地图加载

上一章我们创建了一些实体来测试我们的渲染系统，但现在是时候渲染一个正式的地图了。在本节中，我们将创建一个基于文本的地图配置并加载它。

地图配置

第一步，让我们尝试基于如下所示的二维地图加载一个关卡。

#![allow(unused)]
fn main() {
    const MAP: &str = "
    N N W W W W W W
    W W W . . . . W
    W . . . B . . W
    W . . . . . . W 
    W . P . . . . W
    W . . . . . . W
    W . . S . . . W
    W . . . . . . W
    W W W W W W W W
    ";

其中：
. 是空白位置
W 是墙
P 是玩家
B 是箱子
S 是箱子放置点
N 是空：用于地图的外边缘
}

最终我们可以从文件中加载，但为了简单起见，现在我们先用代码中的常量。

以下是加载地图的实现。

#![allow(unused)]
fn main() {
// Initialize the level// Initialize the level
pub fn initialize_level(world: &mut World) {
    const MAP: &str = "
    N N W W W W W W
    W W W . . . . W
    W . . . B . . W
    W . . . . . . W 
    W . P . . . . W
    W . . . . . . W
    W . . S . . . W
    W . . . . . . W
    W W W W W W W W
    ";

    load_map(world, MAP.to_string());
}

pub fn load_map(world: &mut World, map_string: String) {
    // read all lines
    let rows: Vec<&str> = map_string.trim().split('\n').map(|x| x.trim()).collect();

    for (y, row) in rows.iter().enumerate() {
        let columns: Vec<&str> = row.split(' ').collect();

        for (x, column) in columns.iter().enumerate() {
            // Create the position at which to create something on the map
            let position = Position {
                x: x as u8,
                y: y as u8,
                z: 0, // we will get the z from the factory functions
            };

            // Figure out what object we should create
            match *column {
                "." => {
                    create_floor(world, position);
                }
                "W" => {
                    create_floor(world, position);
                    create_wall(world, position);
                }
                "P" => {
                    create_floor(world, position);
                    create_player(world, position);
                }
                "B" => {
                    create_floor(world, position);
                    create_box(world, position);
                }
                "S" => {
                    create_floor(world, position);
                    create_box_spot(world, position);
                }
                "N" => (),
                c => panic!("unrecognized map item {}", c),
            }
        }
    }
}
}

这里最有趣的 Rust 概念可能是 match。我们在这里使用了模式匹配的基本功能，仅仅是匹配地图配置中每个标记的值，但我们可以进行更高级的条件或类型模式匹配。

更多： 阅读更多关于模式匹配的信息 这里。

现在运行游戏，看看我们的地图是什么样子。

以下是最终代码。

/* ANCHOR: all */
// Rust sokoban
// main.rs

use ggez::{
    conf, event,
    graphics::{self, DrawParam, Image},
    Context, GameResult,
};
use glam::Vec2;
use hecs::{Entity, World};

use std::path;

const TILE_WIDTH: f32 = 32.0;

// ANCHOR: components
#[derive(Clone, Copy)]
pub struct Position {
    x: u8,
    y: u8,
    z: u8,
}

pub struct Renderable {
    path: String,
}

pub struct Wall {}

pub struct Player {}

pub struct Box {}

pub struct BoxSpot {}

// ANCHOR_END: components

// ANCHOR: game
// This struct will hold all our game state
// For now there is nothing to be held, but we'll add
// things shortly.
struct Game {
    world: World,
}
// ANCHOR_END: game

// ANCHOR: init
// Initialize the level// Initialize the level
pub fn initialize_level(world: &mut World) {
    // ANCHOR: map
    const MAP: &str = "
    N N W W W W W W
    W W W . . . . W
    W . . . B . . W
    W . . . . . . W 
    W . P . . . . W
    W . . . . . . W
    W . . S . . . W
    W . . . . . . W
    W W W W W W W W
    ";
    // ANCHOR_END: map

    load_map(world, MAP.to_string());
}

pub fn load_map(world: &mut World, map_string: String) {
    // read all lines
    let rows: Vec<&str> = map_string.trim().split('\n').map(|x| x.trim()).collect();

    for (y, row) in rows.iter().enumerate() {
        let columns: Vec<&str> = row.split(' ').collect();

        for (x, column) in columns.iter().enumerate() {
            // Create the position at which to create something on the map
            let position = Position {
                x: x as u8,
                y: y as u8,
                z: 0, // we will get the z from the factory functions
            };

