assets.bomb_counter_font.clone(),
                        font_size: size,
                    },
                }],
     // ..

We now use only our BoardAssets resource for every visual element of the board.

App

We need to set a BoardAssets resource, but we have an issue. Loading our assets must be in a system, here a startup system, but we need to do it before our plugin launches its setup_board system or it will panic.

So let's prevent this situation by setting our state to Out:

// main.rs

fn main() {
    // ..
-   .add_state(AppState::InGame)
+   .add_state(AppState::Out)
    // ..
}

and registering a setup_board startup system, and moving the previous board setup into it

// main.rs

fn main() {
    // ..
-   app.insert_resource(BoardOptions {
-       map_size: (20, 20),
-       bomb_count: 40,
-       tile_padding: 3.0,
-       safe_start: true,
-       ..Default::default()
-   })
    // ..
+    .add_startup_system(setup_board)
    // ..
}

We can declare the new system:

// main.rs
use board_plugin::resources::{BoardAssets, SpriteMaterial};

// ..
fn setup_board(
    mut commands: Commands,
    mut state: ResMut<State<AppState>>,
    asset_server: Res<AssetServer>,
) {
    // Board plugin options
    commands.insert_resource(BoardOptions {
        map_size: (20, 20),
        bomb_count: 40,
        tile_padding: 1.,
        safe_start: true,
        ..Default::default()
    });
    // Board assets
    commands.insert_resource(BoardAssets {
        label: "Default".to_string(),
        board_material: SpriteMaterial {
            color: Color::WHITE,
            ..Default::default()
        },
        tile_material: SpriteMaterial {
            color: Color::DARK_GRAY,
            ..Default::default()
        },
        covered_tile_material: SpriteMaterial {
            color: Color::GRAY,
            ..Default::default()
        },
        bomb_counter_font: asset_server.load("fonts/pixeled.ttf"),
        bomb_counter_colors: BoardAssets::default_colors(),
        flag_material: SpriteMaterial {
            texture: asset_server.load("sprites/flag.png"),
            color: Color::WHITE,
        },
        bomb_material: SpriteMaterial {
            texture: asset_server.load("sprites/bomb.png"),
            color: Color::WHITE,
        },
    });
    // Plugin activation
    state.set(AppState::InGame).unwrap();
}

Using the generic state system we set up in the previous part we control when we want the plugin to launch.
Here, we want it to launch after we loaded our assets and set up the BoardAssets resource.
That's why we first set our state to Out and set it to InGame once our assets are ready.

Our plugin is now completely modular and has zero hard coded values, everything from the board size to the tile colors can be customized.

Can we edit the theme at runtime?

Yes ! the BoardAssets resource is available to every system,
but everything that is not a Handle won't be applied until the next generation. For a more dynamic system you can check my plugin bevy_sprite_material.

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Author: Félix de Maneville
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