            // Figure out what object we should create
            match *column {
                "." => {
                    create_floor(world, position);
                }
                "W" => {
                    create_floor(world, position);
                    create_wall(world, position);
                }
                "P" => {
                    create_floor(world, position);
                    create_player(world, position);
                }
                "B" => {
                    create_floor(world, position);
                    create_box(world, position);
                }
                "S" => {
                    create_floor(world, position);
                    create_box_spot(world, position);
                }
                "N" => (),
                c => panic!("unrecognized map item {}", c),
            }
        }
    }
}
// ANCHOR_END: init

// ANCHOR: handler
impl event::EventHandler<ggez::GameError> for Game {
    fn update(&mut self, _context: &mut Context) -> GameResult {
        Ok(())
    }

    fn draw(&mut self, context: &mut Context) -> GameResult {
        // Render game entities
        {
            run_rendering(&self.world, context);
        }

        Ok(())
    }
}
// ANCHOR_END: handler

// ANCHOR: entities
pub fn create_wall(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 10, ..position },
        Renderable {
            path: "/images/wall.png".to_string(),
        },
        Wall {},
    ))
}
pub fn create_floor(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 5, ..position },
        Renderable {
            path: "/images/floor.png".to_string(),
        },
    ))
}

pub fn create_box(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 10, ..position },
        Renderable {
            path: "/images/box.png".to_string(),
        },
        Box {},
    ))
}

pub fn create_box_spot(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 9, ..position },
        Renderable {
            path: "/images/box_spot.png".to_string(),
        },
        BoxSpot {},
    ))
}

pub fn create_player(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 10, ..position },
        Renderable {
            path: "/images/player.png".to_string(),
        },
        Player {},
    ))
}
// ANCHOR_END: entities

// ANCHOR: rendering_system
fn run_rendering(world: &World, context: &mut Context) {
    // Clearing the screen (this gives us the background colour)
        let mut canvas =
        graphics::Canvas::from_frame(context, graphics::Color::from([0.95, 0.95, 0.95, 1.0]));

    // Get all the renderables with their positions and sort by the position z
    // This will allow us to have entities layered visually.
    let mut query = world.query::<(&Position, &Renderable)>();
    let mut rendering_data: Vec<(Entity, (&Position, &Renderable))> = query.into_iter().collect();
    rendering_data.sort_by_key(|&k| k.1 .0.z);

    // Iterate through all pairs of positions & renderables, load the image
    // and draw it at the specified position.
    for (_, (position, renderable)) in rendering_data.iter() {
        // Load the image
        let image = Image::from_path(context, renderable.path.clone()).unwrap();
        let x = position.x as f32 * TILE_WIDTH;
        let y = position.y as f32 * TILE_WIDTH;

        // draw
        let draw_params = DrawParam::new().dest(Vec2::new(x, y));
        canvas.draw(&image, draw_params);
    }

    // Finally, present the canvas, this will actually display everything
    // on the screen.
    canvas.finish(context).expect("expected to present");
}
// ANCHOR_END: rendering_system

// ANCHOR: main
pub fn main() -> GameResult {
    let mut world = World::new();
    initialize_level(&mut world);

    // Create a game context and event loop
    let context_builder = ggez::ContextBuilder::new("rust_sokoban", "sokoban")
        .window_setup(conf::WindowSetup::default().title("Rust Sokoban!"))
        .window_mode(conf::WindowMode::default().dimensions(800.0, 600.0))
        .add_resource_path(path::PathBuf::from("./resources"));

    let (context, event_loop) = context_builder.build()?;

    // Create the game state
    let game = Game { world };
    // Run the main event loop
    event::run(context, event_loop, game)
}
// ANCHOR_END: main

/* ANCHOR_END: all */

CODELINK: 你可以在 这里 查看本示例的完整代码。